Standard Quartz Clock

This unit is all that remains of a quartz clock dating from about 1955. The original clock consisted of additional components—a quartz oscillator, power supply and a frequency divider—mounted with this dial unit on an electronics rack. It was developed at the Naval Research Laboratory and installed at the U.S. Naval Observatory to monitor the accuracy of time signals sent to naval radio stations at Annapolis, San Francisco, Hawaii and Balboa in the Panama Canal Zone. The time signal started at the Naval Observatory, traveled by telegraph line to Annapolis and moved by radio relay to the remote stations. Similar transmitting quartz clocks were later installed at each of the stations, and the observatory’s role shifted from transmitting signals to monitoring the signal accuracy from the stations and providing published corrections based on comparisons with observatory standards.

This surviving component is an electromechanical clock with a twenty-four-hour dial, a synchronous motor, an elaborate system of oilers and a strobe system for checking radio signal accuracy. The grey-painted face plate has an identification tag reading: “TD-31/FSM-5/Clock/Serial 1/A UNIT OF TIME STANDARD AN/FSM-5 /MANUFSCTURED FOR NAVY BUREAU OF SHIPS/BY/U.S. NAVAL OBSERVATORY/WASHINGTON DC.” At lower left is a switch and a tape label marked: “PANAMA ONLY.” Nearby in pencil: “Amber.” On the lower right is a brass crank for resetting the clock and a five-digit counter. Above the crank is an eyepiece. The eyepiece gives a low-power microscopic view into the clock movement where a glass dial, engraved with a thousand divisions revolves once a second. It is possible to read the thousandth of a second from the flash provided by an adjacent strobe lamp. The lamp flashes are controlled by another clock or by radio signals.

Beginning in 1934, the U.S. Naval Observatory started to acquire quartz clocks to serve as time standards and to transmit time signals to navy radio stations. In this kind of clock, first built at Bell Telephone Laboratories in 1927, a small crystal of quartz takes the place of a pendulum or balance wheel. The crystal vibrates between 50,000 to 100,000 times per second, with a rate that depends upon how the crystal is cut. Through an electric current, that frequency drives a clock with a synchronous motor. The clock’s gearing divides down the crystal vibrations to a rate that turns the hands. Similar to other observatories, quartz clocks replaced the best pendulum clocks as time standards from 1946 to 1966, when atomic clocks were accepted.

References:

1. Gebhard, Louis A. Evolution of Naval Radio-Electronics and Contributions of the Naval Research Laboratory, NRL Report 8300 (Washington, DC: GPO, 1979).

2. Dick, Steven. Sky and Ocean Joined: The U.S. Naval Observatory 1830-2000. Cambridge, UK: Cambridge University Press, 2003.

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