MQ-4 Natural Gas Sensor Module – Methane (CNG) Gas Detector

MQ-4 natural gas sensor module for methane (CH4) and CNG detection – a metal-oxide semiconductor (MOS) gas detector module.

Overview

The MQ-4 gas sensor is a metal-oxide semiconductor (MOS) gas sensor designed to detect:

• Methane (CH)

• Natural gas (CNG / LNG)

It is widely used for leak detection and combustible gas monitoring.

Working Principle

Metal-Oxide Semiconductor (MOS) Sensing

The MQ-4 uses a tin dioxide (SnO) sensing layer:

1. Heater Activation

• Internal heating coil raises sensor temperature

• Ensures proper chemical reaction conditions

2. Gas Interaction

• In clean air:

  • Oxygen molecules adsorb on sensor surface

  • Increase resistance

• When methane gas is present:

  • CH rel

  3. Resistance Change

  • Gas presence sensor resistance decreases

  4. Signal Conversion

  • Resistance variation converted into:

    • Analog voltage output

    • Digital output (via comparator)

  Measurement Characteristics

  • Detection range: ~200 ppm to 10,000 ppm (CH)

  • High sensitivity to:

    • Methane

    • Natural gas

  Response Characteristics

  • Response time: < 10 seconds

  • Recovery time: moderate

  Electrical Characteristics

  • Operating voltage: 5V (typical)

  • Heater consumption:

    • Significant (due to heating element)

    Output Interface

    Analog Output

    • Voltage proportional to gas concentration

    • Used for:

      • Quantitative measurement

    Digital Output

    • HIGH/LOW signal

    • Triggered by preset threshold

    Threshold adjustable using onboard potentiometer.

    Internal Components

    • SnO sensing layer

    • Heating coil

    • Comparator IC (e.g., LM393)

    • Load resistor (RL)

    • Indicator LEDs

    Operating Behavior

    Warm-Up Time

    • Requires:

      • Initial burn-in (hours for stability)

      • Short warm-up before use

    Gas Detection

    • Methane present outpunal

    Environmental Influence

    • Affected by:

      • Temperature

      • Humidity

      • Airflow

    Environmental Characteristics

    • Works in typical indoor/industrial environments

    • Needs:

      • Proper ventilation for accurate readings

    Limitations

    • Not highly selective:

      • May respond to other combustible gases

    • Requires calibration for accurate ppm measurement

    • High power consumption due to heater

    • Sensor drift over time

    Typical Pin Configuration

    • VCC 5V supply

    • GND Ground

    • AOUT Analog output

    • DOUT Digital output

      • Methane gas detector

      • Combustible gas leakage sensor

      • Analog + digital gas sensing device

      Summary

      The MQ-4 Gas Sensor Module is a MOS-based combustible gas sensor that:

      • Detects methane (CH) and natural gas

      • Uses heated SnO sensing technology

      • Provides analog and digital outputs

      • Offers fast response and good sensitivity

      • Is suitable for gas leakage detection systems