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Envelope Detction for Signal Analysis


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Envelope Detction for Signal Analysis



Computes the envelope of the signal by two methods: 1.LPF method 2.Hilbert Transform

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y=envelope(Signal,Fs) computes the Envelope of the input Signal with a Sampling Frequency 'Fs' and gives the envelope signal by Hilbert transform method as the output y.
The function computes the envelope of the signal by two different methods.

First Method: By Using Low Pass Filter. The Signal is Squared, passed
through LPF and then taken square root.
Second Method: Using Hilbert Transform. Hilbert Transform is taken using the inbuilt function in Matlab

The Function Displays the FFT of the original signal and also the FFT of
the envelope signal by both the methods

The function basically is for computing Envelope Signal for Condition Monitoring of rotating equipments by vibration based bearing fault diagnosis.


The File 's4.mat' is the vibration signal recorded from a OR faulty
bearing with a sampling frequency of 12000Hz. The Fault frequency is 161Hz and is brought out in envelope signal which was hidden in the original FFT.

Don't forget to rate or comment on the matlab central site

Author:Santhana Raj.A

Required Products Signal Processing Toolbox
MATLAB release MATLAB 7.13 (R2011b)
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Comments and Ratings (9)
12 Jun 2014 Santhana Raj


Yep. U guessed right. The shaft speed is about 29Hz.

Thanks for Rating.

06 Jun 2014 Chintan

Hi Santhana,

Very nice code and good example. I just have one question. The other spike at 29.3 Hz, does it correspond to shaft speed?

Many thanks.


08 Mar 2014 Ruiyan

good, can be used normally.thanks very much.

08 Jun 2013 Theodoros  
10 Dec 2012 ahmed albakri

Hi friend , thank you very much

05 Aug 2012 g├╝lsevin  
19 Jul 2012 n chow  
19 Jul 2012 Santhana Raj

@Jan Simon

True, This is just a demonstration of the two methods. Who would want to use different methods when one's ultimate aim is to do some envelope detection.

I thought it would be easier, as any one can compare the methods for their application and use the code from the program by coping those set of lines and reusing them in their main code.

18 Jul 2012 Jan Simon

"clc; close all;" is not a friendly idea. Why do you want to close my figures?

This function cannot be used to create the envelope directly. It is more a demonstration of the two different method with harddoced coefficients, creation of figures and overwriting the output y repeatedly. So before a user can calculate the envelopes matching to a specific problem, substantial re-programming is required.

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