Python code

[dynaman]

Hi guys,

Does anyone have Python code for calculating vibration magnitude and phase shift using a PC sound card?

thanks

Mark.

 

[GregLocock]

no, but a rapid google led me to numpy

import audiolab, scipy
x, fs, nbits = audiolab.wavread(filename)
X = scipy.fft(x)

If you want the magnitude response:

import pylab
Xdb = 20*scipy.log10(scipy.absolute(X))
f = scipy.linspace(0, fs, len(Xdb))
pylab.plot(f, Xdb)
pylab.show()

which all seems jolly relevant to me

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[jimkinney]

Tom Irvine has a Python Blog and a wiki on his Vibration Data website that might be helpful.

http://vibrationdata.wordpress.com/category/python/

http://vibrationdata.com/python-wiki/index.php?title=Main_Page

Good Luck,

Jim

Jim Kinney
Kennedy Space Center, FL

 

[dynaman]

I found that using FFT was quite slow and the results seemed to jump around a lot. My simple approach is to filter the imbalance signal and measure the difference at the zero crossings.

 

[GregLocock]

Time domain filtering has rather lost in popularity to an FFT approach, but if you are after a specific result it is often faster.

For example, real time fast slew rate antinoise systems use time signal filtering, they don't bother with frequency domain.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[dynaman]

Hey guys,

managed to get a simple program to detect phase shift using zero crossings. however I just discovered there is another method called the "wattmeter method". It is more robust from what I understand. Does anyone know how it works and how I could apply it to software code?

thanks

mark.