[time-nuts] COTS cesium standard physics package life

[Scott McGrath]

It depends on the beam tube   There is a fixed amount of Cs in any given beam tube this pool of Cs is consumed during operation.    Once the Cs is depleted the tube will no longer function.    It's possible with intermittent use for the tube to run for decades as long as vacuum maintenance is performed.   Most Cs tubes have a published expected lifetime before replacement is required  while maintaining published specifications.   It's possible to extend tube life somewhat by increasing oven temp and electrode voltages but the signal becomes noisier as a result

Content by Scott
Typos by Siri

> On Sep 29, 2016, at 8:07 AM, Ruslan Nabioullin <rnabioullin at gmail.com> wrote:
> 
> Hi, I'm unable to fully grasp the lifetime specifications of typical COTS cesium standard physics packages, for both old and new designs. For example, the documentation of an older HP standard specifies a shelf life of two years if the ion pump is operated two or three times per year, yet at the same time the ``beam tube warranty'' period is three years.  Does this mean that if the physics package is fully operating (i.e., LOOP OPEN, OPER, or LTC), then it's guaranteed to last at least three years, but if it's completely shut down, except for vacuum maintenance sessions (using the mode CS OFF) two or three times per year, it will last only two years?  Also, what will the expected lifetime of the package be if the standard is kept as a reserve, specifically, continuously-powered with the mode set to CS OFF (so continuous vacuum maintenance), and activated or deactivated to or from, resp., OPER, as needed, excl. the time spent fully operating (i.e., in this case, the time spent in the OPER mode doesn't count)?
> 
> Thanks in advance,
> Ruslan
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