peak counter separator

[jayberns]

Hi,

I'm conducting an experiment using a Michelson Interferometer, which detect peaks that corresponds to the laser's (light source) wavelength. This is a good setup for measuring amplitude of vibration. Using a photo detector, the Intensity versus time graph shows a group of sine waves if the moving object moves approaching the the beam and another group of sine waves shows when the object moves away from the beam. Between those two group waves is called the turning point which separates them, it is identifiable. I want to count the number of peaks in a single group wave, and separate the counted peaks of the other group. What shall I do to detect the turning points so that only the peaks of the group waves will be counted? A sample output seen in an oscilloscope is shown in the attached file. And a little background of the experimental setup to explain things is also attached here. I'm new to using Labview software, and I really need help on this. Can somebody create a sample program so that I can base my program on it?

Thank you very much

[TMC-NI]

Hi Jay,

So, this is very much a niche application, but I will do my best to help you.  First lets look at this on a high level before we delve into LabView code.  You say that the turning point is detectable.  Well, it is detectable to the human eye here mostly because the waves are symmetrical, and at the point at which the symmetries converge is the turning point, naturally. 

So, we need to detect this point, count the number of peaks, and subtract the turning points from the peaks.  In order to do this, you will need to perform some sort of a symmetry test in LabView.  I do not know how many results will have continuous traverses of the mirror back and forth, so I do not know how many symmetrical graphs you will have. 

If we know the number of symmetrical graphs, then we can perform peak-to-peak measurements of the data, match them up to a particular tolerance, and the largest peak-to-peak measurement should have the turning point between it. 

However, before we start that, my best advice to you right now is to use a few online tutorials on how to use DAQ to gather data first. 

This is an excellent source of NI-DAQ information.

Getting Started with NI-DAQ Software

I highly reccomend the first link, the Learn 10 Functions in NI-DAQmx and Solve 80% of Data Acquisition Applications that is very valuable to gather data.

After you are able to get your data to show up in a graph or a chart, then, you will probably want to do some peak measurements.  This seems to be a fairly involved project, especially since you are starting out, so if you can get the data to display in a graph, that may be the best first step to take.  After that, let us know on this thread and we can progress a little further each step.  I think creating an example program at this point would be very much like trying to drink out of a waterhose.