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Topic: MQ2 Sensor und Kalibrierung (Read 570 times) previous topic - next topic

Calethiel

Mar 30, 2018, 05:39 pm Last Edit: Mar 30, 2018, 06:44 pm by Calethiel
Hallo alle zusammen,

mit meinem Arduino Leonardo und dem MQ2 Sensor möchte ich Methan/CO/Rauch messen.
Ich habe hierzu ein Programm mit Sensorkalibrierung gefunden. (Kompletter Sketch siehe unten)
Den MQ2 habe ich 20 Minuten warm laufen lassen.

Bei der Kalibrierung ist der   RO_CLEAN_AIR_FACTOR  mit 9.83 voreingestellt. Der aktuelle Widerstand wird angezeigt.
Die Temperatur beträgt 19.8 Grad und 58,9 % Luftfeuchtigkeit (anzeige DHT22).

Ändere ich diesen Wert auch 5.8 kommt bei der Kalibrierung auch ca. die 5K ohm zustande.

Ausgabe serieller Monitor:
Calibration is done...
Ro=3.28kohm
LPG:0ppm    CO:0ppm    SMOKE:0ppm

Muss ich den Clean Air Factor so einstellen, dass ich auf meine 5K ohm komme, damit dieser richtige Werte detektiert?
Ich würde ihn gerne neben dem gekauften Co/Rauch Sensor im Keller bei meiner Gastherme einsetzen inklusive SMS-Versand bei Alarm usw.

Vielen dank schonmal für die Hilfe.





Sketch:


Code: [Select]
/************************Hardware Related Macros************************************/
#define         MQ_PIN                       (0)     //define which analog input channel you are going to use
#define         RL_VALUE                     (5)     //define the load resistance on the board, in kilo ohms
#define         RO_CLEAN_AIR_FACTOR     (9.83)  //RO_CLEAR_AIR_FACTOR=(Sensor resistance in clean air)/RO,
                                                    //which is derived from the chart in datasheet

/***********************Software Related Macros************************************/
#define         CALIBARAION_SAMPLE_TIMES     (50)    //define how many samples you are going to take in the calibration phase
#define         CALIBRATION_SAMPLE_INTERVAL  (500)   //define the time interal(in milisecond) between each samples in the
                                                    //cablibration phase
#define         READ_SAMPLE_INTERVAL         (50)    //define how many samples you are going to take in normal operation
#define         READ_SAMPLE_TIMES            (5)     //define the time interal(in milisecond) between each samples in
                                                    //normal operation

/**********************Application Related Macros**********************************/
#define         GAS_LPG                      (0)
#define         GAS_CO                       (1)
#define         GAS_SMOKE                    (2)

/*****************************Globals***********************************************/
float           LPGCurve[3]  =  {2.3,0.21,-0.47};   //two points are taken from the curve.
                                                   //with these two points, a line is formed which is "approximately equivalent"
                                                   //to the original curve.
                                                   //data format:{ x, y, slope}; point1: (lg200, 0.21), point2: (lg10000, -0.59)
float           COCurve[3]  =  {2.3,0.72,-0.34};    //two points are taken from the curve.
                                                   //with these two points, a line is formed which is "approximately equivalent"
                                                   //to the original curve.
                                                   //data format:{ x, y, slope}; point1: (lg200, 0.72), point2: (lg10000,  0.15)
float           SmokeCurve[3] ={2.3,0.53,-0.44};    //two points are taken from the curve.
                                                   //with these two points, a line is formed which is "approximately equivalent"
                                                   //to the original curve.
                                                   //data format:{ x, y, slope}; point1: (lg200, 0.53), point2: (lg10000,  -0.22)                                                    
float           Ro           =  10;                 //Ro is initialized to 10 kilo ohms

void setup()
{
 Serial.begin(9600);                               //UART setup, baudrate = 9600bps
 Serial.print("Calibrating...\n");                
 Ro = MQCalibration(MQ_PIN);                       //Calibrating the sensor. Please make sure the sensor is in clean air
                                                   //when you perform the calibration                    
 Serial.print("Calibration is done...\n");
 Serial.print("Ro=");
 Serial.print(Ro);
 Serial.print("kohm");
 Serial.print("\n");
}

void loop()
{
  Serial.print("LPG:");
  Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_LPG) );
  Serial.print( "ppm" );
  Serial.print("    ");  
  Serial.print("CO:");
  Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_CO) );
  Serial.print( "ppm" );
  Serial.print("    ");  
  Serial.print("SMOKE:");
  Serial.print(MQGetGasPercentage(MQRead(MQ_PIN)/Ro,GAS_SMOKE) );
  Serial.print( "ppm" );
  Serial.print("\n");
  delay(8000);
}

