Re: Envelope Theorem

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Posted ByJosé Antonio on August 13, 2002 at 10:41:27:

In Reply to: Re: Envelope Theorem posted byDuncan Carter on August 12, 2002 at 22:44:32:

Hi again.
Let me explain what I've done until now. We're developing a system for testing rotary machines (specifically alternators and starters on a vehicule). I have captured my signal using an accelerometer and pass it to a DSP board. With this signal, I've calculated the envelope of it (using Hilbert transform) and calculate the FFT.

Comparing this spectrum with the spectrums on your papers,they're totally different. I use the method you told me, but the signal turn's very "soft"...I mean, you can't see any peaks when you analize an alternator with bad bearings.

Do you think there's any alternative method to use with my Hilbert's Transform in order to get the results we're expecting?.

Greetings.
José Antonio S.

: : Well..the machine rotates at 4200 RPM, then the frecuency will be of 70Hz.
: Something like 8 kHz for the center frequency of the band pass filtered signal before demodulation would be appropriate.
: Duncan

: :
: : Greetings.
: : José Antonio S.

:
: : : What is the rotating frequency of the machine shafts that you are using?

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Comments:: Hi again. : Let me explain what I've done until now. We're developing a system for testing rotary machines (specifically alternators and starters on a vehicule). I have captured my signal using an accelerometer and pass it to a DSP board. With this signal, I've calculated the envelope of it (using Hilbert transform) and calculate the FFT. : Comparing this spectrum with the spectrums on your papers,they're totally different. I use the method you told me, but the signal turn's very "soft"...I mean, you can't see any peaks when you analize an alternator with bad bearings. : Do you think there's any alternative method to use with my Hilbert's Transform in order to get the results we're expecting?. : Greetings. : José Antonio S. : : : Well..the machine rotates at 4200 RPM, then the frecuency will be of 70Hz. : : Something like 8 kHz for the center frequency of the band pass filtered signal before demodulation would be appropriate. : : Duncan : : : : : : Greetings. : : : José Antonio S. : : : : : : What is the rotating frequency of the machine shafts that you are using?

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