vibration!

[jeff_scharpf]

Hi!

I'm finally starting to dig into our Sound and Vibration toolkit and I love it!

Doing sound pressure level, 1/3 octave, everything looks great.

Trying to do vibration. I put in a 1g (9.8 m/s^2) 250 HZ standard signal from a vibration calibrator, I get the correct RMS value, around 10 m/s^2.

Now, I try to put this into a 1/3 octave vi and I get some resulting graph and number that looks 10 times what it should be. I'm thinking maybe this vi is expecting dB rather than units of m/s^2????

I tried changing the option "dB On" to False, and that didn't help.
Is it valid to send vibration data into the ocatve analysis vi?  Am I doing something wrong?

I should see a bar graph with the octave band near 250 HZ up around 10 m/s^2, and the other bands very low. Well, it picks out the correct freqency band but puts it at over 100..

Any ideas?

Jeff

[Brian F.]

Hello Jeff.

Thank you for posting to the NI Discussion Forums. 

I am glad to hear that you like our Sound and Vibration Toolkit.  It certainly does make for some cool applications.

In terms of your question, I would recommend checking out a very cool example program in our NI Example Finder.  The NI Example Finder can be launched from the Front Panel or the Block Diagram by clicking on Help>>Find Examples.  You will then see a directory structure in the window that is launched.  Please click on Toolkits and Modules>>Sound and Vibration>>Analyzing and Processing Signals>>Octave Measurements>>SVXMPL_Third-Octave Analysis(Simulated).vi. 

This program allows you to scale the measurement to literally any scale via the 'SVL Scale Voltage to EU' VI.  This VI includes as its input, a channel info cluster that is on the bottom left of the front panel.  One of the controls in the cluster is 'engineering units.'  If you click on the white space of the control, about 20 different units will come up: one of which is m/s^2.  So, if you connect your original signal to the input of the 'SVL Scale Voltage to EU' VI, the output should be in m/s^2 and then this can be processed by the Octave VI. 

Let me know if this clears everything up for you. 

Have a great day!

Brian F
Applications Engineer
National Instruments