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Is there any way to correctly measure increase of methane in the air using MQ-4 without heating (Not linking heater legs to GND and V). It is needed to save power. MQ-4 is methane sensor, datasheet: https://www.sparkfun.com/datasheets/Sensors/Biometric/MQ-4.pdf

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closed as unclear what you're asking by Olin Lathrop, Leon Heller, Dmitry Grigoryev, Voltage Spike, Autistic Mar 24 '17 at 21:39

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    \$\begingroup\$ What does the datasheet say? It's very unlikely. \$\endgroup\$ – Leon Heller Mar 24 '17 at 11:09
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    \$\begingroup\$ We're just supposed to know what a "MQ-4" is? Seriously!? And then, how is this not directly answered by the datasheet. Duh! \$\endgroup\$ – Olin Lathrop Mar 24 '17 at 11:11
  • \$\begingroup\$ Appears to be a MOS-type gas sensor. Some are specified for pulsed operation. You need the heater. \$\endgroup\$ – Spehro Pefhany Mar 24 '17 at 11:20
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    \$\begingroup\$ Whatever you measured is pointless. Generally, low cost gas sensors need to be at a particular temperature. That is generally set above normal room temperature. They also generally require that no moisture be absorbed, once again, heating ensures that. \$\endgroup\$ – R Drast Mar 24 '17 at 12:08
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    \$\begingroup\$ Think about it: if it was possible to do the measurement without the heater, why would they put one in? \$\endgroup\$ – Dmitry Grigoryev Mar 24 '17 at 13:14
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No. A flammable gas sensor can be made by heating a wire and measuring its resistance.

If that resistance increases, you know that its temperature has increased. Want to guess why the temperature increased?

If your guess is correct, you will understand that failure to heat the wire will result in failure to initiate the chemical reaction - combustion - and thus failure to detect inflammable gas. The wire can be a catalytic material, and thus catalyses the combustion of inflammable gas at a lower temperature than otherwise possible, so it shouldn't ignite the whole room

In fact the datasheet shows that the active substance in this sensor is tin dioxide. And a Wikipedia search for "tin dioxide" shows this quote :

SnO2 is used in sensors of combustible gases including carbon monoxide detectors. In these the sensor area is heated to a constant temperature (few hundred °C) and in the presence of a combustible gas the electrical resistivity drops.[21] Doping with various compounds has been investigated (e.g. with CuO[22]). Doping with cobalt and manganese, gives a material that can be used in e.g. high voltage varistors.[23] Tin (IV) oxide can be doped with the oxides of iron or manganese.[24]

So this sensor is more sensitive than my speculation, but shows a fall in resistance with inflammable gas concentration. But the basic operation is the same : heat the sample to several hundred degrees C, or it won't work.

(It's not quite as dangerous as it sounds ... you may recognise the mesh around the sensor as a flame preventer - see Humphrey Davey's "Safety Lamp" for another example. And the datasheet labels it as an "Anti explosion network")

If you need a lower power detector, you need an entirely different type of sensor. I don't know of any offhand, but that's what search engines are for.

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  • \$\begingroup\$ I think the MQ-4 is not a catalytic sensor, it uses SnO2, and responds to removal of oxygen at grain boundaries "scavenged" by combustable and other gases, increasing the conductivity of the grain boundaries, and therefore the average of the whole oxide pellet. Of course the rest of your answer is correct - "no!" \$\endgroup\$ – uhoh Apr 5 '17 at 9:14

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