PH_meter_temperature_compensation

Since there is no temperature sensor in the PH meter KIT, this temperature compensation is just a theoretical formula. It hasn't been verified by the specialized equipment.

/*  pHConversion: converts the voltage value into a pH value updating the sensitivity
 *                in function of the temperature change
 *  Parameters: float input    : voltage measured at the sensor output
 *              float cal_1    : voltage measured with the 10.0pH calibration solution
 *              float cal_2    : voltage measured with the 7.0pH calibration solution
 *              float cal_3    : voltage measured with the 4.0pH calibration solution
 *              float temp     : temperature of the test solution
 *              float temp_cal : temperature of the calibration solutions
 *  Return:     float value : the pH of the solution
 *                          - -1 : wrong temperature introduced
 *                          - -2 : wrong calibration temperature introduced
 *
 */
float WaspSensorSW::pHConversion(float input, float cal_1, float cal_2, float cal_3, float temp, float temp_cal)
{
    float value;
    float zero_value;
    float sensitivity;

    if( (temp < 0)||(temp > 100) )
    {
        return -1.0;
    }
    if((temp_cal < 0)||(temp_cal > 100))
    {
        return -2.0;
    }

    // The value at pH 7.0 is taken as reference
    zero_value = cal_2;

    // The sensitivity is calculated using the other two calibration values
    sensitivity = (cal_3-cal_1)/6;

    // Add the change in the conductivity owed to the change in temperature
    sensitivity = sensitivity + (temp - temp_cal)*0.0001984;

    // pH value calculated from the calibration values
    value = 7.0 + (zero_value-input)/sensitivity;

    return value;
}

Manual pH Calibration Calculator (Online)