Winsen MQ135 User manual

Air Quality Gas Sensor
（Model：MQ135）
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

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MQ135 Semiconductor Sensor for Air Quality
Profile
Sensitive material of MQ135 gas sensor is SnO2,
which with lower conductivity in clean air. When
target pollution 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.
MQ135 gas sensor has high sensitivity to ammonia
gas, sulfide, benzene series steam, also can monitor
smoke and other toxic gases well. It can detect kinds
of toxic gases and is a kind of low-cost sensor for
kinds of applications.
Features
It has good sensitivity to toxic 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 gas alarm, industrial gas alarm and portable gas detector.
Technical Parameters Stable.1
Model
MQ135
Sensor Type
Semiconductor
Standard Encapsulation
Bakelite, Metal cap
Target Gas
ammonia gas, sulfide,
benzene series steam
Detection range
10～1000ppm( ammonia gas,
toluene, hydrogen, smoke)
Standard Circuit
Conditions
Loop Voltage
Vc
≤24V DC
Heater Voltage
VH
5.0V±0.1V AC or DC
Load Resistance
RL
Adjustable
Sensor character
under standard test
conditions
Heater Resistance
RH
29Ω±3Ω (room tem.)
Heater consumption
PH
≤950mW
Sensitivity
S
Rs(in air)/Rs(in 400ppm H2)≥5
Output Voltage
Vs
2.0V～4.0V（in 400ppm H2）
Concentration Slope
α
≤0.6(R400ppm/R100ppm H2)
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
Fig1.Sensor Structure
Unit: mm
NOTE: Output voltage (Vs) is VRL in test environment.

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Basic Circuit
Fig2. MQ135 Test Circuit
Instructions: The above fig is the basic test circuit of MQ135.The sensor requires two voltage inputs:
heater voltage (VH) and circuit voltage(VC). VHis 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 RLand it should adopts DC power.
Description of Sensor Characters
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 400ppm H2gas under
different tem. and humidity. Rso means resistance of the
sensor in 400ppm H2gas under 20℃/55%RH.
H2
Air
NH3
Toluene
Concentration (ppm)

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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
Fig6.Responce and Resume
Fig5 shows the changing of VRL in the process of putting
the sensor into target gas and removing it out.
Fig5.Sensitity Curve
Fig5 shows the VRL in H2 gas with different concentration.
The resistance load RLis 4.7 KΩ and the test is finished in
standard test conditions.
Fig7.long-term Stability
Test is finished in standard test conditions, the abscissa is observing time and the ordinate is VRL.
400ppm H2 (RL=4.7k)
Concentration (ppm)
Time (s)
Time (day)

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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.
Fig8. Lead sketch
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.
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
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:

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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.
Zhengzhou Winsen Electronics Technology Co., Ltd
Add: No.299, Jinsuo Road, National Hi-Tech Zone,
Zhengzhou 450001 China
Tel: [phone]
Fax: [phone]
E-mail: [e-mail]
Website: www.winsen-sensor.com