Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site sdcrdcf.UUCP Path: utzoo!linus!decvax!ittvax!dcdwest!sdcsvax!sdcrdcf!darrelj From: darrelj@sdcrdcf.UUCP (Darrel VanBuer) Newsgroups: net.unix-wizards Subject: Re: Almost Accurrate Clock Message-ID: <1356@sdcrdcf.UUCP> Date: Tue, 2-Oct-84 14:28:26 EDT Article-I.D.: sdcrdcf.1356 Posted: Tue Oct 2 14:28:26 1984 Date-Received: Thu, 4-Oct-84 06:02:02 EDT References: <297@rna.UUCP> Reply-To: darrelj@sdcrdcf.UUCP (Darrel VanBuer) Organization: System Development Corp. R+D, Santa Monica Lines: 32 Summary: Power line frequencies are generally pretty accurate (long term), in part because they use the National Bureau of Standards as a reference (e.g. WWV). It's essential to have consistent frequencies when you run a national power sharing grid. Then can notably run slow during high load conditions (e.g. hot summer afternoons, but will (usually) eventually catch up. WWV provides standards for both power and frequencies (their carrier frequencies are all exact multiples of 2.5 MHz. The long term stability of WWV comes from a battery of atomic clocks with accuracies approaching 1 in 10^12 (and short term stability better by a couple orders of magnitude. The big advantage of WWV over any power line clock is with the proper equipment (Heath clock or voice recognition -- your head) it's an absolute standard, rather than relative. We had a serious problem with a powerline clock on our PDP 11/70 after our motor-generator power conditioner was installed; it ran about 58 Hertz output, so our processor ran 40 minutes off each day! If you ever want a really accurate, cheap frequency standard, try your color TV. For the color to come out right, it has to stay quite close to the color burst frequency at the transmitter, so is resyncronized every 60 microseconds to keep it within a tenth of a cycle, or so. The major networks maintain theirs against NBS. (it's 315/88 MHz). -- Darrel J. Van Buer, PhD System Development Corp. 2500 Colorado Ave Santa Monica, CA 90406 (213)820-4111 x5449 ...{allegra,burdvax,cbosgd,hplabs,ihnp4,orstcs,sdcsvax,ucla-cs,akgua} !sdcrdcf!darrelj VANBUER@USC-ECL.ARPA