Carbon dioxide gas sensor detection circuit

火辣西米秀

Carbon dioxide gas sensor detection circuit [Copy link]

The carbon dioxide sensor is a machine used to detect the concentration of carbon dioxide. Carbon dioxide is one of the raw materials for photosynthesis of 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 thermal conductive gas sensor made according to the different characteristics of thermal conductivity 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 being measured.
This sensor has a low impedance, and voltage fluctuations will cause characteristic changes. Therefore, a voltage regulator integrated block and a voltage regulator circuit are used. Since this circuit also detects other gases besides water vapor and carbon dioxide at the same time, it cannot obtain a true carbon dioxide signal. Therefore, different voltages are applied to the two sensors, and the difference between the two outputs is taken to offset the output generated by gases other than carbon dioxide. 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 a true carbon dioxide signal. In this amplifier 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. Therefore, attention should be paid to the design of the circuit and the selection of components. 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 of the two operational amplifiers.