What is the Hipp Toggle ?
If an unpowered clock pendulum is set swinging, will describe an arc that will slowly decline in amplitude. The decline is affected by three interferences.
1) the suspension on which it hangs. This is usually a spring
Matthias Hipp's original Hipp toggle was a simple metal toggle attached the the side of the pendulum rod that closed a contact when the arc of swing fell to a certain minimum amplitude. It then momentarily powered an electro magnet as the Pendulum passed through "zero" or bottom dead centre. This impulse accelerated the pendulum slightly on that swing. The arc increased and the Hipp toggle effect would be invoked again the next time the amplitude had again fallen to the set amplitude.
The clever bit is that the pendulum is subjected to the minimum of mecahnical
interference over significant time intervals - often 30 seconds or more.
Matthias Hipp proposed this idea in 1842. Below is Frank Hope-Jones description of the Hipp toggle. It's reproduced from his 1949 book "Electrical Timekeeping". Frank Hope-Jones was the designer and manufacturer of the 20th century Synchronome master clocks (which did not utilise the Hipp toggle)
The Hipp Toggle principal was not widely used but the British Post Office used it in their telephone exchange clocks master until as late as 1980. There is a good explanation of the Hipp Toggle Post Office No. 36 clock at http://www.hvtesla.com/masters/po36_toggle.html . If necessary have a look ; It may help understand what follows.
I had wanted to make a pendulum clock of my own
for a long time. It was always going to be largely electronic because
my mechanical skills are not great. My inspiration
came from the master clocks with one second pendulums that were so popular
in large buildings during the first three quarters of the 20th century.
The Synchronome clock designed by Frank Hope-Jones being one of the
best. The story of other clocks I have is HERE
I have never been an proper horologist so my "bible"has been the book referred to above and I have tried to abide by the important priciples outlined by HJ. There are other electrically maintained pendulum clock ideas to be found on the internet and no claim is made that this scheme is any better than the others. It is just an interesting experiment in basic electronics and horology.
My "toggle" effect is produced with opto-interupters, rather than mechanical devices. When the infra-red beam which passes between the two small pillars is broken by a passing object, an output pulse is generated for as long as the beam is broken. The type I used have a comparator chip on a small pcb and were sourced cheaply from eBay. (as low as 99p)
A short length of soft sleeving which I will call the "flag" is attached to the 4ba rating thread beneath the bob so that it passed between the the pillars of three opto-interupters as the pendulum swings back and forth, creating the operating pulses as it passes. Soft rubber sleeving is used to prevent damage if the flag accidentally hits the arms of the opto-interupter.
The optos are arranged from right to left in the order A, B, C. When the pendulum is stationary the flag hangs midway between optos A and B - ie. at Bottom Dead Centre (BDC). An important point is that the electro magnets are co-incident with opto A; slightly to the right of BDC.
When the clock is running, as the pendulum swings from its rightmost extremity, it first passes through opto A, then B generating a short pulse from each one as it goes. A and B are 0.5" apart, centralised on BDC.
Opto C is positioned 3/4" to the left of BDC and is the Hipp Toggle sensor. It works like this. Assume the pendulum has sufficient amplitude to swing right through opto C at its leftward extremity. A pulse is generated. It then stops and begins to swing back to the right. As it does it passes through C again, generating a second pulse.
So on every swing that has sufficient amplitude
to pass through opto C twice, two pulses are generated in quick succession.
These are fed to a cmos counter chip (CD4013, a) which is wired to divide
by two. In other words the output of the 4013 counter is clocked HIGH
All the while the pendulum arc is slowly decreasing and eventual (now, after 52 seconds in my clock) there will come a time when the flag does not pass right through opto C but enters it, reverses, and proceeds to the right again generating only ONE pulse. This will clock the counter HIGH and and it will remain HIGH as returns to the right. This is the equivalent of the mechanical vane catching on the V block in a mechanical Hipp Toggle clock.
Then as the pendulum continues its swing back to the right it passes through opto B (1/4" from BDC) generating another pulse. A basic chip known as a NAND GATE (IC3a, CD4011) detects that it now has two HIGH signals on its input terminals - one from opto C which was left in the HIGH state and a HIGH from opto B as the flag arrives. With these two HIGHs on its input its ouput goes LOW, is inverted in IC3b to make a HIGH which triggers a flip flop (IC2b) to HIGH which remains HIGH until the flag passes through opto A which resets it again to LOW.
Thus the HIGH on THIS flip flop (ic2b), as the pendulum travels between opto B and A, is the drive period control for the electro magnet's drive pulse. This drive pulse is switched on with a transistor and the Electro-Magnets are powered during that section of the arc (B>A) giving the pendulum an impulse which maintains the pendulum in motion.
