The English Clock Systems Ltd 'Memory Master' clock is a clever combination of ac mains power and conventional clockwork. The pendulum controls a dead beat escapement powered by a spring in a barrel. The hands of the master clock's dial are driven mechanically from this clockwork train. Every one minute, a synchronous electric motor is allowed to run to rewind the spring and to operate switches to provide an alternate polarity pulse to the slave dials.
If the ac mains power fails, the clock continues to run on its spring reserve for up to 10 hours, and the master clock's dial will continue to show the correct time. The slave dials will all stop as they are powered electrically by 24 volts derived from the ac mains. However, a mechanical memory stores the duration of the power failure, and, on restoration of mains power, the synchronous motor runs continuously to update the slaves until they show the correct time
This clock was manufactured in 1967.
The mains transformer can be seen to the left behind the dial. The half-second beating pendulum is of Invar, and the accuracy of the clock is very high.
A side view of the mechanism, showing the rewind motor (top right) and the mercury filled glass switches to drive the slave dials.
The rear plate of the movement, showing the rewind motor at the top and the mechanical memory wheels below. The pendulum crutch is to the right of the motor.
The ac mains powered rewind motor and the two mercury filled glass switches which provide alternate polarity pulses of 24 volts dc for the slave dials. The switches are each tilted individually on alternate minutes by pins on a wheel, thus switching the slave current one way then the other.
The two memory wheels on the outside of the movement plate have smooth circumferences, each with a recess cut to a smaller diameter for part of their circumference, and are geared together at 12:1. The outer wheel is the 'minutes' wheel and inner is the 'hours' wheel. The lever with pins straddling the two memory wheels will only drop into both recesses cut into the circumferences of the wheels when the memory has 'unwound' to zero. This then causes the synchronous motor to be stalled. During the next minute, the memory wheels continue to turn and lift the lever with pins onto the larger diameter part of the minute wheel, releasing the motor again.
A close-up of the mercury switches.
Gents of Leicester also manufactured this design under the name of 'Chronopher', and a version by Westerstrands in Continental Europe was also made, but to a slightly lower standard.
