Haicom HI-203E, Руководство пользователя, Страница: 12 / 16

3.4 ONE-PULSE-PER-SECOND (1PPS) OUTPUT
The one-pulse-per-second output is provided for applications requiring
precise timing measurements. The output pulse is 1usec in duration.
Rising edge of the output pulse is accurate to +/-1usec with respect to
the start of each GPS second. Accuracy of the one-pulse-per-second
output is maintained only when the GPS receiver has valid position fix.
The 1PPS output is always generated when the GPS receiver is
powered-on. Proper adjustment of the 1PPS output to align with the
GPS second requires calculation of the receiver clock offset and clock
drift-rate as part of the position-velocity-time (PVT) solution. When
enough satellite signals are received to generate valid position fixes, the
1PPS output is adjusted to align with the GPS second in several
seconds. When the 1PPS output is brought in sync with the GPS
second, the 1PPS Valid Signal on the I/O pin becomes active (HIGH);
when the 1PPS output is not yet in sync with the GPS second, the 1PPS
Valid Signal remains inactive (LOW).
As long as enough satellite signals are received to generate valid
position fixes, the 1PPS output remains synchronized to the GPS
second, and the 1PPS Valid Signal remains active. If signal blockage
prevents the receiver from generating valid position fix, the 1PPS output
will drift away from the GPS second and the 1PPS Valid Signal will
become inactive. Upon re-acquiring enough satellites to generate
consecutive valid position fixes, the 1PPS Valid Signal will become
active again, signaling that the 1PPS output is again synchronized with
the GPS second.
For best stable operation of the 1PPS signal, it is to be operated in static
environment having clear view of the sky.
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