About the 60 Hz Frequency Standard

The 60 cycles per second (CPS) frequency standard is a precision instrument designed to generate or verify the 60 Hz signal that is the foundation of synchronous electric timekeeping in the United States. Every synchronous electric clock -- from the Telechron master clocks in this collection to the millions of electric wall clocks that hung in American homes and offices -- depends on the accuracy of the 60 Hz power grid frequency for its timekeeping.

Why 60 Hz Matters for Timekeeping

Henry Ellis Warren, the founder of Telechron, recognized in the early 1900s that the alternating current power grid could serve as a universal time standard. A synchronous motor rotates at a speed determined by the frequency of the AC power supply. If that frequency is maintained at exactly 60.000 Hz, then a synchronous motor turning a clock's gear train will keep perfect time.

Warren successfully lobbied American power companies to maintain their frequency to high accuracy. The result was that by the 1930s, the 60 Hz power grid became the de facto time standard for the entire country. Power companies tracked their cumulative frequency error and made corrections to ensure that the total number of cycles in a 24-hour period was exactly 5,184,000 (60 cycles x 60 seconds x 60 minutes x 24 hours). This process, called "time error correction," meant that while the instantaneous frequency might deviate slightly from 60.000 Hz, over a full day the error was corrected to zero.

The Role of a Frequency Standard

A 60 Hz frequency standard like the one shown here serves several purposes:

• Calibration: It provides an independent reference to verify that the power grid frequency is accurate. By comparing the grid frequency to a precision oscillator, any deviation can be detected and measured.
• Standalone timekeeping: In locations where the power grid frequency is unreliable or unavailable, a standalone 60 Hz source can drive synchronous clocks directly.
• Testing: When restoring or repairing synchronous clocks, a stable 60 Hz source is essential for verifying that the clock runs at the correct speed.

Connection to the Collection

This frequency standard is part of the broader time and frequency measurement capability that supports the clock collection. Together with the cesium beam frequency standard, GPS-disciplined oscillators, and other instruments in the equipment rack, it provides the tools needed to maintain the accuracy of every synchronous clock in the collection and to verify that the power grid is meeting its timekeeping obligations.