add dew point caclualtor for scl

dew-point-calulator.md

@@ -0,0 +1,53 @@
+FUNCTION "FC_DewPoint" : Void
+{ S7_Optimized_Access := 'TRUE' }
+
+VAR_INPUT
+    Temperature_C : Real;   // Air temperature in degrees Celsius
+    Humidity_RH   : Real;   // Relative humidity in percent: > 0 to 100
+END_VAR
+
+VAR_OUTPUT
+    DewPoint_C : Real;      // Calculated dew point in degrees Celsius
+    Valid      : Bool;      // TRUE when calculation is valid
+END_VAR
+
+VAR_TEMP
+    Gamma : Real;
+END_VAR
+
+VAR_CONSTANT
+    B : Real := 17.625;
+    C : Real := 243.04;
+END_VAR
+
+BEGIN
+    // Validate the input range.
+    // RH must be greater than zero because LN(0) is undefined.
+    #Valid :=
+        (#Temperature_C >= -40.0) AND
+        (#Temperature_C <= 50.0) AND
+        (#Humidity_RH > 0.0) AND
+        (#Humidity_RH <= 100.0);
+
+    IF #Valid THEN
+
+        // Gamma =
+        // LN(RH / 100) + (B * Temperature) / (C + Temperature)
+        #Gamma :=
+            LN(#Humidity_RH / 100.0)
+            +
+            ((#B * #Temperature_C) /
+            (#C + #Temperature_C));
+
+        // Dew point =
+        // (C * Gamma) / (B - Gamma)
+        #DewPoint_C :=
+            (#C * #Gamma) /
+            (#B - #Gamma);
+
+    ELSE
+        #Gamma := 0.0;
+        #DewPoint_C := 0.0;
+    END_IF;
+
+END_FUNCTION