In the U.S. the power grid is very accurate over long periods of
time. But what are the odds of running six months without a single
power interruption?

Christopher Tidy wrote:
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.
....

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.

"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


Can't say about the UK but in the US the clocks that run only on the power
grid and depend on the frequency are very accurate over a long period of
time. I would say more like less than a minuit or less over a year period
of time if the clock its self is up to it. During periods of peak loads the
nominal 60 hz may go down a cycle or so and when the load is taken away the
power company will raise the frequency long enough to get the clocks back in
time.

In other words the power company keeps the frequency to an average of
exectally 60 hz over a long period of time. Much more stable than any clock
you could build that depends on a quartz chip.

Christopher Tidy wrote:
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

Couldn't find anything on the UK grid, but the US grid short-term is
generally 10 milliHz or better and (probably) averages a few
milliseconds per year long-term. Take care to accommodate local line
noise because it can trip digital counters; even cheap consumer digital
clocks sometimes don't use line frequency directly for this reason, but
use a loosely coupled PLL instead.

Christopher Tidy wrote:

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

Used to be the case that frequency was governed to certain tolerances and
number of cycles turned out in a 24 period was mandated to be exactly
50*24*3600, with time keeping in mind.

Not sure what the position is since privitisation.

Tim

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

In uk.d-i-y Christopher Tidy wrote:
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.

300s/30Ms = 10ppm.
300s/15Ms = 20ppm.
That's not too taxing.
IIRC, maxim/dallas do some chips that may suit, for way, way less than
40 quid.

In an earlier contribution to this discussion,
Christopher Tidy wrote:

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

My understanding is that the frequency is allowed to fluctuate by a small
amount (don't know how much) but that, over a 24 hour period, exactly the
right number of cycles will be delivered. So your clock should at least be
exactly right once per day.
--
Cheers,
Roger
______
Please reply to newsgroup.
Reply address IS valid, but not regularly monitored.

"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

if the hands are balanced it should not make much difference how long they
are

On Fri, 14 Apr 2006 15:00:33 UTC, (Alan J. Wylie)
wrote:

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.

As a matter of interest...when you see those pictures of the control
room, there are two clocks near top right. One is grid driven, the other
is 'crystal' driven (probably rather better than that, these days). They
*ought* to read the same...

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

"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!)

It really depends where you are - if you are in a rural area with above
ground lines and lots of ice storms, hurricanes, etc. then not too good. In
an urban area with buried lines, power may go uninterrupted for years at a
time.

If it's critical that the clock not stop you can put it on a UPS battery
backup.



"Mike Berger" wrote in message
...
In the U.S. the power grid is very accurate over long periods of
time. But what are the odds of running six months without a single
power interruption?

Christopher Tidy wrote:
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.
...

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.

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

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

I can't find a figure for the accuracy of the time keeping of the UK
power grid.

It's weird. Frequency is allowed to wobble a bit, but it has to average
out very accurately over 24 hours or so, because of the number of clocks
in service.

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

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

Other people have given the rules that are applied (i.e. that the
total number of cycles in 24 hours is constant), but the reason is for
efficienty of electricty transfer. It is very important that all
generators run in sync, so as to minimize transmission losses in the
National Grid, AFAIUI.

Paul

In uk.d-i-y Christopher Tidy wrote:
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.

I probably should have mentioned.
If this is outside.
You can get GPS, for about that price, and if it's a clockface, you can
mount the antenna there, and have it work just fine.

"Ralph Mowery" wrote in message
ink.net...

"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


Can't say about the UK but in the US the clocks that run only on the power
grid and depend on the frequency are very accurate over a long period of
time. I would say more like less than a minuit or less over a year period
of time if the clock its self is up to it. During periods of peak loads
the
nominal 60 hz may go down a cycle or so and when the load is taken away
the
power company will raise the frequency long enough to get the clocks back
in
time.


Well, you got the basic idea right. But it never drifts down 1
cycle/second. Very rarely drops even a tenth of a cycle.

In other words the power company keeps the frequency to an average of
exectally 60 hz over a long period of time. Much more stable than any
clock
you could build that depends on a quartz chip.


Indeed. Part of the standard equipment in the old days was a special
'crystal oven' with tightly controlled temperature. By regulating the
temperature of the crystal inside, the accuracy its vibrations was improved.

