FFT Analysis

We have been conducting ride quality testing of a vehicle as per the attached PDF procedure. Now that we have collected the data we need to process it to establish our results.

Whilst it is simple for us to establish the maximum and average results, the "Ride Index" must be calculated using FFT analysis and we're not sure where to start.

Our customer has performed this testing before using alternative software. Before we purchased our Dewe43 we asked them if there was anything else we should know. Their answer was "The Ride index calculations require sampling in the order of 256 Hz, filtered down to 100 Hz to avoid aliasing contaminating the calculated values."

Unfortunately we are working to a very tight deadline so there is little opportunity for us to work out the best way to do this ourselves. We also need to be confident in the results and as new users, that would be difficult. Your assistance would be greatly appreciated.

I have attached our setup file with the test criteria and have also uploaded some sample data to our sharepoint server. This test was not truly representative of the data we will be analysing because it was just around the local streets. However, it will provide an example of the kind of data that we are capturing.

Note that we have seen the acceleration channels are incorrectly set with a scale of 3.0 which will be changed for the customer's testing.

Hi,

if I understand correctly, you need to calculate the Ride Index from the peaks of the FFT spectrum of the channels AccelX, Y and Z.

Using FFT on these signals in DEWESoft will create a vector, that you can display on a 2D graph. But unfortunately you are not able to create a formula that will automatically find the peaks in the spectrum and do math on them. You need to manually find the peaks and access them using {} brackets. In my datafile I added a FFT that has 0.25 Hz resolution and formulas to calculate the ride index of individual peaks and then the total ride index. FFT resolution is calculated with the following formula: Resolution=(Sample rate/2)/ Number of lines.

The data file "rrv0513-59_V2.dxd" is located on our ftp server in the railway folder . I attached some instrustions on how to access it.

I hope this information helps you with your measurement and if you have any more questions we will gladly help you.