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

Wed Jan 5 13:53:54 EST 2005

Richard and all,

I do agree what Arto said about observing in Finland. Our good'o Russian made LOMO
telescope itself never fails in cold. However, care must be taken with all the
electrical cables when operating the telescope remotely in separate office. The
frozen cables can be easily damaged if jammed when the telescope is aimed. With ST-4
autoguider we get problems with plastic buttons which freeze at about -20C, but a
hair-dryer helps. With hair-dryer you can also heat yourself by blowing warm air
into your jacket when freezing.

Thermal expansion of different materials cause mismatches in the worm wheels, which
gives loud noise for all the (sleeping) neighbours around at 02 local time when
turning the scope :-)

Worst problems usually come when the temperature is warming again. All the humidity
will turn into ice around surfaces of mirrors, lenses etc. Practically everyting is
then frozen. Some times our first task in observing session is to melt and dry the
main mirror using a hair-dryer again (not too hot, of course).

One need to have good batteries in cold weather as well. Once we found that our car
battery did not give enough current in order to start the engine, and no mobile
phone batteries survived in order to call help (at 04 local time). We pushed the car
downhill in order to start the engine but we failed. It was very cold night -30C and
we were really freezing before we got help. After this adventure I had to recover
two hours in extremely hot sauna!

Best regards,

Pertti

Quoting 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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-- 
Pertti Pääkkönen, PhD, Laboratory engineer
University of Joensuu, Department of Physics
Tel: +358 13 351 3238
Fax: +358 13 251 3290