Temperature (and humidity) measurement: Difference between revisions

Temperature (and humidity) measurement (view source)

Revision as of 22:16, 13 June 2020

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→‎Cumulus Calculated Parameters: dew point

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 [http://en.wikipedia.org/wiki/Wet_bulb Wet bulb]
-and [https://en.wikipedia.org/wiki/Dew_point Dew point]
+and [[#How_does_Cumulus_know_the_height_of_the_cloud_base.3F]]
+*The dew point calculation for Cumulus 1 uses a third party library which uses the Davis dew point calculation '''dewpoint := tempinC + ((0.13 * tempinC) + 13.6) * Ln(humidity / 100)'''
+* The dew point calculation for MX follows the standard [https://en.wikipedia.org/wiki/Dew_point calculation in wikipedia].
+Note this means that Cumulus 1 and MX log files have a continuity break when you migrate from one flavour to another.
+<pre>
+	/* =================================================================================================
+	 DEW POINT TEMPERATURE
+	The dew point calculation in Cumulus 1 uses a third party library which uses the Davis dew point calculation '''dewpoint := tempinC + ((0.13 * tempinC) + 13.6) * Ln(humidity / 100)'''
+	============================================================================== */
+	function calcDewPoint(tempDegC,	 tempLetter,	 RHumidity)
+	{
+		var dp = tempDegC + ((0.13 * tempDegC) +13.6) * Math.log(RHumidity / 100);
+		return  calcTempR(dp,	tempLetter);   // return as string in right units for user
+	}
+	/* =================================================================================================
+	 DEW POINT TEMPERATURE
+	 The following is a formula from  https://github.com/nicolasgrancher/weather-js/blob/master/js/weather.js
+	 This matches the formula that MX uses.
+	It has only been edited to add the middle input parameter and to output using a call to CalcTempR
+	============================================================================== */
+/**
+ * Dew point calculation.
+ * @see https://en.wikipedia.org/wiki/Dew_point
+ *
+ * @param Tc temperature in celsius
+ * @param R relative humidity
+ * @returns {number}
+ */
+function dewPoint(Tc,	tempLetter,  R)
+ {  // parameters:		tempDegC, tempLetter, (RHumidity /100)  // added middle parameter, should be accessible anyway, but playing safe
+    if (Tc < 0 || Tc > 60)
+	{
+        return  calcTempR(Tc,	tempLetter);   // return as string in right units for user
+    }
+    if (R < 0.01 || R > 1) {
+        return  calcTempR(Tc,	tempLetter);   // return as string in right units for user
+    }
+    var a = 17.27;
+    var b = 237.7;
+    var alphaTR = ((a * Tc) / (b + Tc)) + Math.log(R);
+    var Tr = (b * alphaTR) / (a - alphaTR);
+    if (Tr < 0 || Tr > 50) {
+        return  calcTempR(Tc,	tempLetter);   // return as string in right units for user
+    }
+        return  calcTempR(Tr,	tempLetter);   // return as string in right units for user
+}
+</pre>
- and [[#How_does_Cumulus_know_the_height_of_the_cloud_base.3F]]
-The dew point calculation uses a third party library which uses the Davis dew point calculation '''dewpoint := tempinC + ((0.13 * tempinC) + 13.6) * Ln(humidity / 100)'''
 [[Humidex]] and [[Wind chill]] and  [[Heat index]] and [[#My heat index/humidex/wind chill is the same as my temperature]]