On Fri, 14 Apr 2006 15:27:23 +0000, Christopher Tidy said:

Hi all, I'm thinking of building an electronic clock control circuit
which uses the 50 Hz mains frequency for time keeping. The reason
for this is that the clock dial is rather large, so probably
wouldn't run for long on battery power, and I don't fancy spending
£40 buying a programmable quartz oscillator chip.

Despite doing some research online and in electrical engineering
books, I can't find a figure for the accuracy of the time keeping of
the UK power grid. Perhaps this is because there aren't official
bounds set for the time error - one of my electrical engineering
books says it is a legal requirement that the frequency be kept "as
close as possible to 50 Hz" - but even if this is the case it should
be possible to determine a typical error figure.

From my point of view I'd regard an acceptable error as 5 minutes
every 6 months. Does anyone know the typical time error seen on the
UK grid, or where I might find this information? Any suggestions
would be much appreciated.

http://www.nationalgrid.com/uk/Electricity/Data/Realtime/

http://www.dynamicdemand.co.uk/chart.htm

During periods of high demand, the frequency will drop slightly. To
compensate, the frequency will later be increased so that there are
the same number of cycles per day, so that the long term accuracy of
synchronous electric clocks is very good. If you don't have a seconds
hand, no-one will even notice the short term inaccuracies.

A quick look at the graphs suggests that the maximum deviation is
about 0.2 / 50 (2.5 seconds in 10 minutes), the period of low
frequency lasts in the order of ten minutes, and corrections are made
immediately after the dip.


--
Alan J. Wylie http://www.wylie.me.uk/
"Perfection [in design] is achieved not when there is nothing left to add,
but rather when there is nothing left to take away."
-- Antoine de Saint-Exupery