Reply by maury ●January 22, 20082008-01-22
On Jan 22, 9:35&#4294967295;am, "djt740" <djt...@hotmail.com> wrote:

> >On Jan 21, 9:53 am, "djt740" <djt...@hotmail.com> wrote:
> >> I'm wondering if you can be of some help to me.
> >> I currently have two waveforms,waveform1 and waveform2 that I'm
> reading
> >> from my oscilloscope into Matlab. I want to find the times in
> waveform2
> >> that a match for waveform1 occurs. I want a 'correlation spike' to
> occur
> >> in my resultant waveform every time Matlab finds a match for waveform1
> in
> >> waveform2.However at the moment this is not occuring. Does the xcorr
> >> function not achieve this functionality?Thanks for any help
> >> Regards
> >> Djt
> >> So far my code is as follows
> >> %%%%%%%%%%%%%%%%%%%%%%%
> >> Firstly open the figure files
>
> >> open waveform1.fig
> >> open waveform2.fig
>
> >> Then read the x and y data fields from each figure...
>
> >> figure(1)
> >> x1=get(findobj(gca,'type','line'),'xdata');
> >> y1=get(findobj(gca,'type','line'),'ydata');
> >> figure(2)
> >> x2=get(findobj(gca,'type','line'),'xdata');
> >> y2=get(findobj(gca,'type','line'),'ydata');
>
> >> finally you can correlate the two Y data sets...
>
> >> cordat=xcorr(y1,y2)
> >> Plot(cordat)
>
> >I don't see anything obviously wrong with your code, just keep in mind
> >that the peaks produced by cross correlation can be relatively broad,
> >so maybe you are looking for a spike, what you want is the lump.
>
> >Chris
> >Chris
>
> Hi Chris,
> What to you mean by 'the lump'?At the moment when I plot the xcorr result
> I get a continuous waveform of varying amplitude.I was expecting a spike
> to occur only when it finds a match in waveform2 for waveform one
> Thanks for your help
> Djt
>
>
>
> - Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -


I suspect your data is sinusoidal.  Find the correlation of sin(wt)
and cos(wt), also autocorrelation of sin(wt), and cos(wt).  Look at
what you get.  That might answer your question.

Maurice Givens
Wright College, Chicago
Reply by djt740 ●January 22, 20082008-01-22
>On Jan 21, 9:53 am, "djt740" <djt...@hotmail.com> wrote:
>> I'm wondering if you can be of some help to me.
>> I currently have two waveforms,waveform1 and waveform2 that I'm

reading

>> from my oscilloscope into Matlab. I want to find the times in

waveform2

>> that a match for waveform1 occurs. I want a 'correlation spike' to

occur

>> in my resultant waveform every time Matlab finds a match for waveform1

in

>> waveform2.However at the moment this is not occuring. Does the xcorr
>> function not achieve this functionality?Thanks for any help
>> Regards
>> Djt
>> So far my code is as follows
>> %%%%%%%%%%%%%%%%%%%%%%%
>> Firstly open the figure files
>>
>> open waveform1.fig
>> open waveform2.fig
>>
>> Then read the x and y data fields from each figure...
>>
>> figure(1)
>> x1=get(findobj(gca,'type','line'),'xdata');
>> y1=get(findobj(gca,'type','line'),'ydata');
>> figure(2)
>> x2=get(findobj(gca,'type','line'),'xdata');
>> y2=get(findobj(gca,'type','line'),'ydata');
>>
>> finally you can correlate the two Y data sets...
>>
>> cordat=xcorr(y1,y2)
>> Plot(cordat)
>
>I don't see anything obviously wrong with your code, just keep in mind
>that the peaks produced by cross correlation can be relatively broad,
>so maybe you are looking for a spike, what you want is the lump.
>
>Chris
>Chris



Hi Chris,
What to you mean by 'the lump'?At the moment when I plot the xcorr result
I get a continuous waveform of varying amplitude.I was expecting a spike
to occur only when it finds a match in waveform2 for waveform one
Thanks for your help
Djt

>
Reply by Rune Allnor ●January 22, 20082008-01-22
On 21 Jan, 15:53, "djt740" <djt...@hotmail.com> wrote:

> I'm wondering if you can be of some help to me.
> I currently have two waveforms,waveform1 and waveform2 that I'm reading
> from my oscilloscope into Matlab. I want to find the times in waveform2
> that a match for waveform1 occurs. I want a 'correlation spike' to occur
> in my resultant waveform every time Matlab finds a match for waveform1 in
> waveform2.However at the moment this is not occuring. Does the xcorr
> function not achieve this functionality?Thanks for any help
> Regards
> Djt
> So far my code is as follows
> %%%%%%%%%%%%%%%%%%%%%%%
> Firstly open the figure files
>
> open waveform1.fig
> open waveform2.fig


Why do you load .fig files? Why not load raw data?

Rune
Reply by Chris Maryan ●January 22, 20082008-01-22
On Jan 21, 9:53 am, "djt740" <djt...@hotmail.com> wrote:

> I'm wondering if you can be of some help to me.
> I currently have two waveforms,waveform1 and waveform2 that I'm reading
> from my oscilloscope into Matlab. I want to find the times in waveform2
> that a match for waveform1 occurs. I want a 'correlation spike' to occur
> in my resultant waveform every time Matlab finds a match for waveform1 in
> waveform2.However at the moment this is not occuring. Does the xcorr
> function not achieve this functionality?Thanks for any help
> Regards
> Djt
> So far my code is as follows
> %%%%%%%%%%%%%%%%%%%%%%%
> Firstly open the figure files
>
> open waveform1.fig
> open waveform2.fig
>
> Then read the x and y data fields from each figure...
>
> figure(1)
> x1=get(findobj(gca,'type','line'),'xdata');
> y1=get(findobj(gca,'type','line'),'ydata');
> figure(2)
> x2=get(findobj(gca,'type','line'),'xdata');
> y2=get(findobj(gca,'type','line'),'ydata');
>
> finally you can correlate the two Y data sets...
>
> cordat=xcorr(y1,y2)
> Plot(cordat)


I don't see anything obviously wrong with your code, just keep in mind
that the peaks produced by cross correlation can be relatively broad,
so maybe you are looking for a spike, what you want is the lump.

Chris
Chris
Reply by djt740 ●January 21, 20082008-01-21
I'm wondering if you can be of some help to me.
I currently have two waveforms,waveform1 and waveform2 that I'm reading
from my oscilloscope into Matlab. I want to find the times in waveform2
that a match for waveform1 occurs. I want a 'correlation spike' to occur
in my resultant waveform every time Matlab finds a match for waveform1 in
waveform2.However at the moment this is not occuring. Does the xcorr
function not achieve this functionality?Thanks for any help
Regards
Djt
So far my code is as follows
%%%%%%%%%%%%%%%%%%%%%%%
Firstly open the figure files
 
open waveform1.fig
open waveform2.fig
 
Then read the x and y data fields from each figure...
 
figure(1)
x1=get(findobj(gca,'type','line'),'xdata');
y1=get(findobj(gca,'type','line'),'ydata');
figure(2)
x2=get(findobj(gca,'type','line'),'xdata');
y2=get(findobj(gca,'type','line'),'ydata');
 
finally you can correlate the two Y data sets...
 
cordat=xcorr(y1,y2)
Plot(cordat)