Winsen MQ137 User guide

Ammonia Gas Sensor

（Model：MQ137）

Manual

Version: 1.4

Valid from: 2015-03-10

Zhengzhou Winsen Electronics Technology Co., Ltd

Statement

This manual copyright belongs to Zhengzhou Winsen Electronics Technology Co., LTD. Without the

written permission, any part of this manual shall not be copied, translated, stored in database or

retrieval system, also can’t spread through electronic, copying, record ways.

Thanks for purchasing our product. In order to let customers use it better and reduce the faults

caused by misuse, please read the manual carefully and operate it correctly in accordance with the

instructions. If users disobey the terms or remove, disassemble, change the components inside of

the sensor, we shall not be responsible for the loss.

The specific such as color, appearance, sizes &etc, please in kind prevail.

We are devoting ourselves to products development and technical innovation, so we reserve the

right to improve the products without notice. Please confirm it is the valid version before using this

manual. At the same time, users’ comments on optimized using way are welcome.

Please keep the manual properly, in order to get help if you have questions during the usage in the

future.

Zhengzhou Winsen Electronics Technology CO., LTD

Zhengzhou Winsen Electronics Technology Co., Ltd www.winsen-sensor.com

Profile

Sensitive material of MQ137 gas sensor is SnO

2,

which with lower conductivity in clean air. When NH3

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.
MQ137 gas sensor has high sensitivity to NH3 gas,
also can monitor organic amine such as
trimethylamine, cholamine well. It can detect kinds
of gases including ammonia and is a kind of low-cost
sensor for kinds of applications.

Model

MQ137

Sensor Type

Semiconductor

Standard Encapsulation

Bakelite, Metal cap

Target Gas

Ammonia Gas(NH3)

Detection range

5～500ppm NH3

Standard Circuit

Conditions

Loop Voltage

Vc

≤24V DC

Heater Voltage

VH 5.0V±0.1V AC or DC

Load Resistance

R

L

Adjustable

Sensor character

under standard

test conditions

Heater Resistance

RH 29Ω±3Ω(room tem.)

Heater consumption

P

H

≤900mW

Sensitivity

S

Rs(in air)/Rs(50ppmNH3)≥2

Output Voltage

△Vs

≥0.5V (in 50ppm NH3)

Concentration Slope

α

≤0.6(R

200ppm/R50ppm NH3

)

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

NOTE: The change of Output voltage(△ Vs) is the

difference value between V

RL

in test environment and

Fig1.Sensor Structure

Unit: mm

MQ137 Ammonia Gas Sensor

Features

It has good sensitivity to NH3 gas in wide range, and has advantages such as long lifespan, low cost and

simple drive circuit &etc.

Main Applications

It is widely used in domestic NH3 gas alarm, industrial NH3 gas leakage alarm, portable NH3 gas detector.

Technical Parameters Stable.1

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Fig3.Typical Sensitivity Curve

The ordinate is resistance ratio of the sensor (Rs/R0), the

abscissa is concentration of gases. Rs means resistance in

target gas with different concentration, R0 means

resistance of sensor in clean air. All tests are finished

under standard test conditions.

Fig4.Typical temperature/humidity characteristics

The ordinate is resistance ratio of the sensor (Rs/Rso). Rs

means resistance of sensor in 50ppm NH3 gas under different

tem. and humidity. Rso means resistance of the sensor in

50ppm NH3 gas under 20℃/55%RH.

NH3

Air

Concentration (ppm)

Basic Circuit

Fig2. MQ137 Test Circuit

Instructions: The above fig is the basic test circuit of MQ137.The sensor requires two voltage inputs:

heater voltage (VH) and circuit voltage(VC). VH is used to supply standard working temperature to the

sensor and it can adopt DC or AC power, while VRL is the voltage of load resistance RL which is in series with

sensor. Vc supplies the detect voltage to load resistance RL and it should adopts DC power.

Description of Sensor Characters

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Fig6.Responce and Resume

Fig5 shows the changing of V

RL

in the process of putting

the sensor into target gas and removing it out.

