Accelerometer Analysis - Frequency vs Time Domain Integration

[Ryan1234]

I am looking for some assistance on vibration analysis.  I am trying to integrate an accelerometer signal to get the velocity.  I am integrating the signal in the time domain and also in the frequency domain.  After the integrations I am plotting the FFT's to compare the results and the two results are significantly different.  I am trying to integrate a signal produced by an accelerometer calibrator and so I know the correct output I should be getting.   I am getting the correct result when I integrate in the frequency domain, but not in the time domain.  I would appreciate it if anyone could lend some insight into this problem.

Ryan

[preston_johnson]

What analysis VIs are you using?  The Sound and  Vibration has some nice and well tested time series integration functions

[Ryan1234]

I am using the Sound and vibration library.  I am very far from being an expert in this area though so I could very easily be missing something.  I have attached my program below along with a sample data file.  The accelerometer calibrator signal provides a 10 m/s^2 rms signal at 159.2 hz. 

[johnsold]

Ryan,

The integral of the Fourier transform is not equal to the Fourier transform of the integral, so I would expect the result you indicated in your original post.

I do not have the SVT toolkit so I cannot look at your VI.

Lynn

[Ryan1234]

Lynn,

That makes sense. 

I am using some functions from the SVT toolkit though, that are supposed to integrate acceleration to velocity and not just blindly integrate the raw data.  I had assumed that the information after the two integrations should be the same, just in a different format.   Since I can't show you my program it may be hard for you to comment but do you still think that the results should be different assuming the integrations are operating correctly?

Ryan

[johnsold]

Ryan,

I do not have enough information to venture an opinion. You'll have to find someone with the toolkit.

Lynn

[Ryan1234]

Lynn, thanks anyway.  I appreciate any help I can get.

Ryan