Differentiating Between Certain Gasses with MQ Sensors

I am looking to detect the concentration of certain gasses and log them. For instance, "at 4:32:24 there was a concentration of 1,000 ppm of Oxygen and 2,000 ppm of Carbon Dioxide at this location" I was looking into the MQ sensors like the MQ-5 here - https://www.amazon.com/ACROBOTIC-Natural-Breakout-Arduino-Raspberry/dp/B07CRDC9F4/ref=sr_1_2?dchild=1&keywords=mq5&qid=1626109541&sr=8-2 which is sensitive to "Natural Gas, Town/Coal Gas, LPG, CH4, CO or Alcohol"

However I am wondering if theses sensors can differentiate between the different gasses it is sensitive to. Does the digital output tell the certain gas detected? Or is the output just "sensor detected 1,000 ppm" without the specific gas?

If it cannot differentiate between gasses, what would be the best option to create a project like this? Thanks for all the help!

Most of the MQ sensors I have looked at are sensitive to multiple gasses, but they can't tell you which one(s) they're sensing.

I suspect that what you want to do will need fancier (more expensive) sensors.

Thanks for the response! I appreciate the confirmation I couldn’t find much online. Would you have any idea what sensors I would look into? When I look up gas sensors 90% of them are the MQ type. If not I will keep researching but thank you for the help!

I can't really help other than to note that I think you're going to need to look at industrial sensors if you want to be sure of what gas you're measuring. I think that any of those chemical substrate type things that you can get for a few bucks are likely to have the same issue with having multiple different chemicals setting them off.

Only if you are looking for cheap, hobby type sensors, which are insensitive, unreliable, difficult or impossible to calibrate and non specific.

Many industrial suppliers stock sensors specific to certain gases, but they are not cheap. Here is an example: https://www.pem-tech.com/ or another Industrial Point Gas Detection Products | Sensidyne

Thank you so much for the response and the helpful information!
I found this that I thought was interesting, it was used in a video showing how to calibrate one of these sensors - https://sandboxelectronics.com/?p=165 the code seems to calibrate the sensor and be able to detect the different types of gasses. People in the video comments were saying it worked, do you think this may be a possible solution?

Edit: even if it is not super accurate, it looks like these curves in the code can be used for any gasses on the sensors, as long as the sensors detect that gas and the R0 is known

The MQ sensors cannot differentiate between the different gases that they detect.

The code in that tutorial merely scales the resistance reading, assuming different gases in isolation are responsible for the reading. Basically it is a lookup table that models the curves shown in the data sheet. Any of the gases named in the figure below can affect the sensor output, in any combination.

Ah ok thanks for the information!

This topic was automatically closed 120 days after the last reply. New replies are no longer allowed.