Whats this clock for and hows it made?

[Ian ParkinParticipant @ianparkin39383]

For about 25 years this clock has hung in a cavity on the back wall of my house ..its a slave clock and i ran it with a synchronous motor driving a cam wheel with a couple of pips giving 2 pulses a minute to the mechanism.

it was taken down to build an garden office for wifey.

its made out of bronze? 10mm thick on the chapter ring

its 400 mm dia

but the inner bronze bit was filled with a cement type material that was painted black this had suffered in the elements…theres some brass bits that the cement was flowed round

whats the reason for this infill?

and where would this clock have lived when it was new?

[John HaineParticipant @johnhaine32865]

Oddly enough I had a movement on the floor beside my desk.  It’s a standard Gents of Leicester slave clock, originally driven by 30 second pulses from a master clock.  Thousands used in offices, factories, etc.  The Robertson clock which I look after has such a movement, like yours with a substantial cast face.  Rather similar to Synchronome slave clocks.  What part of it are you asking how it’s made?  An alternative to a synchronous motor would be an Arduino and a low cost real-time clock, which can be put together for not much more than a tenner.

[SillyOldDufferModerator @sillyoldduffer]

Back when it was expensive to make accurate mechanical clocks, it was common for large organisations who needed to run to a standard time to buy a system consisting of a pricey precision master clock wired to a load of inexpensive slaves scattered round the premises.   Faults apart, all the clocks told the same time, and there could be hundreds of them.

Ian’s slave clock looks good, so I suggest it was aimed at a prestigious institution like a College or Public Building rather than a factory or a chemical works!  The filler may be waterproofing, or perhaps simply intended to create the illusion of solid quality by adding weight.  Even though it has a lovely face, the innards are basic!

Dave

[Ian ParkinParticipant @ianparkin39383]

John

its that middle part with the plaster/cement infill

whats the purpose of it its a 220 mm dia x 20mm deep cavity

why would it not be just a bronze disc ?

 

and where would this clock have lived? On a wall with a large recess for the mechanism and the bronze “pan” ?

[duncan webster 1Participant @duncanwebster1]

You can get very accurate 1 second pulses from a quartz clock movement. The electronics last forever, so I collect clocks which have been thrown out because the case is damaged and use the electronics to drive the Arduino. A real time clock might be more accurate, but you have to put it right twice a year anyway

[BazyleParticipant @bazyle]

As you know the electromagnet is pulsed every 30 seconds so it goes ‘clunk’. The infill of the disc is to stop it acting as a sounding board and making a huge ‘clanggggggggg’.
This is a large outside movement, most are small 8″ dials for the inside. It is interesting in showing the counterbalance weight on the 120 tooth wheel for the bigger hand.
It should be driven by a 300mA (400mA max) current, not a specific voltage, so that the long length of the wiring doesn’t weaken the pulse and use a few hundred ohm in parallel not a diode for back emf suppression to be authentic.

A master clock design has appeared in EIM some 20 years ago.

The 30 second pulse could also be used to drive a 24 hour mechanism with lots of pegs to activate the school lesson bells. I think the one at my school was in the library but was quite quiet.

Ian mentioned using a synchronous motor to derive the pulses. This is even more accurate long term than a quartz movement because the CEGB count the cycles and get the right number every day come wind or rain. It used to be said that they arranged to get it bang on at 9pm for people checking their clocks against the Big Ben Bongs on the BBC news.

[Ian ParkinParticipant @ianparkin39383]

Bazyle

that makes sense for the infill material but if it was outside would the noise matter so much?

 

any ideas on what i should/could  use to replace it?

[Bazyle]

On Bazyle Said:

…

Ian mentioned using a synchronous motor to derive the pulses. This is even more accurate long term than a quartz movement because the CEGB count the cycles and get the right number every day come wind or rain. It used to be said that they arranged to get it bang on at 9pm for people checking their clocks against the Big Ben Bongs on the BBC news.

Hmmm, not sure that’s true!   One of the ways the grid is regulated is by varying the frequency, less energy being delivered per second at 49Hz than at 50Hz, usefully providing a degree of regulation without altering the voltage.  Memory tells me the UK grid was only allowed to vary between 49.5 and 50.5Hz, but this OfGem document suggests this was widened to 49.0Hz to 51.0Hz in 2011.

Interestingly, the change wasn’t made so the grid could be energy regulated it’s because:

The issue of frequency and voltage operating range was initially brought to the Grid Code
Review Panel (GCRP) by generator representatives for discussion in May 2009. In their
view, the current Grid Code obligations were prohibitive in procuring of generation plant
in the global market. It was argued that the UK is no longer a significant enough player in
the global market to influence generator design and therefore as off-the-shelf plant does
not meet Grid Code obligations, a significant additional cost is added.

