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 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.

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.

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

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

Jack Denver schrieb:

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

Great idea! In order to save the odd $40 for a quartz oscillator (read
the OP!), you spend at least $100 on a UPS device. :-)

SCNR and best regards,
OP

Mike Berger wrote:
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?



Depends where you are, I used to have outages a couple times a year, now
the house I'm in I've had exactly one outage in almost 2 years and it
was a pretty good storm that went through.

Aside from that though in both the US and UK the mains frequency has
excellent long term stability. It may gain or lose a few seconds over
the course of the day but it will be dead on over weeks/months.

"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.

"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

"daestrom" wrote in message
...


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.

My cheap and nasty Casio digital watch seems to have lost 2 minutes after I
left it first in my old car, and then in my old car in the shed. Neither
place was particularly warm...

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

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

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

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.

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

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 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.

"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

"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!)

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 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

"Christopher Tidy" wrote in message
...
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
You did not tell us what the drive mechanism is.
If it was similar to the Simplex/IBM master clocks of the time it most
likely advanced every minute by a pulse to an electromagnet.

Now there are several ways you could generate that.
A Small timer motor with a cam like a washing machine timer.
Or an Electronic cct synched by the mains.

If it is for your bedroom you may not want it after the first few hours
as the electromagnet noise will drive you bonkers.
--
John G

Wot's Your Real Problem?

On 14 Apr 2006 21:53:18 GMT, (Andrew Gabriel) said:

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&

You mention Dinorwic/Dinorwig - there's a more detailed posting about
it at

http://groups.google.com/group/uk.rec.subterranea/msg/dd48c794775000bf

--
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

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! ;-)

Michael A. Terrell wrote:

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.

High voltage DC (HVDC) is used to transmit large amounts of power over
long distances or for interconnections between asynchronous grids When
electrical energy is required to be transmitted over very long distances,
it can be more economical to transmit using direct current (An electric
current that flows in one direction steadily) instead of alternating
current (An electric current that reverses direction sinusoidally).
For a long transmission line, the value of the smaller losses, and
reduced construction cost of a DC line, can offset the additional
cost of converter stations at each end of the line. Also, at high AC
voltages significant amounts of energy are lost due to corona discharge
(An electrical discharge accompanied by ionization of surrounding
atmosphere) the capacitance (An electrical phenomenon whereby an
electric charge is stored) between phases or, in the case of buried
cables, between phases and the soil (The part of the earth's surface
consisting of humus and disintegrated rock) or water (Binary compound
that occurs at room temperature as a clear colorless odorless tasteless
liquid; freezes into ice below 0 degrees centigrade and boils above
100 degrees centigrade; widely used as a solvent) in which the cable
s buried. Since the power flow through an HVDC link is directly
controllable, HVDC links are sometimes used within a grid to stabilize
the grid against control problems with the AC energy flow.

Also see
http://www.absoluteastronomy.com/ref...direct_current
http://en.wikipedia.org/wiki/HVDC
http://www.aip.org/tip/INPHFA/vol-9/iss-5/p8.html

wrote:

High voltage DC (HVDC) is used to transmit large amounts of power over
long distances or for interconnections between asynchronous grids When
electrical energy is required to be transmitted over very long distances,
it can be more economical to transmit using direct current (An electric
current that flows in one direction steadily) instead of alternating
current (An electric current that reverses direction sinusoidally).
For a long transmission line, the value of the smaller losses, and
reduced construction cost of a DC line, can offset the additional
cost of converter stations at each end of the line. Also, at high AC
voltages significant amounts of energy are lost due to corona discharge
(An electrical discharge accompanied by ionization of surrounding
atmosphere) the capacitance (An electrical phenomenon whereby an
electric charge is stored) between phases or, in the case of buried
cables, between phases and the soil (The part of the earth's surface
consisting of humus and disintegrated rock) or water (Binary compound
that occurs at room temperature as a clear colorless odorless tasteless
liquid; freezes into ice below 0 degrees centigrade and boils above
100 degrees centigrade; widely used as a solvent) in which the cable
s buried. Since the power flow through an HVDC link is directly
controllable, HVDC links are sometimes used within a grid to stabilize
the grid against control problems with the AC energy flow.

Also see
http://www.absoluteastronomy.com/ref...direct_current
http://en.wikipedia.org/wiki/HVDC
http://www.aip.org/tip/INPHFA/vol-9/iss-5/p8.html


I'm quite familiar with HVDC distribution systems, but more
generators are connected via AC than DC and those DO have to be in phase
and have the frequency controlled to keep the rest of the grid happy.

BTW: HVDC distribution has been discussed to death on both the
news:sci.electronics.design and news:alt.electrical.engineering
newsgroups.

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

"Michael A. Terrell" wrote in
:

snip


I'm quite familiar with HVDC distribution systems, but more
generators are connected via AC than DC and those DO have to be in
phase and have the frequency controlled to keep the rest of the grid
happy.

BTW: HVDC distribution has been discussed to death on both the
news:sci.electronics.design and news:alt.electrical.engineering
newsgroups.


