how to measure frequency from offline data?

[taslim.reza]

Hi!

I have to measure frequency of a signal. The signal is saved for a specific time duration. Is it possible to measure frequency of a signal using offline data? If so, how to do it?

Thanks at advance.

[PeterFoerster]

I would say, you can do the same thing you would with online data. Detect two positive or two negaitve edges, measure the time and invert.

[taslim.reza]

If you could provide any example VI, it would be great help. Thanks.

[PeterFoerster]

Where do you still have problems? What format is your data in? 

[Henrik_Volkers]

Why not post a data slice ?

Ah, and the (sub) vi to save it, or a description of the data type.....

... and the expected  output you are looking for.....

[taslim.reza]

Hi

Plz see the VI. I tried to calculate frequency using this way. The 1st column of the spreadsheet data is time, 2nd is EMG and 3rd is ECG.

Thanks at advance.

[crossrulz]

What do you want to take the frequency of?  I'm guessing the ECG since I actually see periods in it.

What you will want to do here is go through your data with a FOR loop and find where the ECG goes above a threshold (probably 0.1 in this case).  Get the times when this transition happens.  Now you just subtract the current threshold time by the previous threshold time.  That will give you a period in seconds.  Just use the Reciprical function to get the frequency.

[taslim.reza]

Hi @crossrulz ! At first I would like to congratulates you for being knight of NI. Thank you for your reply. I need to measure the frequency of EMG. I understood your point but I have no idea how to do it.... It would be great help if you would help me a bit to do so... thanks again....

[Bob_Schor]

What do you know about analyzing "signals" in sampled data?  Do you know about the relationship between sampling frequency, number of points, and how these affect the ability to estimate the frequency content of the underlying data?  Do you know what an FFT is?  What do you know about the quality of the signal you are trying to analyze?  For example, how precise is the time interval between the samples?  The data that you are showing in your example, for example, do not seem like precisely even samples.

Bob Schor