SIM Time and Frequency Comparison Network in Near Real Time

A network for time and frequency comparisons within the Inter-American Metrology System (SIM) has been developed. The SIM time and frequency network uses the common-view Global Positioning System (GPS) method to compare frequency and time standards maintained at SIM national metrology laboratories, and comparison results are provided in near real time. Participating laboratories are equipped with a SIM measurement system consisting of an eight-channel GPS receiver coupled to a time interval counter, along with a computer that collects and stores data. Each measurement system then transfers data to a server located at NIST, and the server processes the common-view measurement data of all participating laboratories. Results of comparisons are available via the Internet in near real time (10 minutes of delay). This paper shows results of comparisons conducted for two months between four participating laboratories: NRC (Canada), NIST (USA), CENAM (Mexico) and CENAMEP (Panama). We discuss performance of the network and compare SIM results to those published by the BIPM in its monthly Circular-T document.