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

[Tim Shoppa]

Bernd T-Online <BNeubig at t-online.de> wrote:
> I can confirm Rick's statement, that there is no noticable effect of 
> aging on the turnover temperature (TOT).
> Looking at it from physics standpoint, frequncy aging is mainly caused 
> by minor changes of vibrating mass  and/or by changes in elastic 
> properties (both due to various mechanisms). See my earlier thrad on 
> aging mechanisms.
> On the other hand, the turn-over temperature is primarily governed by 
> the cut angle (in connection with the resonator shape etc.). Mass 
> loading, i.e. changes of electrode mass, has also an infuence, but this 
> is much weaker. Roughly stated: a change of the TOT by one degC may be 
> caused by a variation of the mass loading by an amount eqivalent to a 
> frequency change of n*1000 ppm or so. This means that usual long term 
> aging of precision crystals of a few 100 ppb or even one or two ppm may 
> cause changes of TOT in the range of mK or less, which is
> - much smaller than the accuracy of the determination of TOT
> - neglictable compared to the impact of the aging of thermistors and of 
> the frequency determining capacitors and inductors of the sustaining 
> oscillator stage

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.

Tim.