AGEMA Thermovision 900 professional camera - Teardown and commentary by Fraser

[Ultrapurple]

Thanks a million, Fraser - you've done a brilliant job, as usual.

Apparently the previous owner's last words before scrapping the system were "Can anyone smell a slight trace of helium...?"

 

[Fraser]

My pleasure 

Some breaking news.... I have been studying the "Hours Run" meter under magnification and I can see the little bubble on the far left of the tube. There are some bodge wires changing the polarity applied across the tube and I just confirmed that the little bubble is nearest to the negative input. If my understanding of these electrochemical timers is correct, that means this camera had very low hours on it. I saw no evidence of the cooler having been changed so it is the original fitment. She died young 

It may be that the camera was used very infrequently and lost its Helium Charge over time. The cost of a service on the cooler was around £5K in 1994 when this camera was made. The price went up over time and I have a written quote from FLIR provided in the early 2000's for £9K for a cooler service ! Such costs were often deemed too high and the camera scrapped in favour of an uncooled microbolometer based unit.

Fraser

[Fraser]

Another look at the hours meter and I am starting to doubt that it is working. The bubble is so far off the left mark of the scale that it just does not look right. I think I will ignore that meters indication. I enjoy investigating the history and failure of thermal cameras but I believe this one will be a simple case of "Years Vs the Stirling Cooler".

Would I recommend anyone buy one of these older Sterling cooled scanning type cameras to use and expecting a good few years life out of it? In short no, these cameras were great in their day, but the poor Cooler is long past its best. Hours run and any Helium leakage place the odds against such a camera lasting very long in service.

The Peltier cooled scanning cameras like the AGEMA Thermovision 450, 470 and 480 are more likely to give reasonable service as the only gas related concern is the quality of the vacuum in the Vacuum Dewar around the detector die. That vacuum is often very long lived, just as in Thermionic Vacuum Tubes.

Fraser 

[Fraser]

I have decided to upload all the pictures of the K506 Stirling Cooler for those interested.

This is a component that interests me greatly as I want to understand the design and potentially refilling with UHP Helium Gas.

There is likely to be a teardown of this cooler in the near future 

The date code (Motor: 9438/Compressor: 9444) on the cooler indicates that it was built in 1994 so it is now approx 26 years old.

Fraser

[Fraser]

Pictures continued....

[Fraser]

Pictures continued....

[Fraser]

Pictures continued....

[Fraser]

My Lily doing an impression of many who have read this thread 



I can see from the picture views that this sort of camera is a specialist interest. I am both a Mechanical and Electronics Engineer so this sort of tech appeals to me. It is not everyones 'cup of tea' though.

Fraser

[Ultrapurple]

I for one find it fascinating, although I freely admit that in this case I have a vested interest, of sorts.

This is one of those posts whose value will appreciate with time. There can't be very many of these cameras left (fewer still in working order!) and it's nice to see the engineering that went into them before the last one goes to the Great Skip.

[Hydron]

Looking at the pics of the lens mount it appears that the element is a meniscus lens - does it have a negative (as previously assumed) or positive power? I look forward to hearing how it helps get the big mirror lens going!

[Fraser]

Hydron,

It is indeed different to the lens installation found in the AGEMA 870 and 880 that can use the same lenses.

Images of the 870 are to be found here (with 360 degree rotation video)

http://wll.kr/bbs/board.php?bo_table=06&wr_id=795

The 870 and 880 have a concave lens (exact type of lens not known) surface facing the removable lens and the 900 has a convex surface of a Meniscus lens facing the removable lens. The scanner section differs between the 800 series and 900 and this may explain the difference. In the 900 the beam output of the removable lens is refracted down to the the required dimensions for the first (tilting) mirror. The beam converges behind the lens element.

It is not known whether the large lens that Ultrapurple has will work with the lens taken from the THV900 but we are hopeful of compatibility. There remains the ugly possibility that the removable lenses are slightly different between the 800 and 900 series cameras and Ultrapurple mat have a lens incompatible with the 900 series integrated lens. We shall see.

Fraser

[Fraser]

I forgot to say, the lens in the THV900 is a Positive Meniscus lens,

Fraser

[Fraser]

A final comment on the THV900 lens mount and rev able lenses....

The THV900 lens mount is not the same as that used on the THV800 series. Whilst the lens barrels may be the same, or similar, the actual bayonet mount is different. This means that lenses cannot be shared between THV900 and 800 series cameras The THV900 lens mount bayonet fitting is effectively the inverse of that found on the THV800 series. What nasty, scheming, marketing pencil pusher thought of that I wonder ?

Fraser