Unusual Sensor Reading about arduino-mq131-driver

[NXTkoji]

I tried with another MQ-131 (high concentration), brand new, preheated sensor, but the readings were the same as the previous test. Following is the message from the serial monitor.

Calibration in progress...
Calibration parameters
R0 = 977.52 Ohms
Time to heat = 17 s
Sampling...
Concentration O3 : 12.34 ppm
Concentration O3 : 12343.99 ppb
Concentration O3 : 26.09 mg/m3
Concentration O3 : 26089.09 ug/m3
Sampling...
Concentration O3 : 12.34 ppm
Concentration O3 : 12343.99 ppb
Concentration O3 : 26.09 mg/m3
Concentration O3 : 26089.09 ug/m3

[NXTkoji]

Found out that you have specified to change code in your library for high concentration.
' case HIGH_CONCENTRATION :
// Use the equation to compute the O3 concentration in ppm

  // Compute the ratio Rs/R0 and apply the environmental correction
  ratio = lastValueRs / valueR0 * getEnvCorrectRatio();
  // R^2 = 0.9900
  // Use this if you are monitoring low concentration of O3 (air quality project)
  return convert(8.1399 * pow(ratio, 2.3297), PPM, unit);
  
  // R^2 = 0.9985 but nearly impossible to have 0ppm
  // Use this if you are constantly monitoring high concentration of O3
  // return convert((8.37768358 * pow(ratio, 2.30375446) - 8.37768358), PPM, unit);'

Followed the instruction and now I have a better reading.

Calibration parameters
R0 = 977.52 Ohms
Time to heat = 17 s
Sampling...
Concentration O3 : 4.27 ppm
Concentration O3 : 4268.12 ppb
Concentration O3 : 9.02 mg/m3
Concentration O3 : 9020.70 ug/m3

[ostaquet]

Hi @NXTkoji,

The high concentration sensor is manufactured with a detection range from 10ppm to 1000ppm (and not ppb ;-) ).

If you are performing measurements in clean air, I doubt you will reach 10ppm in real measurements.

As an example, the ozone in Belgium is about 107 ug/m3 (https://www.irceline.be/fr/qualite-de-lair/mesures/ozone). It means around 54 ppb (about 0.055 ppm). We are far below the minimum of the sensor.

The value you got in clean air is just a mathematical interpretation.

The high concentration sensor is really designed for the, as named :-), the high concentration sensing.

I hope it helps ;-)