Time and Frequency Metrology

सीएसआईआर-राष्ट्रीय भौतिक प्रयोगशाला

CSIR-National Physical Laboratory

Realization and Maintenance of IST CSIR-NPL has a “Primary Timescale” generating UTC(NPLI), which is traceable to the Coordinated Universal Time (UTC) provided by International Bureau of Weights and Measurers (BIPM) located in Sevres, France. UTC(NPLI) is the realization of UTC at NPLI. The IST (i.e., UTC(NPLI) plus 5:30 hours), generated using a bank of caesium clocks and hydrogen masers, has current systematic uncertainty of ±2.8 nanoseconds with respect to UTC. The timescale system generating IST consists of five caesium clocks, one passive hydrogen maser, two active hydrogen maser, measurement system and an international satellite links for clock comparison and traceability link. The caesium clocks provide absolute atomic reference of the time which has exceptional long-term stability, whereas the hydrogen maser has ultimate short-term stability. UTC(NPLI) is realized as the steered output of an Active Hydrogen Maser (AHM). However, the timescale ensemble has five high performance Caesium clocks as well. All Cs clock output frequencies and steered output from microphase stepper are connected to an automatic switching unit which enables time-based switching of measurement of a pair of clocks through a frequency/phase comparator or a time interval counter.