Martin's introduction to

Impulse Clock Systems

An electric impulse clock system usually consists of one or more public slave clocks, or dials, driven by regular electric impulses generated from a remotely located master clock. The slave clock could just be one large clock dial, or set of four dials, in a tower. In this situation it is convenient to have the master clock down at ground level so that adjustments to the time can be made easily. In a factory or large public building there could be hundreds of dials in offices all over the site. In this situation the advantages of having all dials showing exactly the same time, and all being changed automatically from one central point at daylight saving change times, are obvious. Other devices may be connected into the system, such as workers clocking-in machines, programmer devices to ring bells at certain times, or even bell striking/chiming of the hours. Such systems use very little power and clocks can continue to run from batteries during power failure. That modern buildings have hundreds of battery clocks that have to be changed manually twice a year, and batteries that go flat at random intervals, is quite amazingly inefficient, although cheaper to buy and requiring no skill to install. To me, a building with 20 offices, each with a stand-alone battery clock, is about as sensible as having 20 un-networked computers!

Most electromechanical impulse systems have a master clock with a pendulum electrically maintained, and producing pulses at 30 second intervals. Commonly all clocks are looped in series, and only the specified current, (perhaps 220 m/a), through the whole circuit is important. This means that removing a clock without maintaining the ring stops all the clocks- a common downfall of many a system, due to ignorance. Some systems use parallel clocks at a certain voltage, typically 24 volts. More sophisticated systems may have means to re-synchronise errant slave clocks, or to store unsent pulses during power failure and provide an automatic reset of clocks after power is restored. This is particularly important for large clocks that may require supplementary mains power to move the hands. Some systems have impulses at 1 minute intervals, and some 1 second intervals. Sometimes alternating polarity is used, which is useful in driving silent movement clocks where noise is a problem. Most systems drive the hands of slave clocks by jumping say, half a minute at a time. This is a sure way of identifying an old electromechanical system.

Modern public clock impulse systems are different. An electronic master clock produces pulses, probably at one minute intervals, but the slave dials move slowly- one minute in several seconds for example, and require mains power. The master clock supervises and keeps time correctly synchronised to the wireless standard time transmissions, and will correct automatically for daylight saving time and after power failures.

This is only intended to be a brief outline of what an impulse system is. Others have already done some good work on publishing web pages with detailed technical descriptions of the common master clocks, although not always much attention is paid to slave devices. There are some good sites with more detailed explanations of the various different clock systems, such as Barrie's clock museum, or Pulsynetic site.

Manufacturer's names to look out for, and which often indicate an impulse system, are:

Gent's of Leicester (brand name Pul-syn-etic) also appearing badged as Reliance(GEC)


English Clock Systems (the impulse devision of Smith's, also known as ECS) (Sectric was only used on mains clocks)


Telephone Rentals (TR)


International Time Recorders (ITR)


Temco, Simplex, and many were homemade, often to Synchronome design

And european players such as T&N in Germany


St Hugh's College, Oxford

As an introduction to the world of electric impulse clock systems, some examples of the 1936 installation at St Hugh's College, Oxford, is interesting, particularly as this is the ONLY real original installation of such a system that I have ever had access to, other than feeling frustrated over all those public clocks one sees around outside buildings, which no longer run. Most of these systems which stand idle, require very little maintenance to bring back to life, but they sit idle, wasting away, mostly due to ignorance. No one fits such systems anymore, due to the ease with which anyone can stick up a quartz clock on a nail, and wait for the battery to run down. Most installations are easy to maintain, but SOMEONE has to have an interest in actually keeping an eye on it, at least twice a year for daylight saving changes.

Unfortunately there are few people about now who even KNOW what such a clock system is, let alone able to spare a little TLC to look after it.  This is tragic. Particularly because the owners of such clock system do not know what they have. All they know is that they have a clock or clocks which have stopped and don't work anymore. So they don't know who to ask for help, or what sort of help they need. A call to most modern clock experts will just result in the inevitable response, "It's too old and needs replacing". So in ignorance, that's what happens. Fortunately this happens less often with really old church clocks because usually someone in the church organisation realises what a treasure they have.

Maybe there is a shortage of people with the required skills left now, but what use if those left do advertise? Adverts for impulse clock system maintenance only work if the owners know they have an impulse clock system. If they don't know that, they go to the wrong people. I don't know the answer to this problem, but I feel some education is the only answer, hence this web page.

I wonder just how many public systems still run? I have only known of a handful in the last 20 years, and they have all gone now. The tragedy is, if I had known the St Hugh's clock system existed only 2 years ago, I could have fixed it and saved so much of it being torn out and superceeded by an electronic box. It had lain idle for many years, because apparently no one knew anything about it and how to fix it. The assumption was made that it was terminally broken. In fact, very little wears on such a system, and minor repairs are not difficult.

The system at St Hugh's consisted of a 1936 Gent master clock, driving 2 outside slave clocks in the gables of the main building roof. Also, inside were several wall clocks in important places. Some of these were designed as part of the fabric of the building, particularly those in the library , which was built at this time in the late 30's. The clocks had faces which were part of the carpentry on the building, with slave movements behind. Some of them were several hundred yards away from the master clock. The battery clocks nailed(!) to the front of the old faces are not in keeping with the style of the design.

However, the most exciting find is the Pulsynetic bell striking machine in the chapel loft. This was installed in a most inaccessable position. Even when standing in the loft of the chapel, the machine is about 10 feet above one's head. I see no good reason for it to have been put there, other than to prevent it's maintenance, and in more recent decades, I suspect to hide it's very existence. Mind you, the maintenance men who installed buckets next to it, to catch the rain dripping in, must have noticed it, although they may not have known what it was. The machine pulls on the chapel bell rope to toll the hours, and is set off by hourly impulses from the clock system. However, I can find no one who recalls when it ever last worked! For all we know, it may have been stopped in the war and never reconnected. The system was re-wired sometime, probably in the sixties, but the bell striker was not included- it still had disconnected lead covered cables running from it. This bell must have been a feature of college life once, but did anyone notice when it stopped working?! Some other colleges in Oxford do still toll the hours. I hope one day to be permitted to restore this machine to working order, but I shall re-install it at loft floor level where it can be maintained!

