[Aavso-photometry] Re: How cold is too cold?

[Arto.Oksanen at tietoenator.com]

Hi Richard!

We havent got really cold weather yet for this winter, currently we have some degrees bellow freezing.

The 16-inch Meade LX200 has worked well even on the coldest nights when I have been observing (about -30C or so), but the 10-inch one did break once (the plastic gears were too fragile and lubricants too stiff). Of course the LCD display freezes, but otherways the keypad works if needed.

On very cold night we try to make long time-series of very few objects to minimize the mechanical stress of the telescope.

Our CCD (ST8XE) does not like very cold temperatures. We used to keep the CCD as cold as possible, but around -40C or so the transfer efficiency of KAF-chips drops. The hot and warm pixels are starting to have 'ghosts' on following pixels making calibration impossible. Since finding this we have imaged at -25C (unless ambient is bellow that). The dark current is nearly zero at that temperature too so there is no point going colder. Keeping the same temperature also allows re-using the darks from previous nights. 

I think the camera electronics work well even lower temperatures. We keep the camera in the warm room when it is not in use so the start-up temperature is always warmer than ambient temperature outside.

Some cables, especially the power cable of the CCD is very stiff at low temperatures.

To keep the observers warm we do our CCD work from a warm room next to the telescope building. :)

arto

ps. It is the cars that are more difficult to start after a cold winter observing night if they are not being heated.

--
Arto Oksanen                         arto.oksanen at jklsirius.fi
Jyvaskylan Sirius ry, Kyllikinkatu 1, FI-40100 Jyväskylä, Finland 
Tel: +358-40-5659438                         Fax: +358-14-4157803
Nyrola Observatory  http://www.ursa.fi/sirius/nytt/nytt_info.html 

-----Original Message-----
From: aavso-photometry-bounces at mira.aavso.org [mailto:aavso-photometry-bounces at mira.aavso.org] On Behalf Of Richard Huziak
Sent: 5. tammikuuta 2005 18:04
To: aavso-photometry at mira.aavso.org
Subject: [Aavso-photometry] Re: How cold is too cold?


A local department store is offering a discount for next week based on 
the daily temperature.  Today, I can get a discount of 34%, since it is 
-34 deg C right now.  For us Canadian humans (with small, but very 
intelligent, brains tucked deeply inside thick crania for 
cold-protection), this temperature is no really big deal, except that it 
limits our *visual* observing sessions to only a few hours before we 
have to think about warming up a bit.

However, my question is related to the other half of the equation - 
equipment.  Vance Petriew reminded me of a conversation with Arto 
Oksanan at the Berkeley Conference regarding winter temperatures in 
Finland, where Arto stated that "it's so cold that when he turns the CCD 
cooler on, the camera 'warms up' instead".  Yep - same here.  

Since I use borrowed equipment, I don't want to over-stress what is not 
mine, and our informal rule is not to use the telescopes if the ambient 
temperature is <-20 deg C (mostly because the underpowered motors on the 
smaller scopes have trouble keeping up & make strange noises), and not 
to cool the CCD below -45 deg C.  I recently emailed SBIG and asked what 
minimum operating temperatures for their cameras were and what the 
minimum cooling temperature was.  They replied that they did not 
recommend 'cooling' the camera to below -30 deg C but said nothing about 
survivability of the camera itself, i.e. - what the cold operating 
temperature of the electronics is.  They were concerned what below -30C, 
moisture would leech out of the desiccant and fog the CCD.  I regularly 
cool the camera to -45C and don't see this, maybe due to the usual 10% 
winter humidity, but am concerned a bit about thermal stress.  I run on 
either Meade LX-200 12" or 14" scopes on their fork mounts and use any 
one of the ST-9XE, ST-10XE or TC-237 cameras.

In my experience, commercial equipment may not work well below -20C (if 
cold started), and equipment built to military standards (which the 
cameras are not), should cold-start at -40C with no problems.  

So - Cold Boys!  Those of you that run equipment and cameras under 
extremes of temperature, can you please comment on the surviveability of 
your equipment and problems you have in the cold.  I'd like to be able 
to extend my -20C run temperature if possible, because I am currently 
missing a whole lot of nights where I might be running. :-)

-10C = 14F
-15C = 5F
-20C = -4F
-25C = -13F
-30C = -22F
-35C = -31F
-40C = -40F
-45C = -49F

-- 

* * * * * * * * * * * * *
Richard Huziak
Manufacturing Engineering
SED Systems, Saskatoon
tel. (306) 933-1676
<huziak at SEDSystems.ca>
* * * * * * * * * * * * * 



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