[time-nuts] Temp/Humidity control systems?
attila at kinali.ch
Sun Oct 30 17:51:33 EDT 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
"Automatic digital microwave hygrometer", by Hasegawa, Stokesberry, 1975
"ELECTRICAL PROPERTIES OF ATMOSPHERIC MOIST AIR: A SYSTEMATIC,
EXPERIMENTAL STUDY", by Carlon, 1988
"The Refractive Indices and Dielectric Constants of Air and its Principal
Constituents at 24,000Mc/s", by Essen, Froome, 1951
Don't ask why i have these papers....
Any simple idea will be worded in the most complicated way.
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