hanwei eletronics co.,ltd mq-307a http://www.hwsensor.com tel: 86-371-67169070 67169080 fax: 86-371-67169090 e-mail: sales@hwsensor.com MQ307A co gas sensor the MQ307A is a tin dioxide semiconductor gas sensor which has an excellent performance in co detection. using a mini-bead type sensing element with a periodic temperature change operation method, high sensitivity, selectively, small effect from humidity and other remarkable characteristics have been achieved. the MQ307A realizes the development of reliable co detection devices. structure gas sensitive semiconductor material is a mini bead type and a heater coil and electrode wire are embedded in the element. the sensing element is installed in the metal housing which uses double stainless steel mesh (100mesh) in the path of gas flow. operating conditions when the sensor is operated with high/low periodic operation (fig 2), sensor signal changes according to the temperature dependencycharacteristics. by detecting the sensor signal at sufficient timings (at a high temperature for methane and at a low temperature for co), selective detection of both methane and co has been achieved. fig 3 shows the standard operation circuit and fig 4 shows the sensitivity characteristics of the MQ307A at low temperature. free datasheet http://
hanwei eletronics co.,ltd mq-307a http://www.hwsensor.com tel: 86-371-67169070 67169080 fax: 86-371-67169090 e-mail: sales@hwsensor.com a standard working terms symbol parameter technical terms remarks vh(h) heater voltage high 0.90v 0.10v ac or dc vh(l) heater voltage low 0.2 v 5% dc (polarity is important) v c circuit voltage 6 v r l load resistance adjustable(> 1 k w ? ) p s < 10 mw r h heating resistance 3.8 ? 3.8 w 0.5 w room temperature th (h) heating time(high) 30sec 5 sec th (l) heating time low 120 sec 10sec dt (l) sampling time low < 1 sec at the ending of low voltage heating i (h) heating current low 120 ma vh=0.9v i (l) heating voltage low 40 5 mw vh=0.2v p s power 10 mw p s = (v c - v rl ) 2 / r s ph heating consumption less than 100mw b.environment conditions symbol parameter technical terms remarks tao using temperature -20 o c to 50 o c tas storage temperature -20 o c to 70 o c rh relative humidity 95% rh recommended application ranges (o2) oxygen concentration 21% 1%(standard terms) 0 2 influence sensor performance not less than 18% c. sensitivity characteristics model mq-307a symbol parameter technical terms remarks r s sensitive resistance (20k w ? to 200 k w ) in 200 ppm co ? (30-100) resistance proportion 1.05 to 2.1 rs (30 ppmco) / rs (100 ppmco) ? (100-300) resistance proportion 0.75 to 1.2 rs(300 ppmco) /rs(100ppmco) standard testing terms: temperature : 20 o c 2 o c v c : 5.0 v ? 1% humidity: 65% 5% v h : 0.9 v 1% r l : 50k w 5% preheating time more than 48 hours free datasheet http://
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