The time scale algorithm based on cesium atomic fountain clock and optically pumped small cesium clocks

Realizing the independent control of the national standard time has important practical significance under the current international situation. This paper generates an independent time scale that does not rely on external references by studying the self-developed cesium fountain primary frequency standard and domestic optically pumped small cesium clocks. The specific approach is to use the cesium fountain primary frequency standard as a frequency reference to predict the frequency drift of the optically pumped small cesium clocks. By analyzing the noise characteristics of the optically pumped small cesium clocks, the state equation of the atomic clock was established, and the state of the optically pumped small cesium clock was estimated based on the Kalman filtering algorithm. The calculation of the time scale is based on the frequency state estimation and frequency drift state estimation of atomic clocks as the forecast values, and is achieved through the weight algorithm. The weight algorithm based on prediction error and the weight algorithm based on noise characteristics were studied. The results show that in the case of using Kalman filtering state estimation, the weight algorithm based on prediction error significantly improves the accuracy of the independent time scale. The cesium fountain primary frequency standard was selected as the frequency reference to predict the frequency drift of the optically pumped small cesium clock. The accuracy and long-term stability of the independent time scale calculated were significantly better than those when the time scale itself was used as the frequency reference. Taking the international standard time(UTCr) as the reference, the accuracy of the independent time scale is maintained within 15 ns. The frequency stability with a sampling interval of 1 day was 1.57×10⁻¹⁴, that with a sampling interval of 15 days was 4.29×10⁻¹⁵, and that with a sampling interval of 30 days was 2.87×10⁻¹⁵. It can meet the current national time demand.