NI-DAQmx: AO Update Rate vs. Desired Frequency

Updated Oct 31, 2018

Reported In

Hardware

  • Analog Output Device

Issue Details

What is the relationship between the "Desired Frequency" input in NI-DAQmx analog output and the actual hardware AO Update Rate?
 

Solution

The analog output update rate is determined by front panel controls in the AO . The formula for determining the rate is as follows:
 
AO Update Rate = ((Desired Frequency) * ((Samples Per Buffer) / (Cycles Per Buffer))

This can be understood by noting (Samples Per Buffer) / (Cycles Per Buffer) = Samples Per Cycle. Because the Digital to Analog Converter (DAC) must output N Samples Per Cycle the AO Update Rate will be Desired Frequency * N.

For example, if the Desired Frequency is set to 1000 Hz, Samples per Buffer is 250, and Cycles per Buffer is 5 the following equation results:

AO Update Rate (Samples per Second) = 1000 Cycles per Second * (250 Samples per buffer / 5 Cycles per Buffer)
 
Which breaks down to:

AO Update Rate (Samples per Second) = 1000 Cycles per Second * 50 Samples per Cycle
 
Then:

AO Update Rate = 50,000 Samples per Second = 50 kHz

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