A status report on time scale generation in PTB

This paper deals with the local realization of Coordinated Universal Time UTC by PTB, named UTC(PTB), and PTB´s free atomic time scale TA(PTB). Since February 2010 UTC(PTB) has been derived from an active hydrogen maser steered in frequency by PTB´s primary fountain clocks. Since then and up to early 2015 the time difference UTC - UTC(PTB) was always less than 9 ns. From early on it was foreseen that the steering of UTC(PTB) could also be derived from the ensemble of caesium beam clocks operated in PTB. When doing so in practice, it appeared that the algorithm of combining the inputs of individual clocks was not perfectly chosen. The properties of the time scales as generated up to now as well as the new strategy for a time scale reflecting better PTB´s ensemble of thermal beam caesium clocks is presented in this paper.