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Time and Frequency Standards & References

An overview of Time and Frequency Standards and references, detailing what they are and what they are used for.

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Time and Frequency Standards and References

A time and frequency standard or reference is a precision instrument which provides the user with exact time-of-day and on-time pulse signals together with stable frequencies. Our products may be configured to use a range of signal inputs to provide a comprehensive suite of outputs.

Time Measurement

Another definition for time standard or time reference is that it is basically a measurement of time. There are several globally agreed methods of measuring time as follows:

Universal Coordinated Time (known as UTC)

The definitive universal time standard, UTC is the time calculated as a weighted average of about 200 atomic clocks at National Metrology Institutes and Timing Laboratories around the world. It is compiled by the International Bureau of Weights and Measures (BIPM) in France. UTC is a derivative of TAI (see below), in that leap seconds are added to keep within 0.9 seconds of UT1.

It combines all the atomic regularity of atomic time with the navigational convenience of UT1.

International Atomic Time (TAI)

This is the time standard based on seconds calculated using caesium vibrations. It has nothing to do with time calculated using the Earths rotation (UT1). Using atomic resonance frequency results in a more regular measurement than UT1 because of slight irregularities in the Earth’s rotation. Hence, over time, TAI and UT1 become increasingly out of step.

GMT (Greenwich Mean Time)

Sometimes used interchangeably to mean UT1. GMT now refers to the civil time based on the atomic second kept in the United Kingdom, which is the standard time of the time zone centred on the Greenwich Meridian (zero degrees longitude).

It is the basis upon which global time zones are calculated.

Frequency Standards and References

A frequency standard is a highly stable oscillator which generates a frequency with a high degree of accuracy.

A caesium (cesium) or rubidium standard is based on a Cesium or rubidium oscillator and are extremely precise.