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Convert Dewpoint Temperature specification to RH (Relative Humidity)
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Convert Dewpoint Temperature specification to RH (Relative Humidity)
Convert Dewpoint Temperature specification to RH (Relative Humidity)
Convert Dewpoint Temperature specification to RH (Relative Humidity)
Convert Dewpoint Temperature specification to RH (Relative Humidity)
Convert Dewpoint Temperature specification to RH (Relative Humidity)
Convert Dewpoint Temperature specification to RH (Relative Humidity)
Convert Dewpoint Temperature specification to RH (Relative Humidity)
Convert Dewpoint Temperature specification to RH (Relative Humidity)
Convert Dewpoint Temperature specification to RH (Relative Humidity)
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Some Related Topic Tags
dewpoint, relative humidity, conversion factors, temperature (general)
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  Post Number #1  
Old 24th December 2003, 05:27 PM
Charles Wathen

 
 
Total Posts: 131
Please Help! Convert Dewpoint Temperature specification to RH (Relative Humidity)

Hi gang,
I'm performing a measurement uncertainty, and the chilled mirror hygrometer that I use has an accuracy of:
accuracy: 0.2C dewpoint
repeatability: 0.05C.

I need to convert the above dewpoint temperature spec to RH (relative humidity). I've searched the net for a simple conversion, but I could not find one. I need to maintain the RH value in order to convert that value back to DC volts so I maintain the same parameter.

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  Post Number #2  
Old 25th December 2003, 05:46 AM
Al Rosen's Avatar
Al Rosen

 
 
Total Posts: 3,646
Quote:
In Reply to Parent Post by Charles Wathen

Hi gang,
I'm performing a measurement uncertainty, and the chilled mirror hygrometer that I use has an accuracy of:
accuracy: 0.2C dewpoint
repeatability: 0.05C.

I need to convert the above dewpoint temperature spec to RH (relative humidity). I've searched the net for a simple conversion, but I could not find one. I need to maintain the RH value in order to convert that value back to DC volts so I maintain the same parameter.
Hi Charles:

I don't think it's a simple conversion since it is temperature dependent. Try this link anyway.
http://www.paroscientific.com/dewpoint.htm
  Post Number #3  
Old 25th December 2003, 06:46 PM
Charles Wathen

 
 
Total Posts: 131
Hi Al,
Thanks for the reply. After spending additional time on the net researching this, you were correct: it's temperature dependent. I found an Excel Spreadsheet that has the complicated formula. I took this spread sheet and widened the column for the calcuation to give me the precision I needed.

Our Calibration Lab typically runs at 70F. I took 70F and using a dewpoint of 32F, it calculated the humidity to be 24.3927%. I then took 70F and using a dewpoint of 32.36F, it calcualted the humidity to be 24.75%. The difference between these two values is 0.3573%RH or 0.0036 Vdc on the Fluke 8842A.

The formula used:
T = temperature deg F
D = dewpoint deg F
Code:
6.108*EXP(17.27*(((D-32)*5/9+273.16)-273.16)/(((D-32)*5/9+273.16)-35.86))/(6.108*EXP((17.27*((T-32)*5/9+273.16-273.16))/((T-32)*5/9+273.16-35.86)))*100
If anyone wants a copy of this Excel Spreadsheet, here is the link:
http://ggweather.com/wx_calc.xls
Attached Files: 1. Scan for viruses before opening, 2. Please report any 'bad' files by Reporting this post, 3. Use at your Own Risk.
File Type: xls Dewpoint Temp to RH.xls (338.5 KB, 101 views)
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