(meteorobs) Colour camera advice for Sandia system?

[Chris Peterson]

Hard to generalize. It really depends on your typical humidity and dew 
point. Here in Colorado (which is pretty dry), over the entire state, our 
cameras stay free of dew and frost using nothing more than a fan blowing the 
waste heat of the PC164C camera across the inside of the 5" acrylic dome. It 
hasn't been necessary to add more heating. The domes do get condensation 
(especially in summer when the humidity is up) if the little fans fail, 
however.

You only need to make sure the dome is fractionally above ambient to avoid 
dewing. It should take very little power to do that. Consider that antidew 
heaters for telescopes usually require only a few watts to keep several 
hundred square centimeters of corrector surface clear, and that's without 
active circulation. A small acrylic dome shouldn't have high emissivity; I 
can't imagine any conditions that would require 100W to keep it above 
ambient. Do you actually use that, or do you just switch power to a 100W 
heater, which typically runs with a very low duty cycle? I'd think that if 
your average power is over a few watts, it suggests that the surfaces around 
the dome are far too emissive.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message ----- 
From: "Ed Majden" <epmajden at shaw.ca>
To: <cdnspooky at persona.ca>; "Global Meteor Observing Forum" 
<meteorobs at meteorobs.org>
Sent: Wednesday, August 27, 2008 9:32 AM
Subject: Re: (meteorobs) Colour camera advice for Sandia system?


> Kim:
> Your 5 watt heater is not near enough heat to keep your dome clear.
> The Sandia Sentinel Camera uses a thermostatically controlled heater, a
> small fan for circulation and I have mine set for 100 watts.  This is
> under a small 6-inch or so dome.  Prior to that, I had an 18 inch clear
> dome with equally spaced 100 ohm heating elements in series set equally
> around the dome running at 30 watts each.  I did not use a thermostat.
> You can see the details of the Sentinel System on Jeff Brower's site
> at:
>
> http://members.shaw.ca/jbrower/sentinel/camera.html
>
> Cheers:
> Ed Majden
> B.C. West Coast Network
> Courtenay, B.C. CANADA