This example is a modification for the "Getting Started with Swept Sine (DAQmx).vi" code found in LabVIEW's example finder. The modification allows (currently) for 2 response signals to be measured.
For instructions on how to extend the code further to allow for a higher number of response signals, see the code on the block diagram of the main.vi. There has been a lot of demand for this functionality and thought this edit would therefore be worthwhile.
NOTE: This modification requires edited revisions of some example VIs. You may therefore need to manually change the expected paths of some of the SubVIs to point to those in the "Swept Sine Multiple Response" folder. All of the SubVIs needed are included in the .zip.
The VI performs the following:
Initialize a swept sine measurement by specifying the hardware device and channel settings.
Configure the source by specifying the test frequencies, amplitude, and whether or not you want the sweep to continue repeating.
Set the settling and integration parameters to allow sufficient time for the DUT to settle before the measurement is performed at the new test frequency and sufficient integration time to achieve the desired level of precision.
Explicitly set the sample rate for the measurement. The rate is automatically selected if this VI is not used. The same rate is used for input and output channels.
Specify the device propagation time specific to the data acquisition device being used for the measurement. The device propagation time can be measured using the SVS Measure Propagation Delay VI.
Start the swept sine to perform the hardware configuration and start the output and input tasks. Synchronization of the channels is performed internally in this VI.
Generate the excitation and acquire the stimulus and response data at each test frequency.
Convert the raw data for displaying and reporting measurement results.
Stop the swept sine measurement and clear the output and input tasks to release the device.
Steps to Implement or Execute Code
Download the .zip and unzip the contents into one folder
Run the .lvproj file and open the main.vi (Getting Started w Swept Sine Modified.vi)
You may need to redirect LabVIEW to the correct file paths for some of the SubVIs
Select excitation channel, stimulus channel and one or two response channels (to select more than one, browse for channels and ctrl+click)
The program will plot both the Bode and Nyquist frequency responses
Requirements to Run
LabVIEW 2011 or Later
Sound and Vibration Toolkit 2011
USB 4431, PXI, or PCI 4461
Eden S Applications Engineer National Instruments UK & Ireland