Abnormal MQ-2 gas sensor reading

Other Hardware Sensors
1

Hi there, I am new to Arduino world

Recently I want to create a small project which can detect smoke gas using MQ-2 gas sensors.

I have found some research about MQ-2 sensors that normal reading from the sensor should be between 100-300ppm.

However, the output in the serial monitor of the IDE is below than 100 ppm, even below than 50 ppm when it is not detect any gas, isn't it should be around 100ppm when there is no any gas detect?
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That's all for my question, hope I can get some clarification regarding to my question. Thank you.

2

Welcome to the forum.

They are very cheap and very sensitive, but you can not measure a ppm with it.
They change their resistance with a number of gasses, that's all. The sensor is more a gimmick and not so much a measuring device.

Have you read about the "burn-in" time or "preheat" ? Did you do that ? It is 24 hours (or more).
Adafruit has a tutorial: https://learn.adafruit.com/gas-sensor-comparison/gas-sensor-types

After the burn-in time you could calibrate it with a known amount of ppm. After that, it can give a number for the ppm. But that is not accurate at all, but if you want a number, then you have a number. It might be 10% inaccurate or 100% or 1000%.

What you can detect is a increase or decrease of the gasses it detects.

3

i see...

So may I know how can I measure that, if the sensor detect gas leakage with a specific value for output?

Thanks

4

What kind of gas ?

Adafruit has these gas sensors: https://www.adafruit.com/category/897.
They can be used for a generic air quality sensor.
Those gas sensors have sometimes also a (small) heater, just like the MQ-2 sensor.
They are often calibrated at the factory.

I hope that you are not trying to detect a combustible gas. The MQ-2 sensor with it big heater should not be near such gases. In that case, you should buy a certified gas sensor.

5

oh really?

I saw MQ-2 is able to used for detect methane gas, like gas leakage from kitchen stove...

6

Try telling that to someone who works for a gas company :scream:

7

I saw this video as references, her MQ-2 able to detect the value normally like around 100-500ppm

May i know what should I do the setting to make it alike the video? thanks

8

She got it to work once and made a video. Good luck trying to reproduce that!

1 Like
9

There is no mention in the video of 100-500 ppm.
Do you mean the value of "300" in the code at 4:07 ?
That is the value returned from a analog pin. It can very between 0...1023. See the function analogRead(): https://www.arduino.cc/reference/en/language/functions/analog-io/analogread/
It is a number for the voltage of the analog pin, it is not the ppm.

To get the best out of this sensor:

  1. Burn-in (Preheat) the sensor for at least 24 hours.
  2. Use it indoors. Keep it away from draft (moving air). Keep it in a room that has the same temperature and the same humidity.
  3. Let it warm up for 5 minutes, before reading the value.
  4. If it has been in a different place or if it has been stored for days or weeks, then do the burn-in (preheat) again.
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