On Fri, May 02, 2008 at 01:06:47PM -0400, Ian Chapman wrote: > Crystal usually cut to + or - 100 ppm for a general use like a CPU and it > will not change too much with temperature and age. Ethernet crystals were > at one time cut to a better spec 50 ppm. Special communications crystal can > be a lot better. The mains are very good in most places for the morning > alarm however in remote communities with diesel generators ... no way.
Sounds like all of us are in violent agreement. But before you start thinking that crystals are _too_ wonderful, let me quote from my introduction to using network time standards at http://doolittle.icarus.com/ntpclient/HOWTO "First, a note on typical 1990's and 2000's computer crystals. They are truly pathetic. A "real" crystal oscillator (TCXO) usually has an initial set error of less than 5 ppm, and variation over time, voltage, and temperature measured in tenths of a ppm (and an OCXO can reach ±0.3 ppm stability over ten years and 85°C temperature swing). The devices used in conventional PC motherboards and single board computers, however, often have initial set errors up to 150 ppm, and will vary 5 ppm over the course of a day-night cycle in a pseudo-air-conditioned space." - Larry _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
