slr pm2.5 correction implementation

src/PMS/PMS.cpp

@@ -314,6 +314,36 @@ int PMSBase::pm25ToAQI(int pm02) {
     return 500;
 }
 
+
+/**
+ * @brief SLR correction for PM2.5 
+ * 
+ * Reference: https://www.airgradient.com/blog/low-readings-from-pms5003/
+ * 
+ * @param pm25 PM2.5 raw value
+ * @param pm003Count PM0.3 count
+ * @param scalingFactor Scaling factor
+ * @param intercept Intercept
+ * @return float Calibrated PM2.5 value
+ */
+float PMSBase::slrCorrection(float pm25, float pm003Count, float scalingFactor, float intercept) {
+  float calibrated;
+
+  float lowCalibrated = (scalingFactor * pm003Count) + intercept;
+  if (lowCalibrated < 31) {
+    calibrated = lowCalibrated;
+  } else {
+    calibrated = pm25;
+  }
+
+  // No negative value for pm2.5
+  if (calibrated < 0) {
+    return 0.0;
+  }
+
+  return calibrated;
+}
+
 /**
  * @brief Correction PM2.5
  *

src/PMS/PMS.h

@@ -39,6 +39,7 @@ public:
   uint8_t getErrorCode(void);
 
   int pm25ToAQI(int pm02);
+  float slrCorrection(float pm25, float pm003Count, float scalingFactor, float intercept);
   float compensate(float pm25, float humidity);
 
 private:

src/PMS/PMS5003.cpp

@@ -172,6 +172,10 @@ int PMS5003::getPm10ParticleCount(void) { return pms.getCount10(); }
  */
 int PMS5003::convertPm25ToUsAqi(int pm25) { return pms.pm25ToAQI(pm25); }
 
+float PMS5003::slrCorrection(float pm25, float pm003Count, float scalingFactor, float intercept) {
+  return pms.slrCorrection(pm25, pm003Count, scalingFactor, intercept);
+}
+
 /**
  * @brief Correct PM2.5
  *

src/PMS/PMS5003.h

@@ -42,6 +42,7 @@ public:
   int getPm10ParticleCount(void);
 
   int convertPm25ToUsAqi(int pm25);
+  float slrCorrection(float pm25, float pm003Count, float scalingFactor, float intercept);
   float compensate(float pm25, float humidity);
   int getFirmwareVersion(void);
   uint8_t getErrorCode(void);

src/PMS/PMS5003T.cpp

@@ -205,6 +205,10 @@ float PMS5003T::getRelativeHumidity(void) {
   return pms.getHum() / 10.0f;
 }
 
+float PMS5003T::slrCorrection(float pm25, float pm003Count, float scalingFactor, float intercept) {
+  return pms.slrCorrection(pm25, pm003Count, scalingFactor, intercept);
+}
+
 /**
  * @brief Correct PM2.5
  *

src/PMS/PMS5003T.h

@@ -45,6 +45,7 @@ public:
   int convertPm25ToUsAqi(int pm25);
   float getTemperature(void);
   float getRelativeHumidity(void);
+  float slrCorrection(float pm25, float pm003Count, float scalingFactor, float intercept);
   float compensate(float pm25, float humidity);
   int getFirmwareVersion(void);
   uint8_t getErrorCode(void);