Fig5.Sensitity Curve

Fig5 shows the VRL in NH3 with different concentration. The

resistance load RL is 4.7 KΩ and the test is finished in

standard test conditions.

Concentration (ppm)

Time (s)

Cautions

1 .Following conditions must be prohibited

1.1 Exposed to organic silicon steam

Sensing material will lose sensitivity and never recover if the sensor absorbs organic silicon steam.
Sensors must avoid exposing to silicon bond, fixature, silicon latex, putty or plastic contain silicon
environment.

1.2 High Corrosive gas

If the sensors are exposed to high concentration corrosive gas (such as H2S, SOX, Cl2, HCl etc.), it will
not only result in corrosion of sensors structure, also it cause sincere sensitivity attenuation.

1.3 Alkali, Alkali metals salt, halogen pollution

The sensors performance will be changed badly if sensors be sprayed polluted by alkali metals salt
especially brine, or be exposed to halogen such as fluorine.

1.4 Touch water
Sensitivity of the sensors will be reduced when spattered or dipped in water.

1.5 Freezing
Do avoid icing on sensor’s surface, otherwise sensing material will be broken and lost sensitivity.

1.6 Applied higher voltage

Applied voltage on sensor should not be higher than stipulated value, even if the sensor is not
physically damaged or broken, it causes down-line or heater damaged, and bring on sensors’
sensitivity characteristic changed badly.

1.7 Voltage on wrong pins

For 6 pins sensor, Pin 2&5 is heating electrodes, Pin (1,3)/(4,6) are testing
electrodes (Pin 1 connects with Pin 3, while Pin 4 connects with Pin 6).If
apply voltage on Pin 1&3 or 4&6, it will make lead broken; and no signal
putout if apply on pins 2&4.

Fig7. Lead sketch

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Storage Time

Suggested aging time

Less than one month

No less than 48 hours

1 ~ 6 months

No less than 72 hours

More than six months

No less than 168 hours

Zhengzhou Winsen Electronics Technology Co., Ltd
Add: No.299, Jinsuo Road, National Hi-Tech Zone,

Zhengzhou 450001 China

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Fax: [phone]
E-mail: [email protected]
Website: www.winsen-sensor.com

2 .Following conditions must be avoided

2.1 Water Condensation
Indoor conditions, slight water condensation will influence sensors’ performance lightly. However, if

water condensation on sensors surface and keep a certain period, sensors’ sensitive will be decreased.

2.2 Used in high gas concentration
No matter the sensor is electrified or not, if it is placed in high gas concentration for long time, sensors
characteristic will be affected. If lighter gas sprays the sensor, it will cause extremely damage.

2.3 Long time storage
The sensors resistance will drift reversibly if it’s stored for long time without electrify, this drift is

related with storage conditions. Sensors should be stored in airproof bag without volatile silicon
compound. For the sensors with long time storage but no electrify, they need long galvanical aging
time for stability before using. The suggested aging time as follow:

Stable2.

2.4 Long time exposed to adverse environment
No matter the sensors electrified or not, if exposed to adverse environment for long time, such as high

humidity, high temperature, or high pollution etc., it will influence the sensors’ performance badly.

2.5 Vibration

Continual vibration will result in sensors down-lead response then break. In transportation or
assembling line, pneumatic screwdriver/ultrasonic welding machine can lead this vibration.

2.6 Concussion

If sensors meet strong concussion, it may lead its lead wire disconnected.

2.7 Usage Conditions

2.7.1For sensor, handmade welding is optimal way. The welding conditions as follow:

 Soldering flux: Rosin soldering flux contains least chlorine
 homothermal soldering iron
 Temperature： 250℃
 Time：less than 3 seconds

2.7.1If users choose wave-soldering, the following conditions should be obey:

 Soldering flux: Rosin soldering flux contains least chlorine
 Speed: 1-2 Meter/ Minute
 Warm-up temperature：100±20℃
 Welding temperature：250±10℃
 One time pass wave crest welding machine

If disobey the above using terms, sensors sensitivity will reduce.

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