[time-nuts] Temp/Humidity control systems?

[Dr. David Kirkby (Kirkby Microwave Ltd)]

On 28 October 2016 at 01:05, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:

>The exception is the "cold mirror" type of sensor, which measures the
> >dewpoint by cooling a mirror and bouncing a light off it to sense the
> >temperature where dew condenses on it. Those are expensive, and they
> >require maintenance to keep the mirror clean.
>
> And they are comparatively slow, last I saw one it could only do
> a measurement every second minute.
>

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.

Dave