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

Hi

The real questions are:

1. Over what period of time can you get a replacement under warranty.

2. How long on average is the tube likely to be useful.

There are numbers for each. It just depends on which one you are after.

Bob

On 09/29/2016 01:03 PM, Bob Camp wrote:

So you are implying that the package life is depleted at a roughly equal
rate regardless of whether the package is fully operating, has just the
pump operating, or is completely shut off?

-Ruslan

On 09/29/2016 11:45 AM, Scott McGrath wrote:

Aha, that's what I was thinking---the manual was misleading and made no
sense in this regard.  Thanks!

-Ruslan

I think there are two separate issues to consider:

1. Cesium depletion, which only occurs when the tube is operating with
   cesium oven on, and high voltage at the other end; and

2. Tube vacuum and other physical aspects that may deteriorate over
   time, whether or not the tube is operating.  The routine ion pumping
   helps keep the vacuum up in storage, but is not as effective as the
   continuous pumping that occurs during operation.

This is guesswork, but I suspect the warranty period was based on (1),
which is why it is shorter on the high-performance tubes, which deplete
cesium more rapidly.  There may also have been an assumption that not
many customers were buying Cs standards and putting them in storage.

John

On 9/29/2016 1:16 PM, Ruslan Nabioullin wrote:

On 09/29/2016 01:50 PM, John Ackermann N8UR wrote:

But I'm interested in a different case---having the unit be continuously
in operation (so continuous pumping, not two or three times per the
period), but having the cesium physics package be in rare, intermittent
operation.

-Ruslan

Hi

Not really. What I am suggesting is that the warranty covers a variety of issues. The practical use of the part is normally  something fairly specific. You might leave the unit in the box and never power it up. You might also run it 24 hours a day 7 days a week. Both are pretty common. In the 24 / 7 run case, vacuum is not an issue at all. It’s entirely Cs depletion and that is fairly predictable. In the “never runs” case there are a lot of variables involving seal leak rates, part outgassing and getter capacity. Two of the three are pretty much a guess. That makes the “power off” case much less predictable.

Simply put:

It is rare to find a high performance tube that runs for much over 10 years. It is not uncommon to find a tube that has been on the shelf for a decade or two that works.

Bob

Hi

Are you interested in improving the likelihood of the unit working 30 years out or of it
working 15 years out? The “operating” case will ultimately kill various parts in the standard
that would not die sitting on the shelf. The pumping process may extend the life of the tube…..
What the pumping process will do is reduce the amount of time needed to bring the unit
back to life after it has been on the shelf for 30 years.

Bob

On 09/29/2016 02:02 PM, Bob Camp wrote:

Oh, really?  I thought that cesium depletion is essentially the only
real killer.

-Ruslan

The tubes were never intended to last 10 and more years. Bad for business.
The reality as time-nuts have discovered is that they do. What you have in
this group is an amazing knowledge of how to keep them ticking. Pun
intended.
The comment of raising the oven temp is exactly how I was able to get my
5061 going again.I took this somewhat to an extreme and the crazy thing
works and relocks even today. But here I suspect that the downside of
raising the temp is that it may also shift the frequency or transparency as
a better statement.
Talk about in the noise. Really can't see current.
Regards
Paul
WB8TSL

On Thu, Sep 29, 2016 at 1:46 PM, Ruslan Nabioullin rnabioullin@gmail.com
wrote:

Hi

If you operate the device continuously for 30 years, you will have other parts in
it fail. The MTBF of the system (without the tube) is not infinite.

Bob

The Cs atoms need to be electrically neutral, so their depletion rate shouldn't depend on the presence of HV, just the oven heater.  State selection wouldn't work on ionized atoms, and you also wouldn't want them to be accelerated towards the electron multiplier until after they've reached the ionizer filament at the end of the cavity.  (The longer they spend hanging out with Schroedinger's cat in the Ramsey cavity, the narrower the line width.)

Some of the HP standards (5060, 5061, 5071) have a CS OFF setting that enables the ion pump by itself.  Those tubes should last indefinitely in that mode of operation.  Unfortunately the 5062C didn't have a way to disable the Cs oven while leaving the ion pump active, which is probably why there are so few operational 5062C tubes left.  By now, most are either out of cesium or too gassy for the ion pump to recover.

I added a switch to  my 5062C to allow the vacuum to be maintained without running  the Cs oven.  It gets turned on every so often, maybe a couple of times per year, when I want a noisy signal source with known ADEV characteristics.  Even though the ion pump runs 24/7/365, there are always a few overcurrent cycles on initial powerup for some reason, where the beam current exceeds the trip point and shuts down the power supplies.  Something inside the tube is apparently outgassing during warmup -- whether it's the Cs oven or the hot-wire ionizer ribbon, I don't know.  But the condition always clears itself within a few  seconds.  The same thing happens when I turn my 5061s on after a long period in CS OFF.

• john, KE5FX
  Miles Design LLC

Hi John,

I have a Datum FTS-5060 unit. Did you just open up the heater line to the
beam tube? I like the idea of conserving the Cs when pumping down the tube
for maintenance.

Regards,
Tom

----- Original Message -----
From: "John Miles" john@miles.io
To: "'Discussion of precise time and frequency measurement'"
time-nuts@febo.com
Sent: Thursday, September 29, 2016 6:05 PM
Subject: Re: [time-nuts] COTS cesium standard physics package life

If I remember correctly, the oven power supply runs off of the same bus that powers the rest of the unit, in the 5062C's case.  It took a fair bit of hacking to install the switch and make it do what I wanted.  Not much besides the ion pump and the OCXO remains active with the switch in the 'off' position.

I'd expect the Datum unit to be pretty different in terms  of its schematic and power distribution scheme, but I'd shoot for the same functionality if I were installing a switch in one.

-- john, KE5FX
Miles Design LLC