Advances in Time-Scale Algorithms
Abstract
The term clock is usually used to refer to a device that counts a nearly periodic signal. A group of clocks, called an ensemble: is often used for time keeping in mission critical applications that cannot tolerate loss of time due to the failure of a single clock. The time generated by the ensemble of clocks is called a time scale. The question arises how to combine the times of the individual clocks to form the time scale. One might naively be tempted to suggest the expedient of averaging the times of the individual clocks, but a simple thought experiment demonstrates the inadequacy of this approach. Suppose a time scale is composed of two noiseless clocks having equal and opposite frequencies. The mean time scale has zero frequency. However, if either clock fails, the timie-scale frequency immediately changes to the frequency of the remaining clock. This performance is generally unacceptable and simple mean time scales are not used. This paper will first review previolls time-scale developments and then present some new methods that result in enhanced pcrformance. The historical perspective is based upon several time scales: The AT1 and TA time scales of the National Institute of Standards and Technology (NIST); the A.l (MEAN) time scale of the US Naval Observatory (USNO), the TAI time scale of the Bureau International des Poids et Measures (BIPM), and the KAS-1 time scale of the Naval Research Laboratory (NRL). The new methods have been incorporated in the KAS-2(1) time scale recently developed by Timing Solutions Corporation. The goal of this paper is to present time-scale concepts in a nonmathematical form with as few equations as possible. Many other papers and texts discuss the details of the optimal estimation techniques that may be used to implement these concepts.
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 01, 1992
- Accession Number
- ADA498677
Entities
People
- S. R. Stein