Winsen MQ138 Gas Sensor for VOCGas User Manual
- June 4, 2024
- Winsen
Table of Contents
Winsen MQ138 Gas Sensor for VOCGas
Statement
- This manual copyright belongs to Zhengzhou Winsen Electronics Technology Co., LTD.
- Without written permission, any part of this manual shall not be copied, translated, stored in a database or retrieval system, and also cant spread through electronic, copying, or 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, or 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 product 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 the optimized using ways are welcome.
- Please keep the manual properly, in order to get help if you have questions during the usage in the future.
Profile
The 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 a high sensitivity to toluene, acetone, alcohol, and methanol, also can monitor hydrogen and other organic vapor well. It can detect kinds of organic gases and is a kind of low-cost sensor for kinds of applications.
Features
- It has good sensitivity to organic vapor gas in a wide range, and has advantages such as a long lifespan, low cost, and simple drive circuit &, etc.
Main Applications
- It is widely used in domestic VOC gas alarms, industrial VOC gas leakage alarms and portable VOC gas detectors.
Technical Parameters
| 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 50ppm toluene)
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
Basic Circuit
Instructions
The above fig is the basic test circuit of MQ138. 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 the sensor. Vc supplies the detect voltage to load resistance RL and it should adopt DC power.
Description of Sensor Characters
-
Fig5 shows the VRL in toluene with different concentrations. The resistance load RL is 4.7 KΩ and the test is finished in standard test conditions.
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Fig6 shows the changing of VRL in the process of putting the sensor into target gas and removing it out.
Cautions
Following conditions must be prohibited
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.
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.
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.
Touch water
The sensitivity of the sensors will be reduced when spattered or dipped in water.
Freezing
Do avoid icing on sensor’s surface, otherwise sensing material will be broken and lost sensitivity.
Applied higher voltage
Applied voltage on sensor should not be higher than the stipulated value, even if the sensor is not physically damaged or broken, it causes a down-line or heater damaged, and bring on sensors’ sensitivity characteristics changed badly.
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 put out if apply on pins 2&4.
Water Condensation
Indoor conditions, slight water condensation will influence sensors’ performance lightly. However, if water condensation on sensors surface and keep a certain period, the sensors’ sensitivity will be decreased.
Used in high gas concentration
No matter the sensor is electrified or not, if it is placed in high gas concentration for long time, sensor’s characteristics will be affected. If lighter gas sprays the sensor, it will cause extreme damage.
Long time storage
The sensor’s 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 an airproof bag without volatile silicon compounds. For the sensors with long time storage but no electrify, they need long galvanic aging time for stability before using. The suggested aging time as follow:
| 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 |
Long time exposed to adverse environment
No matter the sensors are electrified or not, if exposed to an adverse environment for long time, such as high humidity, high temperature, or high pollution etc., it will influence the sensors’ performance badly.
Vibration
Continual vibration will result in sensors down-lead response then break. In transportation or assembling line, a pneumatic screwdriver/ultrasonic welding machine can lead this vibration.
Concussion
If sensors meet strong concussion, it may lead its lead wire disconnected.
Usage Conditions
For sensor, handmade welding is optimal way. The welding conditions as follow:
- Soldering flux: Rosin soldering flux contains least chlorine
- homothermal soldering iron
- Temperature： ≤350℃
- Time: less than 3 seconds
If disobey the above-using terms, sensors sensitivity will reduce.
Zhengzhou Winsen Electronics Technology Co., Ltd
- Address: No.299, Jinsuo Road, National Hi-Tech Zone, Zhengzhou 450001 China
- Tel: +86-371-67169097/67169670
- Fax: +86-371-60932988
- E-mail: sales@winsensor.com
- Website: www.winsentech.com
References
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