Aluma 47-10 condensation then ice on sensor

Discussion in 'Aluma Series' started by Colin Hall, Jul 3, 2019.

  1. Colin Hall

    Colin Hall Standard User

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    Hi,

    Has anyone experienced issues with condensation and then ice forming on the sensor? All my lights and flats (LRGB and Ha) show the same "crystalline" shadows at -30C; as the sensor warms the crystals form droplets. , hence my guess that it's water vapour. The camera has a new desiccant plug installed.

    I have taken the filter wheel off and have the camera body exposed in a sealed box (the carry case it was delivered in) with a massive bag of dehydrated silica gel in the hope that this will dry it out BUT does anyone know how this happens and more importantly how to prevent it happening in the future. I have a QSI 6120 that I'm reverting to until this is solved as I've wasted multiple nights in frustration. The QSI 6120 never had such issues or I'd suspect my technique, though that could clearly still be a problem. I've taken frames with the same optical train substituting the 6120 and there are no crsyalline shadows so it's narrowed down to the Aluma; the Aluma filter wheels are clean, I checked, as is the cover glass to the Aluma sensor, also cleaned and checked.
     
  2. Colin Haig

    Colin Haig Staff Member

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    Am wondering if the window heat is not on.
    Am going to ask colleague @Doug to review and comment.
     
  3. Colin Hall

    Colin Hall Standard User

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    Thanks Colin, appreciate the prompt response. I've not seen an option for window heat other than anti-fog (is it the same thing?), which I've turned on to no avail. I'll await Doug's response and leave the Aluma frying out for a few days. It's clear skies in the UK tonight so looks like dusting off the QSI again as I don't want to risk damaging the Aluma and, to be honest, my own sanity with more frustration. Clear skies, Colin
     
  4. Colin Haig

    Colin Haig Staff Member

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    We've discussed.
    We've confirmed your camera passed frost tests as part of our Quality Assurance before it left our facility.
    Did you verify that the desiccant plug is firmly seated and that the o-ring is in place?
    Did you remove the desiccant plug or loosen it?
    When you say the cover glass was cleaned, are you referring to the optical window in the camera body that sits several millimetres above the sensor?
    Or the glass on the top surface of the chip?
    Please confirm you did not open or disassemble the chamber with the sensor inside.

    As a suggested course of action, you could recharge the desiccant as described in the manual on page 47.
    Desiccant should be baked at 350F for 4 hours.
    Further, if you have a low temperature (toaster oven), the Camera with desiccant plug removed should be baked at 130F for minimum of 8 hours.
     
  5. Colin Haig

    Colin Haig Staff Member

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    PS when you go to bake the desiccant plug, make sure to remove the o-ring, as it is only good to about 200F maximum, and then reinstall it on the plug after it cools down and you put back into the camera.
     
  6. Doug

    Doug Staff Member

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    I’ll chime in too.

    This definitely sounds like moisture in the chamber. We haven’t had any issues before with Aluma, so that is a bit surprising.

    By “new” desiccant plug - do you mean you purchased one? Even if you did, I would still recommend baking it before use. There is some risk of leakage in the sealed bag during transport. The desiccant is very high performance and will quickly absorb any moisture it is exposed to.

    So my first recommendation is to bake the plug. Please take care to follow the instructions in the manual exactly. If it’s not hot enough the desiccant will not release the moisture. Of course you don’t want to fry the plug either!

    Please try this first. Let it sit 24 hours after reinstalling the plug before activating the cooler.

    If you see frost again turn the cooler off immediately. This is a windowless sensor. Moisture exposure could eventually damage the sensor. If that happens we’ll want to get the camera back and inspect the seals.
     
