7.3 Plotting FRF data

To plot FRF data, right click on the data of interest in the FRF Data card and select “Plot”. An overview of the dataset will appear in the Matrix Viewer, and selecting individual entries in the Matrix Viewer will plot them in the Graphs card, as illustrated in the following two figures. If the data has only been imported but not yet loaded, then plotting the data will automatically load it as well.

Using the Matrix Viewer

The Matrix Viewer is used to provide a visualization of the complete FRF matrix. By default, the average magnitude of the dataset is visualized. Drop-down menus are also available just below the Matrix Viewer, where the mode can be set to magnitude or coherence, and the averaging can be set to mean, minimum or maximum. Note that coherence may be empty or hidden in case this is not provided in the FRF dataset.

Clicking within the individual boxes of the Matrix Viewer will display the corresponding plot of that specific FRF within the Graphs card.

I: Using the Matrix Viewer (left) to plot a single FRF (right)

II: Using the Matrix Viewer (left) to plot a CMIF and condition number (right)

Plotting a single FRF

As mentioned, the Graphs card will display the FRF (including magnitude, phase and coherence) for whichever entry is selected in the Matrix Viewer, as shown in figure I. For VP-transformed data ($$ \mathbf{Y_{um}} $$, $$ \mathbf{Y_{qm}} $$), the coherence plot will be empty, as coherence is only valid for raw FRF measurements. For additional information and tips on plotting, see 4 Plotting.

To view another FRF, there are two options:

  1. Select another one from the Matrix card;
  2. In the plot in the Graphs card, hover the mouse over the channels in the title and scroll with the mouse wheel. Specific channels can also be selected individually from the dropdown menus in the title, as explained in 4.3 Data selection.

Showing a singular value breakdown (CMIF)

In SOURCE, it is also possible to show the singular value breakdown, often referred to as Complex Mode Indicator Function (CMIF) of any subset of the FRF matrix. Any time you try to plot more than one row along with more than one column of the FRF matrix, the CMIF will automatically be displayed, rather than the individual FRFs. In this mode, the CMIF is displayed in the upper subplot, and the condition number is displayed in the lower subplot, as shown in figure II.

The number of curves shown in the CMIF will be the minimum amount of the number of rows or columns. Reviewing the CMIF is useful for setting the matrix inverse settings in the Analyze module and can be plotted in two ways:

  1. Select the desired entries for the CMIF directly in the Matrix Viewer. Create a box around the FRF data of interest by clicking on one entry, holding SHIFT, and selecting another entry. The two entries should be selected to form the opposite corners of the subset of interest.
  2. In the plot in the Graphs card, select the drop-down menus in the title and select multiple channels and reference channels by holding SHIFT or CTRL while clicking.

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