Hi Radek,
You can always just use the Trigger and Gate Express VI to break apart your signal into period lengths, and then manually calculate each period by subtracting timestamps from the first element of the waveform and the last. Then, maintain a running index of where you left off, and just iteratively calculate periods and store in an array until you've done the whole signal. Now you have an array of periods to calculate the standard deviation. If the signal's not too clear, use a Filter Express VI to clean it up. Hope this helps!
Jeremy L.
National Instruments
Jeremy L.
National Instruments