How to Generate a Custom Signal at a Specific Sample Rate Using the NI PXI-4132

Updated May 7, 2019

Reported In

Hardware

  • PXI-4132

Issue Details

I would like to generate a waveform using the NI PXI-4132 at a specific sample rate.  Which parameters do I have to configure in order to accomplish this goal?

Solution

Using Sequence Mode is the best way to output a waveform from the PXI-4132.  Refer to NI-DCPower Hardware-Timed Voltage Sweep in the Example Finder to see how to program the device in Sequence Mode. 

To program the PXI-4132 to output a signal at a specific rate, careful consideration needs to be put into how long each setpoint in the sequence is present on the output.  When operating in Sequence Mode, the duration for each setpoint is equal to the sum of the duration of the programmed Source Delay and the duration of the Measurement Cycle.

The following picture breaks down the Measurement Cycle timing for the NI PXI-4132:
  • If Auto Zero is disabled the measurement/generation time for a single setpoint in a sequence is equal to the programmed source delay plus the aperture time.
  • If Auto Zero is enabled the measurement/generation time for a single setpoint is equal to the programmed source delay plus twice the aperture time and twice the settling time. The settling time is ~600 µs and is not user-configurable.

The valid aperture time values for the NI PXI-4132 are shown in the table below, expressed in Power Line Cycles (PLC) and milliseconds respectively for 60 Hz and 50 Hz power line frequencies.

In order to set a specific sample rate you should select the greatest value from the aperture time table that is smaller than the sample period and add source delay to get the desired output rate.

By configuring these parameters a specific update rate can be achieved for an output sequence on the NI PXI-4132.

Additional Information

  • As an example, if the desired sample rate is 20 Hz, the sample period is equal to 1/20 Hz = 50 ms.  The greatest value from the aperture time table that is smaller than the sample period is 33.3 ms. At this point the Source Delay input of the niDCPower Set Sequence.vi can be used to add a 16.7 ms delay between each output setpoint, resulting in a 50 ms sample period (33.3 ms + 16.7 ms = 50 ms) and therefore a 20 Hz output rate.
  • Aperture time can be set in LabVIEW using the niDCPower Configure Aperture Time.vi.
  • If Auto Zero is going to be used, the duration of the Auto Zero cycle should be taken into consideration when calculating the Aperture Time and Source Delay values.