How to calculate a output of mq138 sensor for Toluene gas

JeonSY · September 3, 2018, 12:09am

hi guys.

i am using a mq138 sensor with arduino mega 2560 for my project.
(datasheet:http://www.china-total.com/Product/meter/gas-sensor/MQ138.pdf)

of course i have searched source code about that.

here is get a LP sensor source using mq2

gist.github.com

https://gist.github.com/esmarr58/2e9335bfc64077407ed2286408982f61

Arduimo-MQ2.ino

#define         MQ1                       (0)     //define la entrada analogica para el sensor
#define         RL_VALOR             (5)     //define el valor de la resistencia mde carga en kilo ohms
#define         RAL       (9.83)  // resistencia del sensor en el aire limpio / RO, que se deriva de la                                             tabla de la hoja de datos
#define         GAS_LP                      (0)
String inputstring = "";                                                        //Cadena recibida desde el PC
float           LPCurve[3]  =  {2.3,0.21,-0.47};
float           Ro           =  10;
void setup(){
Serial.begin(9600);                                                                  //Inicializa Serial a 9600 baudios
 Serial.println("Iniciando ...");

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i know that is not about mq138 but i needed to know how to using mq sensors because i have not used mq sensors ever..

and next. here is another source for many sensors(mq138, mq135, TGS2600 ...)

github.com

empierre/arduino-mysensors-contribs/blob/master/AirQuality-Multiple_Gas_Sensor1_4.ino

 /*
  Arduino Multiple Air Quality Sensors

  connect the sensor as follows when standalone:

  A H A   >>> 5V
  B	  >>> A0
  H       >>> GND
  B       >>> 10K/20K ohm >>> GND
  
  Contribution: epierre
  Based on David Gironi http://davidegironi.blogspot.fr/2014/01/cheap-co2-meter-using-mq135-sensor-with.html
  
  Precaution:
     The gasses detected by these gas sensors can be deadly in high concentrations. Always be careful to perform gas tests in well ventilated areas.
 
  Note:
     THESE GAS SENSOR MODULES ARE NOT DESIGNED FOR OR APPROVED FOR ANY APPLICATION INVOLVING HEALTH OR HUMAN SAFETY. THESE GAS SENSOR MODULES ARE FOR EXPERIMENTAL PURPOSES ONLY.

  License: Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0)

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the output PPM is 0~5 value if the source run with mq138

now, i know how to use mq sensors!
but i do not know how to get initialized value of toluene.

how to get Toluene curve, Ro, Rs like that?
the source explains to get Toluene with TGS2600.

regards.

jremington · September 3, 2018, 10:35pm

how to get Toluene curve, Ro, Rs like that?

The only possibility is to make your own calibration curve, by placing the sensor in gas mixtures that have known concentrations of tolulene gas, and recording the readings.

These cheap sensors are not very discriminating, and are not useful for accurate measurements of gas concentrations. They are mostly useful for reporting changes in gas concentrations.

JeonSY · September 4, 2018, 1:46am

jremington:
The only possibility is to make your own calibration curve, by placing the sensor in gas mixtures that have known concentrations of tolulene gas, and recording the readings.

These cheap sensors are not very discriminating, and are not useful for accurate measurements of gas concentrations. They are mostly useful for reporting changes in gas concentrations.

Thank you for your reply.
right, this one is so cheap so we also can not trust this perfectly.
i just want to know can i get the toluene gas concentrations by using the source code uploaded github

github.com

empierre/arduino-mysensors-contribs/blob/master/AirQuality-Multiple_Gas_Sensor1_4.ino

 /*
  Arduino Multiple Air Quality Sensors

  connect the sensor as follows when standalone:

  A H A   >>> 5V
  B	  >>> A0
  H       >>> GND
  B       >>> 10K/20K ohm >>> GND
  
  Contribution: epierre
  Based on David Gironi http://davidegironi.blogspot.fr/2014/01/cheap-co2-meter-using-mq135-sensor-with.html
  
  Precaution:
     The gasses detected by these gas sensors can be deadly in high concentrations. Always be careful to perform gas tests in well ventilated areas.
 
  Note:
     THESE GAS SENSOR MODULES ARE NOT DESIGNED FOR OR APPROVED FOR ANY APPLICATION INVOLVING HEALTH OR HUMAN SAFETY. THESE GAS SENSOR MODULES ARE FOR EXPERIMENTAL PURPOSES ONLY.

  License: Attribution-NonCommercial-ShareAlike 3.0 Unported (CC BY-NC-SA 3.0)

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i already have one device to get a toluene gas concentrations, i want to check that device and mq138.
thanks for your reply jremington

jremington · September 4, 2018, 4:27am

can i get the toluene gas concentrations by using the source code uploaded github

Probably not. Who knows where all those numbers came from? I don't believe any of it, because every sensor has to be individually calibrated.

Have you seen this excellent tutorial on using MQ sensors to make an electronic nose?

JeonSY · September 4, 2018, 5:54am

thank you jremington.

but i have to keep searching the right way to get a toluene gas with mq138.
it will not give right output but calibration is next step.
i do not trust the source code has the right way.

i will see that new reference. haha

regard

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How to calculate a output of mq138 sensor for Toluene gas

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