It's not just synchronous-motor clocks that use line frequency as a time reference. I have a Heathkit alarm clock that counts cycles of line frequency as its timebase. I think that was common in the early generations of NMOS clock chips. The clock does have a backup oscillator (powered by a 9 V battery) for use when line voltage disappears, but its accuracy is horrible. I think it's an RC oscillator, and in a power failure of a few hours it will accumulate minutes of time error.
So a bunch of people with analog and digital clocks from that era are likely to notice the drift, particularly at 20 minutes/year. When did 32 kHz crystals get cheap enough that line-powered clocks started using them as a time reference instead of counting line cycles? - Dave On Sun, Jul 26, 2015 at 2:25 PM, Bill Byrom <[email protected]> wrote: > > 60Hz Stability on Power Grid Going Away? > > http://www.radiomagonline.com/deep-dig/0005/60hz-stability-on-power-grid-going-away/33527 > > NERC Frequency Response Standard Background Document > > http://www.nerc.com/comm/oc/rs%20landing%20page%20dl/related%20files/bal-003-1_background_document_clean_20121130.pdf > > It appears from various comments that with no manual time correction, > the accumulated time error in the East Interconnection will typically > gain 20+ minutes/year. The West will gain 8 minutes/year and ERCOT > (Texas area) will gain 2 minutes/year. > > http://www.ercot.com/content/meetings/rms/keydocs/2011/0518/03_manual_time_error_correction_elimination_field_trial.doc > > So don't trust an AC synchronous motor clock in North America. > > -- > Bill Byrom N5BB > > _______________________________________________ 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.
