HI I'm working on MQ gas sensors
when i put this sensor in vacuum chamber i expected the sensor to read low ADC since there is no gas
but actually it reads high
when the vacuum reduces to 0.05 mbar it goes to peak and reaches saturation (reads 1023)
why is this
when no gas it should read zero
can any one help
when no gas it should read zero
Nonsense. Please read the sensor data sheet and study the excellent tutorial here.
These sensors are really only useful for measuring a change in the gas mixture, and they must be "burned in" for 24 to 48 hours before any use.
You didnt get my question I have done all the perquisites the sensor can detect the gas in the environment subjected and also responds well for different concentration of gas. there is no problem about its working but when I put this mq gas sensor in vacuum chamber and subject it to vacuum the sensor reads high value
The vacuum chamber does not have any gas inside then the gas sensor should have RS/RO ratio large
which in datasheet represents a low concentration
but the sensor reads a high concentration value when the sensor it subjected to vacuum which should read a low value but I'm getting it high in absence of gas in vacuum
why is this
can the sensor be operated in vacuum
what happens to the behaviour of the sensing element when in vacuum
why is the sensor reading high in vacuum when gas is absent
Yes, I did get your question. As your test clearly shows, your assumption that the reading should be zero in a vacuum is incorrect.
can the sensor be operated in vacuum
Yes, it can. But it makes no sense to do so.
These sensors must be individually calibrated using known concentrations of the gas you want to detect, in dry air at normal atmospheric pressure. See the datasheet for the details.
thank you for your information
ill get back to you
Your gas sensor consists of a specialized resistor, that absorbs molecules of the gas that is being sensed. More of the molecules absorbed gives a higher reading of the sensor. The resistance at zero concentration is the resistance in pure air, not in a vacuum. You need to provide air that has none of the gas you are analyzing for in it. Also MQ sensors typically have lots of interferences that complicate the calibration process. Perhaps you need some sort of ndir sensor?
You didn't state what gas you are analyzing for? HCN, H2S, Cl2, F2???