Lifetime of Cesium tube
What kind of lifetime can one expect to see from an HP 5061-6101 cesium
tube?
What typical symptoms do these exhibit near the end of their useable
lifetime?
Thanks.
glenn.tracy wrote:
What kind of lifetime can one expect to see from an HP 5061-6101 cesium
tube?
It is my understanding that you can expect about 5 years in continuous use,
or 2 years on the shelf.
What typical symptoms do these exhibit near the end of their useable
lifetime?
The end of life can be due to several things, but most notable is a shortage
of cesium ions to send hurling down the length of the tube, and an excess
of other molecules for the cesium ions to run into. Either condition results
in a shortage of cesium molecules for the detector to detect.
A c-beam is essentially a notch filter. The beam is modulated (mixed?) with
a 9Ghz microwave signal that is derived from a very stable and low noise crystal
reference. When the modulation signal is at the right frequency, the beam
current will peak. There is usually a servo mechanism that keeps the crystal
reference tuned so that the beam current stays on top of this peak.
At end of life, the beam current peak becomes indistinct. There isn't much
distance between the peaks and the valleys, and the servo has trouble figuring
out where the peak is, so it ends up bouncing all over the place. This shows
up as increased phase variations. Ultimately, no peaks can be found and the
crystal oscillator ends up slammed against its maximum, or minimum frequency.
-Chuck
The end of life can be due to several things, but most notable is
a shortage
of cesium ions to send hurling down the length of the tube, and an excess
-
Cesium atoms, not ions, are launched down the tube. They
then get ionized by the hot wire ionizer. -
My understanding talking to the CBT people is that
there is plenty of cesium in the tube to last its expected
life. In most cases, the tube will fail for other reasons
long before the cesium is exhausted.
of other molecules for the cesium ions to run into. Either
condition results
in a shortage of cesium molecules for the detector to detect.
Atoms not molecules
A c-beam is essentially a notch filter. The beam is modulated
No, it's a bandpass filter.
Rick Karlquist
From the Agilent perspective, the expected lifetime of a new
05061-6101 High
Performance CBT is an average of 5 to 6 years of continuous operation. We
don't speculate on non-operating useful life. Lifetime is not a
specification for a number of reasons. The 5061A/B electronics are
not microprocessor-controlled as in the 5071A so there are fewer guards
against the possibility of a CBT being operated outside of its nominal range
of Cs oven temperature, EMult voltage, HWI voltage, etc. Any of
these could have an effect on CBT lifetime.
Agilent is still manufacturing and selling the replacement CBT for the
5061A/B
as products with model numbers 05061-6101 and 05061-6077
(standard-performance). N.B. that in order for the CBT warranty to be valid
for these models it is stipulated that it be operated only in conjunction
with the newer A11 Cs Oven Controller, identified as HP P/N 05061-6144.
CBTs manufactured after December 2002 now have more Caesium to extend their
expected operating life. This is true for all four of our CBT models, the
aforementioned two above as well as the 10890A and 10891A models for the
5071A Primary Frequency Standard. Although there is little or no empirical
data for the improvement in the 05061-6xxx models, initial testing results
on the 10891A model give expectations that the lifetime will average 9 to 10
years instead of the previous 6 years. To back up that
improvement Agilent also increased the warranty on that model 10891A to 5
years. These newer CBTs with increased quantity of Caesium are denoted by
the following serial number prefixes:
05061-6077US4247 5-year warranty
05061-6101US4248 3-year warranty
10890A US4239 10-year warranty
10891A US4240 5-year warranty
HP presented a paper at the Frequency Control Symposium in 1999 that
described lifetime and end-of-life symptoms, geared toward the 5071A. Here
are the first
several lines, to help in searching for the document:
"LONG-TERM EXPERIENCE WITH CESIUM BEAM FREQUENCY STANDARDS
John A. Kusters, Hewlett-Packard Santa Clara, USA
Leonard S. Cutler, Hewlett-Packard Laboratories, USA
Edward D. Powers*, United States Naval Observatory, USA
ABSTRACT
Since its introduction 7 years ago, the Hewlett-Packard cesium beam
frequency standard has been installed in many national laboratories. At the
present..."
As to pumping down a CBT in non-operating storage, the recommendation in the
5071A Operating manual is that it be done every 6 months. This applies a
conservative approach because in addition to time causing eventual increase
in internal vapor pressure, temperature also has an impact. A CBT
or Cs standard stored un-powered in a very cool environment will have less
likelihood of this than one stored in a galvanized-metal
warehouse in full sunshine.
Every 6 months is a good rule of thumb.
As to pump-down procedures, Appendix B in the 5061B Operating/service manual
tells how to use an external HV supply to pump the CBT by itself, should the
HV supply installed in the instrument chassis fail to do the job.
Dave Carlson
---- Original Message -----
From: "Chuck Harris" cfharris@erols.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Thursday, 12 May, 2005 5:36 AM
Subject: Re: [time-nuts] Lifetime of Cesium tube
glenn.tracy wrote:
What kind of lifetime can one expect to see from an HP 5061-6101 cesium
tube?
It is my understanding that you can expect about 5 years in continuous
use,
or 2 years on the shelf.
What typical symptoms do these exhibit near the end of their useable
lifetime?
The end of life can be due to several things, but most notable is a
shortage
of cesium ions to send hurling down the length of the tube, and an excess
of other molecules for the cesium ions to run into. Either condition
results
in a shortage of cesium molecules for the detector to detect.
A c-beam is essentially a notch filter. The beam is modulated (mixed?)
with
a 9Ghz microwave signal that is derived from a very stable and low noise
crystal
reference. When the modulation signal is at the right frequency, the beam
current will peak. There is usually a servo mechanism that keeps the
crystal
reference tuned so that the beam current stays on top of this peak.
