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

[Javier]

Tim Shoppa escribió:
> 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.

Best regards,

Javier, EA1CRB