Re: [time-nuts] COTS cesium standard physics package life

[John Miles]

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
> 

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Re: [time-nuts] COTS cesium standard physics package life

[Tom Miller]

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" 
To: "'Discussion of precise time and frequency measurement'" 


Sent: Thursday, September 29, 2016 6:05 PM
Subject: Re: [time-nuts] COTS cesium standard physics package life



1.  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.)



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.


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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Re: [time-nuts] COTS cesium standard physics package life

[John Miles]

> 1.  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.)

> 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.

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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Re: [time-nuts] COTS cesium standard physics package life

[paul swed]

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 
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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Re: [time-nuts] COTS cesium standard physics package life

[Bob Camp]

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  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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Re: [time-nuts] COTS cesium standard physics package life

[Ruslan Nabioullin]

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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Re: [time-nuts] COTS cesium standard physics package life

[Ruslan Nabioullin]

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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Re: [time-nuts] COTS cesium standard physics package life

[Bob Camp]

Hi

> On Sep 29, 2016, at 1:16 PM, Ruslan Nabioullin  wrote:
> 
> On 09/29/2016 01:03 PM, Bob Camp wrote:
>> 2) How long on average is the tube likely to be useful.
> 
> 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?

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

> 
> -Ruslan
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Re: [time-nuts] COTS cesium standard physics package life

[Bob Camp]

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 Sep 29, 2016, at 1:56 PM, Ruslan Nabioullin  wrote:
> 
> On 09/29/2016 01:50 PM, John Ackermann N8UR wrote:
>> 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.
> 
> 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
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Re: [time-nuts] COTS cesium standard physics package life

[Ruslan Nabioullin]

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

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.


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
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[time-nuts] COTS cesium standard physics package life

[cdelect]

Ruslan,

Yes you can conserve tube life my operating in the Cs off mode (for 5061A
and B).
This mode still powers the ion pump and helps maintain the vacuum.
If the tube is exposed to high temperatures for a long period the Cesium
will slowly escape the oven assy. and reduce the life of the tube.
As long as a vacuum is maintained and the tube is not exposed to high
temps you should still get the specified operational life of the tube. 
If the oven is off the life is not reduced.
The main problem of long storage without occasionally powering the ion
pump is that the pressure in the tube can rise above the starting
pressure of the ion pump. 
In this case an external ion pump supply can help, however the pressure
can get great enough that even that won't help!
I usually recommend running in Cs off mode until needed and insure that
once every 3 months you go back to operate and allow the unit to run for
a few hours.

Cheers,

Corby

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Re: [time-nuts] COTS cesium standard physics package life

[John Ackermann N8UR]

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 01:03 PM, Bob Camp wrote:

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


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
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Re: [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  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 th
 e OPER mode doesn't count)?
> 
> Thanks in advance,
> Ruslan
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Re: [time-nuts] COTS cesium standard physics package life

[Ruslan Nabioullin]

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

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


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
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Re: [time-nuts] COTS cesium standard physics package life

[Bob Camp]

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 Sep 29, 2016, at 8:07 AM, Ruslan Nabioullin  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 th
 e OPER mode doesn't count)?
> 
> Thanks in advance,
> Ruslan
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[time-nuts] COTS cesium standard physics package life

[Ruslan Nabioullin]

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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