PC5271 wiki - User contributions [en]

CO2 Concentration Detector

2025-04-29T12:52:02Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="500px" heights="350px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

From the measurement we can get the following data:

{| class="wikitable"
! Time (s) !! Cylinder pressure (psi)
|-
| 0 || 840.0
|-
| 1 || 837.1
|-
| 2 || 835.7
|-
| 3 || 834.8
|-
| 4 || 834.1
|-
| 5 || 833.7
|-
| 6 || 833.4
|-
| 7 || 833.1
|-
| 8 || 832.9
|-
| 9 || 832.7
|-
| 10 || 832.6
|-
| 11 || 832.5
|-
| 12 || 832.4
|-
| 13 || 832.3
|-
| 14 || 832.2
|}

According to the ideal gas law, the corresponding number of moles can be calculated:

<center>'''<math>\mathbf{PV = nRT}</math>'''</center>

Thus we can get the following tables present the output voltages from the photodetector corresponding to different CO2 concentrations(the volumn of the chamber is 80ml). Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

According to the ideal gas law, the corresponding number of moles can be calculated:

<center>'''<math>\mathbf{PV = nRT}</math>'''</center>

where P is the pressure,V is the volume, n is the number of moles,R is the ideal gas constant, and T is the absolute temperature. In our case, T = 295K, V= 130ml (which is the volumn of the gas cylinder).

<gallery widths="500px" heights="350px">
File:Volumn of cylinder.jpg |Volumn of cylinder
File:Temperature.png|Temperature
</gallery>

Accorading to these above, we can calculate the exact concentartion of CO2(the air chamber's volumn is approximately 80ml), we use the averaged voltage response as a function of CO2 concentration to plot the curve:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T12:51:36Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="500px" heights="350px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

From the measurement we can get the following data:

{| class="wikitable"
! Time (s) !! Cylinder pressure (psi)
|-
| 0 || 840.0
|-
| 1 || 837.1
|-
| 2 || 835.7
|-
| 3 || 834.8
|-
| 4 || 834.1
|-
| 5 || 833.7
|-
| 6 || 833.4
|-
| 7 || 833.1
|-
| 8 || 832.9
|-
| 9 || 832.7
|-
| 10 || 832.6
|-
| 11 || 832.5
|-
| 12 || 832.4
|-
| 13 || 832.3
|-
| 14 || 832.2
|}

According to the ideal gas law, the corresponding number of moles can be calculated:

<center><math>\large\mathbf{PV = nRT}</math></center>

Thus we can get the following tables present the output voltages from the photodetector corresponding to different CO2 concentrations(the volumn of the chamber is 80ml). Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

According to the ideal gas law, the corresponding number of moles can be calculated:

<center>'''<math>\mathbf{PV = nRT}</math>'''</center>

where P is the pressure,V is the volume, n is the number of moles,R is the ideal gas constant, and T is the absolute temperature. In our case, T = 295K, V= 130ml (which is the volumn of the gas cylinder).

<gallery widths="500px" heights="350px">
File:Volumn of cylinder.jpg |Volumn of cylinder
File:Temperature.png|Temperature
</gallery>

Accorading to these above, we can calculate the exact concentartion of CO2(the air chamber's volumn is approximately 80ml), we use the averaged voltage response as a function of CO2 concentration to plot the curve:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T12:49:52Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="500px" heights="350px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

From the measurement we can get the following data:

{| class="wikitable"
! Time (s) !! Cylinder pressure (psi)
|-
| 0 || 840.0
|-
| 1 || 837.1
|-
| 2 || 835.7
|-
| 3 || 834.8
|-
| 4 || 834.1
|-
| 5 || 833.7
|-
| 6 || 833.4
|-
| 7 || 833.1
|-
| 8 || 832.9
|-
| 9 || 832.7
|-
| 10 || 832.6
|-
| 11 || 832.5
|-
| 12 || 832.4
|-
| 13 || 832.3
|-
| 14 || 832.2
|}

The following tables present the output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

According to the ideal gas law, the corresponding number of moles can be calculated:

<center>'''<math>\mathbf{PV = nRT}</math>'''</center>

where P is the pressure,V is the volume, n is the number of moles,R is the ideal gas constant, and T is the absolute temperature. In our case, T = 295K, V= 130ml (which is the volumn of the gas cylinder).

