Biogas concentration detection line

The biogas concentration detection circuit composed of an integrated circuit is shown in the figure. It is suitable for farmers to detect and alarm biogas concentration.
    When the QM-N5 is not in contact with flammable biogas or the gas concentration is extremely low, the conductivity between the A and B electrodes of the QM-N5 is low and the impedance is high, so that the voltage
of the input terminal ⑦ of rC is close to oV, so Its ②~⑥ pins all output low level, and LED 1~LED5 will not light up. The gas-sensing detection probe QM-N5 and the potentiometer RP form a gas-sensing detection circuit , and the gas -sensing detection signal is output from the center end of RP. When QM-N5 detects a certain concentration of biogas, the resistance between its A and B electrodes becomes very small. In this way, the 6V voltage stabilized by VS will pass through A and B+ RP, causing voltage to be added to the IC pin ⑦ . In turn, the corresponding light-emitting diode will light up. The higher the concentration of biogas , the more LED1~LED5 will light up in sequence , so the concentration of biogas can be known.     LED1- LED 5 can choose BT201A red phosphorus gallium arsenide light-emitting diode; VS can choose a voltage stabilizing diode with a stabilizing value of about 6V, such as 2CW7C, 2CW13, etc .; RP can choose a small precision solid potentiometer with a resistance value of 4.7kil. ; G can use 12V laminated battery or 12V power supply after converting AC to DC . The sensing surface of the gas sensor probe must be exposed from the casing so that the gas probe can detect signals to the maximum extent. First, use a syringe to extract an appropriate amount of measured biogas, accounting for 2% to 5% of the total gas, and mix it into the gas bag. The above standard biogas gas is transported through the rubber tube to the vicinity of the gas sensitive detection probe, so that it is affected by the gas. Finally adjust RP. Just make l.EDl just light up.     Since the gas sensor has an initial stabilization time, that is, the internal resistance is very small at the beginning, and it takes a period of time to return to its original stable state. Therefore, it must wait a few minutes before each use to avoid malfunctions. Judgment.