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LMS Test.Lab: The Versatile "Double X" Cursor

Siemens Genius Siemens Genius
Siemens Genius

(view in My Videos)

 

LMS Test.Lab: The Versatile "Double X" Cursor

 

In LMS Test.Lab, the Double X cursor is a wonderful and powerful cursor for data analysis.

 

Double X: The Basics

 

To add a Double X cursor to a display, right click and choose “Add Double Cursor -> X” (Hint: Hold down the CTRL key when right clicking on the display to always get the cursor menu)

 

Picture 1: Right click in display (press CTRL if needed) and "Add Double Cursor -> X"Picture 1: Right click in display (press CTRL if needed) and "Add Double Cursor -> X"

 On the Double Cursor, the left and right cursors can be moved (Picture 2):

  • Left Cursor: Moves both cursors together at the same time. The cursors stay fixed distance apart
  • Right Cursor: Moves only the right cursor, changes the distance between the two cursors

 

Picture 2: Left cursor moves both cursors, right cursor changes widthPicture 2: Left cursor moves both cursors, right cursor changes width

Set the cursor to the frequency range desired to perform an analysis.

 

Double X: Max

 

Need the maximum over a frequency/rpm range?  Want to know the frequency/rpm the max occurs at?

 

Picture 3: Using the Double X cursor to find the maximum value in a frequency rangePicture 3: Using the Double X cursor to find the maximum value in a frequency range

Right click on either the left or right of the Double Cursor and select “Calculations -> Max” (Picture 4).

 

PIcture 4: Right click on the double cursor and choose "Calculations -> Max".  Maximum will be displayed in a cursor legend.PIcture 4: Right click on the double cursor and choose "Calculations -> Max". Maximum will be displayed in a cursor legend.

The maximum appears in cursor legend, along with the frequency at which the maximum value occurs (Picture 5).

 

Picture 5: The maximum value and it's corresponding frequency will be shown in the legend.Picture 5: The maximum value and it's corresponding frequency will be shown in the legend.

Right click on the cursor legend and choose "Copy Values" to paste the maximum value into Excel. 

 

Double X: Frequency Calculator

 

Looking at some time domain data and wondering what the frequency is present (Picture 6)?

 

Picture 6: Damped sine wave time history.Picture 6: Damped sine wave time history.

Right click on the Double X cursor and select “Calculations -> Freq (1/deltaT)” as in Picture 7.

 

Picture 7: Determine the frequency of time data by selecting "Calculations -> Freq(1/T)"Picture 7: Determine the frequency of time data by selecting "Calculations -> Freq(1/T)"

 Double X: Linear Regression

 

Trying to figure out your average acceleration from a RPM vs time trace (Picture 8)?

 

Picture 8: RPM vs time data tracePicture 8: RPM vs time data traceTo determine the rate of speed increase (ie, the acceleration) from the RPM vs time, right click on the cursor and choose "Calculations -> Linear Regression" (Picture 9).

 

Picture 9: To determine the rate of acceleration, right click and choose "Calculations -> Linear regression"Picture 9: To determine the rate of acceleration, right click and choose "Calculations -> Linear regression"

The "Linear regression" function fits a line to the data between cursors.  The slope and offset of this line are displayed in the legend. 

 

Right click on the legend and choose "Copy Values" to copy/paste the slope and offset to Excel.

 

Double X: RMS and Color

 

Want to know the RMS level over a specific frequency range?

 

PIcture 10: Determining the RMS value of a frequency band within a spectrumPIcture 10: Determining the RMS value of a frequency band within a spectrum

 Right click on the Double X cursor and choose “Calculations -> RMS” as shown in Picture 11.

 

Picture 11: Right click on the Double X cursor and choose "Calculations -> RMS"Picture 11: Right click on the Double X cursor and choose "Calculations -> RMS"

Want to highlight the frequency range of interest with a little pizazz?  Add a bit of color by right clicking on the Double X cursor and selecting “Properties”.

 

Picture 12: Select a color for the Double X cursorPicture 12: Select a color for the Double X cursorTurn on “Fill with color:” (Picture 12) and select some beautiful colors (Picture 13)!

 

Picture 13: Double X cursor with filled colorPicture 13: Double X cursor with filled colorEven mix colors with overlapping frequency ranges!

 

Picture 14: Overlapping colors in dual Double X cursorsPicture 14: Overlapping colors in dual Double X cursors

More LMS Test.Lab Display Tips:

Comments
Siemens Legend Siemens Legend
Siemens Legend

Great article!  I've noticed sometimes that the double X cursor calculations do not work for large time histories.  When that happens the time data icon is half blue and half red, rather than all blue.

 

  icon.jpg

 

This indicates that more data points are available than the option "Max. number of samples used for calculations.  To adjust:  1) Go to Tools, Options, Data and increase the number shown for "Max. number of samples used for calculations" by adding one or two zeros to the number.  By default, one million data samples are used.  When displaying more than one million data samples the icon will be half blue and half red, and the calculations will not be done unless you move the double X cursors to inlcude less than than one million data samples.   Press Apply or OK.  2)  Refresh the few on the Navigator and the icon should be all blue and your calculations will now work.

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