Chapter 4
Synchronization
NI PXI-6682 Series User Manual
4-4
ni.com
Operating Environment
For best synchronization performance, follow these operating environment
guidelines, while taking care to remain within the specified operating
temperature limits:
•
Ensure the PXI filler panels are properly installed for unused PXI slots.
Airflow can degrade the NI PXI-6682 Series performance because it
tends to cause rapid changes in temperature. The NI PXI-6682 Series
has precision thermally compensated components, but limiting direct
airflow helps achieve the best performance. Consider placing the PXI
chassis containing the NI PXI-6682 Series in an environment free of
rapid temperature transitions.
•
Perform the same steps as above to ensure that all other
synchronization partners also have a thermally stable environment.
Timing System Performance
The NI PXI-6682 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-6682 Series can also timestamp an incoming
pulse per second signal. The NI PXI-6682 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.
IEEE 1588 Synchronization Best Practices
Network Topology
To obtain the best NI PXI-6682 Series performance, follow these
guidelines to set up the Ethernet network topology:
•
Use short cabling when possible. Ethernet cabling is inherently
asymmetric; the longer the cabling, the higher the asymmetry. This
impacts synchronization performance, because the IEEE 1588
protocol assumes a symmetric network path.
•
Use hubs when connecting to multiple IEEE 1588-capable devices.
Hubs offer low latency and close to deterministic performance for
transporting Ethernet traffic. This latency is on the order of hundreds
of nanoseconds. Using switches degrades performance due to
