Clock type · Public & tower
Master/Slave Electric Clock Systems
Partially verifiedSystems in which a single precision 'master' clock (often a pendulum regulator with electrical contacts) periodically transmits electrical impulses to synchronise multiple simpler 'slave' dials, widely used in railway stations, factories and institutions before radio and network time synchronisation.
Construction and interpretation
A distributed clock system separates a reference timekeeper from the displays it controls. In a common impulse installation, contacts at the master send pulses over wires and an electromagnetic stepping mechanism advances each secondary dial. The secondary is then a display rather than an independent pendulum clock. Other synchronisation arrangements exist, so the documented system must determine whether a particular remote clock is stepped, corrected or otherwise controlled.
Pulse interval, polarity and supply requirements are compatibility questions, not facts that can be read from a dial’s typography. A detached secondary dial may survive without its master, cables or control equipment. Record that missing installation context instead of treating the dial as an incomplete ordinary spring clock. A master can itself be electrically wound while retaining a pendulum regulator: the winding source and the distribution signal perform separate jobs. Institutional inventories and circuit documentation are particularly valuable for reconstructing the original relationship.
| Feature | What it means | Evidence to seek |
|---|---|---|
| Master regulator | Supplies the reference time | Regulator and control documentation |
| Impulse dial | Advances on received signals | Coil, ratchet and pulse specification |
| Distribution wiring | Connects control to remote displays | Original installation records |
| Detached secondary | A surviving part of a larger system | Known master and missing equipment |
Do not connect a secondary dial to an arbitrary battery or controller; visually similar systems may be incompatible.
Evidence to record
- Document pulse requirements rather than experimenting.
- Record institutional provenance and original dial location.
- Distinguish ordinary impulse dials from other synchronised designs.
Movement & mechanism
- Master clock: a precision pendulum regulator fitted with electrical contacts that close at set intervals (commonly every half-minute or minute)
- Slave dials: simple electromagnetic mechanisms with no independent timekeeping ability, advancing only on receipt of an impulse from the master
- Wired distribution network connecting one master to many slave dials across a building or site
- A master clock closes a contact at a regular interval, commonly every half minute
- Slave dials advance by an electromagnet and ratchet on each impulse
- Batteries or mains supply power, and the pendulum is electrically rewound in better designs
Identification
- Slave dials typically have a very simple movement with no mainspring, weight or independent escapement — only an electromagnetic stepping mechanism
- Master clocks are generally substantial precision regulators with visible electrical contact mechanisms
- Wiring terminals on the case back of a dial clock, rather than a winding arbor, indicate a slave dial
- Slave dials with no independent movement, only an impulse mechanism
- Wiring to a central master clock
- Master clocks frequently survive without their slave network
Terminology
- Master clock — the precision timekeeping source in the system
- Slave dial — a synchronised display unit with no independent timekeeping capability
- Impulse — the periodic electrical signal advancing a slave dial
- Master clock
- Slave dial
- Impulse
Known variations
- Half-minute impulse systems
- Minute impulse systems
- Synchronome-type free-pendulum master clocks
- Synchronome, Gents and Continental systems
Collecting notes
Master clocks (particularly those by established scientific-instrument makers) are collected as precision regulators in their own right; slave dials are collected chiefly for institutional provenance (railway, factory, public building) rather than mechanical sophistication.
Photographs
Photographs are illustrative examples of the type, not necessarily the exact object described. Verify details against the source file page.
Sources & references
- General horological literature on electrical timekeeping distribution systems; individual manufacturer histories require further research.
- Britten, F. J., Old Clocks and Watches and Their Makers
- Loomes, B., reference works on British clockmakers (edition-dependent)
- Museum catalogue descriptions of comparable examples
- https://en.wikipedia.org/wiki/Electric_clock
Where sources disagree, the disagreement is stated rather than resolved silently.