[time-nuts] Temp/Humidity control systems?

Attila Kinali attila at kinali.ch
Sun Oct 30 21:51:33 UTC 2016


On Sun, 30 Oct 2016 20:38:49 +0000
"Dr. David Kirkby (Kirkby Microwave Ltd)" <drkirkby at kirkbymicrowave.co.uk> wrote:

> I was just reading the Keysight forum on VNAs. Someone was having issues
> measuring a bit of waveguide 80 m long. Dr. Joel Dunsmore pointed out that
> humidity has an effect in waveguide.
> 
> I'm guessing this is due to the change in permittivity in the air, which
> would be most noticeable near the cutoff frequency of the waveguide. That
> should change the magnitude of the reflection, not just the phase, so it
> might be a relatively cheap way to measure humidity.
> 
> Just thinking aloud. I'm probably talking rubbish.

This has been used for quite some time. Though cheap is relative :-)
A non-representative selection of papers that I have lying around here:

"A Reference Standard for Measuring Humidity of Air Using a Re-entrant Radio
Frequency Resonator", by Huang, Ripple, Moldover, Scace, 2006
http://www.nist.gov/customcf/get_pdf.cfm?pub_id=902995

"Automatic digital microwave hygrometer", by Hasegawa, Stokesberry, 1975
http://dx.doi.org/10.1063/1.1134331

"ELECTRICAL PROPERTIES OF ATMOSPHERIC MOIST AIR: A SYSTEMATIC,
 EXPERIMENTAL STUDY", by Carlon, 1988
http://www.dtic.mil/dtic/tr/fulltext/u2/a199599.pdf

"The Refractive Indices and Dielectric Constants of Air and its Principal
Constituents at 24,000Mc/s", by Essen, Froome, 1951
http://dx.doi.org/10.1088/0370-1301/64/10/303

Don't ask why i have these papers....


			Attila Kinali





-- 
Malek's Law:
        Any simple idea will be worded in the most complicated way.



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