Creating a proper vibration analysis tool with Vibration Assistant

[GFantuzzi]

Hello,

I am new to labview here and have been trying to set up a proper vibration analysis test set up. I have a PCB triaxial accelerometer that outputs voltage per g to a DaqPad 6016.  I have gotten a hold of the Sound and Vibration Toolpak and have been trying to set up a proper program with the Assistant that can evaluate my acceleration vs the frequency.  My goal is to measure vibrations in a rotating impeller that spins upwards 60krpm and determine if there is any knocking or vibrational modes. 

Anyway I believe what I want to use (correct me if I am wrong) is a Power Spectrum (linear, peak-to-peak, RMS averaging) to see the amplitudes at each frequency.  However, I am unfamiliar with the proper sampling rate and number of samples to read.  These variables will change my Power Spectrum graph correct? Also will the units of the power spectrum graph, if I create a proper scaling factor through the daq (according to my sensors sensitivity) be indeed "g"?  I must admit I need to teach myself the fundamentals of the power spectrum and the FFTs, but am pressed for time. 

Can someone help explain how to set up the proper program on the Sound and Vibration Assistant for my needed measurements?  Perhaps I shouldn't be using a Power Spectrum at all for my frequency response?  Also how to I figure out the appropriate sample rates and number of samples as to have consistent and correct data?

Thanks!!

G

[Jake_H]

Hello,

You should be able to create a voltage task with a DAQmx acquire step and then add a custom scale to convert to g's. As for sampling rate and samples to read, you will want to pay attention to the Nyquist Theorem and Aliasing when setting your sample rate and samples to read. Typically, you will want to set your samples to read value to about 1/10 of the sampling rate.

The Power Spectrum step will calculate the signal's power within a certain frequency by using an FFT. The Sound and Vibration Assistant also has a Frequency Response step that will look at the spectrum as a response of an input stimulus. If you're looking for a more detailed explanation of the two, you can look at the SignalExpress Help documentation or the examples folder in SignalExpress Help » Open Example » Sound and Vibration Assistant.