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5-14 Acutime 2000 Synchronization Kit User Guide

System Operation

Timing Pulse Output (PPS)

A pulse-per-second (PPS), 1 microsecond-wide pulse is available on

the Acutime 2000’s interface connector. The pulse is sent once per

second and the leading edge of the pulse is synchronized to UTC or

GPS time. The pulse shape is affected by the distributed capacitance

of the attached cabling and input circuit. The leading edge is typically

less than 20 nanoseconds wide. The pulse's trailing edge should never

be used for timing applications. An accurate timing pulse is available

only when the Acutime 2000 is operating in the static

Overdetermined Clock mode.

Note – GPS time differs from UTC (Universal Coordinated Time) by a

small, sub-microsecond offset and an integer-second offset. The

small offset is the steering offset between the GPS DoD clock

ensemble and the UTC (NIST) clock ensemble. The large offset is the

cumulative number of leap seconds since 1 January 1970, which, on

31 December 1998, was increased from 12 to 13 seconds.

Historically, the offset increases by one second approximately every

18 months, usually just before midnight on 30 June or 31 December.

System designers should note whether the output time is UTC or

GPS time.

Note – The event time reported in 8F-0B and 8-AD is corrected for

the fractional UTC offset if UTC PPS (default) is selected.

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Trimble Outdoors 45005-00-ENG Manuel d'utilisateur Page 62