[time-nuts] Super stable BVA Quartz resonators... BVA??

Bernd T-Online BNeubig at t-online.de
Sun Dec 9 09:21:46 EST 2007

Tim Shoppa wrote:
> For a while, didn't HP sell temperature probes which were in fact
> quartz crystals? Oscillation frequency was converted by some simple
> electronics to a temperature, and at the time (60's?) they were
> exquisitely convenient for measuring way better than a tenth of a
> degree.
> Either the frequency drift was negligible or it
> was so slow that I don't remember any manual removal of frequency
> drift effects.
> I'm guessing the probe crystals were some special cut (don't know which!)
> which was fairly linear or at least monotonic over the measurement
> temperatures. I'm guessing that HP chose a cut which had a very large
> tempco such that tempco dominated over any frequency drift.

They did indeed. This was the HP2801A, later followed by the HP2804A.
It uses a so-called LC-cut (Linear Coefficient) quartz crystal sensor, 
which is a doubly rotated cut with ultra-linear frequency vs. 
temperature characteristic with a slope of 35.4 ppm/K.

For more information see http://hparchive.com/Journals/HPJ-1965-03.pdf

BTW: I proudly own a HP2801A plus two crystal sensor elements. However I 
cannot connect them to the instrument, because the 2801A has a special 
connector for it. It looks like a smaller version of a BNC connector, 
but the bayonet has three "nipples" instead of two. Does anyone on the 
list know what kind of connector that is and where to get the 
counterpart (plug)?



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