16803 frosting up no matter what I do

Discussion in 'Legacy Models (ST, STL, etc.)' started by Mark McComiskey, Oct 3, 2021.

  1. Mark McComiskey

    Mark McComiskey Standard User

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    Will these 0 rings work for the 16803 also?
     
  2. Doug

    Doug Staff Member

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    No. The O-ring for the STX desiccant plug is a BUNA-N size -011, McMaster 9557K463
     
  3. Mark McComiskey

    Mark McComiskey Standard User

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    So, for the last three of four imaging sessions I have undertaken (September-October in Connecticut), after 3-4 hours of operating well, my SIBG 16803 starts to progressively frost over.

    At start, I cool the camera slowly (30 mins to -10C), and then leave the temperature undisturbed. I am not getting dew on the optics (dew shield and heater appear to be doing their job). Ambient temperatures generally start in the low 20s C and have falled over the evening to as low as 10C.

    I have twice recharged the dessicant plug as per the manuals, I have double checked the o-ring and seal.

    Is there anything else I can do to avoid this frosting effect? Or is it just an inevitable outcome after several hours of operation?

    Including a sub in case seeing the issue is helpful.
     

    Attached Files:

  4. Colin Haig

    Colin Haig Staff Member

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    Mark, I can't really tell - we don't see frost tendrils. so I'm going to ask @Doug and @Bill to chime in.

    A few thoughts, and other folks will hopefully have some suggestions:
    - Pull the camera off, bring it indoors, let it adjust to ambient - maybe bag it before bringing it in. Could take an hour or two.
    (eg you don't want condensation all over it - if you have dew outside, the humidity must be pretty high).
    - Put it on the workbench/kitchen table.
    - Prepare it to be used indoors. eg connect to your laptop, plug it in.
    - Orient the camera so you can look down the nose toward the sensor.
    - Fire up MaxIm or CCDOPs (or whatever you are using).
    - Connect and take a 10 second image through the luminance filter.
    - Turn on the cooler - set point should be about -25C or so.
    Let it get cold.
    Take another shot.
    Are you seeing frost or moisture forming inside?

    I'm inclined to think that the moisture is on the OUTSIDE of the chamber window, or on the filter.
    If you are fighting dew with heaters, I'd call it a night.

    What's your relative humidity when you took this sample shot?

    Why not cool the camera more aggressively? 5C per minute is not unreasonable, so you should be able to get it down to -30C from ambient of 15C in just 9 minutes.
    Is the Window Heater turned on?
     
  5. Mark McComiskey

    Mark McComiskey Standard User

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    Colin,

    Thanks. I had heard that cooling the camera more slowly would help avoid frost, so set it to cool slowly when this problem emerged. In the past, I had it set to cool to -10 in 10 minutes.

    This problem never occurs at the start of a session, so , I would need to bring it indoors and leave it on for several hours to run the experiment you are describing. I am happy enough to do that, but what is the thought? To visibly identify any frost that is forming? If it is on the chip, would I be able to see it through the filter?

    In case it helps, here is a link to a series of 50 flats that were taken in a row (it will take a few minutes for them to upload). If you load them up into blink (or something similar) and just scroll through them, you can see the problem emerge over the last 10 or 15 flats.

    https://1drv.ms/u/s!AsHXUvMw3K77g6laJQRvqXF5FyJU2w?e=P9ddVt
     
  6. Colin Haig

    Colin Haig Staff Member

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    If the chamber has moisture, the chip will often frost over before the inside of the chamber window because the CCD ceramic package is the coldest part, being in contact with the TEC cooling stack.

    If the chamber is dry, you won't get frost, so you should be able to cool it to maximum delta T without babying it.

    Hmmm... then I think it's OUTSIDE the chamber.

    If moisture is inside the chamber, and the components (chip, cold finger, TEC) get below 4C, signs of condensation or frost will start to form inside. I'd expect it in the first 30 minutes.

    If it is happening toward the end of the session, ambient is probably nearest the dew point, and so the condensation is forming OUTSIDE the chamber as the cooling outside air contacts the colder surface of the camera. Are you getting moisture on the camera body or the filter wheel or telescop?

    So then the exterior front face of the chamber window, either side of a filter, or back of the flattener are likely suspects then.

    The thought is Process of Elimination. We're trying to figure out if the chamber seal is bad (or dessicant o-ring is worn out).

    If there is moisture is in the chamber, the moisture will condense and show up on the sensor or inside of the chamber window when the cooler gets the temperature low inside the chamber. That's regardless of the ambient temperature and humidity.

    If we don't get any formation, then it's EXTERNAL - and so you've done a fine job of baking the desiccant and drying out the chamber. (attaboy).

    If INTERNAL - then the camera probably needs to go to @Bill to have the seal replaced, and/or purchase a replacement desiccant plug.

    If the filter wheel body is getting condensation (or filters are), maybe wrap a couple dew straps around it.

    BTW usually frost forms fractal tendrils, and I don't seem any in the earlier samples. It looks like it is fogging up near the centre first.

