Re: [ATM] Ball bearing for triangles

[=?Windows-1252?Q?Rapha=EBl_GUINAMARD?= <rguinamard@infonie.fr>]

Tom wrote
>...so the back side may stay
> warmer than the front side because it's facing/exposed to a different
thermal environment than
> the front side.
>
> This difference in environment is one way to make a cloud detector for
your
> robotic observatory.  Sandwich a thermocouple between two plates of
> aluminum.  One plate faces up to sky, the other faces toward ground.  On a
> clear night the upper plate will be colder than lower plate.
It's exactly what they described in the 1.5 m I was speaking:
They put 9 Pt temperature probe on the back of the mirror (and on a radius)
and 9 on the face.
During cloudy night the temp difference on that 28 mm thick mirror was
0.25°C (or 0.25K) and during uncloudy night it was 0.8°C (or 0.8K).
It took about 30' - 1h to reach theses differences

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