An old 'urban lengend' was that the first quartz watches were calibrated
assuming the temperature of the crystal was going to be controlled by the
body heat of the wearer. And that leaving your watch on the dresser over
the week-end would cause it to slow down slightly. Don't know if it is
really true, but it's a nice story.

daestrom

There's nothing "urban legend" about that. To this day, most quartz watch
circuits are not temperature compensated (and obviously there is not enough
power available to put the crystal in an "oven" in a wris****ch) so their
timekeeping will vary slightly based on temperature. Typically a
manufacturer will pick some midpoint between body temperature and room
temperature (I have seen 31C used as at typical #) and use that as the
temperature at which their movements are calibrated at the factory. If the
actual operating conditions vary from that temperature, the watch will drift
slightly from the calibrated rate, but it's no big deal.



"daestrom" wrote in message
...


An old 'urban lengend' was that the first quartz watches were calibrated
assuming the temperature of the crystal was going to be controlled by the
body heat of the wearer. And that leaving your watch on the dresser over
the week-end would cause it to slow down slightly. Don't know if it is
really true, but it's a nice story.

daestrom

The older consumer quartz wrist watches were a little temperature sensitive.
Wearing them could effect their accuracy a little. Whether or not it went
faster or slower, depended on the temperature coefficiency of the particular
quartz crystal and components in the watch and how the local oscillator in
the watch was designed. The manufactures of the higher end watches tried to
have their calibration set up for the watch to be at the average body
surface temperature for approximately 14 hours per day, and at room
temperature for approximately 10 hours per day.

The newer watches are improved to a great extent. Many of the new watches
will keep an average time of better than about 5 to 8 seconds per month.
There are some very expensive models where they will guarantee an average
accuracy of better than 2 to 5 seconds per month. The older watches going
back more than about 8 to 10 years ago were usually not much better than 15
to 20 seconds per month.

--

JANA
_____


"daestrom" wrote in message
...

"Ralph Mowery" wrote in message
ink.net...

"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


Can't say about the UK but in the US the clocks that run only on the power
grid and depend on the frequency are very accurate over a long period of
time. I would say more like less than a minuit or less over a year period
of time if the clock its self is up to it. During periods of peak loads
the
nominal 60 hz may go down a cycle or so and when the load is taken away
the
power company will raise the frequency long enough to get the clocks back
in
time.


Well, you got the basic idea right. But it never drifts down 1
cycle/second. Very rarely drops even a tenth of a cycle.

In other words the power company keeps the frequency to an average of
exectally 60 hz over a long period of time. Much more stable than any
clock
you could build that depends on a quartz chip.


Indeed. Part of the standard equipment in the old days was a special
'crystal oven' with tightly controlled temperature. By regulating the
temperature of the crystal inside, the accuracy its vibrations was improved.

An old 'urban lengend' was that the first quartz watches were calibrated
assuming the temperature of the crystal was going to be controlled by the
body heat of the wearer. And that leaving your watch on the dresser over
the week-end would cause it to slow down slightly. Don't know if it is
really true, but it's a nice story.

daestrom

For any type of accuracy, depending on the power grid is not a dependable
option! There can be noise, interference, and power dips. On the short
term, the power grid will be accurate, but over the long term, it can be out
by a fair amount.

I have an electric clock that is dependent on the power grid for its timing.
This clock can be a few minutes or a few seconds out at times.This is not
from the power company being off frequency. It is most likely caused by
power dips, or noise in the power delivery.

The accuracy of the power companies timing is very accuracy. It has to be in
order to keep synchronized to other systems that they are working with. They
have many generating facilities that are working together, therefore all
their systems have to be synchronized to within fractions of a degree on the
line frequency. From what I am told, here in North America, their margin of
error is within about
1 second per month.

The problem when connecting a device at home to the
power line, such as a clock, the clock can jump off time very easily. It is
susceptible to interference, and power disturbance through their
distribution. I was also told this by an engineer from our local power
company.

Normally, during peak conditions, they allow the frequency to drop very
slightly. It may be as much as 0.5 to 1 Hertz or so. During peak conditions,
they will give it back. This means that all the power generation systems
working together must also drop, and increase by the same amount.

The clocks that I have that are referenced to the AC line, are not
dependable for accurate time. Over a few weeks, I found the quartz clocks to
be more accurate. I can check them with the NIST broadcast.

Here in North America many stores are selling quartz clocks with built in
time receivers. These are getting the time reference from the NIST. The user
only has to put in the approximate time to within about 30 minutes. After 12
hours, the clock will be exactly on time, as long as it can receive the NIST
signal. The clock automatically checks in with the NIST about every 12
hours. If the NIST signal is unavailable, the clock will keep time to the
spec of any consumer type quartz clock. This is about 5 to 10 seconds per
month.