<gallery widths="500px" heights="350px">
File:Volumn of cylinder.jpg |Volumn of cylinder
File:Temperature.png|Temperature
</gallery>

Accorading to these above, we can calculate the exact concentartion of CO2(the air chamber's volumn is approximately 80ml), we use the averaged voltage response as a function of CO2 concentration to plot the curve:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T12:08:33Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="500px" heights="350px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

According to the ideal gas law, the corresponding number of moles can be calculated:

<center>'''<math>\mathbf{PV = nRT}</math>'''</center>

where P is the pressure,V is the volume, n is the number of moles,R is the ideal gas constant, and T is the absolute temperature. In our case, T = 295K, V= 130ml (which is the volumn of the gas cylinder).

<gallery widths="500px" heights="350px">
File:Volumn of cylinder.jpg |Volumn of cylinder
File:Temperature.png|Temperature
</gallery>

Accorading to these above, we can calculate the exact concentartion of CO2(the air chamber's volumn is approximately 80ml), we use the averaged voltage response as a function of CO2 concentration to plot the curve:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T12:07:24Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="500px" heights="350px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

According to the ideal gas law, the corresponding number of moles can be calculated:

<center>'''<math>\mathbf{PV = nRT}</math>'''</center>

where P is the pressure,V is the volume, n is the number of moles,R is the ideal gas constant, and T is the absolute temperature. In our case, T = 295K, V= 130ml (which is the volumn of the gas cylinder).

<gallery widths="500px" heights="350px">
File:Volumn.jpg|Volumn of cylinder
File:Temperature.png|Temperature
</gallery>

Accorading to these above, we can calculate the exact concentartion of CO2(the air chamber's volumn is approximately 80ml), we use the averaged voltage response as a function of CO2 concentration to plot the curve:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

File:Temperature.png

2025-04-29T12:04:28Z

Zhaoyun:

File:Volumn of cylinder.jpg

2025-04-29T12:03:22Z

Zhaoyun:

CO2 Concentration Detector

2025-04-29T12:01:20Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="500px" heights="350px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

According to the ideal gas law, the corresponding number of moles can be calculated:

<center>'''<math>\mathbf{PV = nRT}</math>'''</center>

where P is the pressure,V is the volume, n is the number of moles,R is the ideal gas constant, and T is the absolute temperature. In our case, T = 295K, V= 130ml (which is the volumn of the gas cylinder).

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:57:34Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="500px" heights="350px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

According to the ideal gas law, the corresponding number of moles can be calculated:

<center>'''<math>\mathbf{PV = nRT}</math>'''</center>

where P is the pressure,V is the volume, n is the number of moles,R is the ideal gas constant, and T is the absolute temperature.

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:57:03Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="500px" heights="350px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

According to the ideal gas law, the corresponding number of moles can be calculated:

<center><math>\large\mathbf{PV = nRT}</math></center>

where P is the pressure,V is the volume, n is the number of moles,R is the ideal gas constant, and T is the absolute temperature.

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:55:53Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="500px" heights="350px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

According to the ideal gas law, the corresponding number of moles can be calculated:

<center>'''<math>PV = nRT</math>'''</center>

where
$ P $ = pressure (in pascals, Pa),
$ V $ = volume (in cubic meters, m³),
$ n $ = number of moles (mol),
$ R $ = ideal gas constant (8.314 J·mol⁻¹·K⁻¹),
$ T $ = absolute temperature (in kelvins, K).

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:53:21Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="500px" heights="350px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:53:07Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery widths="300px" heights="200px">
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:52:09Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

<gallery>
File:pressure.jpg|Measurement of Pressure
File:voltage.jpg|Measurement of Voltage
</gallery>
[[File:pressure.jpg|none|thumb|400px|Measurement of Pressure]]

[[File:voltage.jpg|none|thumb|400px|Measurement of Voltage]]

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:51:12Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

[[File:pressure.jpg|none|thumb|400px|CO2 Measurement of Pressure]]

[[File:voltage.jpg|none|thumb|400px|CO2 Measurement of Voltage]]

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:50:04Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

[[File:pressure.jpg|center|thumb|400px|CO2 Measurement of Pressure]]

[[File:voltage.jpg|center|thumb|400px|CO2 Measurement of Voltage]]

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:49:50Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
At a room temperature of 21.9°C and with a gas chamber volume of approximately 80 mL, three sets of voltage measurements were taken using a multimeter under identical pressure conditions.

