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Replicating Specrum Analysis Plots

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Replicating Specrum Analysis Plots

Postby Guest » Mon May 22, 2006 2:36 am

Having purchased a 3424 scope to use mainly as a spectrum analyser I am having trouble reproducing some plots.

I work for a Flight simluator provider and we have to do a vibration analysis to make sure the Simulator is producing the correct vibrational effects for the situation. We borrowed an expensive HP hardware spectrum analyser last year and it is these plots I am struggling to replicate. The Simulator has an three axis accelerometer fitted and according to the scope the signal is about 80 mA at peak.

I am only interested in the 0-32Hz range but as I see it the minimum setting on picoscope seems to be 76Hz. I have been using the *2 function so that only what I'm interested in is displayed. The plots I'm trying to replicate are anotated, Bandwidth; 120mHz, Range; 6dBV RMS; 5. The Y axis is scaled from 100nanoV squared to 1mV squared and anotated 5dB/div.

These plots are then checked against Boeing masters for the appropriate aircraft. The masters are anotated PSD - G²/Hz on the Y axis, is this equivalent to dB on the Picoscope plots?

How can I setup the picoscope software to reflect these conditions?

Postby Guest » Mon May 22, 2006 3:43 am

Whoops I meant the signal was 80mV at peak!

Postby Sarah » Mon May 22, 2006 12:09 pm


Thank you for your email.

I do not think the scale you mention is the same as dB as dB is a logarithmic scale. Unfortunately I do not know anything about the scale you mention however I suspect it may not be logarithmic.

You could change the Picoscope Y axis to Volts through Settings, Options. This may help you in replicating what you are looking for.

Best Regards

Postby enirwin » Wed May 24, 2006 2:52 pm

dB and PSD are not the same, but I don't think it will be too difficult to get PSD. I think you can do it in Excel. The process should be as follows:

Set up the spectrum analyzer to display the frequency range of interest.

Make sure the spectrum analyzer is the active window and select "copy as text" from the edit window.

Go to Excel and select the first cell of your range then pick "paste special" from the edit menu. Select the "paste link" option and make sure that the "display as icon" option is NOT selected. This will paste dynamic links to the PicoScope software that will update automatically. You will have one column for frequency and one column for dB.

In a new column, convert dB to g's using the scaling factor for your accelerometer.

Now you have g's and frequency. From here it should be a simple matter of calculating g2/Hz for each point an plotting vs frequency on a log-log graph using Excel's chart wizard.

Hope this helps.
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