Carbon dioxide gas sensor detection circuit

A carbon dioxide sensor is a machine used to detect carbon dioxide concentration. Carbon dioxide is one of the raw materials for photosynthesis in green plants, and 95% of the dry weight of crops comes from photosynthesis. Therefore, using carbon dioxide sensors to control concentration has become an important factor affecting crop yields.

The carbon dioxide gas sensor is a thermally conductive gas sensor made according to the different thermal conductivity characteristics of different gases. The structure of the sensor is quite simple. It consists of two pairs of platinum wire coils. One pair of coils is sealed in standard air for temperature compensation, and the other pair of coils is in contact with the gas to be measured.

This kind of sensor has low impedance, and voltage changes will cause changes in characteristics. Therefore, a voltage stabilizing integrated block and a voltage stabilizing circuit are used. Because this circuit also detects other gases besides water vapor and carbon dioxide, it cannot obtain a true carbon dioxide signal. Therefore, it is necessary to apply different voltages to the two sensors and take the difference between the two outputs to offset the gases other than carbon dioxide. of gas generated output. In this circuit, two sensors are connected in series and voltages of 0.5V and 1.3V are applied respectively. Its output is amplified by an operational amplifier and subtracted to obtain the real carbon dioxide signal. In this amplification circuit, the output of the sensor is very small. When the carbon dioxide concentration is 10%, the output is about 3mV, so it is easily affected by noise, so attention should be paid to the circuit design and device selection. C3, C4, and C5 are used to eliminate noise, W1 is used to adjust the voltage, W2 and W3 are used to adjust the output of the sensor in the air to zero, and W4 is used to adjust the amplification rate of the two operational amplifiers.