pointing update failures

Discussion in 'Aluma AC Series CMOS' started by James Bruce McMath, Nov 28, 2023.

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  1. James Bruce McMath

    James Bruce McMath Cyanogen Customer

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    We are suddenly getting pointing update failures under a clear sky. A sample image is attached, Log read like this:

    03:04:56 ==== Starting target New Observation 1030 ====
    03:04:56 ACPS Observation New Observation 1030(1 of 1)
    03:04:56 (belongs to Project Wilson_Tests, Plan AR AIR Exposure tests)
    03:04:56 (turning on sidereal tracking)
    03:04:56 Pointing updates are enabled
    03:04:56 Catalog Maximum Mag = 18.0
    03:04:56 Start slew to New Observation 1030...
    03:04:58 Start rotate to PA 0.0 deg (raw rotator angle 186.0)
    03:04:58 (wait for slew to complete)
    03:05:42 (slew complete)
    03:05:42 [flip check: Tn=360s HAc=-12871s GW=F HAz=-12510s DWz=F WF=no]
    03:05:42 Updating pointing...
    03:05:42 (taking 16 sec. exposure, Luminance filter, binning = 2)
    03:05:42 (using High Gain StackPro readout mode)
    03:05:42 (starting exposure)
    03:06:01 (exposure complete)
    03:06:03 (exposure complete and image downloaded)
    03:06:03 Calibrating image...
    03:06:04 **Calibration failed. Original image saved.
    03:06:04 **MaxIm reports No suitable calibration groups were found.
    03:06:05 Image finished
    03:06:05 Plate-solve pointing image.
    03:06:06 2 image stars found
    03:06:06 922 catalog stars found
    03:06:06 ** No matching stars found. Check your estimated center-point RA/Dec, and your image scaling and quality.
    03:06:06 Start slew to offset...
    03:06:07 (wait for slew to complete)
    03:06:08 (slew complete)
    03:06:08 (taking 16 sec. exposure, Luminance filter, binning = 2)
    03:06:08 (using High Gain StackPro readout mode)
    03:06:08 (starting exposure)
    03:06:26 (exposure complete)
    03:06:28 (exposure complete and image downloaded)
    03:06:28 Calibrating image...
    03:06:28 **Calibration failed. Original image saved.
    03:06:28 **MaxIm reports No suitable calibration groups were found.
    03:06:30 Image finished
    03:06:30 Plate-solve pointing image.
    03:06:30 2 image stars found
    03:06:30 996 catalog stars found
    03:06:30 ** No matching stars found. Check your estimated center-point RA/Dec, and your image scaling and quality.
    03:06:30 Attempting all-sky plate solution (time-consuming)...
    03:07:32 Failed: No matching stars found. Check your estimated center-point RA/Dec, and your image scaling and quality.
    03:07:32 Astrometry.net may be offline or image quality is too poor.
    03:07:32 Start slew to New Observation 1030...
    03:07:33 (wait for slew to complete)
    03:07:35 (slew complete)
    ACP console log closed 28-Nov-2023 03:07:35 UTC

    Please advise. Thanks
     

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    James Bruce McMath, Nov 28, 2023
    #1
  2. Colin Haig

    Colin Haig Staff Member

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    Looks like your sensor has ice / frost on it. When was the last time it's desiccant was recharged?
     
    Colin Haig, Nov 29, 2023
    #2
  3. James Bruce McMath

    James Bruce McMath Cyanogen Customer

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    That is what we thought. It was the dark spots in the center of brighter stars that raised the question. How often would you expect to need to recharge it? We will need to obtain a spare unit and cycle it.
     
    James Bruce McMath, Nov 29, 2023
    #3
  4. Colin Haig

    Colin Haig Staff Member

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    Colin Haig, Nov 29, 2023
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  5. James Bruce McMath

    James Bruce McMath Cyanogen Customer

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    Well, we were thinking this did not look like simple frost. It turns out it was a light case of frost over a rather extensive contamination of some sort that has appeared over time. The attached flats show a progression (June 8th, Sept. 28th, Oct. 10th). We have no idea where this could have come from or what it is, as the chamber has not been opened. This camera was sent in for warranty repairs of the temperature sensor last spring. Your thoughts, please.
     

