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canex
Joined: 26 Oct 2000
Posts: 164
Location: USA |
 Wed Mar 20, 2002 2:32 pm
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Obviously, I am casting pearls at swine. The references are given in the previous posts. Read them for yourself, as you do not believe me.
Your math is correct if you are talking in relative terms (i.e., % of % relative humidity, error of 100% relative to 7% = 7%). I was talking in absolute terms and assumed that you were (i.e., % relative humidity, error of 100% is 7% + or - 100%). The dry bias error is huge as noted earlier. The random error is on the order of 10% in relative terms. |
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canex
Joined: 26 Oct 2000
Posts: 164
Location: USA |
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Wed Mar 20, 2002 2:59 pm
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I'm sorry, I didn't answer all of your questions, as if it makes any diference. Here are some more pearls.
The standard used to determine that the relative humidity sensors measure too low is a frost-point hygrometer, a research-grade, cryogenically cooled instrument designed specifically to measure humidity at low temperatures.
I have already provided measures of how low the sonde values are for two temperatures, but to address your specific request, they are low by a factor of 1.1 at -30C up to 2.5 at -70C. You're good at math, you can determine the error in terms of percent (relative).
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Sore Throat
Joined: 01 Sep 2000
Posts: 1802
Location: x |
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Thu Mar 21, 2002 4:08 am
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Thank you canex.
So a relative humidity measurement of 25% at -30 degrees, low by a factor of 1.1, would actually be 27.5%.
and "up to" a factor of 2.5 would mean that a measurement of 25% relative humidity at -70 degrees, would "theoretically" equate to a "true" relative humidity of 62.5%.
By my calculations, a 250% measurement error.
There aren't many examples of places that we use measuring devices that are subject to a 250% measurement error.
But then you did say, "up to".
...and we know how you like to stretch the edge of the envelope.
I do appreciate your help though...
honestly. |
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