ISO: MWIR cameras with trashed cryos

[adammunich]

Howdy all,

I am wondering if anyone has MWIR cameras on hand that have trashed cryocoolers, but otherwise complete electronics. I am interested in seeing if I can bring them back to life, as I recently purchased all the parts needed to get things *very* cold and am curious if it's even remotely possible to bring these cameras back to life through external cooling?

[Fraser]

A bit of info on the Stirling cryo-cooled sensor design....

The stirling cooler cools a "cold finger" that has the imaging detector pixel or FPA bonded to it.
The cold finger, detector pixel or FPA is located inside a vacuum Dewar.
The detector pixel or FPA is connected to the outside world via through-glass connections in the Dewar.

Disassembling such a design will normally result in a dead detector or FPA. You would really need to attach a cryo-cooler output to the cold finger without disrupting the connections and alignment of the detector or FPA. Good luck with this project but do not risk too much money on it.

Fraser

[adammunich]

Yup, I fully anticipate that doing this is going to require careful destruction of the stirling cooler with a diamond saw such as to not destroy he dewar also. This is what makes it a good challenge!

[Fraser]

Sounds like a fun project. Good luck with it 

[CatalinaWOW]

Having done something similar in a past life I am pretty sure it is possible with a number of configurations.  Think through what you are doing and work carefully.  It is worth thinking about thermal shock.  Stirling coolers cool relatively slowly and the dewar design may depend on that.

[adammunich]

I ran across one and decided to take a gamble.

As it were, this camera had both a broken cryo and a broken shutter. After about 2 minutes the cryo would jam and stop working. Hours meter exceeds 10,000, so not surprised.

On a hunch, I tossed a bag of ice onto the cooler and wouldn't ya know, it started working again, and got down to 70K. Looks like it might have just been out of tolerance somewhat. So naturally, I tossed a TEC onto there and now it can run continuously. 

https://photos.google.com/share/AF1QipP0O5RIUZStGbkBPRQKvljUOdOrEhTu2eJ51S5ZAMAGlBCHrcOhHxMSCXDhD-a3TQ?key=WFh1UElRTFlpZVpQVWVERFBldnNuSkFHM3ctUGFR

The shutter is still broken, parts of the motor's linkage have rusted through (looks like water damage). I think I might be able to replace this with a DSLR shutter though, or, do some kind of fancy metal work to repair the linkage. Have not decided yet.

[frenky]

Perhaps you culd also use cheap peltier element to cooldown this "cold finger"?

[adammunich]

Unfortunately TECs stop being practical around -70c. I have a free piston cryo that could get to 70K though, it looks like it won't be needed just yet.

[Bill W]

The shutter is still broken, parts of the motor's linkage have rusted through (looks like water damage). I think I might be able to replace this with a DSLR shutter though, or, do some kind of fancy metal work to repair the linkage. Have not decided yet.

Depends how closely you will need to match the timing of the original mechanism.  It does not look like there is feedback for shutter operation so the camera is likely to be simply expecting it to work.  For example 'drive solenoid closed, wait 4 frames, shutter will be closed by now, save closed frame(s) for correction, drive solenoid open, wait 4 frames, display image as normal.

regards
Bill

[adammunich]

Yup, it is definitely not smart. I just have only about 4mm of clearance for a b=new shutter assy though, so whatever I find must be able to fit!

[george.r]

After seeing a recent thread by Fraser on a lucky find of one such camera (and learning stirling cooled cameras were a thing), I am also interested in them. Well, onto the stack of "projects to one day research about" they go. Eager to see what comes of this, though

[Fraser]

George-r,

Some reading for you before buying Stirling cooled cameras.......

https://www.eevblog.com/forum/thermal-imaging/thermal-camera-purchasing-the-perils-of-buying-a-cooled-camera/

Fraser

[george.r]

Much appreciated, Fraser. I now know more than I did before, and for that I'm thankful!