On 1/11/21 5:36 PM, Nigel gm8pzr via time-nuts wrote:

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).

Hi

Root cause (as mentioned earlier) seems to be a problem with the seal on the
inner “magic guts” of the device. There are units that seem to run on and on forever
with no issues, so it’s not a 100% sort of thing. The problem goes back to fairly
early CSAC production lots and seems to have been a tough one for them to
take care of.

We had some early CSAC units die that way and they were replaced without much hassle.
They had not seen any sort of extended (as in weeks / months) high temperature
exposure. They had been through standard testing which would take them over the
entier temperature range. While the failure mode could have been the same, there is
no way to be 100% sure.

Bob

Woods Hole Oceanographic Institute was (and still is to the best of my
knowledge) using CSAC's in their long deployment ocean bottom seismometers,
and was seeing premature failures.

I think they did a paper on the issue, but I'd have to dig for it...

Brent

On Mon, Jan 11, 2021 at 9:06 PM Nigel gm8pzr via time-nuts <
time-nuts@lists.febo.com> wrote:

We had one with <<100hours on it, working when stored (in temperature controlled office), failed vacuum when powered up 6 months later.

It was replaced without hassle  (well, no hassle to us, not sure if Jackson had to fight with the manufacturer).

I have heard from sources inside and outside the company that the issue has been fixed, so the newer ones should be good to go for most applications.  (they still have a somewhat restricted temperature range).

-Jordan

-----Original Message-----
From: time-nuts time-nuts-bounces@lists.febo.com On Behalf Of Bob kb8tq
Sent: Tuesday, January 12, 2021 8:23 AM
To: gandalfg8@aol.com; Discussion of precise time and frequency measurement time-nuts@lists.febo.com
Subject: Re: [time-nuts] CSAC State of Play

Hi

Root cause (as mentioned earlier) seems to be a problem with the seal on the inner “magic guts” of the device. There are units that seem to run on and on forever with no issues, so it’s not a 100% sort of thing. The problem goes back to fairly early CSAC production lots and seems to have been a tough one for them to take care of.

We had some early CSAC units die that way and they were replaced without much hassle.
They had not seen any sort of extended (as in weeks / months) high temperature exposure. They had been through standard testing which would take them over the entier temperature range. While the failure mode could have been the same, there is no way to be 100% sure.

Bob

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Yes. See:

"A Second Look at Chip Scale Atomic Clocks for Long Term Precision Timing"
http://www.obsip.org/documents/Gardner_IEEE_Oceans_2016.pdf

/tvb

On 1/12/2021 8:14 AM, Brent wrote: