[time-nuts] HP 5065A questions

[Richard (Rick) Karlquist]

On 9/25/2016 6:42 PM, Skip Withrow wrote:

> 1. What the heck is rubidium cell flooding, and how does the TEC in the
> 5065A fix this problem?  None of the -many- rubidium oscillators that I
> have been inside before has a TEC, and I have never seen the subject
> addressed.
> The manual suggests that it may take several weeks at the 1A current to fix
> the problem (normal operation of the 5065A applies .7V across the TEC).

Cell flooding is one of the dirty little secrets of Rb standards.
I worked on the 10816 mini rubidium.  There is supposed to be liquid
rubidium in a reservoir somewhere.  We used the tip off as the
reservoir.  The oven design (optimistically IMHO) attempted to have
a heat leak on the tip off that kept it cooler than the rest of
the cell, yet the oven was still supposed to isolate the cell
temperature from the environment.  Capillary action was supposed
to keep the liquid rubidium in the tip off.  However, it might
come out of the unit was jiggled or turned over or stored, powered
down, in a hot place.  Then, Rb might get on the optical window,
and then you have a serious error in frequency.  The (again optimistic)
concept was that you would just run the unit for a long time until
the rubidium on the window hopefully evaporated and ended up in the
tip off.  Yeah, right.

The 5065 (a VASTLY superior design compared to the 10816) was much
less likely to be jiggled or turned over, and at least had a
TEC to cool the Rb reservoir in case it got flooded.

Rick