HANWEI ELECTRONICS CO ., LTD MQ –7 http://www.hwsensor.com TECHNICAL DATA MQ-7 GAS SENSOR FEATURES * High sensitivity to carbon monoxide * Stable and long life APPLICATION They are used in gas detecting equipment for carbon monoxide(CO) in family and industry or car. SPECIFICATIONS A. Standard work condition Symbol Parameter name Technical condition Remark Vc circuit voltage 5V±0.1 Ac or Dc VH (H) Heating voltage (high) 5V±0.1 Ac or Dc VH (L) Heating voltage (low) 1.4V±0.1 Ac or Dc RL Load resistance Can adjust RH Heating resistance 33Ω±5% Room temperature TH (H) Heating time (high) 60±1 seconds TH (L) Heating time (low) 90±1 seconds PH Heating consumption About 350mW b. Environment conditions Symbol Parameters Technical conditions Remark Tao Using temperature -20℃-50℃ Tas Storage temperature -20℃-50℃ Advice using scope RH Relative humidity Less than 95%RH O2 Oxygen concentration 21%(stand condition) Minimum value is over 2% the oxygen concentration can affect the sensitivity characteristic c. Sensitivity characteristic symbol Parameters Technical parameters Remark Rs Surface resistance In 100ppm Of sensitive body 2-20k Carbon Monoxide а(300/100ppm) Concentration slope rate Less than 0.5 Rs (300ppm)/Rs(100ppm) Standard working Temperature -20℃±2℃ relative humidity 65%±5% RL:10K Ω±5% condition Vc:5V±0.1V VH:5V ±0.1V VH:1.4V±0.1V Preheat time No less than 48 hours Detecting range: 20ppm-2000ppm carbon monoxide D. Structure and configuration, basic measuring circuit Structure and configuration of MQ-7 gas sensor is shown as Fig. 1 (Configuration A or B), sensor composed by micro AL 2O3 ceramic tube, Tin Dioxide (SnO 2) sensitive layer, measuring electrode and heater are fixed into a crust made by plastic and stainless steel net. The heater provides necessary work conditions for work of sensitive components. The enveloped MQ-7 have TEL:86-371-67169070 67169080 FAX:86-371-67169090 Email: sales@hwsensor.com

HANWEI ELECTRONICS CO ., LTD MQ –7 http://www.hwsensor.com 6 pin ,4 of them are used to fetch signals, and other 2 are used for providing heating current. Parts Materials 1 Gas sensing SnO2 layer 2 Electrode Au 3 Electrode line Pt 4 Heater coil Ni-Cr alloy 5 Tubular ceramic Al2O3 6 Anti-explosion Stainless steel gauze network (SUS316 100-mesh) 7 Clamp ring Copper plating Ni 8 Resin base Bakelite 9 Tube Pin Copper plating Ni Fig.1 A A A向 Standard circuit: Heating voltage 5v (High) 60s As shown in Fig 2, standard measur ing circuit of VRL MQ-7 sensitive components consists of 2 parts. one V H is heating circuit having time control function (the high voltage and the low voltage work RL circularly ). The second is the signal output circuit, Vc it can accurately respond changes of surface resistance of the sensor. Heating voltage 1.4v (Low) 90s Fig.2 Electric parameter measurement circuit is shown as Fig.2 E. Sensitivity characteristic curve MQ-7 100 Fig.3 is shows the typical sensitivity characteristics of 10 the MQ-7 for several gases. in their: Temp: 20℃、 Humidity: 65%、 o R /1 O2 concentration 21% s R RL=10kΩ CO Ro: sensor resistance at 100ppm H2 0.1 LPG CO in the clean air. CH4 Alcohol Rs: sensor resistance at various air concentrations of gases. ppm 0.01 10 100 1000 10000 Fig.3 sensitivity characteristics of the MQ-7 TEL:86-371-67169070 67169080 FAX:86-371-67169090 Email: sales@hwsensor.com

HANWEI ELECTRONICS CO ., LTD MQ –7 http://www.hwsensor.com MQ-7 Fig.4 is shows the typical 1.5 Fig.4 1.4 dependence of the MQ-7 on 33%RH 1.3 1.2 85%RH temperature and humidity. o 1.1 /R 1 Ro: sensor resistance at 100ppm CO in s R 0.9 air at 33%RH and 20degree. 0.8 0.7 Rs: sensor resistance at 100ppm CO at 0.6 Temp 0.5 different temperatures and humidities. -10 0 10 20 30 40 50 OPERATION PRINCIPLE . 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 Fig. 5 shows alterable situation of RL signal output measured by using Fig. 2 circuit output In 100ppmCO In air In air VH5v 60s 90s 1.4v Signal Fig.5 signal 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 minute from high voltage to low voltage ). Sensitive layer of MQ-7 gas sensitive components is made of SnO 2 with stability, So, it has excellent long term stability. Its service life can reach 5 years under using condition. SENSITVITY ADJUSTMENT Resistance value of MQ-7 is difference to various kinds and various concentration gases. So, When using this components, sensitivity adjustment is very necessary. we recommend that you calibrate the detector for 200ppm CO in air and use value of Load resistance that( R) about 10 KΩ(5KΩ to 47 KΩ). L When accurately measuring, the proper alarm point for the gas detector should be determined after considering the temperature and humidity influence. The sensitivity adjusting program: a. Connect the sensor to the application circuit. b. Turn on the power, keep preheating through electricity over 48 hours. c. Adjust the load resistance RL until you get a signal value which is respond to a certain carbon monoxide concentration at the end point of 90 seconds. d. Adjust the another load resistance RL until you get a signal value which is respond to a CO concentration at the end point of 60 seconds . Supplying special IC solutions, More detailed technical information, please contact us. TEL:86-371-67169070 67169080 FAX:86-371-67169090 Email: sales@hwsensor.com