National Instruments NI PXI-6682 User Manual

Also see for NI PXI-6682: Installation guide User manual

Chapter 4 SynchronizationNI PXI-6682 Series User Manual 4-4 ni.comOperating EnvironmentFor best synchronization performance, follow these operating environmentguidelines, while taking care to remain within the specified operatingtemperature limits:• Ensure the PXI filler panels are properly installed for unused PXI slots.Airflow can degrade the NI PXI-6682 Series performance because ittends to cause rapid changes in temperature. The NI PXI-6682 Serieshas precision thermally compensated components, but limiting directairflow helps achieve the best performance. Consider placing the PXIchassis containing the NI PXI-6682 Series in an environment free ofrapid temperature transitions.• Perform the same steps as above to ensure that all othersynchronization partners also have a thermally stable environment.Timing System PerformanceThe NI PXI-6682 Series can generate or receive a 1 Hz pulse per secondsignal on any PFI or PXI Trigger terminal. You can set up this signal totransition on the seconds boundary of the synchronized system time. Youcan then use this signal to analyze system performance by connectingtwo or more pulse per second signals to an oscilloscope and measuringthe latency between them. Adjustments can be made to account fordeterministic latency. Refer to the NI-Sync API Reference Help for moreinformation. The NI PXI-6682 Series can also timestamp an incomingpulse per second signal. The NI PXI-6682 Series will timestamp theexternally generated pulse per second with its internal timebase. Bycomparing this timestamp with the nearest seconds boundary, you canquickly determine the synchronization performance.IEEE 1588 Synchronization Best PracticesNetwork TopologyTo obtain the best NI PXI-6682 Series performance, follow theseguidelines to set up the Ethernet network topology:• Use short cabling when possible. Ethernet cabling is inherentlyasymmetric; the longer the cabling, the higher the asymmetry. Thisimpacts synchronization performance, because the IEEE 1588protocol assumes a symmetric network path.• Use hubs when connecting to multiple IEEE 1588-capable devices.Hubs offer low latency and close to deterministic performance fortransporting Ethernet traffic. This latency is on the order of hundredsof nanoseconds. Using switches degrades performance due to