The MQ-9 is a CO and CH₄ gas detection sensor form Winsen. The sensing material of the MQ-9 is SnO2, which has a low conductivity in clean air. It detects carbon monoxide (1.5V) by method of cycling high and low temperature. The sensor’s conductivity gets higher with the CO and CH₄ gas concentration rising. The sensing range is 10-500ppm CH₄. A simple circuit makes measuring this change in conductivity and turning it into data fairly straight-forward, but does require some calibration.
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Range: 10~500ppm CO,300~10000ppm CH4
Dimensions: Ø19 x 24mm
Supply voltage: 5V