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60 Hertz Standard

May 27, 2024

Extremely precise timekeeping is now ubiquitous as a consequence of precision quartz crystal and surface acoustic wave oscillators in cellphones and computers. These are synchronized by signals on the Internet. In the mid-20th century, several crude technologies were employed for accurate timekeeping, one of which was synchronization with transmitted data from shortwave radio stations. In North America, these were the National Institute of Standards and Technology (NIST; formerly, the National Bureau of Standards, NBS) time station, WWV, and the Canadian National Research Council time station, CHU.

A television station at which I worked one summer during my undergraduate college days had a precision pendulum clock that synchronized all clocks in the station. The pendulum clock itself was manually synchronized to the television network daily/a>. One radio station at which I worked had a clock synchronized by the Western Union time service using a signal transmitted over telephone wires.

Clock in the main railway station in Zürich, Switzerland

A very expensive clock face design, as illustrated by a clock in the main railway station in Zürich, Switzerland.

In September, 2012, Apple paid Swiss Federal Railways (SBB) an undisclosed sum to settle a copyright lawsuit over its use of the SBB iconic clock face in its IOS 6 clock application.[1]

The clock face was designed in 1944 by Hans Hilfiker (1901-1993).

(Wikimedia Commons image by Jürgen Götzke . Click for larger image.)

About fifty years ago, I designed and built a digital clock (see figure). At that time, digital clocks were rare; and, rarer still were ones that showed seconds as well as hours and minutes. The time base for this clock was derived from the 60 hertz utility frequency of electrical power in the United States. The clock was very accurate, since this frequency is closely maintained, principally for the purpose of sharing power across members of the North American power transmission grid. For this purpose, phase as well as frequency must be synchronized.

Digital clock with seconds indication, constructed in 1975.

My digital clock with seconds indication, constructed in 1975 and still operational. The temperature indicator, showing 54.4 °F at the time of this photo, was added at a later date. It's connected by wire to a temperature sensor at my front porch. Today, it's very easy to build a device that uses WiFi to extract both an accurate time and local temperature from Internet websites. (Photo by the author. Click for larger image.)

In 1897, at the start of the electrical age, utility frequencies in North America ranged from 25 Hz to 140 Hz. Various incidental factors caused a convergence on 60 Hz in the United States, while other countries selected 50 Hz.[2] As explained in a 1997 paper by Edward I. Owen,[2]
"The choice was between 50- and 60-Hz, and both were equally suited to the needs. When all factors were considered, there was no compelling reason to select either frequency. Finally, the decision was made to standardize on 60-Hz as it was felt to be less likely to produce annoying light flicker."

Henry E. Warren (1872-1957), an 1894 electrical engineering graduate of the Massachusetts Institute of Technology (MIT, Cambridge, Massachusetts), installed an electric clock at the Boston L Street generating station of the Edison Illuminating Company to maintain the frequency of its alternating current (AC) generator at 60 Hz.[3] Warren's proclivity for invention was apparent early in his career, since he was co-inventor with MIT classmate, George C. Whipple (1866-1924), of an 1895 patent for an electric thermometer.[4] His synchronizing clock was further proof that Thomas Alva Edison (1847-1931), who had advocated direct current (DC) electrical power distribution, had lost the war of the currents. Warren's clock used a self-starting synchronous motor, the first of its kind, and a pendulum.[3]

Henry E. Warren in 1952

Henry E. Warren (1872-1957).

Warren, who is credited with 134 inventions, was founder of the Warren Telechron Company, fully acquired by General Electric in 1943.

Telechron went out of business in 1992 after selling millions of household electric clocks.

Warren is credited as inventor of a clock that used a vibrating metal wire instead of a pendulum, but I was unable to find any patent for this.

Wikimedia Commons image by Neonedge, from the Lombard Governor Company Brochure. "Lombard's Second 50 years in Ashland."

After graduation from MIT, Warren started his engineering career in Michigan, finally returning to Boston in 1902, starting a machine shop, and founding the Warren Gear Works.[3] In 1912, he founded the Warren Clock Company to make battery powered pendulum clocks.[3] These were not very good timekeepers, and Warren decided to focus his interest on fully electric clocks.[3] The result was his invention of the synchronous motor, an AC motor that rotates at the same frequency as its power source. However, a clock based on such a motor would only be as accurate as the frequency of its power source; thus his goal of getting electrical generators, such as that of the L Street station, to maintain an accurate frequency.[3]

Warren's October 23, 1912, installation of his synchronizing clock at the L Street station marked the start of the Warren Clock Company, where he began production of his Type A master station clock.[3] This device had two hands on a single clock face, and the frequency regulation was manual - The generator operator monitored the two hands to determine whether his electric generator was spinning too fast or too slow.[3] His company's final model, the Type E, was introduced in 1929.[3] By the end of the 1940s, Warren Telechron Company clocks were used to regulate the power frequency of more than 90% of U.S. power transmission lines.[3] In 1937, Warren estimated that electric clock usage by electricity customers would easily defray the cost of his frequency regulating clocks.[3]

In its early days, the Warren Telechron Company had a large market share for home electric clocks, but the advent of quartz timekeeping in the 1950s and the later introduction of digital clocks vastly eroded its profitability.[3] General Electric had bought a 49% interest in the Warren Clock Company in 1917, and it fully absorbed the company in 1943 into its Clock and Timer Division after Warren's retirement.[3] Warren was awarded the IEEE Lamme Medal in 1935 by the American Institute of Electrical Engineers, now the Institute of Electrical and Electronics Engineers (IEEE), for "outstanding contributions to the development of electrical clocks and means of controlling central station frequencies."[3]

Figs. 1-2 of H. E. Warren, 'Time-indicating apparatus,' US Patent No. 1,502,493, July 22, 1924.

An example of one of Henry E. Warren's early patents.

Shown are figures one and two from his US Patent No. 1,502,493, "Time-indicating apparatus," issued July 22, 1924.[5]

The first claim of this patent reads, "In an instrument of the character described, a standard clock, a synchronous motor, two hands mounted concentrically, connections between one hand and the standard clock and between the other hand and the synchronous motor, so proportioned that both hands revolves normally at the same rate, and connections between the synchronous motor and the driving mechanism of the standard clock whereby the spring of the latter is kept constantly wound."

(Click for larger image.)


  1. Iain Thomson, "Apple pays up for stealing design from Swiss Railways," The Register, October 12, 2012.
  2. Edward 1. Owen, "The origins of 60-Hz as a power frequency," IEEE Industry Applications Magazine, November/December 1997.
  3. Allison Marsh, "This Clock Made Power Grids Possible," IEEE Spectrum, February 29, 2024.
  4. G. C. Whipple And H. E. Warren, Electrical thermometer, US Patent No. 540,008, May 28, 1895 (via Google Patents).
  5. H. E. Warren, "Time-indicating apparatus," US Patent No. 1,502,493, July 22, 1924

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