Trimble Outdoors AcutimeTM2000 Synchronization Kit External Event Input, Cable Delay Compensation

5 System Operation

5.2.5External 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.

5.2.6Cable 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.

Acutime 2000 Synchronization Kit User Guide 5-9