zmodfb.m

Rotating shafts experience a an elliptical motion called whirl. It is important to decompose this mo

function [Bout,x,y]=zmodfb(y,Fs,NFFT,TD)
%[B,x,y]=zmodfb(y,Fs,NFFT)
%
% compute the forward/backward Campbell/specgtrogram
%
% INPUT:
%	y	(n x 2) each column is measured from a different sensor
%                          ///////
%                          __
%                         |s1|   y(:,1)
%                         |__|
%                          __
%                        /    \    ________|/
%                       |      |   | s2    |/   y(:,2)
%                        \____/    --------|/
%
%    Fs		Sampling frequnecy
%
%   OUTPUT:
%		B 	spectrogram/Campbel diagram
%		x	x-axis coordinate vector  (time or Speed)
%		y	y-axis coordinate vector  (frequency [Hz])
%
%  use:
%		imagesc(x,y,20*log(abs(B))), colormap(jet)
% 	   to obtain a plot
%
% by: 	I. Bucher
% Date	6-Sep-95

if nargin<2, Fs=1000; end
if nargin<3, NFFT=[]; end % i.e. automatic selection of NFFT
[B1,F,x]=specgram(y(:,1),NFFT,Fs);
[B2 ]=specgram(y(:,2),NFFT);
[n m]=size(B1);
B=[flipud(B1-i*B2) ; B1(2:n,:)+i*B2(2:n,:)];
ny=2*n-1; y=([0:ny-1]/(ny-1) - 0.5)*(Fs);
if nargout<1,
    if nargin>3
        surf(x,(y(:)),(abs(((B)))))
        shading interp
          figure(gcf)
    else
   newplot;
   imagesc(x,(y(:)),20*log10(abs(((B)))))
   
   colormap(jet)
   figure(gcf)
end
else,
   Bout=B;
end