[[File:pressure.jpg|center|thumb|400px|CO2 Measurement of Pressure]]

[[File:voltage|center|thumb|400px|CO2 Measurement of Voltage]]

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:48:55Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
We measured three sets of voltage values under the same pressure conditions, with the gas chamber at room temperature (21.9°C) and a volume of approximately 80 mL.

[[File:pressure.jpg|center|thumb|600px|CO2 Measurement of Pressure]]

[[File:voltage|center|thumb|600px|CO2 Measurement of Voltage]]

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

File:Pressure.jpg

2025-04-29T11:47:42Z

Zhaoyun:

File:Voltage.jpg

2025-04-29T11:47:30Z

Zhaoyun:

CO2 Concentration Detector

2025-04-29T11:47:10Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
We measured three sets of voltage values under the same pressure conditions, with the gas chamber at room temperature (21.9°C) and a volume of approximately 80 mL.

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|600px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:46:51Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==
We measured three sets of voltage values under the same pressure conditions, with the gas chamber at room temperature (21.9°C) and a volume of approximately 80 mL.

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|750px|CO2 Concentration vs. Photodetector Output Voltage]]

From the results presented in the figure, it can be observed that the curve exhibits an approximately linear trend, indicating that the detector output responds steadily to changes in CO2 concentration. Thus, under identical environmental conditions, the CO2 concentration can be inferred directly from the measured output voltage.

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:39:19Z

Zhaoyun: /* Introduction */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.
[[File:System.png|center|thumb|500px|System Overview Diagram ]]

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|750px|CO2 Concentration vs. Photodetector Output Voltage]]

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:39:13Z

Zhaoyun: /* Procedure */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|750px|CO2 Concentration vs. Photodetector Output Voltage]]

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:38:54Z

Zhaoyun: /* Procedure */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]
[[File:System.png|center|thumb|500px|System Overview Diagram ]]
# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|750px|CO2 Concentration vs. Photodetector Output Voltage]]

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

File:System.png

2025-04-29T11:37:48Z

Zhaoyun:

CO2 Concentration Detector

2025-04-29T11:28:05Z

Zhaoyun: /* Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|500px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|750px|CO2 Concentration vs. Photodetector Output Voltage]]

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

CO2 Concentration Detector

2025-04-29T11:27:44Z

Zhaoyun: /* Results and Analysis */

CO2 Concentration Detector

2025-04-29T11:27:16Z

Zhaoyun: /* Results and Analysis */

CO2 Concentration Detector

2025-04-29T11:27:05Z

Zhaoyun: /* Procedure */

CO2 Concentration Detector

2025-04-29T11:25:48Z

Zhaoyun: /* Introduction */

CO2 Concentration Detector

2025-04-29T11:25:28Z

Zhaoyun: /* Team Members */

CO2 Concentration Detector

2025-04-29T11:25:17Z

Zhaoyun: Created page with "== Team Members == Zhao Yun A0295128X Xie Zihan A0295111M Zhang Wenbo A0307226L"

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

Talk:CO2 Concentration Detector

2025-04-29T11:22:34Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|250px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|300px|CO2 Concentration vs. Photodetector Output Voltage]]

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

Talk:CO2 Concentration Detector

2025-04-29T11:22:10Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|250px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|left|300px|CO2 Concentration vs. Photodetector Output Voltage]]

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

Talk:CO2 Concentration Detector

2025-04-29T11:21:24Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|250px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|left|thumb|300px|CO2 Concentration vs. Photodetector Output Voltage]]

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

Talk:CO2 Concentration Detector

2025-04-29T11:20:40Z

Zhaoyun: /* Procedure */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|center|thumb|250px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|300px|CO2 Concentration vs. Photodetector Output Voltage]]

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

Talk:CO2 Concentration Detector

2025-04-29T11:20:22Z

Zhaoyun: /* Results and Analysis */

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|thumb|250px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|center|thumb|300px|CO2 Concentration vs. Photodetector Output Voltage]]

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

Talk:CO2 Concentration Detector

2025-04-29T11:19:49Z

Zhaoyun: /* Conclusion */ new section

== Team Members ==

Zhao Yun A0295128X

Xie Zihan A0295111M

Zhang Wenbo A0307226L

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.

