[time-nuts] Temp/Humidity control systems?

Poul-Henning Kamp phk at phk.freebsd.dk
Thu Oct 27 20:05:33 EDT 2016

In message <20161027134312.GA18158 at panix.com>, Ron Bean writes:

>And since this is time-nuts: Measuring humidity accurately is tricky. 
>According to people who have tested them, commercial electronic humidity 
>sensors, when tested in a lab, have never come anywhere close to the 
>accuracy claimed in the data sheet.

The main problem in measuring humidity is physical gradients:  It is
incredibly hard to create a volume of homogenous humidity on a planet
which has gravity, and for that reason, a lot of labs are not anywhere
near as accurate as they think they are.

>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.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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