Chapter 4
Synchronization
NI PXI-6682 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 performance because it tends to
cause rapid changes in temperature. The NI PXI-6682 has precision
thermally compensated components, but limiting direct airflow helps
achieve the best performance. Consider placing the PXI chassis
containing the NI PXI-6682 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 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
can also timestamp an incoming pulse per second signal. The NI PXI-6682
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 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
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