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NI PXI-6683 Series User Manual
PPS
The NI PXI-6683 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-6683 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-6683 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-6683 Series can achieve sub-microsecond synchronization. The following section
describes some guidelines for achieving the best possible performance from your NI PXI-6683
Series module. While the NI PXI-6683 Series will function properly if you follow the
specifications, the following guidelines may increase the synchronization performance.
Operating Environment
In order to achieve the best synchronization performance, refer to the following guidelines to
provide a thermally stable environment. Also, ensure you remain within the specified operating
temperature limits:
•
Place the PXI or PXI Express chassis containing the NI PXI-6683 Series module in an
environment free of rapid temperature transitions.
•
Ensure that PXI filler panels are properly installed for unused PXI or PXI Express slots
since inconsistent airflow and temperature transitions across thermally sensitive
components can degrade the NI PXI-6683 Series module performance.
•
Perform the same steps listed above for any other synchronization partners/systems.
Timing System Performance
The NI PXI-6683 Series can generate or receive a 1 Hz pulse per second signal on any PFI or
PXI Trigger terminal. You can set up this signal to transition on the seconds boundary of the
synchronized system time. You can then use this signal to analyze system performance by
connecting two or more pulse per second signals to an oscilloscope and measuring the latency
between them. Adjustments can be made to account for deterministic latency. Refer to the
NI-Sync API Reference Help
for more information. The NI PXI-6683 Series can also timestamp
an incoming pulse per second signal. The NI PXI-6683 Series will timestamp the externally
generated pulse per second with its internal timebase. By comparing this timestamp with the
nearest seconds boundary, you can quickly determine the synchronization performance.