Abstract:
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NIST now offers a new remote calibration service designed to assist laboratories who maintain a highly accurate local time standard. The service monitors the local time standard by continuously comparing it to the national time standard, and by reporting the results in near real-time. This new service, called the NIST Time Measurement and Analysis Service or TMAS, works by making simultaneous common-view measurements at NIST and at the customer's laboratory of up to eight Global Positioning System (GPS) satellites. NIST delivers a time measurement system to each customer that makes the measurements and sends the results to NIST via the Internet for instant processing. Customers can then view their standard's performance with respect to NIST in near real-time, using an ordinary web browser. Time is measured with a combined standard uncertainty of 15 nanoseconds, and frequency is measured with an uncertainty of < 1 x 10^?13 after 1 day of averaging. This paper describes the multi-channel GPS common-view technique used by the service and the measurement system sent to each customer. It also explains how NIST calibrates each measurement system prior to shipment, how measurement results are reported to the customer, and how the measurement uncertainties are estimated.
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