Time Interval Analyzers & Universal Counters

■ STANDARD OF TIME AND MEASURING INSTRUMENTS ● Definition of One Second Frequency f is expressed as shown below if the number of times a phenomenon repeats per second is represented by N. f = N/1 [1/s] = 1/T [Hz] T is the time for which the phenomenon occurs once and is called a period. The frequency and the period (time) are related as inverses of each other and represent essentially the same physical quantity. The time we define as “one second” derived from the time it takes the earth to make one revolution around the sun. That is, one second is determined to be 1/31,556,925.9747 of the time taken by the earth to revolve around the sun one time. However, this is inconvenient for use as a standard since a sufficient frequency stability cannot be obtained unless observation is made over several years because this determination is based on long periods of celestial body movements. For this reason, a method to utilize the inherent electromagnetic waves of atoms has been in practically use since the 1960’s. It is known that atoms have inherent discrete energy levels. In transition of these atoms between two energy levels, the difference between these energies is absorbed or emitted as an electromagnetic wave. At present, 9,192,631,770 periods of the frequency emitted by 133Cs atoms are defined as one second and Cs atom frequency standards are used as national standards. This time standard of using atoms has a precision of 10 because it utilizes an invariable high frequency.