[time-nuts] -hp- 10811 repair (Thermistor)

[Rick Karlquist]

Bruce Griffiths wrote:
>> One concern is:
> How accurate does one' thermometer which one uses to calibrate the
> thermistor bridge setpoint have to be?
>
> Bruce

The thermistors HP used were quite accurate, so you didn't
need a thermometer.  You just calculated the correct resistor
value for the temperature you wanted.  The characterization of
the crystals themselves was done in an oil bath with fairly
precise thermometers, however, the accuracy only needed to
be on the order of a degree C or so.  This is because of the
very broad peak, or plateau.  It was easy to get the crystal
temperature set correctly so that the electronics dominated.
The fact that the electronics were not so great helped.

Rick