power density spectrum

[edfritsch]

I am using strain gage accelerometers to collect X, Y and Z axis acceleration data on separate channels as a means of quantifying vibration in the cab of an off-road motor vehicle.  Using the DASYLab "formula module" I have scaled the output of the accelerometers to read directly in gs, i.e. 32 ft/s/s = 1 g.

If I use the DASYLab "fft module" to provide a power density spectrum for a g vs time waveform generated by one of my accelerometers, what are the y scale units that are delivered by the "Y/t chart module"?  I know the x scale units in the chart are Hz.

I am trying to produce a data display figure that has the same format as power spectral density data presented in the figures in Mil-Std-810G Method 514.6 Annex C.  That document presents sprectral data in the form of curves of (g^2)/Hz vs frequency.

So far none of the data I've collected in my vehicle, looks anything like the data shown in the in the mil spec.

[MHa]

Hello,

you would like generate this type of visualization?

Best regards,

MHa

[edfritsch]

Here is an example of the type of figure I'm trying to generate from X (longitudinal), Y(transverse) and Z(vertcal) accelerometer data.  I have client who wants to use accelerometers to make physical measurements of the vibrations in the cab of an off road vehicle, and my client wants the data I collect protrayed in the same form as the following chart which comes from the mil spec.  The figure below is an example from the mil spec  The data I have is X, Y, and Z acceleration vs. time data.  I'm looking for the tool or method or combination of tools and methods that will get me from the data I have to a chart like the one shown below.

[BROhan]

Hi edfritsch,

I was wondering what hardware you were using to take these measurements in DASYLab. Could you please let us know?

[edfritsch]

I've used an Iotech DAQBOOK/200 connected to the Dell computer through a network connection to manage data collection.  An Iotech DBK 43A amplifier conditioned signals from my three accelerometers (3 separate Sensotec 060-F482-0).

I’ve logged data at 2000 samples/sec and 5000 sample/sec with similar results.  Data logging was accomplished using DASYLab 8.0 data acquisition software.

I'm still looking for an answer to my original question which was "What are the Y-axis units on the power spectral density plot that the DASYLab FFT module produces?" 

[CJ_Butler__DASYLab_Pro]

When you select the Power Density Spectrum function in the FFT (Real FFT of a Real Signal), the Unit changes to (#0 * #0) / Hz

This notation means that it will take the incoming unit, noted as #0, and the outgoing unit is that unit squared / Hz.

If the incoming unit is g, then g^2/Hz is the unit of the computed signal.

You can get DASYLab to display the unit, by going to the Y/t Chart Display window, select the Display menu, Window, Display Y Unit.

[edfritsch · Accepted solution]

Thank you for reading the question I asked, considering it and answering that question instead of going on about some other marginally related topic. I sincerely appreciate your knowledge and your willingness to share it.