signal processing

[bikash77]

Anyone please help...

I am trying to detect the cardiovacular abnormality using a PPG signal which has been acquired on Labview using usb DAQ 6009. The signal appears well. But the problem is that I want to process it to get different information about the peak values in the signal. I also am able to get the value of the first peak but there is also a secondary peak in the signal which i am not able to detect the amplitude. I am also attaching the image of the signal, Please if anyone can tell me how to use the labview to process the signal to get the amplitude of the second peak would be a great help in there part.

Regards

Bikash

[DAD]

I don't have much familiarity with the Sound and Vibration tools so I can't say if there's something there that would help.  The peak detect function isn't going to work because you don't really have a peak.  The approach I'd try would be to calculate the slope of the signal for short segments of the waveform (you could try breaking your data in segments of n points and run them through the Linear Fit library function to get the slope).  Your sample has a negative slope that goes almost to 0 then back negative before hitting the bottom. 

[bikash77]

Thanks for your valuable feedback.. I am very new to labview...so can you please suggest me the process of doing the breaking up of the signal.

[aeastet]

I would take your signal and calculate the slope and look for the slope change. It should be apparent when you see the change in the curve as long as these curves a simular over time. are you trying to do this real time?

[bikash77]

Yes I am doing it real time by using a infrared LED and a photo diode to sense the change in the intensity of the light when the finger is placed in between the led and the photo diode...It is the same concept used in pulse oximeter. And I have caculated the slope of the rising end but the falling end is creating problem and am not able to detect that smal peak in the falling edge of the signal. Here I am also attaching the excel file of the real time data of a signal. If can please help to find a solution.

[aeastet]

How big of a window are you using to look for the slope change?

[johnsold]

Try subtracting a straight line which matches the slope on either side of the small peak.  Then you should have a real peak with a zero baseline.

Lynn

[aeastet]

you might get away with double integration of the signal. Look for when it is changing. This is a siple trick that work for me sometimes. Try double integration of the signal and see what the output looks like you should see a couple of big bumps and a small one. You could use a peak detector from there.

[bikash77]

Hey Johnson.. 

I didnt get your question...

I also tried double integrating the signal but the result is coming as a linerly increasing graph in time domain

[bikash77]

Hey Lynn..

Substrating from a straight line will not work as the seconk peak or u can say tht the entire signal which comes is not having the same peak value everytime..substration may work if the waveform is a constant one. But in my case the waveform is the reflection of the volumetric change in our blood when the herat pumps...