|
Automated Computer Time Service
|
NIST disseminates time and frequency signals by radio, satellite, telephone, and the Internet. The time codes for each of these services include advanced alert for changes to and from daylight saving time and advanced notice of insertion of leap seconds. Since 1923, NIST radio station WWV in Fort Collins, Colo., has provided around-the-clock shortwave broadcasts of time and frequency signals. A sister station, WWVH on Kauai, Hawaii, was established in 1948. The stations broadcast at 2.5, 5, 10, and 15 MHz (WWV also broadcasts at 20 MHz), and reliably cover the continental United States and the Pacific at time accuracy of 1 ms to 10 ms and a frequency accuracy of 1 × 10-7. Broadcasts include standard frequencies and time intervals, time of day (both voice and digital code), astronomical time corrections, and public service announcements (marine weather, geophysical alerts, Omega and GPS status information, and radio propagation information). Telephone access: (303) 499-7111 for WWV, (808) 335-4363 for WWVH In 1956, low-frequency station WWVB near Ft. Collins, Colo., began broadcasting at 60 kHz. These broadcasts provide more predictable propagation than that of either WWV or WWVH, but the data rate is so low that only a slow digital time code can be broadcast. Time uncertainty is on the order of 0.1 ms to 1 ms and frequency uncertainty is 1 × 10-11 for measurements over one day. The recent upgrade of the station output power from 10 kW to 50 kW provides for very good coverage of the entire continental United States. An increasing number of consumer products (clocks and watches) use signals from this station to routinely reset their time and to provide automated handling of changes to and from daylight saving time. Automated Computer Time Service We also offer an Automated Computer Time Service that uses commercial telephone lines to deliver a digital time code for computers and automated systems. The service delivers a digital signal with a time uncertainty of 1 ms to 100 ms depending on the modem and mode used and a frequency uncertainty of 1 × 10-8 for measurements over one day. In its most accurate mode, the telephone-circuit delay is measured and removed in the delivery to the user. The Network Time Service, patterned after the Automated Computer Time Service, delivers a time code through the Internet using several different protocols. The time uncertainty is limited by path delays in the Internet but can be much less than 100 ms. Time servers for this service are located, not only in Boulder and Gaithersburg, but also at other locations on the West and East Coasts of the United States. Usage of this service, now at nearly 40 million calls per day, is growing rapidly. Software for this service is available from www.bldrdoc.gov/timefreq/service/its.htm Contact: D.
Wayne Hanson
Date
created:
August 17, 2001 |