MQ-131 Ozone Gas Sensor with EasyC returns incorrect low readings

TECHNICAL SUPPORT Sensors & Modules
1

Customer:

I’m trying to use the MQ-131 Ozone gas sensor with EasyC on my microcontroller. After correctly connecting the EasyC connector, I ran the example sketch MQ-131-All-EasyC from the MQ sensor library. The output is not meaningful—it gives values around 1.2 ppm, which is not possible in breathable air. I’ve tested this with multiple identical sensors and multiple microcontroller models. Are these the correct parameters, or do they need modification?

Originally submitted via email support on 2 April 2025. Migrated to the forum for community visibility.

2

Soldered Support:

The MQ library is currently being updated. The regression A and B values likely need to be adjusted.

These sensors have cross-detection and will also detect other gases besides their target gas. The 1.2 ppm value may be the lowest reading possible, and the value should spike when near the target gas.

3

Customer:

I have two observations:

  1. The output value decreases when I turn on an ozone generator near the sensor. The opposite is expected.

  2. The output value increases when the sensor is touched by hand.

Also, I checked the Winsen website and found they offer two models: one for low concentration and one for high concentration ozone gas. The sensor on your board appears to be the high concentration model, but the datasheet on your website is for the low concentration model. Can you confirm whether you have the correct datasheet for the sensor on your board?

4

Soldered Support:

The output value increasing when touched by hand is expected—it’s a type of noise for these sensors.

Regarding datasheet matching, that was done earlier. I’ve notified the team about this concern, though I can’t yet confirm if you’re correct. Thank you for bringing it to our attention.

Have you left the sensor powered on for 48 hours before taking measurements with the ozone generator? These sensors have a warm-up period.

I’ve also asked my colleague working on the MQ library update which parameters are being used for the MQ-131. Letting the sensor warm up for a long time and setting the correct regression parameters should lead to more accurate readings.

5

Soldered Support:

Here are the parameters being used for the MQ-131:

Regression method type: 0
RS/R0 in clean air: 1
Coefficient a: 0.4 b: -0.4708