COTS cesium standard physics package life
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:
On 09/29/2016 11:45 AM, Scott McGrath wrote:
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
Aha, that's what I was thinking---the manual was misleading and made no
sense in this regard. Thanks!
-Ruslan
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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
On Sep 29, 2016, at 2:08 PM, Ruslan Nabioullin rnabioullin@gmail.com wrote:
On 09/29/2016 02:02 PM, Bob Camp wrote:
The “operating” case will ultimately kill various parts in the
standard that would not die sitting on the shelf.
Oh, really? I thought that cesium depletion is essentially the only real killer.
-Ruslan
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- Cesium depletion, which only occurs when the tube is operating with
cesium oven on, and high voltage at the other end; and
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.)
- 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.
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
- Cesium depletion, which only occurs when the tube is operating with
cesium oven on, and high voltage at the other end; and
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.)
- 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.
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
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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
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