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NIST-F1, source of the official time of the United States. NIST-F1 is a cesium fountain clock, a type of atomic clock, in the National Institute of Standards and Technology (NIST) in Boulder, Colorado, and serves as the United States' primary time and frequency standard. The clock took fewer than four years to test and build, and was developed ...
NIST physicists Steve Jefferts (foreground) and Tom Heavner with the NIST-F2 cesium fountain atomic clock, a civilian time standard for the United States. NIST-F2 is a caesium fountain atomic clock that, along with NIST-F1, serves as the United States' primary time and frequency standard. [1] NIST-F2 was brought online on 3 April 2014. [1] [2]
In 1901, in response to a bill proposed by Congressman James H. Southard (R, Ohio), the National Bureau of Standards was founded with the mandate to provide standard weights and measures, and to serve as the national physical laboratory for the United States. Southard had previously sponsored a bill for metric conversion of the United States. [13]
WWV Transmitter Building (2002 or earlier) WWV's 15 MHz antenna WWV is a shortwave ("high frequency" or HF) radio station, located near Fort Collins, Colorado.It has broadcast a continuous time signal since 1945, and implements United States government frequency standards, with transmitters operating on 2.5, 5, 10, 15, 20, and 25 MHz. [1]
In a time period from 1959 to 1998, NIST developed a series of seven caesium-133 microwave clocks named NBS-1 to NBS-6 and NIST-7 after the agency changed its name from the National Bureau of Standards to the National Institute of Standards and Technology. [10] The first clock had an accuracy of 10 −11, and the last clock had an accuracy of ...
WWVB is a longwave time signal radio station near Fort Collins, Colorado and is operated by the National Institute of Standards and Technology (NIST). [1] Most radio-controlled clocks in North America [2] use WWVB's transmissions to set the correct time.
From 1909, US National Bureau of Standards (now NIST) based the US time standard on Riefler pendulum clocks, accurate to about 10 milliseconds per day. In 1929 it switched to the Shortt-Synchronome free pendulum clock before phasing in quartz standards in the 1930s.
Riefler clocks had internal switch contacts for this purpose, which delivered a 1 Hz time signal to external equipment. The first time standard for the United States, provided by the Bureau of Standards (now NIST), was from 1904 to 1929 generated by Riefler clocks. [5]