SYSTRON DONNER 6520
Hi folks,
I am looking forward to aligning the internal 10 Mhz oscillator.
Of course the service manual will be the best to have.
Actually the one I own is -10 hz out.
Cheers
73's IU0CIX
BIPM produces a correction to TAI that is intended to allow the
best reconstruction of what TT would be. These corrections are
known as TTBIPMyy, where yy is the year that the particular
correction was constructed.
I have plots of several TTBIPM versions, e.g.
https://www.ucolick.org/~sla/leapsecs/ttbipm17.png
The beginning of any TTBIPMyy shows the 1e-10 rate change
that became evident in the early 1970s and was corrected
as of 1977-01-01.
Even after that correction TTBIPM shows an annual wobble.
That annual wobble is more clear in the last plots on
https://www.ucolick.org/~sla/leapsecs/earlyAT.html
Looking back this evokes questions about the HP cesium standards.
I expect that HP had taken pains to be sure that their rate was
relatively insensitive to changes in temperature.
How did HP miss that their rate was sensitive to humidity?
Does anyone have references to literature explaining what was known
about these seasonal rate variations of HP cesium standards?
--
Steve Allen sla@ucolick.org WGS-84 (GPS)
UCO/Lick Observatory--ISB 260 Natural Sciences II, Room 165 Lat +36.99855
1156 High Street Voice: +1 831 459 3046 Lng -122.06015
Santa Cruz, CA 95064 https://www.ucolick.org/~sla/ Hgt +250 m
Looking back this evokes questions about the HP cesium standards.
I expect that HP had taken pains to be sure that their rate was
relatively insensitive to changes in temperature.
How did HP miss that their rate was sensitive to humidity?
Hi Steve,
Note that all clocks have environmental sensitivities so adjectives like
"insensitive" or "sensitive" are less helpful than numerical
coefficients or upper/lower bounds. As far as I know the 5061A clocks
you refer to met their specs.
That said, there was evidence in the 80's of a slight humidity
coefficient. It was complicated by the fact that it had a several month
time constant, and thus far less visible than, for example, temperature.
Here's some reading:
"The Effects of Ambient Conditions on Cesium Clock Rates"
by Lee Breakiron
http://time.kinali.ch/ptti/1987papers/Vol%2019_17.pdf
"Analysis of the Seasonal Effects on Cesium Clocks to Improve the
Long-term Stability of a Time Scale"
by Bava, Cordara, Pettiti, Tavella
http://time.kinali.ch/ptti/1987papers/Vol%2019_18.pdf
"A Study of Long-term Stability of Atomic Clocks"
by David Allan
http://time.kinali.ch/ptti/1987papers/Vol%2019_34.pdf
"The Effect of Humidity on Commercial Cesium Beam Atomic Clocks"
by Gray, Machlan, Allan
https://tf.nist.gov/general/pdf/790.pdf
"Some Causes and Cures of Frequency Instabilities (Drift & Noise) in
Cesium Beam Frequency Standards"
by Allan, Hellwig, Jarvis, Howe, Garvey
https://tf.nist.gov/general/pdf/111.pdf
The 5071A, which came out in 1992, has significantly better specs than
previous commercial cesium clocks.
/tvb
On 5/6/2023 9:12 PM, Tom Van Baak via time-nuts wrote:
The 5071A, which came out in 1992, has significantly better specs than
previous commercial cesium clocks.
/tvb
In the early 90's, HP commissioned some environmental testing of some
5071's by IIRC JPL. It took place over an extended period of time
(the better part of a year). Certainly, one of the numerous parameters
tested was humidity. They averaged the 5071 frequency long enough to
get to where it reaches the flicker floor, in order to reduce the noise
that might mask the environment effects. IIRC, they were able to
measure down to parts in 10^15, which is way above the pay grade
of the 5071. Nevertheless, I am pleased to report that NO environmental
effects were detected at JPL. We were not really surprised at this
result, having taken measures to mitigate such effects, but still you
never know in advance if we overlooked some environmental sensitivity.
Our error budget for environmental during the design phase was to
reduce any particular effect to 2 orders of magnitude below the spec;
IE 10^-14 vs a spec of 10^-12.
I don't know too much about the 5061's, but the discovery of the
so-called "top cover effect" by De Marchi put some doubt into 5061
environmental robustness. (The top cover effect refers to the
frequency shifts when the top cover is removed, etc due to microwave
leakage in the harmonic generator waveguide apparatus.) Humidity
could affect the oxidation of the mating surfaces. The completely
new microwave hardware used in the 5071 does not have microwave
leaks.
Possibly humidity could also affect the analog double integrator.
Rick N6RK