[time-nuts] Re: humidity and early HP cesium standards

[Richard (Rick) Karlquist]

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