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    James Bruce McMath, Dec 1, 2023
    #5
  6. James Bruce McMath

    James Bruce McMath Cyanogen Customer

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    Here is another set of images showing the whole frame. The left one is taken in red and the right in blue.
     

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    James Bruce McMath, Dec 1, 2023
    #6
  7. Doug

    Doug Staff Member

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    Still looks like frost to me.
     
    Doug, Dec 1, 2023
    #7
  8. Colin Haig

    Colin Haig Staff Member

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    Agreed - it definitely looks like frost.
     
    Colin Haig, Dec 1, 2023
    #8
  9. Danny Flippo

    Danny Flippo Cyanogen Customer

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    I am assisting Bruce with this issue. Attached is a photo of the camera sensor that shows residue on the sensor behind the chamber window. This photo was taken at room temperature. The camera may have been frosting, but this residue is not dew or frost and remains after the moisture dissipates.
     

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    Danny Flippo, Dec 1, 2023
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  10. James Bruce McMath

    James Bruce McMath Cyanogen Customer

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    I will invite you to look again at the picture I posted last of the whole chip. Frost would not form a pattern like that teardrop.
     
    James Bruce McMath, Dec 1, 2023
    #10
  11. Colin Haig

    Colin Haig Staff Member

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    Have you baked the desiccant?
     
    Colin Haig, Dec 1, 2023
    #11
  12. Danny Flippo

    Danny Flippo Cyanogen Customer

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    Yes, twice. But please see my post above with a photo of the sensor at room temperature.
     
    Danny Flippo, Dec 1, 2023
    #12
  13. Colin Haig

    Colin Haig Staff Member

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    I have reviewed the images, as has Doug. When frost forms, it usually starts around a nucleus, and then it may leave the nuclei behind when it warms up.

    I disagree with your assessment of the teardrop not being attributable to moisture condensing on the surface of the sensor. It absolutely can look like this.

    Doug and I will discuss possible next steps and get back to you.
     
    Colin Haig, Dec 1, 2023
    #13
  14. Danny Flippo

    Danny Flippo Cyanogen Customer

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    Colin, have you seen the photo I posted in post number 9 of this thread? There very well could have been moisture, but there is residue left behind after it evaporates.
     
    Danny Flippo, Dec 1, 2023
    #14
  15. Colin Haig

    Colin Haig Staff Member

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    Yes Danny.

    How long did you have the recharged desiccant plug in place?
    Typically it needs at least 24-48 hours to be effective.
     
    Colin Haig, Dec 1, 2023
    #15
  16. James Bruce McMath

    James Bruce McMath Cyanogen Customer

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    Yes, of course. We thought there was frost in the first place, but it did not look like frost normally does. Several of us have had S-Big cameras and thus have experience with frost and desiccant recharging.
     
    James Bruce McMath, Dec 1, 2023
    #16
  17. Colin Haig

    Colin Haig Staff Member

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    At this point, we have to figure out how to solve what has happened.
    Because this Aluma AC2020M-22011805 has a windowless back side illuminated sensor, removing contaminants is a clean room job.
    @Doug and I will get back to you.
     
    Colin Haig, Dec 1, 2023
    #17
  18. James Bruce McMath

    James Bruce McMath Cyanogen Customer

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    Colin, the picture Danny posted is at room temperature. It is not frost. There is no cover over this chip. Can it be cleaned and how would one do that? Also, where did this come from? Was the camera opened when it was serviced?
     
    James Bruce McMath, Dec 1, 2023
    #18
  19. Doug

    Doug Staff Member

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    Yes, the chamber was opened; however, we have a process to handle that safely with windowless sensors. A temporary sensor window is installed. During our (re)assembly process the camera is thoroughly baked out and the desiccant recharged.

    You should NEVER allow frost to build up like that on a windowless sensor. At the first sign of trouble you should stop operating it and immediately bake out the desiccant. Liquid on the sensor, which of course is what frost becomes when warmed up, is very bad! It can leave a slight residue, but far worse if the water is present for too long it will eventually corrode the sensor, which is of course permanent damage.

    Hopefully the water wasn't sitting on the sensor for a long period of time. It's a super delicate operation, but we can try to clean it.
     
    Doug, Dec 1, 2023
    #19
  20. James Bruce McMath

    James Bruce McMath Cyanogen Customer

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    What is the path fwd on this?
     
    James Bruce McMath, Dec 1, 2023
    #20
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