Gas Sensor
Gas Sensor is a device normally used to detect the different types of gases. As a human we can smell up to 400 different types of gases, like that Gas Sensors can detect the different types of gases, so we can say that gas sensor is an Electronic-Nose that used to detect the smell or gases. Different types of Gas sensors are available depends on the nature of the gas for example MQ-4 gas sensor is used to identify the methane gas, MQ-6 gas sensor is used to identify the LPG gas.
This type of gas sensor is easily interfaced with Microcontrollers like Raspberry, Arduino, ARM, etc...
MQ-2-GAS-SENSOR
Gas sensors are classified in to different types based on its inbuilt sensing element, this sensing element will changes depend on the gases. Now we are focused on the “MQ” type model number gas sensors, because they are very popular and those are very efficient, let’s check out the different types of gas sensors.
List of Gas sensors
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Methane,
Butane, LPG, Smoke |
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MQ3 |
Alcohol, Ethanol, Smoke |
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MQ4 |
Methane, CNG Gas |
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MQ5 |
Natural gas, LPG |
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MQ7 |
Carbon Monoxide |
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MQ8 |
Hydrogen Gas |
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MQ9 |
Carbon Monoxide, flammable gasses |
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MQ131 |
Ozone |
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MQ135 |
Air Quality |
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MQ136 |
Air Quality |
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MQ137 |
Ammonia |
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MQ138 |
Benzene, Toluene, Alcohol, Propane |
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MQ214 |
Methane, Natural Gas |
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MQ216 |
Natural gas, Coal Gas |
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MQ303A |
Natural gas, Coal Gas |
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MQ306A |
LPG, butane |
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MQ307A |
Carbon Monoxide |
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MQ309A |
Carbon Monoxide |
Applications of Gas sensors
- Robotics as an Electronic-Nose
- Industries to identify the hazard gases
- Home application as an LPG gas detection
- Smoke detection for fire alert
- Air quality checking as atmosphere gases detection like oxygen,co2.
- Automobiles as a Vehicle pollution checking.
- Coal mines to identify the poison gases
- Breathe analyzer
- Air conditioners
Note: Output voltage of any type of sensor will depend on the internal resistance of the sensing element.
Gas sensor working
Gas sensor detects the concentration of gases in the atmosphere, based on the gas concentration the potential difference across the gas sensor will vary by changing its internal resistance of the sensing element.
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| GAS-SENSOR-SCHEMATIC |
After the giving power supply, we know that the voltage will change corresponding to its resistance. Based on this phenomenon the internal resistance of the sensing element in the gas sensor will depend on the input gas concentration, for example, the amount of the input gas concentration will increase, then internal the resistance of the sensing element will decrease, so the output voltage gradually increases.
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| GAS-SENSOR-OUTPUT |
NOTE: Internal resistance
of the gas, sensor depends on the inbuilt sensing element
Gas sensor sensing element Working
The ability of the sensing element will depend on the manufacturing material. Generally, Gas sensors sensing materials are designed by using a chemiresister to change the resistivity. Chemiresister is Tin Dioxide(Sno2), it is an N-type semiconductor so it contains free electrons to donate(donor). When you energized the device oxygen particles in the atmosphere/air will attract the electrons, so the electrons move towards the surface of the gas sensors then the conductivity is very less(high resistance), whenever the free electrons come back to their original conductive is high(low resistance). There is a chemical bond between the atmospheric gases and electrons of the gas sensor, here we noticed that internal current flow will be controlled by atmospheric gases(input gas concentration)
How gas sensors are modeled
Gas sensors are available in two types of packages one is Gas sensor module and other is Gas sensor device. If we want to use the Gas sensor in any circuit design you have to make connections or interface that requires the pin configuration of the Gas sensor, let’s look into the pin configuration of the Gas sensor.
Gas sensor Module: 4-Pins
1.Vcc (positive terminal supply)
2.Gnd(negative terminal supply)
3.D0 (Digital Output)
4.A0 (analog output)
Gas sensor Device :
6-Pins
A,H,A,B,H,B. It required some external circuitry to interface in any design
From the above discussion, we can say that the Gas sensor Module is very easy to interface in any design circuits, but the Gas sensor device needs some extra circuit to the interface.
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| GAS-SENSOR |
How to use Gas sensor | Gas sensor module:
Gas sensor module has 4 pins such as Vcc, Gnd, A0, D0 as discussed above.
1.Vcc is connected to battery positive terminal
2. Gnd is connected to battery negative terminal
3. D0 is connected to the output device.
4. A0 No connection
Note: Here we are using only Digital output(D0).
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| Gas-sensor-circuit |
It requires some external circuitry,
1.LM359
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| Gas-sensor-circuit |
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