    Anyway, whatever's going on, bringing it inside and dialing up the cooler should show you in a few minutes what is going on.

    I'll take a look at the flats. Thanks for sending them over.
     
  7. Doug

    Doug Staff Member

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    It does rather sound like it's on the window. The window will be chilled slightly by having the cold CCD underneath it, and in humid conditions that can get you below the dew point.

    Do you have the window heater turned on?
     
  8. Mark McComiskey

    Mark McComiskey Standard User

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    There is a window heater!? I can't find any reference to that in the manual. How would go about turning it on? And what are the conditions that would warrant doing so (high humidity, I suppose, so not needed in the winter?

    I should add that when this problem happens, if I shut down the camera for 20 minutes and let it warm up, the first few subs look good before the problem reemerges. I am guessing that points to the camera (inside or window) rather than the filters or the flattener?
     
  9. Doug

    Doug Staff Member

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    Yes, there is a heater. In MaxIm DL this is where you would look:

    https://cdn.diffractionlimited.com/help/maximdl/HIDD_SETUPST7.htm

    CCDOPS has a similar option.

    It is possible that the filters or flattener is fogging, but it's more likely to be the chamber window because it's slightly cooled by the sensor underneath it (via convection).

    The purpose of the heater isn't to actually warm up the window; it's to create a bubble of slightly warm air in the front of the camera. That prevents dew from forming.

    I don't know about you... but it's really humid here in the winter! I'd turn it on if your humidity is above maybe 70-80%.
     
  10. Mark McComiskey

    Mark McComiskey Standard User

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    Wow. Why is there no mention of that in the STX 16803 manual? That could be just the trick.

    Very humid here in the autumn. Winter is off and on. I didn't have any dew/humidity problems Nov-March of last year, but hopefully this well help ensure I don't get any.
     
  11. Mark McComiskey

    Mark McComiskey Standard User

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    I opened up the Maxim DL 6 camera set up advanced options dialogue and the window heater option is greyed out. Is there something else I need to do to get access to this option?

    Capture.JPG
     
  12. Doug

    Doug Staff Member

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  13. Mark McComiskey

    Mark McComiskey Standard User

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    That worked, thank you. I have that option set to on now. Does the camera remember that setting when it is used by another program? I use SGP to automate my sessions, and it does not have this option for this camera.
     
  14. Mark McComiskey

    Mark McComiskey Standard User

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    So an unfortunate bout of insomnia has been put to use to identify the location of the problem. My imaging session tonight showed the same kind of problem as in prior sessions (see attached images). When I noticed this, I went out to the scope. No sign of condensation at all on the objective lens, the flattener, or the filters. When I removed the camera from the flattener, it was clear there was moisture on the camera window.

    I removed the filter wheel entirely and took a photo. The circle on the chip is just a shadow of the circle on the window. Remarkably localized and coherent "dew" circle.

    Any idea how I can prevent this from happening? It has ruined virtually all my images since mid September.



    Spot.jpg
     
  15. Colin Haig

    Colin Haig Staff Member

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    Is it on the outside or inside of the window?
     
  16. Mark McComiskey

    Mark McComiskey Standard User

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    Yes, it is on the outside.
     
  17. Colin Haig

    Colin Haig Staff Member

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    Probably there is some contamination on the window that is acting as a condensation nucleus.
    Window heat is the option.
    Cleaning may help.
    You could also bag the whole camera and add a bunch of desiccant packs (silica gel would do) to the sealed bag, to get any remnants out.
    But the first humid night, you may be back in the same situation.
     
  18. Doug

    Doug Staff Member

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    The heater should fix that. It should stay on if you don't power down the camera when switching to another application.

    Maybe check that the heater is plugged in. If you pop the lid off the camera, and orient it with the connector panel facing you, the heater will be glued onto the far side of the chamber. There will be some wires running to a small connector on the circuit card. Make sure that's plugged in and the heater isn't damaged. Power up the camera and verify that the heater gets warm when it is turned on.

    The purpose of the heater isn't to warm up the chamber walls. It's supposed to create a small "hot spot" of warm air in the front of the camera. The idea is to keep the air in front of the window above the dew point.
     
  19. Mark McComiskey

    Mark McComiskey Standard User

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    Reporting back.

    I took the camera off the rig and thoroughly cleaned the window. No sign of any dirt, dust, smudges or damage after the cleaning. Tried the camera outside again, and within three hours, the wet spot was back and in the same place.

    So I took the camera off again and ran it indoors, with the red cover off, to check the heater as described above. Heater cable is plugged in and seem glued in, so no danger of it coming loose.

    Set camera to -10C and waited half an hour. The brown "heater tape" measured 105F using the probe of a thermopen (accurate to within a degree F). The opposite side of the black frame around the window measured about 95F. Not sure if those are correct or not.

    Set everything back up, brought it outside, and three hours later, the wet spot was back...

    Any ideas?
     
  20. Colin Haig

    Colin Haig Staff Member

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    Where are you located, what's the temp, humidity, and dewpoint when this happened?
    Can you confirm the window heat is on when you are outside?
     

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