Although a high-performer in the age of mechanical clocks, 50Hz mains was never a precision time source, partly because of line noise and breaks,  and I think it’s less stable today.

Be interesting to compare the mains today with a selection of quartz watch oscillators ranging from very cheap to very expensive.   In 2024 I’d bet money that a moderately good cheap quartz module will keep better time than a mains powered synchronous motor.  And it’s horribly easy by comparison with GPS, to show that quartz isn’t the best available either.

Dave

 

[duncan webster 1Participant @duncanwebster1]

I’ve got an Arduino drive clock which gets it’s reference frequency by dividing down the mains. When I remember I’ll set it back on right (as near as can be, it has a 30 second slave) leave it running for a few weeks and compare via pips. At the moment all I can say is it seems pretty good since I moved it out of the kitchen. The ignite for the gas stove drove it wild. Of I ever make another I’ll pay more attention to shielding

[BazyleParticipant @bazyle]

I don’t recall frequency playing a part in power calculations in my A-level physics.

Interesting rabbit hole. I remember domestic ovens often having synchronous motor clocks, more recently I had a microwave oven displaying the time, I made LED clocks some 40 years ago, and my ’60s house has wiring for mains clocks over the mantlepiece and kitchen door. Some of these must have seemed so revolutionary when they became possible after the national grid was established. Was there any frequency control before nationalisation?

In 2000 the first digital cable TV boxes had a clock display linked back to GPS receivers at the head ends a side benefit as digital TV relies on very accurate time references.

[SillyOldDuffer]

On SillyOldDuffer Said:

On Bazyle Said:

…

Ian mentioned using a synchronous motor to derive the pulses. This is even more accurate long term than a quartz movement because the CEGB count the cycles and get the right number every day come wind or rain. It used to be said that they arranged to get it bang on at 9pm for people checking their clocks against the Big Ben Bongs on the BBC news.

Hmmm, not sure that’s true!   One of the ways the grid is regulated is by varying the frequency, less energy being delivered per second at 49Hz than at 50Hz, usefully providing a degree of regulation without altering the voltage.  Memory tells me the UK grid was only allowed to vary between 49.5 and 50.5Hz, but this OfGem document suggests this was widened to 49.0Hz to 51.0Hz in 2011.

Every power station I did work at in my youf (9 in the UK, 7 abroad) had control room clocks linked to mains frequency and their local clock (A Hipp clock in those days, probably NTP or GPS nowadays). The grid is regulated so that the 50Hz frequency averages out to exactly 50hz despite permissible variations through the day,.

[Michael GilliganParticipant @michaelgilligan61133]

Interesting page here, Ian

https://gentsofleicester.com/portfolio-page/#

’though it does not feature your dial, the author may be pleased to hear from you.

[ see the closing lines ]

MichaelG.

[Mark Rand]

On Mark Rand Said:

On SillyOldDuffer Said:

On Bazyle Said:

…

Ian mentioned using a synchronous motor to derive the pulses. This is even more accurate long term than a quartz movement because the CEGB count the cycles and get the right number every day come wind or rain. …

Hmmm, not sure that’s true!  …

Every power station I did work at in my youf (9 in the UK, 7 abroad) had control room clocks linked to mains frequency and their local clock (A Hipp clock in those days, probably NTP or GPS nowadays). The grid is regulated so that the 50Hz frequency averages out to exactly 50hz despite permissible variations through the day,.

The Wikipedia article on Utility Frequency doesn’t confirm that, or not at least the way I read it.   The section on Time Corrections says:

Today, AC power network operators regulate the daily average frequency so that clocks stay within a few seconds of the correct time. In practice the nominal frequency is raised or lowered by a specific percentage to maintain synchronization. Over the course of a day, the average frequency is maintained at a nominal value within a few hundred parts per million.[20] In the synchronous grid of Continental Europe, the deviation between network phase time and UTC (based on International Atomic Time) is calculated at 08:00 each day in a control center in Switzerland. The target frequency is then adjusted by up to ±0.01 Hz (±0.02%) from 50 Hz as needed, to ensure a long-term frequency average of exactly 50 Hz × 60 s/min × 60 min/h × 24 h/d = 4320000 cycles per day.[21] In North America, whenever the error exceeds 10 seconds for the Eastern Interconnection, 3 seconds for the Texas Interconnection, or 2 seconds for the Western Interconnection, a correction of ±0.02 Hz (0.033%) is applied. Time error corrections start and end either on the hour or on the half-hour.[22][23]

I don’t see a commitment for grid frequency to be exactly 50Hz, or that there will be exactly 4320000 cycles per day.  The Swiss specification sets a ‘a long-term frequency average per day’, which isn’t Mark’s “exactly 50Hz”.  Maybe the UK grid is more exactl, but a doubt it.