On the next swing the pendulum will again pass right through opto C because of the slightly increased swing amplitude and the process will repeat in as many seconds as the energy given by drive pulse will allow. (now 50 seconds in my clock)
A feature of this design is that the pendulum arc is closely controlled by the position of opto C relative to BDC. ie. .75" This works out to be about 1.9 degrees or 0.95 semi arc. This is quite a small arc which is good for time-keeping and the system has been so reliable that an even smaller arc might be entirely possible.
Here's a short video showing the pendulum as it was in an earlier implementation when the "flag" was in front of the bob which was a serious mistake because axial rotation of the bob introduced errors. The LED on Opto C can be seen to blink twice until, after about 30 seconds, it only blinks once (circled). A drive pulse is generated as described above. Please note that sometimes the quickest of the double blinks appear a single blink due to the frame rate of the video.
The purpose of Ic1 (6x Schmidt trigger inverters) is to speed up the pulse edge transitions from the opto-isolators. Used in pairs,the original pulse polarity is maintained.
The completed electronic cHipp Toggle unit
We now have a drive pulse positioned 1/4" either side of BDC which, when amplified by the transistor switch, powers the EMs for 220 milliseconds; that period being set by the distance between opto A and B.
Frank Hope Jones in the Synchronome clock, powered his pendulum at fixed 30 sec intervals with the potential energy of a gravity lever hanging up on a catch so that the energy imparted as the bob passes through BDC was always the same.
The pendulum impulse in this clock is delivered magnetically to the armature beneath the bob. The force of attraction of a magnet varies as an inverse square law of the decreasing distance to the approaching armature.
In my clock, the energy that pulses the EMs does
not come directly from the battery but from a capacitor charged to precisely
5 volts from a voltage regulator. This ensures that exactly the same
energy is available on every impulse. The capacitor value was found
by trial and error to empty its charge during the 220 millisecond period
that the drive is energised. Because of the capacitor the current through
the EMs decreases exponentially over the 220 millisecond drive period.
The oscilloscope image below shows the falling voltage applied across the drive coils during the 220 milliseconds pendulum drive period. A side effect of this system is there is virtually no back EMF generated when the swicthing period ends, so protection of the switching transistor is not needed.
Due to inductance, the current waveform is slightly different..In particular it has a slower rise.
The armature beneath the pendulum is of low remnance steel taken from a GPO relay. There are no fixed magnets in this design.
Here is the circuit diagram of this "capacitor
How it works. The Qbar output of ic2b in the Hipp toggle circuit , which is normally HIGH, is connected to the input (i/p) on the left. This turns on 2n3906 transistor which in turn turns on the 2n5193 pnp transistor above. TThe 3300uf capacitor is charged quickly to 5 volts exactly . The 5 volts comes from the 2940-5 low drop out voltage regulator (2940-5).
When the cHipp Toggle circuit calls for a pendulum impulse, Q of ic2b turns on the EM's drive transistor (lower right), At the same instant Qbar goes low , removing the 5 volt feed to the 3300uf capacitor. The capacitor is now the only source of current for the EMs during the drive pulse period. (220 Milliseconds)
* the 16ohm and 33ohm resistors in the electro-magnet circuit were adjusted to achieve a time between impulses of about 30 seconds. Later the period was changed to over 50 seconds.
The cHipp Toggle clock has no friction other than that of the suspension spring and the air through which it passes. It has a very small arc which is tightly controlled so circular error has virtually no impact. The is no escapement to interfere with the motion of the pendulum except for the precisely controlled impulse which are now every 50 seconds. Temperature control by Invar rod must equal that of the gridiron pendulum and, anyway, the temperature control in a centrally heated home does not allow the wild variations experienced 100 years ago when such clocks were the norm. Therefore I am tempted to believe that an electrically impulsed clock of this type might be as good a pendulum clock as can be constructed whilst running in free air. Only the often mentioned quartz rod pendulum rods might offer a small improvement.
It was Frank Hope-Jones's Synchronome clock system (and his previously mentioned book) that inspired me to make this clock. One of the advantages of the Synchronome system is that the current consumption of a Synchronome clock is miniscule whereas any electronic clock has a continuous drain. Of course, in a modern quartz clock this drain is reduced to a tiny current but the cHipp toggle clock is drawing 90 Ma continuously because of the three opto-isolators, LEDS indicators and the electronics.
This is not much of a problem as I've used a trickle charged 6 volt lead acid battery in case of a power cut.
