At 05:29 PM 11/23/2013, you wrote:
>Is there a sensor to measure the degree of humbleness a human .......
>
>Actually , I have question about capacitive humidity sensors.  I was=20
>told that they typically measure relative humidity ( RH ).  I don't=20
>get that.  Why would they not measure AH ( absolute humidity ) ...=20
>that is .... the amount of moisture per volume of air ( grams per=20
>cubic meter ).  Or does the capacitor accept water contingent on the=20
>temperature ?   My visualization was two giant capacitor plates with=20
>air circulating between them.  The amount of water in the air would=20
>change the capacitance.  Then I started thinking about the fact that=20
>temperature would affect the density of the gases in the air.  Would=20
>that affect the amount of moisture per volume of air ?  Then my brain expl=
oded.
>
>Gus in Denver

The equilibrium amount of moisture absorption in a hygroscopic polymer
is closely correlated to the air RH, with smaller effects from temperature
and pressure.

Here's an example chart for a different material (wood) that has the
(small) temperature effect shown:

http://www.csgnetwork.com/emctablecalc.html

cp. a typical capacitive polymer temperature sensor with a tempco of about
0.1% RH/K, and you can see it's of a similar magnitude.

That's the "what", the "why" is left as an exercise. ;-)

--sp

--=20
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