Motivation

Experiments

• Experiment 1: Instrument calibration


1. Purpose


• Because the analog value returned by each sensor may be inaccurate, and the carbon dioxide concentration in each area may be slightly different, it must be corrected before use.


2. Method


1. Connect the power supply to 3.3V and use arduino to measure the analog value of output A0. Its stable value is about 3.3/5*1024=675.84.


2. Let the sensor enter a steady state and operate in an unventilated environment for at least 48 hours.


3. At this time, the analog value of the atmospheric carbon dioxide concentration (about 400 ppm) was measured, and we measured 705 ppm.


4. The known carbon dioxide concentration is adjusted by a CO₂ incubator, and the ppm can be obtained according to the formula conversion, and the analog value of the concentration is obtained.
   Ex: We put the carbon dioxide sensor into 5% carbon dioxide and measured its analog value to 530.


5. We assume that the carbon dioxide logarithmic concentration is negatively linearly related to the output analog value, and can be found by the known two points.



3. Formula


1. X% = 10000X ppm Ex: 5% CO₂ concentration = 50000 ppm


2. Let we assume the unknown CO₂ concentration is C ppm.



$$slope={V_{50000}-V_{400}\over log50000-log400}={V-V_{400}\over logC-log400}$$


• From the graph, we have shown that V₅₀₀₀₀ = 530 、V₄₀₀ = 705
• Therefore, we can get the slope value.
• After shifting the equation we will get

$${logC-log400}={V-V_{400}\over slope}$$
$$C={10^{log400+{V-V_{400}\over slope}}}$$


• We can then get the unknown CO₂ concentration from this formula.
4. Picture


• We put CO₂ sensor into the CO₂ incubator and measure its analog value.



• Experiment 2: CO₂ trend line verification


1. Purpose


• To verify whether the logarithmic concentration of carbon dioxide is negatively linear with the output analog value.


2. Method


• Use a CO₂ incubator to adjust the known carbon dioxide concentration and measure its analogy to see if it is on this line.


3. Result


• We put our sensor in the environment of CO₂ 2.7%, and we measured that the analog value 550, which is quite match with the theoretical analog value 552.




• Precaution


• It is best to preheat for the first time for 24 hours, use it for more than six hours, preheat for 1-2 hours, power off for more than 72 hours, and preheat for 24 hours.


• Materials used


1. Arduino UNO


2. MG811 CO₂ Sensor
1. Heating power supply: 7.5-12V
2. Operating Temperature: -20 – 50 °C
3. Measuring range: 400-10000ppm CO₂


3. Float flowmeter or CO₂ incubator



4. Arduino code

Wiring