Improvement of the Time Scale of NPLI

Suman Sharma, P. Banerjee, and Arundhati Chaterjee

Abstract:	The National Physical Laboratory, India (NPLI), is responsible for maintenance and development of the Indian Standard Time (IST) and also contributes through the GPS network to the generation of UTC coordinated by BIPM. The objective of the Time Unit is to implement a smoother timescale at NPLI. Recently, NPLI has made some special efforts to improve the uncertainty between UTC and UTC (NPLI). One basic clock ensemble algorithm is implemented to make the timescale of UTC (NPLI) by combining the intercomparison data of five cesium clocks. Some initial tests have been carried out to check the validity of this algorithm, and they observed a significant improvement in the UTC – UTC (NPLI) Circular T values and frequency offset with respect to UTC. This is necessary to judge the efficacy of the algorithm. A few iteration processes and/or some sort of modification may be anticipated to optimize the algorithm further. The output of the optimized process is normally fed to a microphase stepper to steer the timescale. Data from only one cesium is currently submitted to BIPM, but the aim is to submit data from all five cesium atomic clocks to BIPM in the near future. NPLI also plans to take intercomparison data from the eight Indian Space Research Organisation (ISRO) cesium clocks. By optimally ensembling of these clocks and the addition of data from these clocks, NPLI may generate an improved timescale. The uncertainty for the NPLI – PTB time link in Section 6 of BIPM Circular T is 2.5 ns for Type A and 7.0 ns for Type B, giving a total uncertainty of 7.4 ns. If the NPLI TTS2 receiver is calibrated on-site at NPLI by a travelling calibration BIPM receiver, then the Type B uncertainty may be reduced further to 5.0 ns. Various efforts are underway to improve the uncertainty UA and UB. TWSTFT has the capability of achieving 0.1 ns jitter. NPLI is planning to procure a TWSTFT system to initiate such a link. This paper describes these studies and presents the analysis of these observations
Published in:	Proceedings of the 40th Annual Precise Time and Time Interval Systems and Applications Meeting December 1 - 4, 2008 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	669 - 678
Cite this article:	Sharma, Suman, Banerjee, P., Chaterjee, Arundhati, "Improvement of the Time Scale of NPLI," Proceedings of the 40th Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, December 2008, pp. 669-678.
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