Target: C7H8、CH3COCH3、C2H5OH、H2
Model: MQ138
Detection range: 5~500ppm
Detection principle: Semiconductor
Characteristics: High sensitivity to C7H8、CH3COCH3、C2H5OH、CH2O
Size: φ19×24.2
Working conditions: Loop Voltage:5±0.1V
Heater Voltage:5±0.1V
Heater consumption:≤950mW

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Sensitive material of MQ138 gas sensor is SnO2, which with lower conductivity in clean air. When VOC gas exists, the sensor’s conductivity gets higher along with the gas concentration rising. Users can convert the change of conductivity to correspond output signal of gas concentration through a simple circuit.
MQ138 gas sensor has high sensitivity to toluene, acetone, alcohol, methanol, also can monitor hydrogen and other organic vapour well. It can detect kinds of organic gases and is a kind of low-cost sensor for kinds of applications.


It is widely used in domestic VOC gas alarm, industrial VOC gas leakage alarm and portable VOC gas detector.


It has good sensitivity to organic vapour gas in wide range, and has advantages such as long lifespan, low cost and simple drive circuit &etc.


Model MQ138
Sensor Type Semiconductor
Standard Encapsulation Bakelite, Metal cap
Target Gas toluene, acetone, alcohol, hydrogen
Detection range 5~500ppm
Standard Circuit Conditions Loop Voltage Vc 5.0V±0.1V DC
Heater Voltage VH 5.0V±0.1V AC or DC
Load resistance RL Adjustable
Sensor character under standard test conditions Heater Resistance RH 30Ω±3Ω(room temp.)
Heater consumption PH ≤950mW
Sensitivity S Rs(in air)/Rs(in 50ppm toluene)≥2
Output Voltage △Vs 0.5V (in 50ppmtoluene)
Concentration Slope α ≤0.6(R200ppm/R50ppm toluene)
Standard test conditions Tem.  Humidity 20℃±2℃;55%±5%RH
Standard test circuit Vc:5.0V±0.1V; VH:5.0V±0.1V
Preheat time Over 48 hours

* The description and specifications might be changed without notice. Please contact us for the latest information before placing orders.

Technical Support:

Customized technical design and function, LOGO and package are available without extra charge (including molding fee) for mass volume.

The sensors don't have sleeping mode. It can be set in program if needed.

All Winsen products go through strict inspections and tests to make sure they are 100% qualified before shipping out.

The sensor has been fully tested (not calibrated) before leaving the factory. However, after transportation and storage, the environment conditions change, and the surface of the sensor absorbs moisture, mixed gas, pollution matters, etc. It is recommended that customers perform aging and calibration after sensors become stable according to the program and use occasions of the whole device.

15﹪-90﹪RH without condensation,greater or less than this range or long-term high temperature and high humidity will affect the life of the sensor.

Our sensors are certified with CE, 3C, ROHS, anti-explosion, fire prevention, and coal mining safety according to different applications. And we provide assistance for new certification.

Many factors can cause the sensor to fail such as broken wires in transportation, poisoning, falling off of the sensitive material, damage to the heating wire (device), etc. Please find specific cause in each category with Winsen’s aftersales.

Winsen provides professional consultation and service before and after sales. We will recommend the best fitting sensor for your demand. If you have any problem, don’t hesitate to email us to

Due to high volume of daily incoming emails and time zone difference, we may not be able to reply your emails immediately. But we will reply to your inquiry in 24 business hours.