Time normal
A time standard is a measurement standard of timekeeping .
These are extremely precise clocks whose time is used to set or calibrate other clocks. For this purpose a clock is used which, according to the present state of the art, has the lowest rate error , nowadays an atomic clock .
The following is responsible for the time standard:
- in Germany the Physikalisch-Technische Bundesanstalt in Braunschweig
- in Switzerland the Federal Office of Metrology (METAS) and
- in Austria the Federal Office for Metrology and Surveying .
historical development
In past centuries z. B. the clocks in church towers or town halls are the time norms for a city. With the beginning of astronomical chronology , the solar time was determined on a reference meridian . Until about the 1970s, the astronomical determination of world time from the ephemeris was the primary standard of world time.
The mechanical clocks were later replaced by quartz clocks that are accurate from one second to several years. In quartz watches, solid-state quartz is excited to oscillate by a piezoelectric excitation .
Simultaneously with the miniaturization and mass production of these clocks, a new clock technology with even higher accuracy was developed with the atomic clocks. In atomic clocks, quantum mechanical vibrations of atoms are used as a time standard. The second is currently defined according to the cesium atomic clock : it is the time in which 9,192,631,770 oscillations of a cesium atom occur. Today's Coordinated Universal Time (UTC) is a recording of the seconds measurement via atomic time (TAI) with the annual determination via Universal Time (UT1 / 2).
Web links
- Atomic time Displays the atomic time of the Physikalisch-Technische Bundesanstalt
- Realization of the second with description of the primary frequency standards at METAS