== Procedure ==

The experiment aimed to quantify the CO2 concentration by monitoring the voltage output from a photodetector, which corresponds to the transmitted infrared light intensity at the characteristic wavelength of 4.26 μm. A broadband infrared light source was used, and a narrow-band filter isolated the desired wavelength. The gas chamber used for the measurements had a fixed volume of 80 mL. The procedure was as follows:

# '''System Setup'''
* A broadband infrared light source was used to emit light through the gas chamber (volume: 80 mL).
* A narrow-band optical filter centered at 4.26 μm was placed before the photodetector to ensure only light at this wavelength reached the sensor.
* A photodetector (light intensity sensor) was connected to a data acquisition system, which recorded the output voltage corresponding to the detected light intensity.
[[File:07e559e7cb1ccaf8d405442afb2907c.jpg|thumb|250px|System Setup]]

# '''Initial Measurement'''
* With ambient air (approximately 400 ppm CO2) in the gas chamber, the initial sensor output voltage ''V0'' was measured and recorded as the baseline.

# '''CO2 Injection and Voltage Recording'''
* Controlled increments of CO2 gas were introduced into the 80 mL gas chamber, gradually increasing the CO2 concentration.
* After each increment, the output voltage ''V'' from the photodetector was measured and recorded.
* The process was repeated for multiple concentration levels to establish the relationship between CO2 concentration and sensor voltage output.

# '''Data Recording and Analysis'''
* The voltage outputs ''V0'' (initial) and ''V'' (at each CO2 level) were systematically recorded.
* A calibration curve was plotted with CO2 concentration on the x-axis and photodetector output voltage on the y-axis, representing the detection characteristic.

== Results and Analysis ==

The following tables present the measured output voltages from the photodetector corresponding to different CO2 concentrations. Each voltage value represents an individual measurement, and an average is calculated from three groups.

{| class="wikitable"
! Time (s) !! CO2 (%) !! Group 1 (mV) !! Group 2 (mV) !! Group 3 (mV)
|-
| 0 || 0.042 || 241.9 || 238.0 || 237.6
|-
| 1 || 32 || 233.1 || 215.9 || 223.3
|-
| 2 || 48 || 176.0 || 166.6 || 173.6
|-
| 3 || 58 || 165.6 || 160.8 || 156.6
|-
| 4 || 65 || 149.7 || 155.4 || 156.7
|-
| 5 || 70 || 139.0 || 143.0 || 139.3
|-
| 6 || 73 || 129.0 || 132.2 || 129.1
|-
| 7 || 76 || 132.7 || 129.4 || 133.7
|-
| 8 || 79 || 121.2 || 115.7 || 125.6
|-
| 9 || 81 || 120.5 || 115.5 || 121.6
|-
| 10 || 82 || 116.0 || 114.2 || 114.6
|-
| 11 || 83 || 110.7 || 113.1 || 113.0
|-
| 12 || 84 || 107.7 || 107.6 || 108.2
|-
| 13 || 85 || 104.7 || 102.3 || 102.4
|-
| 14 || 86 || 99.0 || 101.4 || 100.8
|}

''Table: Raw voltage measurements across three groups''

We use the averaged voltage response as a function of CO2 concentration:

<math>
V(c) = 280.45 \cdot e^{-0.01057 \cdot c}
</math>

where:
* ''V'': output voltage (in mV)
* ''c'': CO2 concentration (in %)

[[File:1745923203643.png|thumb|300px|CO2 Concentration vs. Photodetector Output Voltage]]

== Analysis ==

=== Nonlinear Voltage Response to CO2 Concentration ===
The relationship between output voltage and CO2 concentration is not strictly linear. In the low concentration range (e.g., from 0.042% to around 30%), the voltage drops slowly, whereas at higher concentrations the decline becomes significantly steeper. This behavior can be attributed to the logarithmic nature of infrared absorption and the nonlinear response of the photodetector—where sensitivity increases as light intensity decreases.

