The Research and Realization of TA (NIM) System of National Atomic Time Standard of China

TA (NIM) system which is the latest atomic time system was constructed in NIM (National Institute of Metrology) in 2008 to improve the standard of atomic time and the frequency stability and accuracy of China. In this system, the H-maser is reference clock which is steered directly by cesium fountain clock, and local atomic time TA (NIM) is generated by algorithm. The technical scheme of TA (NIM) system was studied in detail, which includes instrument and equipment, working principle of system and algorithm design. And also the software in the system has been completed under the present condition of the timekeeping laboratory. After the operation of the TA (NIM) system and software for half an year, the intercomparison of TA (NIM),TAI and UTC (NIST) showed that the TA (NIM) system is the optimal under the present condition of laboratory. There are two advantages in the TA (NIM) system. Firstly, time stability of one day is lower than 1ns compared to UTC (NIST) and few countries can reach the standard. Secondly, frequency accuracy of long-term keeps the same as that of cesium fountain clock, and achieves 10^-15 order, approaches to international standards.