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Posted: 1/31/2011 5:25:30 PM EDT
What is it about the night vision tube manufacturing that creates so much variables in the end product?  One would think the variations could be isolated by now and eliminated to create a consistant tube across the line like most other products today.  What is it that I dont know about why theres such a great variety of the same tube? Are some of the employees suffering from a hang over from the previous evening ? I've had rifle scopes that I saw dust and crud internally on the lenses, but thats from a dirty "clean" room and a careless worker I suspect.  I suppose theres much more to night vision tubes, but what would that be? thanks
Link Posted: 1/31/2011 6:39:27 PM EDT
[#1]
Tubes are just very hard to make that perform well on a consistent basis. There are something like 480 manufacturing steps in making a night vision tube. Many that are made don't perform well. I don't know what the exact percentages are but so many variables come into play it is just not a exact science. Kind of like diamonds, no two are the same.

They certainly have gotten better but when a batch of tubes are made there is no guarantee as to what you will get.
Link Posted: 1/31/2011 8:13:47 PM EDT
[#2]
I think alot of the quality control issues have to do with the microscopic scale on which the manufacturing steps occur.



Gen2 photocathodes are on the order of around 3000 angstrongs ( 0.3 Micron ) thick from memory while Gen3 PCs are around 30,000 angstroms ( 3 microns ) yet the thickness of each is just as critical to the final product with minor variations leading to significant changes in the final product.  Some parts of the photocathode, such as the cesium layer are almost atomically thin. They expose the photocathode to a vapor of Cesium and then expose it to oxygen in a controlled environment. When putting down a monolayer like that, they best you can do is adjust the time it's exposed to the cesium vapor to try and get the right thickness.



The AlO "Thin Film" is similarly thin and they make it by dipping the MCP into a suspended laquer, coating in AlO and baking away the lacker and sintering the film.



The holes in the MCP are on the order of 2 microns across now, millions of them. But the fibers that make up the plate are drawn one at a time!



These things can't be engineered perfectly. They make a process then they make it better. I saw a picture of one of the first GaAs photocathodes in operations once and it was terrible. I think it was about 400 uA/lm response. Terrible but a great leap forward at the time. They've come a long way since then.



But the end product is only as good as the process. The process isn't perfect at those scales and it's amazing that things still work as well as they do. Yields improve, but there's only so much you can do about improving the process.



A better question would be "How do they make the tubes work as well as they do and how do they get the yields so high"...  



Manufacturers like L3 and ITT really are amazing and they don't publish their secrets. But if you want to learn how tubes are made ( from a general perspective ) Then there's some excellend material written about this by Illes P Csorba who used to be an engineer for Litton once.



Once you read some of his works, you'll be amazed they can create this kind of technology with any consistency at all!



Regards

David
Link Posted: 1/31/2011 8:33:36 PM EDT
[#3]
Cj, very interesting, makes me wanna ensure I buy with a good warranty Gonna have to save the bills for that 5 year Pinnacle warranty
Link Posted: 1/31/2011 10:11:20 PM EDT
[#4]
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