A new addition to my museum. 21/1/26:
Photos coming soon…
I’ve been lucky enough to acquire a GPO Gents Master Clock No. 36. It’s an electrically controlled clock fitted with a one second beating pendulum. It supplies one second, six second, and half minute electrical pulses for the operation of pulse clocks and telephone equipment. It also incorporates an additional count wheel and contact springs to provide six second impulse outputs for driving Veeder clocks.
Clock No. 36 was introduced in 1925 to meet the requirements of new automatic telephone exchanges, which required a six-second pulse for timing and metering purposes.
Vintage master and slave clock systems were designed to provide synchronised timekeeping across multiple locations from a single, accurate source. It was used in schools, factories, railway stations, and offices from the late 19th century through the mid-20th century. These systems ensured uniform time display throughout large facilities.
The Master Clock:
The master clock serves as the primary and most accurate timekeeping device in the system. It maintains precise time and distributes synchronisation signals to the connected slave clocks. Many vintage master clocks relied on high quality pendulum mechanisms or regulated movements to achieve exceptional accuracy.
Signal Transmission:
The master clock generates electrical timing pulses at fixed intervals, commonly once per minute. These pulses are transmitted via wired connections to all slave clocks in the system. The impulse operated a solenoid which mechanically moved the minute hand forward by one minute or half a minute, ensuring consistent synchronisation.
The Slave Clock:
Slave clocks rely on the master clock for time accuracy. Depending on their design, slave clocks may contain a basic movement that is periodically corrected or may depend entirely on the master clock’s signals to advance their hands.
Synchronisation Process:
Slave clocks receive electrical impulses from the master clock that advance or correct their time. Some models move their hands forward incrementally with each pulse, while others receive periodic correction signals to maintain alignment with the master clock.
Wired Systems:
Vintage master slave clock systems typically used dedicated electrical wiring. This wiring allowed reliable signal transmission over long distances within large buildings or campuses. The connections are shown below.
Interesting information:
Thanks to Vic for the GPO Clock info.