At end of life, the beam current peak becomes indistinct. There isn't
much
distance between the peaks and the valleys, and the servo has trouble
figuring
out where the peak is, so it ends up bouncing all over the place. This
shows
up as increased phase variations. Ultimately, no peaks can be found and
the
crystal oscillator ends up slammed against its maximum, or minimum
frequency.
-Chuck
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Richard (Rick) Karlquist (N6RK) wrote:
The end of life can be due to several things, but most notable is
a shortage
of cesium ions to send hurling down the length of the tube, and an excess
- Cesium atoms, not ions, are launched down the tube. They
then get ionized by the hot wire ionizer.
I stand corrected.
- My understanding talking to the CBT people is that
there is plenty of cesium in the tube to last its expected
life. In most cases, the tube will fail for other reasons
long before the cesium is exhausted.
Only if the tube is made in a suboptimal way. To quote your
collegue Dave Carlson:
"CBTs manufactured after December 2002 now have more Caesium
to extend their expected operating life."
I think that would tend to indicate that the tubes are expected
to run out of cesium at end of life.
of other molecules for the cesium ions to run into. Either
condition results
in a shortage of cesium molecules for the detector to detect.
Atoms not molecules
Molecule: A unit of matter, the smallest portion of an element or
compound that retains chemical identity with the substance in mass.
A single Cesium atom is the smallest portion of the Cesium element that
retains chemical identity with Cesium in mass. It is both an
atom, and a molecule. So is gold, iron, copper, nickel, ..., but not
oxygen, nitrogen, fluorine, chlorine, ...
A c-beam is essentially a notch filter. The beam is modulated
No, it's a bandpass filter.
A notch filter is simply a very narrow filter. It can be bandpass,
or band reject, depending on which engineer wrote the definition.
The C-beam is a notch filter that happens to be a bandpass filter.
-Chuck
The MAy 2005 issue of IEEE Spectrum has a short article about a new design
of a Cesium standard. The inventor is John Kitching of NIST.
The claim is this new design will be less expensive and smaller than the
existing design.
I have included a couple of quotes from the article
"Right now the cesium-vapor chamber takes up a few cubic millimeters. Throw
in the laser, the optics and the electronics and were up to maybe a
cubic centimeter."
"Besides being cheap, the new atomic clocks will also be frugal with power"
So maybe when the existing Cesium standards wear out they can be replaced
with a new and cheaper one. I might even be able to afford a new one :-)
Bill K7NOM
Hi Bill:
I wouldn't trade in my Cs just yet. Have a look at the performance:
http://tf.nist.gov/ofm/smallclock/Performance.htm
73,
Brooke Clarke, N6GCE
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com
Bill Janssen wrote:
The MAy 2005 issue of IEEE Spectrum has a short article about a new design
of a Cesium standard. The inventor is John Kitching of NIST.
The claim is this new design will be less expensive and smaller than the
existing design.
I have included a couple of quotes from the article
"Right now the cesium-vapor chamber takes up a few cubic millimeters. Throw
in the laser, the optics and the electronics and were up to maybe a
cubic centimeter."
"Besides being cheap, the new atomic clocks will also be frugal with power"
So maybe when the existing Cesium standards wear out they can be replaced
with a new and cheaper one. I might even be able to afford a new one :-)
Bill K7NOM
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What kind of lifetime can one expect to see from an HP 5061-6101 cesium
tube?
What typical symptoms do these exhibit near the end of their useable
lifetime?
Glenn,
Not sure about 5061 tubes, or the post-2002 tubes,
but I've been told high-performance 5071A tubes
last about 7 years (they usually run out of cesium)
while standard performance 5071A tubes should
last about 20 years (still plenty of cesium in the
oven but by this time the EM detector wears out).
I haven't had any of my 5071A die yet. Doug - can
you tell us how long your first 5071A tube lasted?
As for shelf-life, you can read about the official way
to store and periodically pump them. But I'm quite
certain that many of us have surplus units that
probably haven't been powered for years and some
of them end up working fine.
/tvb
At 07:33 PM 5/12/2005, Bill Janssen wrote...
"Right now the cesium-vapor chamber takes up a few cubic millimeters. Throw
in the laser, the optics and the electronics and were up to maybe a cubic centimeter."
"Besides being cheap, the new atomic clocks will also be frugal with power"
Sounds like the makings of a fine wristwatch, especially if it's not a cube. :-))
I don't know about 5061 era tubes but my understanding of 5071 era tubes is
similar to what Tom said.
High-perf tubes use about a gram of cesium per year and originally had six
grams, so last about six years.
Standard perf tubes which run at lower oven temperature using less cesium
last around twenty years.
Old prices of those tubes were something like $35K or $25K.
I bought a used 5071A and my estimate from looking at the log was that it
had run around 300 days previously.
I ran it four weeks, then stopped to update firmware, then ran continuous
operation for exactly 365*5 days before it apparently ran out of cesium
couple months ago. So probably six years total (but I can only be certain
of last 5.1 years).
Couple years ago Agilent started loading high-perf tubes with nine grams of
cesium so expect to last around nine years.
And they lowered the price to around $22K for high-perf and std-perf
(high-perf gets five year warranty and I think std-perf gets longer warranty
but I am not sure). I choose high-perf, updated firmware again, and have
been running continuous the four weeks since MJD 53474 (and hope to continue
for nine years; my primary use is driving my two geodetic quality GPS
receivers which are part of global monitoring networks IGS/JPL).
Agilent instructions remind you that a good way to "store" 5071A tubes is to
keep them in your 5071A set to Standby.