Goal

• What is MQ2
• How to operate

Practice

What is MQ2

• MOS(Metal Oxide Semiconductor) type gas sensor
• Can detect LPG, Smoke, Alcohol, Propane, Hydrogen, Methan, Carbon Monoxide(CO)
• Detects gas using the change of resistance of the sensing material

Specification

Operating Voltage	5V
Load Resistance	20 KΩ
Heater Resistance	33Ω ± 5%
Heating Consumption	< 800mw
Sensing Resistance	10 KΩ - 60 KΩ
Concentration Scope	200 300 - 10,000 ppm)
Preheat Time	Over 24 hours

What is ppm(Parts-per-million)

• Describe the amount of gas by volume in the air
• The ratio of one gas to another

Internal Structure

• MQ2 is enclosed in two layers of fine stainless steel mesh. It called Anti-explosion network
• It prevents an explosion by heater element which is inside the sensor
  • MQ2 is sensing flammable gases such as LPG, Propane and so on
• It leads only gaseous elements to pass inside the chamber

• The star-shaped structure
• H
  • Heats the sensing element and are connected through **Nickel-Chrominum coil(conductive alloy)
• A & B
  • Output signals to platinum wires
  • It is connected to the body of the sensing element
  • Conveys small changes in the current

• The Tin Dioxide(SnO₂) is the most important material being sensitive towards combustible gases
• The ceramic substrate merely increases heating efficiency and ensures the sensor area is heated to a working temperature constantly

How deos it work?

• The tin dioxide is heated in air at high temperature

• Oxygen is adsorbed on the surface
  • Donor electrons in the tin dioxide are attracted toward oxygen
  • This situation prevents electric current flow and the voltage goes down

• Oxygen decreased as it reacts with gases
  • Eletrons are then released into the tin dioxide
  • Then, it allows current to flow freely through the snesor and the voltage goes up

• i.e. Cencentration of gases ∝ Voltage
  • Cencentration of gases ↑ -> Voltage ↑
  • Cencentration of gases ↓ -> Voltage ↓

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References

• How MQ2 Gas/Smoke Sensor Works?