Another thought would be to get a low cost GPS that can accept an external
antenna and external power supply. This will give you the most accurate
possible time for home use.

You can also go to the NIST site with your computer, and get very accurate
time. It should be within about 100 to 200 ms. Going from memory, I believe
it will tell you its error to your computer. By hitting the reset key, you
can sometimes get it down to within a few milliseconds.

--

JANA
_____


"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

In message , Christopher Tidy
writes
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.


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.

It has to be significantly more accurate than that

Power stations have to be in sync with one another - which requires good
accuracy and stability

--
geoff

Ralph Mowery wrote:


Can't say about the UK but in the US the clocks that run only on the power
grid and depend on the frequency are very accurate over a long period of
time. I would say more like less than a minuit or less over a year period
of time if the clock its self is up to it. During periods of peak loads the
nominal 60 hz may go down a cycle or so and when the load is taken away the
power company will raise the frequency long enough to get the clocks back in
time.

I read an article a few years ago that discussed how the frequency is
regulated in the US. I can't find it now. I think it was by David
Mills
from the University of Delaware. As I reacall, there are 2 power grids
in the US. The Eastern grid is controlled by an automated system
at some power plant in Ohio. The Western grid is controlled manually.
I wish I could find the article, it had some interesting stuff.

Things are probably done in a similar fashion in the UK.

- Mooron

In uk.d-i-y raden wrote:
In message , Christopher Tidy
writes
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.


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.

It has to be significantly more accurate than that

Power stations have to be in sync with one another - which requires good
accuracy and stability

Actually not - the power grid will work just fine at 49.7Hz average.
The way that large generators work, at all times other than when you're
starting one up, they are fixed to the grid frequency.
If you try to turn one harder, it just generates more electricity, and
tends to 'push' the whole system higher in frequency.
Of course, one generator can't do this appreciably.

There is no actual need for a national centralised frequency
setting, because of the way it works, as long as some power stations
switch off/on up/down, when the frequency gets above or below 50Hz.
This can be done fine with a 48-52Hz analog meter in the control rooms
of each power station.

Christopher Tidy wrote:
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


Try asking on time-nuts

http://www.leapsecond.com/time-nuts.htm




--
Dave K MCSE.

MCSE = Minefield Consultant and Solitaire Expert.

Please note my email address changes periodically to avoid spam.
It is always of the form: month-year@domain. Hitting reply will work
for a couple of months only. Later set it manually.

"JANA" wrote in message
...
For any type of accuracy, depending on the power grid is not a dependable
option! There can be noise, interference, and power dips. On the short
term, the power grid will be accurate, but over the long term, it can be
out
by a fair amount.
----------------
In fact, long term accuracy is very good- correction is made to ensure that.
Short term accuracy may drift but is regularly compensated for. One system
that I know had corrections made every minute. Nice homegrown control but
wasn't compatible with the overall system when the utility joined the
Western Grid.
----------

I have an electric clock that is dependent on the power grid for its
timing.
This clock can be a few minutes or a few seconds out at times.This is not
from the power company being off frequency. It is most likely caused by
power dips, or noise in the power delivery.
-------
And how is this clock driven? If it is a digital clock or electronic then
your point may be valid.
If it has a hysteresis synchronous motor then it will depend strictly on the
frequency and not noise or "dips". However, these may be hard to find
nowadays.
--------

The accuracy of the power companies timing is very accuracy. It has to be
in
order to keep synchronized to other systems that they are working with.
They
have many generating facilities that are working together, therefore all
their systems have to be synchronized to within fractions of a degree on
the
line frequency. From what I am told, here in North America, their margin
of
error is within about
1 second per month.
------------
All machines on the system will be synchronised - at the same frequency- and
drifting up and down together if frequency is changing. You will not have
frequency differences between machines on a system. There are variations in
phase but anything that can be measured as a frequency change -can't be- as
by then the system is unstable and it is lights out. ( if one machine is
0.01Hz fast or slow, then instability can occur in less than a second. )
It appears that you are referring to the process of connecting a machine to
the system and doing this smoothly does require being within a few degrees
in phase and only a small frequency difference in order to minimise "bumps"
and heavy power surges when the system pulls the machine into full
synchronism. This, of course, has nothing to do with control of time.
------------

