The National Institute of Standards and Technology (NIST) maintains UTC(NIST), a time scale synchronized with the International Atomic Time (UTC) coordinated by the International Bureau of Weights and Measures (BIPM). UTC(NIST) uses an ensemble of atomic clocks, primarily hydrogen masers and cesium beam clocks, which are continuously monitored for stability and frequency offset.
Clock stability is estimated using Allan deviation (ADEV) and Time deviation (TDEV), while phase difference and stability measurements are performed every 12 minutes using a “pivot” clock as a reference. The time scale personal-computer (TSPC) processes clock measurement data using the AT1 algorithm to generate TA(NIST), a composite oscillator representing the weighted average of individual clock stability.
UTC(NIST) is produced by applying coordination adjustments to TA(NIST) to achieve synchronization and syntonization with UTC. Leap seconds are inserted into UTC(NIST) time codes but do not affect the physical UTC(NIST) signals. The time scale includes internal systems for redundancy and environmental control to maintain operational continuity.
Keywords: Atomic Clocks, Time Scales, UTC-NIST
