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| www..com 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 Ac or Dc 5V0.1 VH (H) Heating voltage (high) Ac or Dc 5V0.1 VH (L) Heating voltage (low) Ac or Dc 1.4V0.1 RL Load resistance Can adjust RH Heating resistance Room temperature 33 5% TH (H) Heating time (high) 601 seconds TH (L) Heating time (low) 901 seconds PH Heating consumption About 350mW b. Environment conditions Symbol Tao Tas RH O2 Parameters Using temperature Storage temperature Relative humidity Oxygen concentration Technical conditions -20...+50 -20...+50 Less than 95%RH 21%(stand condition) the oxygen concentration can affect the sensitivity characteristic Remark Advice using scope Minimum value is over 2% c. Sensitivity characteristic Parameters Technical parameters Remark Surface resistance In 100ppm Of sensitive body 2-20k Carbon Monoxide Concentration slope rate Less than 0.5 Rs (300ppm)/Rs(100ppm) Temperature -202 relative humidity 65%5% RL:10K 5% Vc:5V0.1V VH:5V0.1V VH:1.4V0.1V No less than 48 hours Detecting range: 20ppm-2000ppm carbon monoxide symbol Rs (300/100ppm) Standard working condition Preheat time 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 AL2O3 ceramic tube, Tin Dioxide (SnO2) 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: sensor@371.net www..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. 1 2 3 4 5 6 7 8 9 Parts Gas sensing layer Electrode Electrode line Heater coil Tubular ceramic Anti-explosion network Clamp ring Resin base Tube Pin Materials SnO2 Au Pt Ni-Cr alloy Al2O3 Stainless steel gauze (SUS316 100-mesh) Copper plating Ni Bakelite Copper plating Ni Fig.1 A A A Heating voltage 5v (High) 60s VRL RL Vc Heating voltage 1.4v (Low) 90s Standard circuit: As shown in Fig 2, standard measuring circuit of MQ-7 sensitive components consists of 2 parts. one is 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 of surface resistance of the sensor. Electric parameter measurement circuit is shown as Fig.2 E. Sensitivity characteristic curve 100 Rs/Ro 0. 01 10 100 1000 VH M-7 Q 10 1 C O H 2 LPG C4 H Al cohol ai r Fig.2 Fig.3 is shows the typical sensitivity characteristics of the MQ-7 for several gases. in their: Temp: 20 Humidity: 65% O2 concentration 21% RL=10k Ro: sensor resistance at 100ppm CO in the clean air. Rs: sensor resistance at various 0. 1 ppm 10000 concentrations of gases. Fig.3 sensitivity characteristics of the MQ-7 TEL:86-371-67169070 67169080 FAX:86-371-67169090 Email: sensor@371.net www..com HANWEI ELECTRONICS CO ., LTD MQ -7 http://www.hwsensor.com 1. 5 1. 4 1. 3 1. 2 1. 1 1 0. 9 0. 8 0. 7 0. 6 0. 5 - 10 0 10 M-7 Q 33% H R 85% H R Fig.4 Fig.4 is shows the typical dependence of the MQ-7 on temperature and humidity. Ro: sensor resistance at 100ppm CO in air at 33%RH and 20degree. Rs: sensor resistance at 100ppm CO at Tem p Rs/Ro different temperatures and humidities. 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 1.4v 60s 90s 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 SnO2 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( RL) about 10 K (5K to 47 K ). 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: sensor@371.net |
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