Synchronizing Multiple NI 4461/4462 Devices Across PXI Chassis using 665x 10MHz (Cont. Acquisition)

Publish Date: Oct 21, 2015 | 0 Ratings | 0.00 out of 5 | Print | Submit your review


This example shows how to use NI-665x devices to synchronize multiple NI 4461/4462 devices in two chassis through synchronization of backplane chassis. Once the cards are synchronized, continuous analog input acquisition is done through the DSA cards and phase-shift between the acquired signals is measured in degrees.

The NI PXI-6653 features a precision 10 MHz OCXO. The frequency accuracy of this clock is several orders of magnitude greater than the frequency accuracy of the native 10 MHz PXI backplane clock (PXI_CLK10). An NI PXI-6653 or NI PXI-6652 module in Slot 2 of a PXI chassis can replace the native PXI 10 MHz backplane frequency reference clock (PXI_CLK10) with the more stable and accurate output of the OCXO or TCXO. All other PXI modules in the chassis that reference the 10 MHz backplane clock benefit from this more accurate frequency reference. The OCXO or TCXO does not automatically replace the native 10 MHz clock; this feature must be explicitly enabled in software.

For this example, the 10MHz Clock on Master 6653 over-rides it's native backplane clock (PXI_CLK10) as well as CLKIN of Slave 6653. All other PXI modules in the chassis phase lock to the over-ridden backplane clock. In this way, all the sample clocks of the cards are synchronized. To start acquiring data from all the cards at the same time, a global trigger is issued. The global software trigger is a single pulse with programmable delay that is fired on a software command. This signal is always routed synchronously with a clock.
This example performs continuos analog input acquisition on all the channels.

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niSync_DSA - Clk10 - DAQmx AI
Example 2 Chassis_Cont_ChanExp



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