[time-nuts] 60Hz line data

[Dave Martindale]

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 <time at radio.sent.com> 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
>
>