Electronic gas sensor. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Indicators, detectors, metal detectors

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The device shown below is used to detect gas leaks.

The sensor responds to methane, ethanol, hydrogen, isobutane. This list can be changed by simply applying a different sensor to the circuit. Comrades from the Figaro office produce a bunch of different sensors that respond to various gases.

The device diagram is like this (to get a large diagram, you need to click on the small one):

(click to enlarge)

Let's take a quick look at the functional nodes of the circuit.

So the sensor itself SE1 is a plate with a certain oxide, which is heated by a built-in heater.

In clean air, the resistance of the sensor is approximately 10 kOhm. When gas particles appear in the air, the resistance of the sensor begins to fall - the stronger, the greater the gas concentration. When a certain threshold is reached, the comparator on the chip DA2 changes its state and the generator starts to work DD1.1. As a result, the LED blinks. HL2 and the buzzer beeps with a terrible squeak SP.

Knot on DD1.3 delays turning on the device by approximately 2 minutes. This is due to the fact that the sensor heater needs time to heat up and recover. Indicator HL3 lights up just after 2 minutes and indicates that the sensor is ready for operation.

The whole thing is powered by a stabilized 5 volt source on the chip DA1.

About details

About customization

First of all, we break the positive power output of the circuit (somewhere around the first LED) and set up a voltage regulator with a resistor R1. We set 5 volts as accurately as possible. Then we restore the circuit and connect to the network. After about 2 minutes, the LED should light up. HL3. Again we measure the voltage at the output of the stabilizer, and, if necessary, adjust it. We measure the voltage at the output 2 microcircuits DA2 and resistor R6 set a couple of tens of millivolts less than measured at pin 3 of the same microcircuit. Next, we take a lighter (gas, of course) and begin to let the gas into the physiognomy of the sensor. The LED should light up HL2 and beep the buzzer. Sensitivity adjustable by resistor R6.

At this point, the setup can be considered complete.

In conclusion, I would like to note that it is not recommended to install the sensor in humid places, since its resistance depends on humidity. Therefore, do not install it directly above or next to a home gas stove.

Publication: radiokot.ru

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