Re: [ATM] Electronics help needed - temperature control

[Mark Holm <mdholm@telerama.com>]

Hey guys, you are reading too much into what I wrote.

By differential, I mean exactly what Don's dew heater circuit does:
compare the mirror temperature to air temperature and control something
based on that difference signal.  The changes from the dew heater are:
1. Power a fan instead of a heater; 2. Invert the control response so
that the the fan runs faster (or just turns on) when the mirror is
warmer than the air and, as the mirror approaches air temperature,
either stop or slow down the fan.

Several people have built scopes with two speed fans already, but use
manual control.  Also, as I noted, Alan Adler (and maybe Brian Greer)
have pointed out that air temperature typically continues to fall during
the night and mirrors lag.  Since it is a dynamic system, why not
conquer it with feedback?  Of course, a two speed switch may be all the
feedback you really need.

Mark Holm
mdholm@telerama.com

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