Calibration of time and frequency via GPS at The National Laboratory

Purpose

The National Laboratories have the task to maintain the national references standards for each measurement quantity and to spread metrological competens and traceability to industry and society at large. The national reference standards are the highest level of traceability in Sweden.

A calibration performed at a National Laboratory fullfils all typical traceability and accreditation requirements that commonly exist in industry and society at large. 

Method

For calibration of more accurate time and frequency standards, we offer on-site calibration using the GPS satellite system as an intermediate reference. This requires installation of equipment for reception and storage of data from the GPS.

The method, known as GPS Common View, is similar to that used by RISE to provide international traceability.

We can also verify and calibrate the time synchronising and positioning performance of different types of GNSS receivers. 

The method involves calibrating a frequency standard, clock or time scale (DUT) relative to UTC(SP) by means of simultaneous measurements of GPS satellite signals performed by both the customer and by RISE.  The use of common satellites eliminates many of the common measurement errors.  In addition, the changes that are observed in the time intervals [UTC(SP) – DUT] provide an estimate of the DUT frequency relative to UTC(SP).

All instrumentation needed (GPS receiver, time interval counter, software, etc.) can be supplied and installed by RISE. For continuous monitoring over a longer period of time, equipment can be rented from RISE.

Deliveries

For continuous monitoring, the measured values registered by the customer are transferred automatically to RISE.  The calculation of the results are performed automatically by RISE with the results being sent to the customer by (for example) e-mail.  The results can also be provided through a webpage. How often this is done is agreed with the customer, but can in principle be done on a daily basis.  The accuracy of frequency measurement, averaged over a day, is better than ±1E-13, but does depend on the quality of the DUT.