[time-nuts] questions on uncompensated crystal oscillators
Hal Murray
hmurray at suespammers.org
Wed Jul 5 16:16:19 EDT 2006
> Even if you get the crystal adjusted at the factory to say 5ppm, can
> it be guaranteed that all the other effects combined stay at <45ppm
> over the lifetime of the product (these days it's about 6-12 months
> depending on the warranty period)?
After initial calibration, the main consideration is temperature. You should
be able to get a graph from the vendor and/or make your own. It depends on
the angle of the crystal cut. I've seem a graph with a family of curves at
different angles.
The ballpark is 1 ppm per C, so if you can limit your temperature range to
room-temperature you can probably make something work. That's from my PC
using NTP as a calibration. You can probably do better if you work with the
vendor.
Secondary considerations are power supply voltage and aging.
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