Performance and Operation of the NRC Primary Cesium Clock, CsV

Abstract

Since May 1, 1975, the NRC primary cesium beam frequency standard, CsV, has operated as a primary clock, generating directly a new time scale, PT(NRC CsV). Steps in the development of CsV from a frequency standard to a clock, and new error evaluations using the two NRC auto-tuned atomic hydrogen masers as stable frequency references are outlined. Details of both mechanical and electronic construction leading to successful clock operation are also discussed. The design of a new 12.632 MHz frequency synthesizer and modulator with very low spurious sidebands is outlined. Methods of partial re-evaluation of systematic errors and frequency offsets during clock operation, a procedure necessary in order to maintain primary standard accuracy, are described. The accuracy of PT(NRC CsV) is estimated to be about ±9 ns per day if all systematic errors are additive, and about ±5 ns per day if they act independently in a random manner. The frequency stability of PT(NRC CsV) is about 1 to 2 × 10-14 for periods greater than 4 hours, the short term stability being determined by the low cesium beam resonance amplitude of 1.6 to 2.0 pA normally employed for clock operation. Replenishment of the two cesium ovens is expected to be necessary at intervals of several years.