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'[PICLIST] FW: [PIC]: Cheap and easy 100 Hz MPU clo'
2000\11\17@003924 by Anton Schoultz

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John,

Is this for a battery powered or mains device?

If mains, and your mains frequency is 50hz, then you can pick up
100 Hz after the bridge rectifier.

I have used this clock source in South Africa - I found that although
there was quite a bit of drift on a daily cycle, the AVE frequency is
very accurate. The clock would drift by 30sec or so, but at the end
of the year it was still within 30 sec. (fast in the day, slower
at peak loads)

Don't know if that helps. USA is 60Hz (120hz rectified). The UK
also use 50Hz if memory serves.

If you're using a portable solution then I'd go with a higher frequency
crystal and a binary divider chain, such as the suggestion made by
Barry.


Regards

Anton Schoultz
spam_OUTantonsTakeThisOuTspamePOS.co.za
tel: +27 11 267-9564




{Original Message removed}

2000\11\17@020747 by Nigel Goodwin

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In message <000c01c05058$e3c07940$.....211ea8c0KILLspamspam@spam@lothlorien.co.za>, Anton
Schoultz <antonsspamKILLspamEPOS.CO.ZA> writes
>Don't know if that helps. USA is 60Hz (120hz rectified). The UK
>also use 50Hz if memory serves.

Yes the UK uses 50Hz, and it's highly accurate - it might vary slightly
over an hour or two, but it used to be corrected every night (I presume
it still is, if not more frequently?). Mains synchronised clocks are
extremely accurate.
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2000\11\17@062118 by Alan B. Pearce

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>I have used this clock source in South Africa - I found that although
>there was quite a bit of drift on a daily cycle, the AVE frequency is
>very accurate. The clock would drift by 30sec or so, but at the end
>of the year it was still within 30 sec. (fast in the day, slower
>at peak loads)

I believe in New Zealand, one power station that was designated as the "master"
had two clocks side by side. One was a mains run clock, and the other a
grandfather pendulum clock. The grandfather clock was used as the master time
keeper, and the electric clock used to keep the average time over a 24 hour
period exact to the grandfather clock. This meant that any slow down in mains
frequency during the day due to load could be matched overnight by a suitable
frequency increase as measure dby the clocks. I never saw the clocks, but the
sort of discrepancy you describe is the sort of thing that was told to me.

I do not know if this is still done this way, or if there is a more automated
way of doing it now.

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2000\11\17@173902 by Bob Ammerman

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I do work with power plants in the US, control systems for major hydro
facilities.

A _lot_ of effort goes into maintaining a highly accurate long-term
frequency.

Basically, the power plants deliberately overgenerate to push the frequency
a little higher and undergenerate to pull it back down. Obivously all the
plants on the same power net must remain in sync,

Some plants are given the job of driving things in the right direction by an
"Energy Control Center" which tracks the long term error in the frequency.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2000\11\18@100553 by Peter L. Peres

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>Bob Ammerman:
>I do work with power plants in the US, control systems for major hydro
>facilities.

I have always been curious whether in a big country with a unified grid
centralized timing signalling is used to sync the plants ? Because I think
that it is very hard to do it otherwise (plants syncing to what they
'see' on the outgoing lines) on a grid with significant time lags.

Peter

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