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From: "Matthew Kendall"
References: <5Q1H9.32847$zX3.firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
Subject: Re: 100Hz from 25.6kHz crystal.
X-Newsreader: Microsoft Outlook Express 5.50.4920.2300
Date: Wed, 04 Dec 2002 16:17:44 GMT
NNTP-Posting-Date: Wed, 04 Dec 2002 09:17:44 MST
Organization: Shaw Residential Internet
"John Fields" wrote ...
> TYPE FREQ TOL TEMPCO AGING SHOCK
> C-2 20ppm -0.04ppm/°C² 5ppm/yr 5ppm
> CA-310 30ppm +/- 0.714ppm/°C 5ppm/yr 10ppm
> In the tempco column, the C-2 data is exactly as taken from their
> data sheet, while the CA-310 is represented as +/-50ppm over the
> range of -10 to 60°C. on their data sheet. I don't really
> understand the notation for the C-2 ...
The spec means -0.04ppm per degree squared. The characteristic of these
tuning fork type crystals is parabolic. The so-called turnover temperature
is usually chosen to be around 25C. Both above and below this temperature
the frequency error is negative, and gets progressively worse the further
For example, for this crystal at 30C (or 20C) the error
would -0.04*5^2=1ppm. For 40C (or 10C) the error is -0.04*15^2=9ppm. For 50C
(or 0C) the error is -0.04*25^2=25ppm.
These crystals are reasonably good when held at a temperature near the
turnover point (e.g. strapped to your wrist), but are poor over wide
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