[time-nuts] Temp/Humidity control systems?

Attila Kinali 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

 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....

			Attila Kinali

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

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