摘要
The atomic time scale UTC(NIM) kept by National Institute of Metrology (NIM) is one of the physical realizations of the Coordinated Universal Time (UTC), and it is the national time and frequency primary standard in China. Since 2017, some new hydrogen masers with better predictability have joined the NIM atomic clock ensemble. Based on the enlarged clock ensemble, the time scale algorithm of UTC (NIM) has been modified, a paper time is generated from a hydrogen maser ensemble which is traceable to UTC, and UTC (NIM) is steered with reference to this paper time. The new algorithm has been applied since August 2019, and the time stability of UTC(NIM) has been improved from about 0.6 ns/5 d to around 0.2 ns/5 d, the time deviation of UTC(NIM) from UTC has been kept roughly within ±5 ns.