[time-nuts] 60Hz line data

[Bob Camp]

Hi

The utility of the watch crystal is greatly enhanced in a wrist watch by
the calibration process on the watch. When they use one in an AC powered
clock (say a clock / radio / alarm) , it’s as a backup device. Power goes out
and the crystal keeps time. They don’t do much (any at all) calibration in this
application. The resultant time error is “ok” for an hour or so. It would be 
really objectionable over a week or a month.

Bob

> On Jul 27, 2015, at 12:31 AM, Bill Byrom <time at radio.sent.com> wrote:
> 
> In the early 1970's both LED and LSI integrated circuit technology
> advanced to the point that digital wristwatches were introduced. These
> used 32,768 Hz crystals. Use of this technology was made in digital desk
> clocks (such as alarm radio clocks), but I think that for many years it
> was much less expensive to use the AC line as a frequency standard.
> Early Mostek clock IC's used the 50/60 Hz powerline as the reference and
> didn't include provisions for a crystal.
> 
> The first digital clock I owned was a flip card clock radio in around
> 1970. An AC line powered synchronous motor slowly flipped minute and
> hour cards. A few years later I had a Radio Shack LED wristwatch.
> 
> I see that 32,768 Hz crystals can now be purchased for US $0.15 each in
> lots of 100.
> 
> --
> Bill Byrom N5BB
> 
> 
> 
> On Sun, Jul 26, 2015, at 07:08 PM, Dave Martindale wrote:
>> 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
>>> 
>>> 
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