Why Is My PXI-6682 Off By 19 Seconds When Using GPS Protocol? Primary Software: Driver Software>>NI-SyncPrimary Software Version: 1.0 Primary Software Fixed Version: N/A Secondary Software: N/A
Problem: When I use the PXI-6682 module with a GPS (Global Positioning System) time reference it is off by 19 seconds when compared to a secondary GPS device. Why is this occurring? Solution: GPS Time is not corrected to match the rotation of the Earth and is currently 19 second offset with International Atomic Time (TAI). GPS time does not take into account leap seconds or other factors which are periodically added to Coordinated Universal Time (UTC). The atomic clocks on satellites are set to GPS time, which is where this offset can be seen. When using a GPS time reference the NI-Sync driver returns the current time using the TAI timescale. This allows PXI-6682 to be used with IEEE 1588, IRIG-B, and GPS time protocols. Using the TAI timescale gives the PXI-6682 the ability to drive a IEEE-1588 network with GPS time and it will be the correct timescale. Because of the multipurpose nature of the PXI-6682 it will not automatically correct the PXI-6682 time reference to match the GPS time. If the TAI time scale does not work for your application the time source can be manually adjusted by using the NI-Sync property node and selecting "Clock Adjustment Offset". Reference the following screenshot.  Related Links: Products & Services: NI PXI-6682 Developer Zone Tutorial: GPS Synchronization Architecture for DSA Devices Attachments:
Report Date: 12/28/2007 Last Updated: 08/28/2008 Document ID: 4GRC2OQX |
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