[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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