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LMS Test Lab Impact Testing

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Hello, 
I have done an experimental modal analysis on a beam.
For this analysis I have showen the frequecy band [0 1600Hz].
For this, I find the FRF functions in this frequency band.

 

 

3.png

 

But, now I want to inlarge the frequency band (for exemple [0  2560 Hz]) .

I don't know how to change it .
Is there anyone that can help me to change the bandwitdh without repeating the measuring test.
Thank you a lot, 
Best regards, 
Asia

 

 

2 REPLIES

Re: LMS Test Lab Impact Testing

Hi Asia,

Can you go to Impact Testing->Impact setup workbook->bandwidth minor worksheet, you should see the bandwidth there:

Picture1.jpg

 

If the bandwidth is 1600hertz here or go to Navigator, select a FRF measurement right click->Properties..->Details to look for sample frequency.  If the sample frequency is 3200 hertz, I'm sorry to tell you, you must recollect the data, and adjust the bandwidth to higher frequency before measuring the FRFs.

 

If you didn't acquired data in higher bandwidth in the beginning, we cannot create higher bandwidth frequency data after the measurement.

 

Hong

Re: LMS Test Lab Impact Testing

[ Edited ]

Hello,

 

If you measured FRF data to a Bandwidth of 1600 Hz, you can process that data to 80% of that bandwidth because 80% of your data is alias free.  To increase the modal analysis to a higher frequency, you need to have FRF data to that frequency (that is alias free).  To calculate modes to 2560 Hz for example, you would measure FRF data to a Bandwidth of 3200 Hz or a Span of 2560 Hz.

 

Kevin