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

[Tom Van Baak]

 > 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