Calculation of Relative Humidity using Wet/Dry Bulb on DT85

The dataTaker DT85 16 channel general purpose data logger

Calculation of Relative Humidity using Wet/Dry Bulb on DT85

Postby pwarnes » Mon Oct 23, 2017 9:29 am

Dear all,

I have been experimenting using a DT85 Series 2 to measure relative humidity using the Wet/Dry bulb method. I have been taking the measurements using a pair of K type thermocouples - one of which is 'wet.'

I have tried using the routine outline in the FAQ through DeTransfer. The problem is that the calculation in the formula is quite different from that using a psychrometric chart of a phone app (both of which roughly agree to within a few percent).

For example: A measurement this morning produced a Dry bulb reading of 19.4 degrees C and a wet bulb reading of 15.0 degrees C.

Using the routine posted on your FAQ, this comes out at RH of 45.1%

The calculations on my phone app came out at 62.6% and our wall chart at 66% (only 3.4% difference between them) which are significantly different from the DeTransfer program on your web site.

Does anyone have a better formula that calculates RH more accurately?

Regards

Philip
pwarnes
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