This sensor detects carbon mono oxide present in the atmosphere. Sensitive material of MQ-7 gas sensor is SnO2(Tin Oxide), which with lower conductivity in clean air. It makes detection by a method of cycle high and low temperature, and detect CO at low temperature(heated by 1.5V).
The sensor’s conductivity gets higher along with the CO gas concentration rising. At high temperature(heated by 5.0V), it cleans the other gases adsorbed at low temperature. Users can convert the change of conductivity to the corresponding output signal of gas concentration through a simple circuit.
It has good sensitivity to carbon monoxide in a wide range and has advantages such as long lifespan, low cost, and simple drive circuit &etc.
WORKING PRINCIPLE OF MQ-7 Gas Sensor:
The MQ-7 gas sensor is composed of the micro AL2O3 ceramic tube, Tin Dioxide (SnO2) sensitive layer, measuring electrode and heater are fixed into a crust made of plastic and stainless steel net. The heater provides necessary work conditions for work of sensitive components. The enveloped MQ-7 Gas Sensor have 6 pins, 4 of them are used to fetch signals, and other 2 are used for providing heating current.
A standard measuring circuit of MQ-7 Gas Sensor sensitive components consists of 2 parts. One is a heating circuit having time control function (the high voltage and the low voltage work circularly ). The second is the signal output circuit, it can accurately respond changes in surface resistance of the sensor.
The surface resistance of the sensor Rs is obtained through effected voltage signal output of the load resistance RL which series-wound. The relationship between them is described:
Rs\RL = (Vc-VRL) / VRL
when the sensor is shifted from clean air to carbon monoxide (CO), output signal measurement is made within one or two complete heating period (2.5 minutes from high voltage to low voltage ). A sensitive layer of MQ-7 Gas Sensor sensitive components is made of SnO2 with stability, So, it has excellent long-term stability. Its service life can reach 5 years under using condition.
USES OF THE MQ-7 Gas Sensor :
It is widely used in domestic CO gas leakage alarm, industrial CO gas alarm, and portable CO gas detector. They are used in gas detecting equipment for carbon monoxide(CO) in family and industry or car.
- Circuit voltage: 5V±0.1
- Heating voltage (high) : 5V±0.1
- Heating voltage (low) : 1.4V±0.1
- Load resistance: Adjustable
- Heating resistance: 33Ω±5%
- Heating time (high): 60±1 seconds
- Heating time (low): 90±1 seconds
- Heating consumption: About 350mW
- Using temperature : -20C to +50C
- Storage temperature : -20C to +50C
- Relative humidity: Less than 95%RH
- Oxygen concentration: 21%(stand condition) the oxygen concentration can affect the sensitivity characteristic
- Surface resistance Of sensitive body: 2-20k
- Concentration slope rate: Less than 0.5
- Vc: 5V±0.1V
- VH: 5V±0.1V
- VH: 1.4V±0.1V
- Preheat time: No less than 48 hours
Materials To Be Required :
- MQ-7 Carbon Monoxide Sensor
Connection with Arduino :