How Can I Synchronize Two or More DSA Instruments? Primary Software: Driver Software>>NI-DSAPrimary Software Version: N/A Primary Software Fixed Version: N/A Secondary Software: N/A
Problem: How can I synchronize two or more DSA instruments? Solution: In order to synchronize multiple Dynamic Signal Analyzers (DSA) properly, they should share the same sample clock. The DSA instruments from National Instruments require that the sample clock be passed through the Real-Time System Integration (RTSI) Bus. This is the small connector on the back and top of the PCI boards. Some things to consider: Which clock will be actually routed via RTSI, the clock used by the delta sigma converter or the clock generated by the DDS logic? Can the Sample clock only be routed via RTSI or could it be done via I/O connector? If the NI 4451 or NI 4452 is used, you can use the RTSI bus to share the board clock accross the RTSI clock line on the bus. To synchronize more than one board, export the AI Start Trigger on the RTSI 0 and the board clock on the RTSI clock line. The clock is only available on the RTSI connector and not the I/O Connector because it is a high accuracy 26.2144 MHz clock and cannot be placed on the I/O connector. For the NI 4551 or NI 4552, you can do the above mentioned only on NI-DAQ Compatibility mode, if NI-DSA driver is used (that is you are using the SHARC DSP chip to use the boad in the Instrument mode), you will not be able to share the clock. In other words, you cannot synchronize multiple NI 45xx working on DSA mode by exporting the clock. The clock that goes accross the RTSI bus is 128 times faster than the desired sampling rate. The delta sigma converters use the 26.2144 MHz clock which is divided down according to the desired alias free frequency span. For example, to have a 20 kHz alias free range for the NI 44xx, 40 kS/s should be selected. For the NI 45xx instruments in DSA mode, the frequecy span can be directly specified, and the digital filters and sampling will be automatically calculated by the driver. For all DAQmx based DSA cards such as the NI 446x and NI 447x, there is a new feature in DAQmx 8.0 and newer called Multidevice Tasks which simplifies the synchronization process. By utilizing this feature, the Sample Clock Timebase, Sync Pulse and Start Trigger are automatically routed between all DSA devices specified in the DAQmx task. Related Links: KnowledgeBase [3U0G7O9N]: Multidevice Task Support For DSA Devices Attachments:
Report Date: 03/16/1999 Last Updated: 05/15/2006 Document ID: 1JF7B90O |
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