I have made a start on a second clock. This will use the case of a PO No36 clock and the chassis of an "ME Jubilee electric clock" I've no idea yet what principles will be employed
I have also bought two more Synchronomes one of which ( a late MK2) has two BO22439-3 printed circuit boards which send alternate polarity drives for half minute and one second dials. Work is in progress to trace out the circuit diagram. These boards must be rare as their is no published information on the internet - or a mention in the Synchronome bible by Miles. Please email me if you have any info on these boards.
Originally the clock was fitted with a Synchronome dial mechanism that required an impulse every 30 seconds. This was taken from opto B and a simple divider circuit included to make the impulse every 30 seconds. This has now been didpensed with and it's now fitted with the Gents, silent, seconds indicating, alternate polarity slave clock mechanism mentioned in the introduction. The dial motor resistance is 3.4 ohms and the required drive current is 220Ma. The dial was printed on silver card with a laser printer.
Pulses from optos A and B are "or'd" and inverted in ic3d (circuit above) and fed to the circuit below.
The incoming double pulse is converted to a single pulse of about 220 milliseconds duration with a period of one second by 4013a (ic3a). This is divided by 2 in 4013b. The two opposite phase (Q & Qbar) phase outputs are gated with the single pulse to produce positive going pulses of 220 milliseconds duration alternately, to drive the H-bridge. It was just luck that the spacing of Optos A & B were 220 Milliseconds apart and that the pulse resulting at 4013b i/p was a suitable length to drive the Gents dial movement.
The gem in this circuit is the tiny H-Bridge module sourced from ebay for a mere 99p post paid. Rated up to 10 volts and 1.5 amps its more than adequate to drive the dial motor. Pictured above with a £1 coin for scale, it features two H-bridges, so a couple of additional series dials could be run separately from the B output.
The steady current consumption is now 100ma - mostly due to the LEDs in the Opto-interupters and the other indicators.
How well does it work ?
The clock is capable of keeping extremely good time. The
temperature compensation is not perfect and has not been adjusted on
test. There are still short lengths of brass (top suspension) and steel
(suspension spring, 1.5 inches steel making up the shortfall of the
1 metre Invar rod and the 4 Ba rating thread) which could be compensatated
for in some way. The bob expands upwards and will compensate to some
extent to the downward expansion of the parts listed above - albeit
at different rates due to their mass.
In the initial trials I found some variations in rate
which were difficult to explain and the following mechanical improvements
The constrction of the clock has been an on/off process over 2 years. During that time I've been lucky enough to make the aquaintance (online) of a chap who has written a program for the RaspberryPi (mini computer) that can monitor and record the going of a clock in remarkable detail. Originally designed for the Synchronome system it accepts and records the timing of the 30 second pulses against internet time (NTP) I've used the divide by 30 board which formed part of my clock in its first configuration to feed the Pi monitoring system.
Here is a graph of the last week of running which shows that it has kept well within +/- 0.5 seconds during that period. The small gaining and loosing periods exactly agree with the variations in pressure which occured.
Wednesday 31st May to Thursday 8th June 2017
The vertical scale of this graph is +/- 0.5 seconds. The loosing rate on Wednesday 31st was corrected in the afternoon with a small weight adjustment. Slightly high pressures predominated until Sunday when low pressure arrived. At end of the period shown the pressure was 1001 Mb - about 12 Mb below what I think is the mean pressure here.
This description of the construction and monitoring of the cHipp toggle clock finishes here. The timekeeping has been seen on several more ocassions to be within the +/- 0.5 seconds per week similar to the graph above. It seems to me that without barometric compensation and possibly perfection of the temperature compensation this represents the limit of accuracy of a simple pendulum clock in free air.
However I'll continue the blog in due course showing the results of the computer monitoring of an actual No.36 clock which I've just put to work. It is, of course, an example of a mechanical Hipp Toggle clock as mentioned at the beginning of this article..
The TWO Po No.36 clocksI have
At first I put up the MK4 clock (lefthand picture) and commenced monitoring with the Raspberry Pi. The results were so heavily affected by randon spikes on the graphed results that I took it down and tried the Synchronome built Mk6 (righthand picture) to see if the problem was with the clock..It wasn't. I will have to find the source of the glitches so will will not dwell on them. I will however show here a graph of the performance of the cHipp Toggle clock to show how a useful graph looks.
The cHipp clock gained about a second in two weeks and did so smothly, changing with temperature and barometric pressure. Maybe there is some overall gaining as well.. I'll wait another two weeks to be sure..
Here's what the PO36 reults look like:
I can at least see the general rate and was therfore able
to make a weight change at 21.00 . This is all very uninteresting so
I won't update againg until I've got rid of the spikes and can really
see how the PO36 compares over a similar period.
last updated 10/12/17
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