Mention of HVDC reminds me that the Channel link is one such (at least,
I think that's what I remember). So that prompts me to ask, how closely
synchronised are the UK and France, and indeed the other European countries
with each other?

(Hope I haven't missed this question somewhere else in this huge
thread!)

--
Rod

"Michael A. Terrell" wrote in message
...


wrote:

High voltage DC (HVDC) is used to transmit large amounts of power over
long distances or for interconnections between asynchronous grids When
electrical energy is required to be transmitted over very long distances,
it can be more economical to transmit using direct current (An electric
current that flows in one direction steadily) instead of alternating
current (An electric current that reverses direction sinusoidally).
For a long transmission line, the value of the smaller losses, and
reduced construction cost of a DC line, can offset the additional
cost of converter stations at each end of the line. Also, at high AC
voltages significant amounts of energy are lost due to corona discharge
(An electrical discharge accompanied by ionization of surrounding
atmosphere) the capacitance (An electrical phenomenon whereby an
electric charge is stored) between phases or, in the case of buried
cables, between phases and the soil (The part of the earth's surface
consisting of humus and disintegrated rock) or water (Binary compound
that occurs at room temperature as a clear colorless odorless tasteless
liquid; freezes into ice below 0 degrees centigrade and boils above
100 degrees centigrade; widely used as a solvent) in which the cable
s buried. Since the power flow through an HVDC link is directly
controllable, HVDC links are sometimes used within a grid to stabilize
the grid against control problems with the AC energy flow.

Also see
http://www.absoluteastronomy.com/ref...direct_current
http://en.wikipedia.org/wiki/HVDC
http://www.aip.org/tip/INPHFA/vol-9/iss-5/p8.html


I'm quite familiar with HVDC distribution systems, but more
generators are connected via AC than DC and those DO have to be in phase
and have the frequency controlled to keep the rest of the grid happy.


You seem to be laboring under the idea that all the AC generators tied to
the grid have to be carefully regulated to stay in sync with each other
through some incredibly precise timing.

That isn't the case. A generator is brought on-line by carefully regulating
the speed and getting it in phase. That is a bit tricky. But once tied to
the grid, 'keeping in sync' is done by the load current and physics. In
fact, base load units don't even have frequency control once on-line. The
speed set-point for the governor is run several hz up out of the way and the
turbine controls are controlled by a 'load' setting. The operator dials in
the amount of MW load they are supposed to carry, and the controls monitor
MW and steam flow. They don't respond at all to frequency changes unless
the frequency rises to the point the unit is in danger of over-speeding.

During grid disturbances, base load units will naturally speed up/slow-down
as grid frequency changes, maintaining their load output based on
'load-set'. Only 'regulating duty' plants monitor generator speed/freq and
make any sort of adjustment based on changes in speed/freq. And
'regulating' units make up a fairly small fraction of all AC units.

The vast majority of AC generators will 'stay in sync' just by virtue of the
physics of synchronous machines. Only if under-excited, or significant
reactance in their output line are they likely to 'pull out' of sync with
the grid. (and that's a *bad thing*)

daestrom

----------------------------
wrote in message
...



Michael A. Terrell wrote:

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.

High voltage DC (HVDC) is used to transmit large amounts of power over
long distances or for interconnections between asynchronous grids When
electrical energy is required to be transmitted over very long distances,
it can be more economical to transmit using direct current (An electric
current that flows in one direction steadily) instead of alternating
current (An electric current that reverses direction sinusoidally).
For a long transmission line, the value of the smaller losses, and
reduced construction cost of a DC line, can offset the additional
cost of converter stations at each end of the line. Also, at high AC
voltages significant amounts of energy are lost due to corona discharge
(An electrical discharge accompanied by ionization of surrounding
atmosphere) the capacitance (An electrical phenomenon whereby an
electric charge is stored) between phases or, in the case of buried
cables, between phases and the soil (The part of the earth's surface
consisting of humus and disintegrated rock) or water (Binary compound
that occurs at room temperature as a clear colorless odorless tasteless
liquid; freezes into ice below 0 degrees centigrade and boils above
100 degrees centigrade; widely used as a solvent) in which the cable
s buried. Since the power flow through an HVDC link is directly
controllable, HVDC links are sometimes used within a grid to stabilize
the grid against control problems with the AC energy flow.

Also see
http://www.absoluteastronomy.com/ref...direct_current
http://en.wikipedia.org/wiki/HVDC
http://www.aip.org/tip/INPHFA/vol-9/iss-5/p8.html

So?
Note that Michael said "single" power grid.

You are considering a point to point asynchronous connection between two
systems. A DC link is often used for this purpose even in some cases where
the converter stations are back to back but an asynchronous tie is required
because of differing frequencies (Japan)or simply because otherwise there
are problems maintaining a synchronous tie between two large systems
(Alberta and points west and south-Saskatchewan and points east and south).

It is true that they can be at different frequencies but...

within each system, machines have to be in synchronism. In the case of the
NW power pool, a DC backbone is used, as you suggest indirectly, in order to
maintain stability of the system which implies that it is used to maintain
synchronism in a system which might have problems otherwise.


--

Don Kelly @shawcross.ca
remove the X to answer

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.

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.

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

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! ;-)

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

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.