[time-nuts] CSAC State of Play

[Lux, Jim]

On 1/11/21 5:36 PM, Nigel gm8pzr via time-nuts wrote:
> A few years ago SA45s CSAC modules were all the rage, and I was more than happy to acquire a few
> as fallout from a UK MOD project.
>
> It wasn't too long after though that reports were suggesting earlier failures than expected, but I can't for the life of me remember why.
> Something underwater does come to mind, a long term project that wasn't perhaps as long term as expected, either way someting went pear shaped, anyone have any idea of what it was and the current state of play?

When manufacturing moved from the original Symmetricom plant, they sort 
of "lost the recipe", and they had an outgassing problem internally. 
There is a getter in there to hold the vacuum, but eventually it "fills 
up".  I don't recall if it was a seal that leaked, or some material that 
was gassy. The problem has been solved.

The hotter you run them, the faster the getter fills up. So there are a 
bunch of these that have greatly restricted temperature ranges even for 
storage/non-operating(35C max.. I remember asking them whether they ship 
them with ice packs, because the back of the UPS truck in California in 
Summer is way higher than 40C)

You can check the heater current to see if it's too gassy - as the 
vacuum goes away, it takes more heat to keep the physics package at the 
right temperature.


Said Jackson did some analysis on CSACs that would not be on 24/7, and 
came up with a fairly decent lifetime.

The story is that they were used in an underwater application (where 
temperature isn't an issue), but, in fact, they also sat on the deck of 
the ship in the sun, and had early failures (or faster than expected 
rise in heater current).





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> Nigel, GM8PZR
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