MQ-2 Smoke/LPG/CO Gas Sensor Module

Overview

This sensor module utilizes an MQ-2 as the sensitive component and has a protection resistor and an adjustable resistor on board. The MQ-2 gas sensor is sensitive to LPG, i-butane, propane, methane, alcohol, Hydrogen and smoke. It could be used in gas leakage detecting equipments in family and industry. The resistance of the sensitive component changes as the concentration of the target gas changes.

Features

  • Continuous Analog output
  • 3-pin interlock connector
  • Low cost and compact size

Standard Working Condition

Symbol Parameter Name Technical Condition Remarks
VC Circuit voltage 5V±0.1 AC or DC
VH Heating voltage 5V±0.1 AC or DC
RL Load resistance adjustable
RH Heater resistance 33Kohm±5% Room temperature
PH Heating consumption Less than 800mW

Environment Condition

Symbol Parameter Name Technical Condition Remarks
TO Operating Temp. -20°C-50°C
TS Storage Temp. -20°C-70°C
RH Relative Humidity <95%
O2 Oxygen Concentration 21%(standard condition) Oxygen concentration can affect sensitivity Minimum value is 2%

Sensitivity Characteristics

Symbol Parameter Name Technical Condition Remarks
RS Sensor Resistance 3Kohm-30Kohm (1000ppm iso-butane) Detecting concentration scope:
200ppm-5000ppm LPG and propane
300ppm-5000ppm butane
5000ppm-20000ppm methane
300ppm-5000ppm H2
100ppm-2000ppm Alcohol
α (3000ppm/1000ppm iso-butane) Concentration slope rate ≤0.6
Standard detecting Condition Temp.: 20°C±2°C VC: 5V±0.1
Humidity:65%±5% VH:5V±0.1
Preheating Time Over 24 hours

Typical Application Schematics

typical_app

Theory

The protection resistor (4.7Kohms) and the adjustable (0-50Kohms) are in serial which forms a load resistor RL (4.7-54.7Kohms). The sensor’s resistance RS and RL forms a voltage divider. The output voltage on the signal pin could be read by Arduino or MCU via ADC.  Given a value of RL , Power Supply Voltage, and output voltage, RS could be derived.  Based on the chart provided in the MQ-2 datasheet, RS in clean air under given temperature and humidity is a constant,which is the “initial” resistance of the sensor named RO. RO of the resistor could be derived from RS. The main job of the calibration is to calculate the RO by sampling and averaging the readings when the module is placed in the clean air. Once the RO is derived, the concentration of target gas could be calculated by using the RS/RO ratio as the input. To achieve more accuracy, a segmented look-up table should be used. However, in the demonstration, a linear formula is used as an approximation to the original curve.

Arduino Sample Code

Demo Output

SEN-000004.demoDemo output as the sensor approaches a lit cigarette

Dimensions

dimensions

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