In message <[email protected]>, Hal Mu rray writes:
>Do you have data or references for that? If I heard it from anybody less >credible, I'd guess it was an urban legend? Was it accurate 50 years ago? Several people deeply involved in the Danish electricity grid have told me the same thing: The utilities prided themselves by their frequency precision and used a lots of synchronous motor clocks internalll. At the local powerplant, they would call up the speaking clock every day at noon, compare it to the clock in the control-room and log the difference. (I have seen this myself as a kid.) >The winter/summer variation doesn't make sense to me. If the PLL can cover >daily changes, anything lower frequency would be covered for free. The winter/summer variation has also puzzled me, but the consenus seems to be that it was caused by electrical heating running through the night, preventing them for regaining the lost cycles due to business load during the day. (The danish grid was surprisinly marginally provisioned until everybody started conserving electricity after the OPEC-stunt in the winter 1973-74.) >It's easy to collect data. Take an AC wall wart type transformer and connect >it to a modem control pin that the kernel is setup to use for NTP's PPS >signals. (Contact me off list if you want the software.) I've done that many years ago, right when the deregulation too effect in Denmark, and the average frequency dropped by 0.05Hz because they could save fuel that way. Since then the frequency has just wandered aimlessly around 50Hz, leaving the phase to do a random walk. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [email protected] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. _______________________________________________ LEAPSECS mailing list [email protected] http://six.pairlist.net/mailman/listinfo/leapsecs