=== System Imperfections and External Influences ===
Due to limitations in the experimental setup, complete gas sealing could not be achieved, potentially causing gas leakage or imperfect mixing. In addition, uncontrolled external infrared sources may have introduced optical noise into the system, affecting the sensor output. This optical interference is one of the main contributors to measurement uncertainty and reduces the system’s repeatability and precision.

== Conclusion ==

In this project, we successfully developed a CO2 sensing system based on infrared absorption at the characteristic wavelength of 4.26 μm. By monitoring the voltage output of a photodetector and analyzing its response to varying CO2 concentrations, we demonstrated a clear and repeatable inverse correlation between gas concentration and detector output.

Although minor deviations were observed—primarily due to environmental noise, limited gas sealing, and optical interference—the overall results confirmed the system's sensitivity to CO2 levels. The fitted exponential model further validated the expected behavior derived from the Beer–Lambert law.

Despite inherent measurement uncertainties, the system reliably responded to changes in CO2 concentration, indicating the successful realization of a functional gas sensor prototype.

Talk:CO2 Concentration Detector

2025-04-29T11:19:01Z

Zhaoyun: /* Results and Analysis */

Talk:CO2 Concentration Detector

2025-04-29T11:18:41Z

Zhaoyun: /* Results and Analysis */

Talk:CO2 Concentration Detector

2025-04-29T11:17:11Z

Zhaoyun: /* Results and Analysis */ new section

Talk:CO2 Concentration Detector

2025-04-29T11:16:02Z

Zhaoyun: /* Procedure */

File:07e559e7cb1ccaf8d405442afb2907c.jpg

2025-04-29T11:14:35Z

Zhaoyun:

Talk:CO2 Concentration Detector

2025-04-29T11:14:06Z

Zhaoyun:

File:1745923203643.png

2025-04-29T11:12:26Z

Zhaoyun:

Talk:CO2 Concentration Detector

2025-04-29T11:08:02Z

Zhaoyun: /* Procedure */ new section

Talk:CO2 Concentration Detector

2025-04-29T11:06:55Z

Zhaoyun: /* Team Members */

Talk:CO2 Concentration Detector

2025-04-29T11:06:23Z

Zhaoyun:

Talk:CO2 Concentration Detector

2025-04-29T11:04:21Z

Zhaoyun: /* Introduction */ new section

== Introduction ==

Carbon dioxide (CO\textsubscript{2}) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO\textsubscript{2} concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO\textsubscript{2} exhibits a strong absorption peak at a wavelength of 4.26~$\mu$m, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO\textsubscript{2}. According to the Beer-Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis.

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26~$\mu$m, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO\textsubscript{2} concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.

== Introduction ==

'''Carbon dioxide''' (CO2) is a critical greenhouse gas whose concentration monitoring is essential for various applications, including environmental protection, industrial process control, and indoor air quality management. One effective method for detecting CO2 concentrations relies on the molecule's specific absorption characteristics in the infrared region.

CO2 exhibits a strong absorption peak at a wavelength of 4.26 μm, which corresponds to its fundamental vibrational mode. By exploiting this property, we can design an optical detection system that measures the intensity attenuation of infrared light at this wavelength as it passes through a gas chamber containing CO2. According to the Beer–Lambert law, the degree of light absorption is directly related to the concentration of the absorbing gas, enabling quantitative analysis:

<math>
A = \log_{10} \left( \frac{I_0}{I} \right) = \varepsilon \, c \, L
</math>

In this project, we aim to develop such a detection apparatus. The system comprises an infrared light source centered at 4.26 μm, a gas chamber, and an infrared detector. By monitoring the reduction in light intensity after it traverses the gas chamber, the CO2 concentration can be inferred. This method offers non-invasive, real-time measurement capabilities and has the potential for high sensitivity and specificity.