"Christopher Tidy" wrote in message
...
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.

Best wishes,

Chris Tidy


Chris,

OK it's going back a few years, but when the CEGB had their National
Grid Control Centre at Park ST London SE1 the number of cycles per day
was very accurately ensured to be correct (A pair of Ferranti Argus
500 Process Control computers each had an ultra accurate crystal
clocks in them feeding displays in the control room) and the Control
Enginners could let the frequency drift a tad hour by hour but had to
get it right over 24. They dispersed the control to various regional
centres (Winnersh, St Albans and three others I cannot remember but I
think that the principle remains the same.

AWEM
(who in a past life occassionally sweated blood over those computers!)