Winsen MQ137 Ammonia Gas Sensor Manual

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Profile

The MQ137 gas sensor uses SnO2 as its sensitive material, which has lower conductivity in clean air. When NH3 gas is present, the sensor's conductivity increases with rising gas concentration. Users can convert the conductivity change into a corresponding output signal representing gas concentration using a simple circuit. The MQ137 gas sensor offers high sensitivity to NH3 gas and can also monitor organic amines like trimethylamine and cholamine. It detects various gases, including ammonia, and is a cost-effective sensor for many applications.

Features

• Good sensitivity to NH3 gas across a wide range.
• Advantages include long lifespan, low cost, and a simple drive circuit.

Main Applications

• Domestic NH3 gas alarms
• Industrial NH3 gas leakage alarms
• Portable NH3 gas detectors

Technical Parameters

Fig1. Sensor Structure

Diagram shows the physical structure of the sensor with dimensions. Key dimensions indicated are approximately 19.0±0.2 mm in diameter and 24.2±0.5 mm in height. It features a metal cap and a bakelite base, with 6 pins for connection.

Basic Circuit

Fig2. MQ137 Test Circuit

The test circuit diagram illustrates the basic setup for the MQ137 sensor. It requires two voltage inputs: heater voltage (VH) and circuit voltage (Vc). VH (5.0V ± 0.1V AC or DC) supplies the working temperature, while Vc (5.0V ± 0.1V DC) provides the detection voltage. A load resistance (RL) is connected in series with the sensor. The output voltage (VRL) is measured across RL.

Calculation Formulas:

• Resistance of Sensitive materials (Rs) = (Vc / VRL - 1) × RL
• Power consumption of Sensitive materials (Ps) = Vc² × Rs / (Rs + RL)²

Description of Sensor Characters

Fig3. Typical Sensitivity Curve

This graph shows the relationship between gas concentration (ppm) on the x-axis and the resistance ratio (Rs/Ro) on the y-axis. Rs represents the sensor's resistance in the target gas (NH3) at various concentrations, while Ro is the resistance in clean air. The curve indicates that as NH3 concentration increases, the sensor's resistance ratio (Rs/Ro) decreases. Tests are conducted under standard conditions.

Fig4. Typical temperature/humidity characteristics

This graph illustrates the effect of temperature and humidity on the sensor's resistance ratio (Rs/Rs0) for a 50ppm NH3 gas concentration. The x-axis represents temperature (°C), and the y-axis shows the resistance ratio. Different curves are plotted for various relative humidity levels (20%RH, 40%RH, 55%RH, 85%RH). The data shows how temperature and humidity influence the sensor's response.

Sensitivity Curve and Response

Fig5. Sensitivity Curve

This graph displays the sensor's output voltage (VRL) in response to different concentrations of NH3 gas. The x-axis shows the gas concentration (ppm), and the y-axis shows VRL (Volts). The graph is based on a load resistance (RL) of 4.7 kΩ and was tested under standard conditions. It shows a decreasing trend of VRL as NH3 concentration increases.

Fig6. Response and Resume

This graph illustrates the sensor's response and recovery time. The x-axis represents time (seconds), and the y-axis shows the output voltage (VRL). It depicts how VRL changes when the sensor is exposed to the target gas and then removed from it, showing the sensor's dynamic behavior.

Cautions

1. Conditions Must Be Prohibited

• 1.1 Exposed to organic silicon steam: Sensing material will lose sensitivity permanently if exposed to organic silicon steam. Avoid contact with silicon bond, fixature, silicon latex, putty, or any environment containing silicon.
• 1.2 High Corrosive gas: Exposure to high concentrations of corrosive gases (e.g., H₂S, SOx, Cl₂, HCl) can corrode the sensor structure and cause significant sensitivity attenuation.
• 1.3 Alkali, Alkali metals salt, halogen pollution: Sensor performance degrades when exposed to alkali metals salts (especially brine) or halogens like fluorine.
• 1.4 Touch water: Sensitivity is reduced when the sensor is splashed or dipped in water.
• 1.5 Freezing: Avoid icing on the sensor's surface, as it can break the sensing material and cause loss of sensitivity.
• 1.6 Applied higher voltage: Applying voltage higher than the stipulated value, even if it doesn't cause physical damage, can damage the sensor's internal components or heater, leading to altered sensitivity characteristics.
• 1.7 Voltage on wrong pins: For 6-pin sensors, pins 2 & 5 are for heating, and pins (1,3) / (4,6) are for testing. Applying voltage on test pin pairs (1&3 or 4&6) can break the leads. Applying voltage on pins 2&4 will result in no signal output.

Fig7. Lead sketch

Diagram shows a 6-pin sensor with pins labeled 1 through 6. Pins 2 and 5 are identified as heating electrodes. Pins 1 and 3 are a test electrode pair, and pins 4 and 6 are another test electrode pair.

2. Conditions Must Be Avoided

• 2.1 Water Condensation: While slight condensation may have a minor effect, prolonged condensation on the sensor surface will decrease sensitivity.
• 2.2 Used in high gas concentration: Prolonged exposure to high gas concentrations, whether electrified or not, affects sensor characteristics. Lighter gas sprays can cause extreme damage.
• 2.3 Long time storage: Storing sensors without power for extended periods can cause reversible resistance drift, dependent on storage conditions. Store in an airtight bag without volatile silicon compounds. Sensors stored without power require a long aging period for stability. Suggested aging times are provided: Less than one month (≥ 48 hours), 1-6 months (≥ 72 hours), More than six months (≥ 168 hours).
• 2.4 Long time exposed to adverse environment: Extended exposure to adverse conditions like high humidity, high temperature, or high pollution will negatively impact sensor performance, regardless of whether it is powered.
• 2.5 Vibration: Continuous vibration can cause sensor down-leads to respond and eventually break. This can occur during transportation or on assembly lines using pneumatic screwdrivers or ultrasonic welding machines.
• 2.6 Concussion: Strong concussions may lead to disconnected sensor lead wires.
• 2.7 Usage Conditions:
  • 2.7.1 Handmade welding: Optimal welding conditions include using lead-free and halogen-free soldering flux, a homothermal soldering iron, a temperature of ≤ 350°C, and a welding time of less than 3 seconds. Deviating from these terms will reduce sensor sensitivity.

Contact Information

Zhengzhou Winsen Electronics Technology Co., Ltd

Add: No.299, Jinsuo Road, National Hi-Tech Zone, Zhengzhou 450001 China

Tel: +86-371-67169097 / +86-371-67169670

Fax: +86-371-60932988

Email: sales@winsensor.com

Website: www.winsen-sensor.com