Add power spectra to a colormap

[HansL]

Hello,

I am trying to append data to a colormap (sound and vibration toolkit), so I can make measurements over a long period > 300 seconds. The input data for the colormap is a power spectra. My first thought was to make a shift register for the data, but there seems to be no way to split the data into time and a power spectrum .

Hans

[RikPrins]

could you maybe illustrate this issue with a small example?

Regards,

RikP - National Instruments Applications Engineering

[HansL]

The idea is to make a transient vibration measurement of a diesel engine, which steadily increases the rpm over a couple of minutes. In order to do this a multiple Fourier transformation can be done with the STFT vi which gives a power spectra to a colormap (as shown in the picture below). This works for short time domains like 10 seconds, but doesn’t work for a measurement time of 4 minutes.

Ideally the power spectra is written/appended to the colormap every second (visually).

I tried to append data with a shift register, which works for a simple graph, but couldn’t get it working for the power spectra.

Regards,

Hans

[falkpl]

This should work, I have essentially done this like the following:

for t=0 to T1

     Take FFT.

      Take Histogram (or sum of power inside) of fft (bin into frequency bins)- you will now have some more descrete version of the fft

      Autoindex histogram out of loop.

You will have a 2d array with total power inside of a frequency bin on y axis and time on the Z axis.

Remember that the intensity map of this will be whibed out by large dynamic ranges so you might have to use a log Z scale or normalize the data in some other way.

Paul