  7. Colin Hall

    Colin Hall Standard User

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    Hi Colin, no I didn't open the sensor up, just took the filter wheel off. I carefully cleaned the glass under the shutter only. Doug - I purchased a spare plug when I ordered from you. I'll remove the plug, take off the o-ring and bake at 180C as you recommend, reinstall and leave for 24 hours. If I see condensation / ice again I will immediately RMA the camera. I paid way too much money for it to get damaged this way!! Thanks for the prompt responses gents. Really impressed by your support, it's what we amateur astronomers need when fretting over our tech. I'll let you know how I get on even if successful. Question - how regularly should I bake the desiccant?
     
  8. Colin Haig

    Colin Haig Staff Member

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    Yes, keep us up to date. As far as the frequency of baking, it depends; 6 months is not unreasonable. Sooner if any moisture in there. As the 47-10 is a windowless sensor (no cover glass above the 47-10 sensor silicon) it is important to keep it dry.
    Am fairly certain baking the desiccant will solve it; we stand by our products and do whatever necessary to make it right.
     
  9. Doug

    Doug Staff Member

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    I agree with Colin - no point taking any chances with a windowless sensor. I'd bake it every six months.

    I know a lot of users just keep using the camera until it frosts up - can take a couple of years in some cases. But that is NOT a good approach, especially with the windowless sensors. The whole point of the desiccant plug is that it allows for simple periodic maintenance by the customer - without sending the camera in for service!

    Some other companies just cram a lot of desiccant in behind the sensor, and tell you to send it in for service when it saturates.
     
  10. Colin Haig

    Colin Haig Staff Member

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    Hi Colin Hall, was this resolved?
     
  11. Colin Hall

    Colin Hall Standard User

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    Hi Colin, I’ve not had a combination of clear skies and free time to test it yet. Whilst i’m On-line, i RMA’d my AO, could someone give me an update please.

    Cheers
     
  12. Colin Haig

    Colin Haig Staff Member

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    Thanks for letting me know Colin. We do want to find out the status of the apparent moisture in the Aluma 47-10 chamber.
    I understand the need for the time and skies. Perhaps you could shoot a flat field / light exposure with the observatory dome/roof closed.

    My colleague @Tim will investigate the status of your AO RMA, and it may be Monday our time before we have an update, as its now 18:15 EDT, and much of the staff have left for the weekend.
     
  13. Colin Hall

    Colin Hall Standard User

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    Hi Colin

    Sure, i can shoot a flat field no worries; I’m on holiday in Cornwall until Monday 22nd but will shoot a few FFs when i get back. Any particular criteria e.g. leave the camera cooler running for x mins at y deg C before shooting? Re: AO, thank you.
     
  14. Colin Haig

    Colin Haig Staff Member

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    It would be best if you could:
    1. find an existing, light frame or FF that was your first evidence of the problem (so we know what you originally experienced),

    2. To start the test, you might point the camera sideways, maybe a touch nose-down, so moisture does not drip/form on the sensor itself.
    Set the cooler at +5C (above freezing), let it stabilized for say 15-30 minutes.
    Take a few flat images and examine them.
    If no evidence of problems at +5C, then lets move on, so we will take the temperature down in steps.

    3. Set the cooler for 0C, and say take a flat image every minute for 15 minutes or so until it stabilizes, and see if anything forms.
    If you start to see a problem, warm up the camera, and stop.
    We don't want any moisture forming on the chip - the Teledyne e2v chip is windowless, so the water would form on the silicon, and that is a problem.

    4. Repeat the process at -5C, and then if that is okay, keep going down, eg to -10C, -20C, -30C (and depending on your ambient temperature, you might get lower than -20 or -30. e.g. if in the house, and it's 22C, you might only get the chip to -26C). Go as low as it will go.

    Once you're done, warm it up.
    If you find evidence of contamination, send us the FITS file evidence, and we will figure out what to do from there.
     
  15. Colin Haig

    Colin Haig Staff Member

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    P.S. Enjoy the Cornish vacation!
     
  16. Colin Hall

    Colin Hall Standard User

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    Fantastic Colin, exactly the instructions I needed! Just to manage expectations, could be a few weeks before I can find the grimness BUT I have diarised to harass m myself LOL. Re: Cornwall, many thanks.
     

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