Why Does the Frequency Oscillate in the Output of My PCI-6733?Hardware: Signal Sources (AWG/FG/AO)>>Analog Output Devices>>PCI-6733
Problem: I am trying to generate a square wave of 10682 Hz with an update rate of 800 kS/s on the PCI-6733. Why does the frequency of the output signal oscillate? Why am I not getting a stable frequency output? Solution: The output frequency is not stable because the PCI-6733 can only generate discrete frequency values for a given update rate. These set of discrete values are obtained by dividing the update rate by a integer value. For example, if you have an update rate of 800 kS/s, the PCI-6733 can generate 10810 Hz and 10667 Hz with an accuracy of 1 Hz. These two values are obtained by dividing 800 kS/s by 74 and 75, respectively. If you try to generate 10682 Hz, the 2 closest levels to this value are 10810 Hz and 10667 Hz, so the output oscillates between these two values. You can use the same integer division to determine the set of stable frequencies that can be generated for other values of the update rate. Related Links: Product Manuals: NI 6731/6733 Specifications (June 2007) Attachments:
Report Date: 12/28/2006 Last Updated: 05/14/2009 Document ID: 44R155B8 |
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