dew_point.cpp

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#include "dew_point.h"
 
namespace sensesp {
 
// dew point
 
DewPoint::DewPoint() : FloatTransform() {}
 
void DewPoint::set_input(float input, uint8_t inputChannel) {
  inputs[inputChannel] = input;
  received |= 1 << inputChannel;
  if (received ==
      0b11) {  // for 2 channels, use 0b11. For 3 channels, use b111 and so on.
    received = 0;  // recalculates after all values are updated. Remove if a
                   // recalculation is required after an update of any value.
 
    // Dew point is calculated with Arden Buck Equation and Arden Buck valuation
    // sets For more info on the calculation see
    // https://en.wikipedia.org/wiki/Dew_point#Calculating_the_dew_point
 
    float temp_celsius = inputs[0] - 273.15;
    float relative_humidity = inputs[1];
 
    // valuation set for temperatures above 0°C
    float b = 17.368;
    float c = 238.88;
    const float d = 234.5;
 
    // valuation set for temperatures below 0°C
    if (temp_celsius < 0.0) {
      b = 17.966;
      c = 247.15;
    }
 
    float gamma =
        log(relative_humidity * exp((b - (temp_celsius / d)) *
                                    (temp_celsius / (c + temp_celsius))));
    float dew_point = (c * gamma) / (b - gamma);
 
    this->emit(dew_point + 273.15);  // Kelvin is Celsius + 273.15
  }
}
 
}  // namespace sensesp