[time-nuts] C-Beam Usage

Tom Van Baak tvb at leapsecond.com
Fri Jan 14 18:20:00 UTC 2005


> Do you run the C-Beam(s) 24/7 or only fire them up enough in advance of
> when you want to check other things?
>

If you're curious you'll keep the Cs on and monitor
its progress against the other standards.

If you're practical you'll use the minimum necessary
for your accuracy requirements. In many cases this
means that a Rb or GPSDO is all you ever need.

I've heard of some people who run off the OCXO in
their cesium standard (the 5061A "Cs Off" mode) and
turn on the Cs for a couple of hours once a month
simply to recalibrate the OCXO.

The OCXO inside Cs standards tend to be very high
quality so this makes a lot of sense. If the drift rate
is down to 1e-10/day your accuracy easily stays
within a few parts in 10^9th per month with almost
no drain on finite Cs resources. Or you can turn it
on once a week, etc.

The short-term stability of this solution is often better
than Rb or GPSDO.

> Obviously the question relates to the life expectancy of the tubes and the
> cost involved in replacing one.
>

I'm told Cs tubes reach end of life either when they
run out of fresh Cs metal in the oven on one end of
the tube *or* when the leading dynode of the electron
multiplier is saturated with used Cs on the other end
of the tube.

I also heard that high performance tubes (HP option
004) are more likely run out of Cs while standard tubes
are more likely to die of EM saturation in the long-term.

A Cs standard running in Cs Off mode is not subject
to either of these.

If someone has more reliable or inside information please
let us know.

/tvb






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