The problem when connecting a device at home to the
power line, such as a clock, the clock can jump off time very easily. It
is
susceptible to interference, and power disturbance through their
distribution. I was also told this by an engineer from our local power
company.
---------
Depending on how the clock is driven as indicated above.
----

Normally, during peak conditions, they allow the frequency to drop very
slightly. It may be as much as 0.5 to 1 Hertz or so. During peak
conditions,
they will give it back. This means that all the power generation systems
working together must also drop, and increase by the same amount.
---------
Daestrom had it right. In fact a drop of 0.5Hz is abnormal and is an
incident that should be looked into. 0.05 Hz is more typical.
There is a reason for "allowing the frequency to change" when load changes.
It is deliberately built into the prime mover governors. This droop allows
proper power sharing between machines. An overall system control then
adjusts all machines to bring the frequency back to normal or to make
necessary time corrections (Load-frequency control).

The clocks that I have that are referenced to the AC line, are not
dependable for accurate time. Over a few weeks, I found the quartz clocks
to
be more accurate. I can check them with the NIST broadcast.
..
Here in North America many stores are selling quartz clocks with built in
time receivers. These are getting the time reference from the NIST. The
user
only has to put in the approximate time to within about 30 minutes. After
12
hours, the clock will be exactly on time, as long as it can receive the
NIST
signal. The clock automatically checks in with the NIST about every 12
hours. If the NIST signal is unavailable, the clock will keep time to the
spec of any consumer type quartz clock. This is about 5 to 10 seconds per
month.
-----------
As far as I know, the utilities compare to NIST and make corrections on a
much more frequent basis. There is also a contradiction with what you said
above "From what I am told, here in North America, their margin of
error is within about
1 second per month."

That sounds better than 5 to 10 seconds per month.

I think the problem may be with the way your clock is driven, not with the
time error of the grid.
--

Don Kelly @shawcross.ca
remove the X to answer
----------------------------



Another thought would be to get a low cost GPS that can accept an external
antenna and external power supply. This will give you the most accurate
possible time for home use.

You can also go to the NIST site with your computer, and get very accurate
time. It should be within about 100 to 200 ms. Going from memory, I
believe
it will tell you its error to your computer. By hitting the reset key, you
can sometimes get it down to within a few milliseconds.

--

JANA
_____


"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

Roger Mills wrote:

My understanding is that the frequency is allowed to fluctuate by a small
amount (don't know how much) but that, over a 24 hour period, exactly the
right number of cycles will be delivered. So your clock should at least be
exactly right once per day.

Even a stopped clock doubles that... ;-)

Mathew

In uk.d-i-y, Christopher Tidy wrote:
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.

I'd be tempted to use a wall-wart instead of a battery, and probably an
MSF mechanism if it was strong enough.

--
Mike Barnes

On Fri, 14 Apr 2006 16:23:18 GMT, "Brian Sharrock"
wrote:

In the 'old' days; mains powered clocks (squirrel cage, synchronous) were
common.

Although a squirrel cage uses a synchronous stator winding, it isn't a
synchronous motor, at least not to this level of timekeeping. Their
rotors are powered by an induced current in the rotor (the squirrel cage
itself), not any sliprings or brushgear. This current is only induced if
the rotor experiences a moving or changing magnetic field - i.e. it
rotates at a different speed to the field in the stator. They can't
generate a torque unless there is some "slip", the speed difference
between synchronous speed and actual rotation. It's notable that the
more the slip, the more the output torque - so these motors can deliver
substantial power under load.

A frictionless, resistanceless, hysteresisless squirrel cage motor doing
no work would accelerate up to synchronous speed and then hold that
speed spinning freely, doing no work and producing no torque. An
idealised but possible motor might always run at a known slip which
could be compensated for by gearing. In practice such effects as
temperature and lubricant viscosity make this unpredictable, at least
for clockmaking accuracy.

Clocks use shaded pole motors, which are synchronous. As these don't
have the same increased torque response to slip they're inherently low
torque and thus only useful for clocks or other light tasks.

Correction and apology:
I said: ( if one machine is
0.01Hz fast or slow, then instability can occur in less than a second. )

That is wrong. 3.6 degrees/second implies about 25 seconds to steady state
instability. This is , of course, too simplistic as such a sustained
frequency difference will not occur - either the errant machine is pulled
back into synchronism or has been tripped out -hopefully without bringing
the whole system down.

