Bob Fehrenbach wrote:
>
> Martin McCormick <martin@DC.CIS.OKSTATE.EDU> wrote:
> >        How about a correction factor which adjusts itself based on the
> >temperature?  At 25 C, no correction and then increasing correction as
> >the temperature deviates from 25 DEG C.
>
>    If the change in temperature only affected the crystal, the results
>    might be somewhat predictable and hence could be conpensated.
>    Unfortunately, there are other factors such as the oscillator circuit,
>    the crystal caps etc.  We sprayed 'freeze mist' on a PIC running
>    with a watch crystal and the frequency went UP!.  If the crystal
>    were the only factor the frequency should have gone down.
>
If I remember correctly, the freq vs temp vs curve has a maximum around
250C.
If you go cooler, or warmer, the frequency drops. That is, if memory
serves
correctly...

If you want to keep that frequency stable, you have to keep the
temperature
stable too. The rate of drift increases with increased temperature, but
it is
not so easy to keep a component cool without a peltier junction device.
The
easier answer is to heat it up to, say, 600C with a transistor biased
with a
temperature sensor.

The rate of drift only picks up big time at around 800C, so it should be
ok.

--
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za
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