How to calibrate an MQ-135 gas sensor (CO2)

Using Arduino Sensors
1

In firts place i need calibrated the sensor MQ135 for CO2 GAS and then get the concentration of CO2 ppm.

Is there any tutorial?

Help me please

THANKS

2

Do you have a calibration gas with a known concentration of CO2?

Air is pretty good - it has 400ppm CO2 if you get fresh air from outdoors. If you have a tank of Nitrogen or Oxygen, you can use that to get a reading for zero CO2.

A quick scan of the datasheet for the MQ135 shows that it responds to a lot of gases. If someone farts nearby, it will detect it and you can't tell which gas it was. Actual CO2 sensors cost $80-$400 for the cheap ones.

3

Thanks for your help.

How calculated RZERO with that?

void setup() {
Serial.begin(9600);
}

void loop() {

int adc_MQ = analogRead(A0); //Lemos la salida analógica del MQ
float voltaje = adc_MQ * (5.0 / 1023.0); //Convertimos la lectura en un valor de voltaje

Serial.print("adc:");
Serial.print(adc_MQ);
Serial.print(" voltaje:");
Serial.println(voltaje);
delay(100);
}

4

Tutorial (first Google hit).

From the MQ-135 data sheet: Ro = sensor resistance at 100ppm of NH3 in the clean air.

5

If you have a tank of Nitrogen or Oxygen, you can use that to get a reading for zero CO2.

Not a could idea.

First, these sensors NEED oxygen around 21% to work (lookup how MOx sensor work).

Second, you shoud calibrate sensors within the working range. Since the lowest concentration you are probably going to measure is the background concentration in outdoor air (400ppm) you need a calibration standard with a higher concentration, i would suggest something around 3000ppm.

Regards,
Alex