Chapter 4
Synchronization
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National Instruments Corporation
4-3
NI PXI-6682 Series User Manual
To achieve proper synchronization of the NI PXI-6682 Series, ensure that
the IRIG-B source used conforms to the requirements listed above. Note
that most IRIG-B sources conform to these requirements.
IEEE 1588
The NI PXI-6682 Series is capable of performing synchronization
over Ethernet using IEEE 1588. It is possible to configure the
NI PXI-6682 Series to synchronize to GPS or IRIG-B and then function
as an IEEE 1588 grandmaster. It is also possible to configure the
NI PXI-6682 Series to synchronize to IEEE 1588, in which case, the
standard defines how the master will be selected. If the NI PXI-6682 Series
is selected as IEEE 1588 master, and it is not configured to synchronize to
GPS or IRIG-B, it will use its internal free-running timebase, which will be
updated to the host computer’s system time during power up.
PPS
The NI PXI-6682 Series is capable of using a PPS (pulse per second) signal
for synchronization. Any PFI, PXI_Trigger or PXI_Star line can be
configured as the PPS input terminal. When synchronizing based on a PPS,
the first pulse received will set the NI PXI-6682 Series internal timebase to
either an arbitrary time supplied by the user, or the host computer’s system
time. Each subsequent pulse received will be interpreted as a second’s
boundary (the pulse occurring exactly 1 second after the previous pulse).
As each pulse is received, the NI PXI-6682 Series will adjust its internal
timebase to match the frequency of the PPS source.
For best results when using PPS Time Reference, ensure that the device
supplying the PPS signal is capable of providing a stable, consistent 1Hz
signal. Error can be induced into the system if the reference signal contains
significant jitter, or if the reference frequency strays from 1 Hz.
Synchronization Best Practices
The NI PXI-6682 Series can achieve sub-microsecond synchronization.
The following section describes some guidelines for achieving the best
possible performance from your NI PXI-6682 Series module. While the
NI PXI-6682 Series will function properly if you follow the specifications,
the following guidelines may increase the synchronization performance.
