convert displacement to acceleration

[MiamiVipul]

Hello:

I am using Labview 7.1 and Vibration toolkit to collect data with two displacement sensors. The eddy-current type displacement sensors collect displacements in two perpendicular directions. I need to produce the power spectrum of the vibrations using these displacement signals. I was trying to find an example that convert displacement to acceleration, but almost everything I found are in the reverse direction, as acceleration been common to vibrations. I have attached my VI (with a sub-vi) that I'm using to collect displacement and I need to show power spectrum. Currently, I have connected displacement directly to Spectrul Measurement Express VI. Can you please show how I can use double differentiation to get acceleration. Again, please post in Labview 7.1.

Thanks a lot.

Vipul.

[Jennifer O]

Hi Vipul,

There are signal processing VIs which perform integration.  I am attaching a simple example that takes a signal (square wave in the example) and integrates it twice.  It displays 3 signals, the original, the integrated, and the second integral. 

Regards,

Jennifer O.
Applications Engineer
National Instruments

[MiamiVipul]

Dear Jennifer:

I'm collecting displacement and I need to find the acceleration. According to your posting, I'm not sure how I get acceleration by integration. I believe I need to do a double differentiation to find the acceleration.

Someone at NI Tech Sympo today (in Cincinnati) told me that I can do it but I may run into problems with noise. Do you know of any examples that can guide me to get acceleration from displacement signal.

Thanks a lot.

Vipul.

[Jennifer O]

Hi Vipul,

I apologize for my error in posting Integration.  The same method can be adapted for double differentiation, simply replace the two Integral x(t) functions with derivative x(t) functions.  You may need to ignore the first and last samples since they will spike without reference of what the previous/next sample is.  This can be addressed with inputs for initial and final condition.  Refer to the LabVIEW help for more information on the derivative x(t) function. The following might also help you get started: How to Take a Derivative in LabVIEW.

Regards,

Jennifer O.

[MiamiVipul]

Dear Jennifer:

Your comments and the link will definitely help me in getting a head-start.

Thanks a lot.

Vipul.