Unfortunately there is little left of the original system at St Hugh's. Apart from the master itself, which was obviously considered decorative, if not functional, and the bell striker, only the wiring and the 13 cell battery remained. The power unit had been stripped out and replaced by an electronic box, which drives the outside clocks on Main Building, now replaced by modern slave units. Fortunately, as most of the wiring is intact, it is relatively easy to add slave clocks once more. Had I been a couple of years earlier I could have saved the original slave clocks on Main Building, but more importantly, I could have saved the original special clocks built in to the library structure. Apparently these were dumped with the comment that they could never be made to work again!


Since producing the above pages, I have removed the bell striking machine which is being overhauled ready to be re-installed once again. Evidence suggests that it never got much use and most likely was stopped during the second world war, never to go again. On May 1st college held a bell ringing party at which the bell was rung at midday for a number of people listening below. The overwhelming decision was taken, over the champagne, to get the machine working again. Hopefully this will be ready for the new michaelmas term. In addition, both the library clocks have been restored to their original state. The clock in the Fulford room was fairly straight forward, but the clock in the main library required new woodwork to repair the damage to the face. The library is in a different building to the master clock, and a small part of the wiring between buildings had been removed, although most was intact. A few other slave dials are being replaced in key positions.

Christmas 2001- Latest NEWS!

After 60 years, Miss Ady's clock strikes once more!

At last the renovation of the bell strike machine is complete and on Christmas Eve, the "formidable" strike was heard again for the first time in sixty years!

Believed to have been switched off around 1940, the machine lay idle and forgotten. Next to the machine was found a 1930's carton of grease, and on the guide piller, a small patch of candle wax, left from when the pre-war maintenance man used to stand his candle there in order to see to do periodic lubrication. Very little wear was noticeable on the mechanism, and a thorough clean and rebuild, and a few careful adjustments, were all that were required to make it run again. The machine has been re-sited lower down in the belfry, so that it can be maintained more easily without being forgotten! To see a picture of me at work in the bell tower, click here. To hear that bell strike for yourself, click here.

In the St Hugh's Chronicle Number 8, Jubilee Edition for 1935-36, Miss Gwyer, the Principal, states in her letter:

"Next (gift to college) comes Miss Ady's clock, with its 'formidable' strike and its two faces, visible one over the main door and the other over the garden door of the old building. The council has siezed the occasion to electrify the whole system of College clocks, which now tick in unison. "

I am sure Miss Ady would be delighted to know her gift has been given new life, after such a brief and rudely curtailed start. Miss Ady died soon after her retirement, in 1958, aged 76.


Autumn 2002, Bell stopped again!!

Problems in bell tower briefly silenced the clock again after 9 months!

Unfortunately the stress of being used again after so long proved too much for the wire rope connecting the bell ringing machine with the bell hammer. The wire had severely corroded at the point where it was connected to the hammer and parted company with it. This was potentially a major problem because this is inaccessable from inside the building, effectively being outside on top of the roof of the chapel. My worst fear had been the inaccessability of the hammer and its unknown condition. Complaints were immediately received from residents in the neighbourhood who could no longer tell the correct time, also bemoaning the fact that the next nearest striking church clock is not such a good timekeeper.

Fortunately the situation was not as hopeless as at first feared. College was due to erect some scaffolding to access that area of the roof for another purpose, and once this had been erected, I was able to fix the rope easily and have the bell ringing again in time for Christmas 2002.

Advantage was taken to photograph the bell, and some further interesting information was found. The bell itself was cast in 1936 by John Taylor & Co of Loughborough, No 242. This changed my theory that the bell was part of the chapel building before the clock was installed. In fact it must have been installed into an empty bell tower as part of the clock installation of 1936. I suspect this was a standard bell foundry used by Gent of Leicester when clock orders were received which included providing a bell.

This was also an opportunity to take some unusual views of the college: view1 , view2 , view3 , view4 , view5

The problems may not be over. Some concern is currently being expressed over the condition of the structure of the tower and major work is being contemplated. If that happens I expect the bell will be silenced yet again.


Pulsynetic (Gent) Master Clock on the landing by the chapel. This is serial No 4001, dated 26/3/36.
Here is a view of the power supply in a cupboard above, as found! The batteries are long neglected and the charger was removed when the new master clock "module" was installed. However, luckily the programme device to produce the hourly pulse for the bell ringer is still in situ

Some shots of the Pulsynetic bell striking machine as found in the chapel loft: Click on any thumbnail for a larger view:

The bell striking machine high up in the chapel loft Attempt at a closer view! Attempt at a closer view! And after restoration..... The restored machine Finished Installation


I am currently maintaining the clock system in the Oxford Examination School. Take a look at their web site at which you will find pictures of the huge slave clocks in the main halls. This is currently a Pulsynetic system but previously, it is a well known historical fact that the original system was installed by 1883. This was replaced by the newer system in 1959. We are not sure that these dials, some of which are 30 inches across, were those orginally put in by Shepherd, but the wooden housings certainly seem to be original. The Shepherd patent 3696 for this design, was dated 1881. The master clock and one of the slave mechanisms is preserved, although not on display, in Oxford University museum.

To see my Wants list of equipment I am still seeking, click here.

To see a catalogue of various different slave clocks and devices(big file, slow to load over a modem) click here.

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