This also applies to incoming machines- either they get in line or get
kicked out-now!.
--

Don Kelly @shawcross.ca
remove the X to answer
----------------------------

On Fri, 14 Apr 2006 16:23:18 GMT, "Brian Sharrock"
wrote:

In the 'old' days; mains powered clocks (squirrel cage, synchronous) were
common.

This is Usenet isn't it? There'll be complaints....

Of course not all clock motors are shaded pole. The Warren Model A was,
back in 1916 (I think the first synchronous clock motor)

However the well-known Westclox / Sangamo design of the '30s and onwards
used an induction rotor - effectively a "squirrel cage". This gave good
starting torque, but obviously had the slip problem. To keep it locked
and synchronous there was also a permanent magnet rotor. This gave
adequate torque at synchronous speed, without slip, but wouldn't have
been able to start the clock unaided.

Some British designs used a single permanent magnet rotor and required a
mechanical pushbutton, or an extra winding for starting.

On Fri, 14 Apr 2006 16:50:40 GMT, raden wrote:

In message , Christopher Tidy
writes
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.


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.

There won't be any cumulative errors.


It has to be significantly more accurate than that

Power stations have to be in sync with one another - which requires good
accuracy and stability

True they have to be phased up to the grid exactly before they connect
to it, or *BANG* turbine blades through the turbine hall roof. I've
been to a power station where it had happened. If they connect
successfully then they'll stay in sync.

The exact frequency is not overly critical but is kept as accurate as
possible for the benefit of users who depend on the frequency being
accurate, steelmills rolling steel for instance.

FWIR the control console at "Grid Control Centres" used to have a
standard synchronous electric clock showing grid time, and a clock
showing exact GMT (How ??, unless exact 50Hz was distributed about the
country) . It was normal for "grid time" to lose a bit during the day,
depending on load, and then make up for it overnight.

Quite a manual process in 1969. ;-)

It must be better now !

DG

Andy Dingley wrote:

On Fri, 14 Apr 2006 16:23:18 GMT, "Brian Sharrock"
wrote:

In the 'old' days; mains powered clocks (squirrel cage, synchronous)
were common.

This is Usenet isn't it? There'll be complaints....

Of course not all clock motors are shaded pole. The Warren Model A
was, back in 1916 (I think the first synchronous clock motor)

However the well-known Westclox / Sangamo design of the '30s and
onwards
used an induction rotor - effectively a "squirrel cage". This gave
good starting torque, but obviously had the slip problem. To keep it
locked and synchronous there was also a permanent magnet rotor. This
gave adequate torque at synchronous speed, without slip, but wouldn't
have been able to start the clock unaided.

Some British designs used a single permanent magnet rotor and required
a mechanical pushbutton, or an extra winding for starting.

I have an old Smith Sectric electric clock that was, I think, new in
1942. It maintains time accurately as compared with a radio clock, so
long as the power doesn't fail. When I was very young I remember being
the only person in the house who could get it going again after a power
cut. One was supposed to set the time and jab in the setting knob to
start it, but that seldom worked. At about the age of five I discovered
the best way was to remove the motor cover and spin the wheels inside.

Edgar

In message , Edgar Iredale
writes
Andy Dingley wrote:

On Fri, 14 Apr 2006 16:23:18 GMT, "Brian Sharrock"
wrote:

In the 'old' days; mains powered clocks (squirrel cage, synchronous)
were common.

This is Usenet isn't it? There'll be complaints....

Of course not all clock motors are shaded pole. The Warren Model A
was, back in 1916 (I think the first synchronous clock motor)

However the well-known Westclox / Sangamo design of the '30s and
onwards
used an induction rotor - effectively a "squirrel cage". This gave
good starting torque, but obviously had the slip problem. To keep it
locked and synchronous there was also a permanent magnet rotor. This
gave adequate torque at synchronous speed, without slip, but wouldn't
have been able to start the clock unaided.

Some British designs used a single permanent magnet rotor and required
a mechanical pushbutton, or an extra winding for starting.

I have an old Smith Sectric electric clock that was, I think, new in
1942. It maintains time accurately as compared with a radio clock,

Did you really mean to say that it keeps better time than a radio clock
?

--
geoff

Jack Denver wrote:
It really depends where you are - if you are in a rural area with above
ground lines and lots of ice storms, hurricanes, etc. then not too good. In
an urban area with buried lines, power may go uninterrupted for years at a
time.

If it's critical that the clock not stop you can put it on a UPS battery
backup.