Mains frequency was excellent for general purpose time-keeping for about a century, but is gradually being supplanted by NTP or GPS, both of which leave mains frequency in the dust.   Mains frequency is allowed to vary by up to 1Hz, maybe more, per day,  and although Europe aims to maintain a ‘long-term frequency average of exactly 4320000 cycles per day’,  the nominal value is only within a few hundred parts per million.   That’s equivalent to an ordinary quartz crystal, and considerably inferior to the cheap 20ppm 32768Hz crystals found in quartz clocks and wrist-watches.

Bear in mind that what’s considered excellent frequency stability by an electrical engineer, doesn’t impress a radio engineer!  And the guys who do atomic clocks aren’t impressed by radio.   We’ve come a long, long way since the nation’s clocks were commonly driven by 50Hz synchronous motors.

Dave

 

 

[Michael GilliganParticipant @michaelgilligan61133]

If I recall correctly, Dave … the UK commitment [mainly to facilitate the use of synchronous-motor clocks]  was something like them always indicating “within the pips” of the BBC time signal.

In consumer terms this would have reasonably been considered accurate … ‘though of course we know that the truth is much more complex!

MichaelG.

[John HaineParticipant @johnhaine32865]

Er, 86400 cycles per day?

[John Haine]

On John Haine Said:

Er, 86400 cycles per day?

Oops!  I should properly engage brain before posting!

[Ian ParkinParticipant @ianparkin39383]

Micheal G

thanks for that page I’m not sure mines a Gents clock

but this quotation looks very much like my clock

[Michael GilliganParticipant @michaelgilligan61133]

Ian

I thought John Haine had already [near enough] identified your slave movement as a Gents item.

Apologies to you both if I misinterpreted what John wrote.

MichaelG.

[Ian ParkinParticipant @ianparkin39383]

Michael

theres no makers name at all on any of the  parts

but it does look like a gents movement but again no marks at all

[Michael GilliganParticipant @michaelgilligan61133]

Well they were very thorough about their patenting, and rights protection.

… so I would be surprised if it was a knock-off.

MichaelG.

.

Edit: __ not sure how this EHG paper comes to be on clockhappy.com but it may be of general interest:

https://clockhappy.com/listings/images/listing_images/originals/listing_92/image_14.pdf

 

Another Edit: __ although the home-page doesn’t disclose much, a little more digging got me here:

https://clockhappy.com/clock/92

[SillyOldDufferModerator @sillyoldduffer]

Interesting where Ian’s Slave Clock took me!  Starting with his nice bronze face driven by a synchronous motor, we got into a discussion about the relative accuracy of 50Hz mains.

This website is the best on the subject I’ve found, and it includes this real-time frequency meter, where the needle can be watched moving, and it is shifting more than I expected at the moment:

http://www.mainsfrequency.uk/fm-meter

Or, clicking this link draws a graph shows live GB mains frequency variation during the last 10 minutes.   It is GB rather than UK because Northern Ireland is not synchronised with the mainland.

The site makes this observation, my bold: from the distribution of measured frequencies, the network tends to operate most of the time at frequencies below 49.99Hz or above 50.01Hz. It only spends perhaps 15% of its time between 49.99Hz and 50.01Hz. Data from National Grid confirms this.  In other words, it’s positively unusual for the mains to be accurately close to 50Hz!

Here’s the exciting bit!  Turns out there’s a forensic technique that precisely identifies the time an audio recording was made from the slight mains hum that’s always present.   As mains frequency effectively varies randomly, the pattern of small frequency changes around 50Hz reveal exactly when the recording was made.  And disruptions in the pattern prove the recording has been edited.   Never seen it feature on a TV CSI show though!

Dave

[duncan webster 1Participant @duncanwebster1]

Reducing frequency reduces power because all the motors connected to the grid slow down a bit, and when we had manufacturing industry there were a lot of motors. One plant I visited in Leeds had a 3000 hp motor driving a car shredder, and that wasn’t an unusually high load for a plant

[John HaineParticipant @johnhaine32865]

[John HaineParticipant @johnhaine32865]

Three more photos of the movement above.  The internals have no branding, the Gents name appears moulded onto the back of the Bakelite cover that encloses the movement and also on the face (not shown).

[noel shelleyParticipant @noelshelley55608]

I find this forum so very interesting ! Frequency has been talked of in the context of it’s accuracy and Voltage can be all over the place, but loosely 240V as the national standard. As a boy we lived in Bornemouth in the late 50s, the sockets were the very modern for the time 13A flat pin, BUT the voltage was 200V, 50cs. What other voltages or frequencies were used in the UK ? Noel.

Jason may choose to re title this as a new thread ?

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