Want to immediately snap to peaks or valleys in your data? Don’t mess around with a standard cursor… use an automatic cursor!
NOTE: The examples in this article pertain to the peak cursor, but they are equally applicable to a valley cursor.
To add an automatic cursor to a display, right click and choose “Add Automatic Cursor -> Peak/Valley Cursor”.
Tip: Hold down the CTRL key when right clicking on the display to always get the plot menu.
Figure 1: Right click in the display to display the cursor options. Select the Automatic Cursor.
The peak cursor will automatically fix itself to the highest amplitude peak in the plot. The valley cursor will automatically fix itself to the lowest valley in the plot.
Tip: The peak cursor is especially useful for quickly determining peaks in an FRF.
Figure 2: The automatic cursor snaps to peaks.
Properties of the cursor can be adjusted by right clicking on the cursor and selecting “Properties”. Popular adjustments include
Changing the font size
Adjusting the number of decimal places displayed
Adding a cursor label
Displaying / hiding the intersection values
Figure 3: Adjust the properties of the cursor itself with the “Cursor Properties” dialogue.
After making some adjustments, the cursor is now displayed as below.
Figure 4: The defaults of the peak cursor have been adjusted.
It is also possible to control the parameters of how the cursor selects peaks and valleys.
Adjusting the Automatic Cursor Parameters
Right click on the cursor and select “Automatic Peak/Valley Parameters…”
Figure 5: Access the cursor parameters via the “Automatic Peak Parameters” menu selection.
There are a few parameters of interest in the Automatic Cursor dialogue box:
Source data: This determines what data in the plot the automatic cursor will be applied to. The options are “First Curve”, “Selected Curve” and “All Curves”.
Max number of extrema: This determines the number of peaks or valleys the cursor will snap to. For example, if the value is set to “5”, at most, 5 cursors will be snapped to the data.
Figure 6: Increase the “Max number of extrema” to get additional automatic cursors to populate.
Source range: This determines the x-axis range over which the automatic cursor will be applied. By default, the peak cursor is applied to whatever data is displayed within the x-axis limits of the plot. If the source range is set to fixed, the automatic cursor will only be applied to the specified x-axis range regardless of what the limits on the plot are.
Amplitude threshold: Determines the amplitude band in which the data peaks can be considered real peaks (or valleys). The threshold is expressed in dB below the highest value in the curve for peaks and in dB above the lowest value in the curve for valleys. In Figure 4 (above), the lowest amplitude peak that would have a cursor snapped to it is 50dB below the highest amplitude value.
Gate: Gate determines how much amplitude variation there should be after a change in the direction of the signal in order for the change to be considered a peak or valley. The gate is expressed in % of the dB range. Adjusting the gate can be useful so that “real peaks” are selected instead of noise (see Figure 7, below).
Figure 7: Increasing the gate from 1% to 5% results in the actual peak to be chosen instead of noise on the peak.
Automatic cursors are a great way to quickly determine peaks and valleys in data without painstakingly adjusting standard cursors.