Interesting thought. Would the clock then be driven by the
line frequency or the oscillator frequency of the UPS?

Mark

Mathew Newton wrote:

Roger Mills wrote:

My understanding is that the frequency is allowed to fluctuate by a small
amount (don't know how much) but that, over a 24 hour period, exactly the
right number of cycles will be delivered. So your clock should at least be
exactly right once per day.

Even a stopped clock doubles that... ;-)

Mathew


Not if it's digital.


--
HELP! My sig file has escaped! ;-)

In article ,
"Andrew Mawson" writes:
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.

I'm out of touch now, but CEGB used to keep UK power grid at
50Hz +- 0.1Hz. No one ever came up with a good reason it had
to be that accurate, but they did it "just because they
could", to quote someone I spoke with at the Winnersh control
room about this some years back.

I wrote a more detailed article about this a few years ago,
which discusses various notable historic events, like how the
power grid had to handle the majority of the UK using the toilet
at the same instant, which resulted in the largest ever surge in
demand on the UK power grid (which with advanced planning, it
handled just fine)...
http://groups.google.com/group/sci.e...1a4f753?hl=en&

--
Andrew Gabriel

Andrew Mawson wrote:

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!)


If all those areas are connected to a single power grid they still
have to stay in sync, even if the control system is broken into regional
centers.


--
HELP! My sig file has escaped! ;-)

Paul Cooper wrote:

Other people have given the rules that are applied (i.e. that the
total number of cycles in 24 hours is constant), but the reason is for
efficienty of electricty transfer. It is very important that all
generators run in sync, so as to minimize transmission losses in the
National Grid, AFAIUI.

Paul


Any generator that is not in sync with the grid will either be slowed
down by higher current loading, or it will become a motor and catch up
to the other units. The speed AND phase of a generator has to match the
grid before it can be connected, or it can literally be ripped loose
from its mounts and destroyed. The basic system to do this is a set of
lamps connected between the two generators. The new generator has it
speed slowly adjusted till the brightness is cycling VERY slowly, then
at a time when all the lamps are out it is switched into the grid.
After it is connected it synchs itself completely, then the operator
increases the fuel or water supply to generate electricity. This has to
be monitored to keep the generator below it rated output, to keep the
windings from overheating.


--
HELP! My sig file has escaped! ;-)

The latter during power cuts, the former the rest of the time, the way most
UPS's are designed.


"Mark and Gloria Hagwood" wrote in message
news:fLT%f.41355$bm6.26995@fed1read04...

Interesting thought. Would the clock then be driven by the line frequency
or the oscillator frequency of the UPS?

Mark

Andrew Gabriel wrote:

I'm out of touch now, but CEGB used to keep UK power grid at
50Hz +- 0.1Hz. No one ever came up with a good reason it had
to be that accurate, but they did it "just because they
could", to quote someone I spoke with at the Winnersh control
room about this some years back.


.1 Hz is not an unreasonable standard to keep. The wider the
variation that is allowed in the control loop, the easier for the whole
system to become unstable and shut down as the controls disconnected
equipment from the grid that was too fast, or too slow. You are working
with massive mechanical systems that will self destruct if you allow
sudden changes while under load. Think of what happens when a long
train tries to stop. If the couplings didn't have some play to adsorb
the shot, the train would derail when the engineer tried to use the
brakes. Its just basic physics.


--
HELP! My sig file has escaped! ;-)

Hi all,

Thanks very much for all the information. Sorry for the original
cross-post; I was expecting very few replies.

In answer to some of your questions, the clock is a WWII German
"Dehomag" slave clock, originally designed to be driven by a master
clock. It has no second hand. The minute hand appears to be balanced,
but the hour hand not. The clock is about 14" across, so not huge, but
it's exceptionally heavy as nearly everything is made from 1 mm steel
plate. Here's a picture of the clock:

http://www.mythic-beasts.com/~cdt22/dehomag.jpg

I can't decide whether to repaint it black, as it was when manufactured,
or to leave it grey. It's for my bedroom, so if it were to stop during
power cuts I wouldn't mind. It sounds like the 50 Hz grid frequency will
be a plenty accurate time keeping source, and it's an interesting
solution to the problem. We live in a pretty rural area so I'll try to
design a circuit which will be fairly resistant to noise. I had already
planned to put a Schmitt trigger on the input from the step-down
transformer.

Once again, thanks for all the advice. It's much more than I got from
the National Grid - the phone number on their website doesn't even work!

Best wishes,

Chris