COTS cesium standard physics package life
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
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@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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
The real questions are:
-
Over what period of time can you get a replacement under warranty.
-
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 rnabioullin@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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On 09/29/2016 01:03 PM, Bob Camp wrote:
- 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
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
I think there are two separate issues to consider:
-
Cesium depletion, which only occurs when the tube is operating with
cesium oven on, and high voltage at the other end; and -
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:
- 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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
On 09/29/2016 01:50 PM, John Ackermann N8UR wrote:
- 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
Hi
On Sep 29, 2016, at 1:16 PM, Ruslan Nabioullin rnabioullin@gmail.com wrote:
On 09/29/2016 01:03 PM, Bob Camp wrote:
- 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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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 rnabioullin@gmail.com wrote:
On 09/29/2016 01:50 PM, John Ackermann N8UR wrote:
- 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
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
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