## Compute dew point temperature from RH&T

Posted: August 1, 2017 in physical chemistry, physics, thermodynamics
Tags: , , , , , , , , , , , , Relative humidity (RH) and temperature (T) data from an RH&T sensor like the DHT22 can be used to compute not only absolute humidity AH but also dew point temperature TD There has been a fair amount of interest in my formula which computes absolute humidity (AH) from measured relative humidity (RH) and temperature (T) since it adds value to the output of RH&T sensors. To further extend this value, I have developed another formula which computes dew point temperature TD from measured RH and T.

Formula for computing dew point temperature TD

In this formula (P Mander 2017) the measured temperature T and the computed dew point temperature TD are expressed in degrees Celsius, and the measured relative humidity RH is expressed in %

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Strategy for computing TD from RH and T

1. The dew point temperature TD is defined in the following relation where RH is expressed in % 2. To obtain values for Psat, we can use the Bolton formula[REF, eq.10] which generates saturation vapor pressure Psat (hectopascals) as a function of temperature T (Celsius)  These formulas are stated to be accurate to within 0.1% over the temperature range –30°C to +35°C

3. Substituting in the first equation yields Taking natural logarithms Rearranging Separating TD terms on one side yields – – – –

P Mander August 2017