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

Tim Shoppa shoppa at trailing-edge.com
Sun Dec 9 09:09:47 EST 2007


Javier <javier at nebulosa.org> wrote:
> Tim Shoppa escribi?:
> > 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.
> >
> >   
> At least one model is the 2804A. Not much info about it in the Agilent 
> web site, but according to the 1986 catalog 'the temperature sensor is a 
> quartz crystal whose precise angle of cut gives an stable and repeatable 
> relationship between the resonant frequency and temperature'. But also 
> is mentioned there that 'The only adjustment necessary to remove effects 
> of thermal history on the sensor is a simple ice point or triple point 
> calibration adjustment using the front panel thumbwheel switches'.
>
> Since the ice-point calibration would only be able to remove an offset, 
> I understand that this is the manual removal of frequency drift effects. 
> Of course, I suppose that the dritft would be small compared with the 
> quartz temperature coefficient. Anyway, a 10544 oscillator has a cold 
> offset that can easily be of 1000Hz, so if at 80 deg. C the offset is 
> zero, and at 25 deg. C the offset is 1000Hz, you easily have a rough 
> 15Hz/deg C average tempco in that range - and the aging drift for this 
> oscillator is quite less than that.

Very interesting, Javier. I'm guessing the 2804A was a 70's
implementation if it had thumbwheels. Thanks for posting the details
you found!

The unit I remember was not digital in the readout sense - it
worked like a Fluke differential voltmeter, where you dial in some
big rotary switches until you get a null on an analog meter. I
may be confusing a 60's era Fluke temperature probe with the HP
probes though!

Who else would've been building quartz temperature probes in the
60's? Fluke, Beckman, ??? And what cut crystal matches the
need for a huge and mostly linear tempco?

Tim.



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