On 3 Oct 2008 at 13:41, Steve Rooke wrote: > Call me crazy but I wonder if my accurate relative period of time > could be derived from the 230VAC 50Hz mains supply over here. Now, > before you yell at me, consider this, I have a couple of mains driven > clocks in the house and only seem to need to change the time on them when > we go from Standard Time to Daylight Saving Time. Agreed, the > instantaneous frequency of the mains is not always spot on but the long > term average seems to be kept pretty accurate or we would all have to keep > changing our mains timed clocks. If I knew the standard deviation of the > mains, I could probably calculate the period of time I'd have to gate my > breadboard "frequency counter" to achieve a certain accuracy.
A bit of Googling finds: Frequency: "a variation not exceeding 1 per cent above or below the declared frequency;" (http://www.statutelaw.gov.uk/content.aspx?LegType=All+Legislation&title=e lectricity+safety+quality+continuity&searchEnacted=0&extentMatchOnly=0&con fersPower=0&blanketAmendment=0&sortAlpha=0&TYPE=QS&PageNumber=1&NavFrom=0& parentActiveTextDocId=1590332&ActiveTextDocId=1590368&filesize=4590 - section 27(3)(a)) Electric clock time: "NGET will endeavour (in so far as it is able) to control electric clock time to within plus or minus 10 seconds" (http://www.nationalgrid.com/NR/rdonlyres/4894C7AA-DCD2-4835-9986- 57338C31C86A/9922/BC3_i3r18.pdf - section BC3.4.3) BTW wrt earthing via the incoming water main - in the UK, plastic pipe is commonly used for incoming water mains these days. 73 Chris G3RSE _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
