On 2017-02-05 02:14, David Woolley wrote:
> On 05/02/17 00:22, Robert Scott wrote:
>> I hope to achieve a frequency accuracy of 5 PPM. Once that
>> measurement is made, I store it for subsequent use in my app.
> The equipment doesn't have a very long service life and is in a
> temperature controlled environment, as I think both ageing and
> thermal effects can violate the 5ppm limit.
I keep my systems running with max performance power profiles to
avoid internal frequency and temperature variation, which could
alter drift, and they stay within about +/-1ppm, but after any
power off, drift jumps ~1ppm, settling down to a new range.
For common XO parts, tolerance and stability are +/-30ppm over
90C range and aging +/-3ppm/year, say .7ppm/C and 6ppm/year
worst case, so the environment would need controlled within 3C
for 5 months, after days of continuous running to stabilize,
to stay within your limit.
You could run your calibration until results over the previous
six hours stabilized, but your calibration would first need
to run itself against your timing system, to ensure that it has
stabilized.
It would need recalibrated any time it was powered off, after
days of continuous running to stabilize.
Excessive vibrations could cause the limit to be exceeded at
any time, as crystals are piezo transducers.
--
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
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