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Henan Hanwei Electronics Co., Ltd www.hwsensor.com
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MQ-7 Semiconductor Sensor for Carbon Monoxide
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Sensitive material of MQ-7 gas sensor is SnO2, which with lower conductivity in clean air. It make
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detection by method of cycle high and low temperature, and detect CO when low temperature (heated
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by 1.5V). The sensor’s conductivity is more higher along with the gas concentration rising. When high
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temperature (heated by 5.0V), it cleans the other gases adsorbed under low temperature. Please use
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simple electrocircuit, Convert change of conductivity to correspond output signal of gas concentration.
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MQ-7 gas sensor has high sensitity to Carbon Monoxide. The sensor could be used to detect
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different gases contains CO, it is with low cost and suitable for different application.
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Character Configuration
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*Good sensitivity to Combustible gas in wide range
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* High sensitivity to Natural gas
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* Long life and low cost
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* Simple drive circuit
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Application
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* Domestic gas leakage detector
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* Industrial CO detector
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* Portable gas detector
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Technical Data Basic test loop
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Model No. MQ-7 Vc VRL
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Sensor Type Semiconductor
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Standard Encapsulation Plastic
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Detection Gas Carbon Monoxide RL
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VH
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Concentration 10-10000ppm CO
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GND
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Circuit Loop Voltage Vc ≤10V DC
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Heater Voltage VH 5.0V±0.2V ACorDC（High） The above is basic test circuit of the sensor.
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1.5V±0.1V ACorDC（Low） The sensor need to be put 2 voltage,
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Heater Time TL 60±1S（High）90±1S（Low） heater voltage（VH）and test voltage（VC）.
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VH used to supply certified working
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Load Adjustable temperature to the sensor, while VC used
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RL to detect voltage (VRL) on load resistance
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（RL）whom is in series with sensor. The
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Resistance sensor has light polarity, Vc need DC
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power. VC and VH could use same power
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Heater 31Ω±3Ω（Room Tem.） circuit with precondition to assure
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RH performance of sensor. In order to make
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the sensor with better performance,
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Resistance suitable RL value is needed:
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Power of Sensitivity body(Ps):
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Heater ≤350mW Ps=Vc2×Rs/(Rs+RL)2
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PH 2KΩ-20KΩ(in 100ppm CO )
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consumption
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Character
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Sensing
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Rs
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Resistance
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Sensitivity S Rs(in air)/Rs(100ppm CO)≥5
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Slope α ≤0.6(R300ppm/R100ppm CO)
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20℃±2℃；65%±5%RH
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Tem. Humidity
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Vc:5.0V±0.1V；
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Condition Standard test circuit VH（High）: 5.0V±0.1V；
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VH（Low）: 1.5V±0.1V
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Preheat time Over 48 hours
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Tel: 86-371-67169070/80 Fax: 86-371-67169090 Email: sales@hwsensor.com
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Henan Hanwei Electronics Co., Ltd www.hwsensor.com
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Resistance of sensor(Rs): Rs=(Vc/VRL-1)×RL
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Sensitivity Characteristics Influence of Temperature/Humidity
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Fig.1 shows the typical sensitivity characteristics of 1.9
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the MQ-7, ordinate means resistance ratio of the sensor
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1.7 Fig2 60%RH
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(Rs/Ro), abscissa is concentration of gases. Rs means
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1.5 30%RH
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resistance in different gases, Ro means resistance of
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sensor in 1000ppm Hydrogen. All test are under standard 85%RH
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test conditions.
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Rs/R0 1.3
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1.1
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0.9
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0.7
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0.5
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-20 -10 0 10 20 30 40 50 ℃
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Fig.2 shows the typical temperature and humidity
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characteristics. Ordinate means resistance ratio
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of the sensor (Rs/Ro), Rs means resistance of sensor
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in 100ppm CO under different tem. and humidity.
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Ro means resistance of the sensor in environment of
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100ppm CO, 20℃/65%RH
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Structure and configuration
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Structure and configuration of MQ-7 gas sensor is shown as Fig. 3, sensor composed by micro AL2O3 ceramic tube, Tin
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Dioxide (SnO2) sensitive layer, measuring electrode and heater are fixed into a crust made by plastic and stainless steel
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net. The heater provides necessary work conditions for work of sensitive components. The enveloped MQ-7 have 6 pin, 4
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of them are used to fetch signals, and other 2 are used for providing heating current.
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Tel: 86-371-67169070/80 Fax: 86-371-67169090 Email: sales@hwsensor.com
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Henan Hanwei Electronics Co., Ltd www.hwsensor.com
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Notification
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1 Following conditions must be prohibited
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1.1 Exposed to organic silicon steam
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Organic silicon steam cause sensors invalid, sensors must be avoid exposing to silicon bond,
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fixature, silicon latex, putty or plastic contain silicon environment
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1.2 High Corrosive gas
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If the sensors exposed to high concentration corrosive gas (such as H2Sz, SOX，Cl2，HCl etc), it will
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not only result in corrosion of sensors structure, also it cause sincere sensitivity attenuation.
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1.3 Alkali, Alkali metals salt, halogen pollution
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The sensors performance will be changed badly if sensors be sprayed polluted by alkali metals salt
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especially brine, or be exposed to halogen such as fluorin.
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1.4 Touch water
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Sensitivity of the sensors will be reduced when spattered or dipped in water.
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1.5 Freezing
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Do avoid icing on sensor’surface, otherwise sensor would lose sensitivity.
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1.6 Applied voltage higher
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Applied voltage on sensor should not be higher than stipulated value, otherwise it cause down-line or
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heater damaged, and bring on sensors’ sensitivity characteristic changed badly.
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1.7 Voltage on wrong pins
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For 6 pins sensor, if apply voltage on 1、3 pins or 4、6 pins, it
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will make lead broken, and without signal when apply on 2、4 pins
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2 Following conditions must be avoided
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2.1 Water Condensation
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Indoor conditions, slight water condensation will effect sensors performance lightly. However, if water
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condensation on sensors surface and keep a certain period, sensor’ sensitivity will be decreased.
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2.2 Used in high gas concentration
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No matter the sensor is electrified or not, if long time placed in high gas concentration, if will affect
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sensors characteristic.
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2.3 Long time storage
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The sensors resistance produce reversible drift if it’s stored for long time without electrify, this drift is
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related with storage conditions. Sensors should be stored in airproof without silicon gel bag with clean air.
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For the sensors with long time storage but no electrify, they need long aging time for stbility before using.
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2.4 Long time exposed to adverse environment
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No matter the sensors electrified or not, if exposed to adverse environment for long time, such as
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high humidity, high temperature, or high pollution etc, it will effect the sensors performance badly.
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2.5 Vibration
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Continual vibration will result in sensors down-lead response then repture. In transportation or
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assembling line, pneumatic screwdriver/ultrasonic welding machine can lead this vibration.
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2.6 Concussion
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If sensors meet strong concussion, it may lead its lead wire disconnected.
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2.7 Usage
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For sensor, handmade welding is optimal way. If use wave crest welding should meet the following
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conditions:
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2.7.1 Soldering flux: Rosin soldering flux contains least chlorine
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2.7.2 Speed: 1-2 Meter/ Minute
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2.7.3 Warm-up temperature：100±20℃
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2.7.4 Welding temperature：250±10℃
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2.7.5 1 time pass wave crest welding machine
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If disobey the above using terms, sensors sensitivity will be reduced.
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Tel: 86-371-67169070/80 Fax: 86-371-67169090 Email: sales@hwsensor.com
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miguel5612
6 years ago