On Mon, 22 Nov 2004, Olin Lathrop wrote:

> Michael Rigby-Jones wrote:
>>> If the stability is rated say at 50ppm, is that to say
>>> that over the range it can vary up to +/- 0.005% of
>>> the nominal value?  Or am I interpreting that wrong?
>>
>> Tempco is usualy specified in ppm/C. In your case, for every degree C
>> change the crystal could change by 0.005% of it's nominal value.
>
> This is correct if the temperature stability were specified as 50ppm/degC,
> however that is not what "stability" means.  In this case it is far more
> likely (would have to see the real data sheet to be sure) that the
> manufacturere is saying the crystal frequency will always be within 50ppm of
> the specified value over the full operating range.  That's actually a rather
> low spec crystal.  50ppm/degC would be a terrible spec for a crystal.  I
> don't think you can get one that bad.

You are right, they usually come in 40ppm and 25ppm varieties ;-)

Peter
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