Do CCD Sensors 'Go-off' if used too much??

[davedownsouth]

Just a quick, probably very obvious question, but I have a Atik One 6 CCD camera and until very recently I have not bothered to run Darks as I do not think my images have needed them (alway take my shots at -20"C).  After discovering PHD2 and guiding, I am now taking much longer exposures, up to 20 minutes, but more usually 10 - 15 minutes, and I have started to notice on closer inspection of the processed images, that there are several pixel hot spots showing.  I have put this down to the increase exposure length and have decided to make some Dark libraries (not like there is any chance of using the scope properly with this weather  ).  So, all this week, when I have got back from work, I have set the scope up with the CCD, set the temp to -20"C, ensured the end cap is on and the scope is wrapped in black cloth (just in-case) and have been taking 50 shots at various exposures / binnings; namely 3, 5, 10, 15 & 20 minutes at 1x1 and 3, 5 & 10 minutes at 2x2.  By my reckonings, by 9 am on Friday morning I should have finished.  After a lot of pre-rammble, my question is, am I risking knackering up my CCD sensor by basically having it running for 14 hours solid for four nights in a row.  I guess I will find this out quite easily by just re-running the 50 x 3 minute exposures on Friday night and comparing what the set of Darks looks like compared to when I ran it five nights previously; if it is a lot worse, I have buggered the camera .  I really hope this will not be the case, but any insight from the experts out there  .

[MarsG76]

Even if that were the case, I've never heard of anyone using a sensor or a camera so much that their sensor was damaged. I think you would have to run the sensor for something in the vicinity of 100,000 hours to damage the sensor if ran within operational specs. The parts that die long before anything electrical as moving parts like shutters and even the peltier coolers.

This is one aspect of your CCD use you should be the least concerned with, I say, enjoy it and use it till it does stop... But I'd say you'd be looking to upgrade long time before you "use it up".

[Thalestris24]

Hi

With a cooled ccd probably 10 darks will do... https://starizona.com/acb/ccd/advimcal.aspx I'm not sure -20 deg is necessary - I've never run mine at that low a temperature, just -10 seems fine, though it might depend on the camera.

Louise

[rl]

Just using the CCD at -20 for days should not be an issue at all. These things have incredibly long lifetimes that tend to get longer at lower temperatures. What might become an issue is if the temperature is rapidly cycled a lot and the CCD packaging isn't rated to -20; the continual heat/ cool cycling might just fracture a hermetic seal due to CTE (Coefficient of Thermal Expansion) mismatch between the glass cover and the ceramic case, or between the silicon chip and the case. I don't think this is what you're doing so I would'nt worry about it!

RL

[Davey-T]

My old Atik 314L+, one of the first ones, has steadily gained lots more white pixels over the years to the extent now I've had to make a bad pixel map as calibration fails to remove them all, only ever run at -10C as can't achieve any lower on summer nights.

Dave

[Thalestris24]

ps you may not need darks for short exposures. For 3 mins you probably don't need them but if you do, then x3 or x5 will be enough. I have a qhy8l so might not be comparable. I do get amp glow with longer exposures e.g. 10min and above so definitely need some darks for those. With long exposures make sure everything is light tight!

Louise

[ollypenrice]

I dream of having 'several' hot pixels on my chip. My big Kodaks have several hundred! They do deteriorate with age but your use of the term 'several' strongly suggests that you should maybe start to worry in about thirty years... 

I use a bad pixel map and a hot pixel filter. My stacks are clean. Dither will also deal with a few hots with total efficiency.

Olly

[davedownsouth]

Cheers for all the answer .  

Hi

With a cooled ccd probably 10 darks will do... https://starizona.com/acb/ccd/advimcal.aspx I'm not sure -20 deg is necessary - I've never run mine at that low a temperature, just -10 seems fine, though it might depend on the camera.

Louise

Yes, 50 frames is probably way, way over the top, but as the camera would just have been sitting in a box all this week , I thought I would push the boat out, then I started getting worried about killing the camera, but it sounds like I am worrying too much .  

The camera will go -38"C ambient, so, living i the Uk, I have never not been able to get -20, even on a summers night.  In winter, when it is really cold, I am going to push it to -40"C and see what happens .

[Thalestris24]

Cheers for all the answer .  

Yes, 50 frames is probably way, way over the top, but as the camera would just have been sitting in a box all this week , I thought I would push the boat out, then I started getting worried about killing the camera, but it sounds like I am worrying too much .  

The camera will go -38"C ambient, so, living i the Uk, I have never not been able to get -20, even on a summers night.  In winter, when it is really cold, I am going to push it to -40"C and see what happens .

Hi

I like to be more conservative with hardware limits and instinctively don't push circuits to the max if it's not necessary

Louise

[rl]

You need to find the temperature point where the dark counts become less than the read noise; there's not a lot of point in cooling beyond that. It will only stress the kit more than you need to, Thalestrys's point is a good one. Just drop the temp in 5 deg steps and see where the noise levels out. 

RL 

[D4N]

I'd be quite happy to leave mine at -20C but some nights it gets a lot colder than that here and I'm not sure if the CCD will actually produce enough heat to stay at that. I guess I'll find out eventually and it if doesn't keep it stable I'll just set it a bit lower and produce another dark library for cold nights [emoji301]️

/Dan

Sent from my iPad using Tapatalk

[rl]

It depends whether the temperature controller can reverse the current through the peltier cooler. If it can, holding -20 with an outside temperature below that won't be a problem. Despite the name, Peltier coolers are actually much more efficient at heating than cooling. The biggest problem is that the temperature might oscillate a degree or two around -20 because of the efficiency improvement when heating.

If the current can't be reversed, the CCD will simply track the ambient. 

RL