/****************** MQResistanceCalculation ****************************************
Input:   raw_adc - raw value read from adc, which represents the voltage
Output:  the calculated sensor resistance
Remarks: The sensor and the load resistor forms a voltage divider. Given the voltage
        across the load resistor and its resistance, the resistance of the sensor
        could be derived.
************************************************************************************/
float MQResistanceCalculation(int raw_adc)
{
 return ( ((float)RL_VALUE*(1023-raw_adc)/raw_adc));
}

/***************************** MQCalibration ****************************************
Input:   mq_pin - analog channel
Output:  Ro of the sensor
Remarks: This function assumes that the sensor is in clean air. It use  
        MQResistanceCalculation to calculates the sensor resistance in clean air
        and then divides it with RO_CLEAN_AIR_FACTOR. RO_CLEAN_AIR_FACTOR is about
        10, which differs slightly between different sensors.
************************************************************************************/
float MQCalibration(int mq_pin)
{
 int i;
 float val=0;

 for (i=0;i<CALIBARAION_SAMPLE_TIMES;i++) {            //take multiple samples
   val += MQResistanceCalculation(analogRead(mq_pin));
   delay(CALIBRATION_SAMPLE_INTERVAL);
 }
 val = val/CALIBARAION_SAMPLE_TIMES;                   //calculate the average value

 val = val/RO_CLEAN_AIR_FACTOR;                        //divided by RO_CLEAN_AIR_FACTOR yields the Ro
                                                       //according to the chart in the datasheet

 return val;
}
/*****************************  MQRead *********************************************
Input:   mq_pin - analog channel
Output:  Rs of the sensor
Remarks: This function use MQResistanceCalculation to caculate the sensor resistenc (Rs).
        The Rs changes as the sensor is in the different consentration of the target
        gas. The sample times and the time interval between samples could be configured
        by changing the definition of the macros.
************************************************************************************/
float MQRead(int mq_pin)
{
 int i;
 float rs=0;

 for (i=0;i<READ_SAMPLE_TIMES;i++) {
   rs += MQResistanceCalculation(analogRead(mq_pin));
   delay(READ_SAMPLE_INTERVAL);
 }

 rs = rs/READ_SAMPLE_TIMES;

 return rs;  
}

/*****************************  MQGetGasPercentage **********************************
Input:   rs_ro_ratio - Rs divided by Ro
        gas_id      - target gas type
Output:  ppm of the target gas
Remarks: This function passes different curves to the MQGetPercentage function which
        calculates the ppm (parts per million) of the target gas.
************************************************************************************/
int MQGetGasPercentage(float rs_ro_ratio, int gas_id)
{
 if ( gas_id == GAS_LPG ) {
    return MQGetPercentage(rs_ro_ratio,LPGCurve);
 } else if ( gas_id == GAS_CO ) {
    return MQGetPercentage(rs_ro_ratio,COCurve);
 } else if ( gas_id == GAS_SMOKE ) {
    return MQGetPercentage(rs_ro_ratio,SmokeCurve);
 }    

 return 0;
}

/*****************************  MQGetPercentage **********************************
Input:   rs_ro_ratio - Rs divided by Ro
        pcurve      - pointer to the curve of the target gas
Output:  ppm of the target gas
Remarks: By using the slope and a point of the line. The x(logarithmic value of ppm)
        of the line could be derived if y(rs_ro_ratio) is provided. As it is a
        logarithmic coordinate, power of 10 is used to convert the result to non-logarithmic
        value.
************************************************************************************/
int  MQGetPercentage(float rs_ro_ratio, float *pcurve)
{
 return (pow(10,( ((log(rs_ro_ratio)-pcurve[1])/pcurve[2]) + pcurve[0])));
}

HotSystems

Setze deinen Sketch bitte in Code-Tags, dann ist dieser für alle, auch auf mobilen Geräten, besser lesbar und du bekommst evtl. mehr Helfer dadurch.
Verwende dazu die Schaltfläche </> oben links im Editorfenster.
Dazu den kompletten Sketch markieren.
Gruß Dieter

I2C = weniger ist mehr: weniger Kabel, mehr Probleme. 8)

Calethiel


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