(meteorobs) Colour camera advice for Sandia system?

[Alister]

If they were air-tight, they could be filled with Nitrogen!

When talking about moisture content of the air, one must be careful. As a 
meteorologist, I prefer using grams of water vapor per kg of air, because 
*mass* of water vapor must be conserved, assuming no exchange. The biggest 
variable is the temperature of the equipment - at some point it will be cool 
enough for water vapor to condense, except with some heat input. But since 
after a rain, it is more obvious, then there is indeed a leak. You'd want to 
seal on the day with the lowest dewpoint, not when the dew evaporates, 
because the water vapor is still there, you just can't see it.

Wherever the "back door" seal is, that's where a dessicant ought to be 
placed.

Given these issues, maybe I should not jump too quickly from my Sandia 
system!

Alister.
----- Original Message ----- 
From: "stange" <stange34 at sbcglobal.net>
To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
Sent: Wednesday, August 27, 2008 11:46 PM
Subject: Re: (meteorobs) Colour camera advice for Sandia system?


>
> Chris has it right.
>
> The only flaw in the all-sky camera PVC design is the junctions between 
> the
> segments are not air tight seals. They should be sealed either with a thin
> gasket or a thin bead of RTV smoothed with a finger tip....AFTER you have
> made a satisfactory adjustment of all mechanical variables in the
> construction and camera alignment.
>
> The internal heat from the Sun followed by the cooling night allows a 
> period
> of time between off and turn on of the thermostat. During that period the
> inside-outside temperature differences cause an air exchange that contains
> moisture. This is especially noticeable after a rain. The internal portion
> of the dome can condense the moisture usually around the dome perimeter
> first. When the thermostat comes on, the moisture is gradually vaporized
> again but it still remains inside the housing to repeat the condensation.
>
> I have a trace problem of this, but am reluctant to upset the calibration 
> of
> my camera to disassemble and seal the airgaps. If I get a more important
> problem later I will seal it right.
>
> I use those white granules in a plastic container lowered down next to the
> camea to remove moisture. The granules look wet afterward but care must be
> taken that NONE touch any metal surface. Highly corrosive.  -YCS
>
>
> ----- Original Message ----- 
> From: "Chris Peterson" <clp at alumni.caltech.edu>
> To: "Global Meteor Observing Forum" <meteorobs at meteorobs.org>
> Sent: 2008/08/27 21:17
> Subject: Re: (meteorobs) Colour camera advice for Sandia system?
>
>
>> An allsky camera should not experience fogging on the inside. If it does,
>> it
>> needs to be opened and allowed to dry. Certainly a desiccant can be used
>> inside, but it will probably only provide a small amount of protection. 
>> If
>> the system is sealed and heated, it really should be fine. The main
>> problem
>> is condensation on the outside of the acrylic dome. You need to provide
>> enough warm air circulating on the inside to keep the outside surface
>> temperature above ambient. It's a balancing act between the emissivity of
>> the acrylic (and to some extent, the surrounding surfaces) and its 
>> thermal
>> conductivity.
>>
>> Allsky cameras utilizing convex mirrors are very easy to keep dry, since
>> radiant heat can be easily applied to the bottom side of the mirror, 
>> using
>> a
>> heating pad or light bulbs.>
>> Chris
>>
>> *****************************************
>> Chris L Peterson
>> Cloudbait Observatory
>> http://www.cloudbait.com
>>
>>
>> ----- Original Message ----- 
>> From: "Pat Branch" <pat_branch at yahoo.com>
>> To: <cdnspooky at persona.ca>; "Global Meteor Observing Forum"
>> <meteorobs at meteorobs.org>
>> Sent: Wednesday, August 27, 2008 8:16 PM
>> Subject: Re: (meteorobs) Colour camera advice for Sandia system?
>>
>>
>>> To help with the fogging, I might suggest getting a bag of silica gel
>>> from a craft store. Keep it at the base. When it gets used you can dry
>>> it in a microwave.
>>
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