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Acutime 2000 Synchronization Kit User Guide 5-9
5 System Operation
5.2.5 External Event Input
The Acutime 2000 provides an External Event Input that allows the
user to time tag external event pulses. The event capture mechanism
is triggered on the low-to-high transition of the external event input.
The time tag provides a resolution of 320 nanoseconds and represents
the time at which the event pulse occurred at the Acutime 2000
connector input. Therefore, it is offset by the amount of delay in the
cable. The time tag information is reported in packet 0x8F-0B (or 8F-
AD). This feature is intended for use with relatively infrequent event
pulses. A practical limit on event pulse frequency is about 10 Hz. To
prevent the Acutime 2000 hardware and firmware from being overrun
with event pulse inputs, make sure that an event pulse will not occur
until the time tag from the previous event pulse reported in packet
0x8F-0B (or 8F-AD) is received.
5.2.6 Cable Delay Compensation
The PPS output from the Acutime 2000 is calibrated to be aligned
with UTC/GPS at the connector. The PPS you receive is delayed by
the amount of propagation delay in the cable between the Acutime
2000 and your equipment. You can compensate for this delay by
setting the PPS offset field of packet 0x8E-4A. The propagation delay
through the cable depends on the cable type used, but in general, the
delay is approximately 1.25 nanosecond per foot of cable. Negative
PPS offset values cause the PPS output to occur early, which
compensates for the propagation delay of the cable.