Merge pull request #212 from airgradienthq/feature/correct-pm2.5-formula

correct pm2.5 formula to show value on display

src/PMS/PMS.cpp

@@ -270,6 +270,41 @@ int PMSBase::pm25ToAQI(int pm02) {
     return 500;
 }
 
+/**
+ * @brief Correction PM2.5
+ * 
+ * @param pm25 Raw PM2.5 value
+ * @param humidity Humidity value (%)
+ * @return int 
+ */
+int PMSBase::compensated(int pm25, float humidity) {
+  float value;
+  if (humidity < 0) {
+    humidity = 0;
+  }
+  if (humidity > 100) {
+    humidity = 100;
+  }
+
+  if(pm25 < 30) {
+    value = (pm25 * 0.524f) - (humidity * 0.0862f) + 5.75f;
+  } else if(pm25 < 50) {
+    value = (0.786f * (pm25 / 20 - 3 / 2) + 0.524f * (1 - (pm25 / 20 - 3 / 2))) * pm25 - (0.0862f * humidity) + 5.75f;
+  } else if(pm25 < 210) {
+    value = (0.786f * pm25) - (0.0862f * humidity) + 5.75f;
+  } else if(pm25 < 260) {
+    value = (0.69f * (pm25/50 - 21/5) + 0.786f * (1 - (pm25/50 - 21/5))) * pm25 - (0.0862f * humidity * (1 - (pm25/50 - 21/5))) + (2.966f * (pm25/50 -21/5)) + (5.75f * (1 - (pm25/50 - 21/5))) + (8.84f * (1.e-4) * pm25* (pm25/50 - 21/5));
+  } else {
+    value = 2.966f + (0.69f * pm25) + (8.84f * (1.e-4) * pm25);
+  }
+
+  if(value < 0) {
+    value = 0;
+  }
+
+  return (int)value;
+}
+
 /**
  * @brief   Convert two byte value to uint16_t value
  *

src/PMS/PMS.h

@@ -28,6 +28,7 @@ public:
   uint16_t getHum(void);
 
   int pm25ToAQI(int pm02);
+  int compensated(int pm25, float humidity);
 
 private:
   Stream *stream;

src/PMS/PMS5003.cpp

@@ -121,6 +121,17 @@ int PMS5003::getPm03ParticleCount(void) {
  */
 int PMS5003::convertPm25ToUsAqi(int pm25) { return pms.pm25ToAQI(pm25); }
 
+/**
+ * @brief Correct PM2.5
+ * 
+ * @param pm25 PM2.5 raw value
+ * @param humidity Humidity value
+ * @return float 
+ */
+int PMS5003::compensated(int pm25, float humidity) {
+  return pms.compensated(pm25, humidity);
+}
+
 /**
  * @brief Check device initialized or not
  *

src/PMS/PMS5003.h

@@ -24,6 +24,7 @@ public:
   int getPm10Ae(void);
   int getPm03ParticleCount(void);
   int convertPm25ToUsAqi(int pm25);
+  int compensated(int pm25, float humidity);
 
 private:
   bool _isBegin = false;

src/PMS/PMS5003T.cpp

@@ -164,6 +164,17 @@ float PMS5003T::getRelativeHumidity(void) {
   return pms.getHum() / 10.0f;
 }
 
+/**
+ * @brief Correct PM2.5
+ * 
+ * @param pm25 PM2.5 raw value
+ * @param humidity Humidity value
+ * @return float 
+ */
+float PMS5003T::compensated(int pm25, float humidity) {
+  return pms.compensated(pm25, humidity);
+}
+
 /**
  * @brief Check device initialized or not
  *

src/PMS/PMS5003T.h

@@ -29,6 +29,7 @@ public:
   int convertPm25ToUsAqi(int pm25);
   float getTemperature(void);
   float getRelativeHumidity(void);
+  float compensated(int pm25, float humidity);
 
 private:
   bool _isBegin = false;