Poincare Map

[Darin.K]

Good answer, sounds like a 'real' project not a contrived homework assignment.

Being a driven system changes things for me a little bit.  You can imagine your measurement as watching your oscillator with a strobe light which fires at the same frequency as you are driving the oscillator.  If you are driving a fundamental mode, then the oscillator will appear to stand still, at other frequencies it may appear to undergo a slow oscillation, or there may be chaos.  Your strobe light is the displacement measurement.  What you need to figure out is how to trigger that measurement.  I don't know what type of shaker you have, but I'd try to put an accelerometer on it to get the drive frequency and use as a time reference.  As to what phase of the drive you choose to sample, that is determined by a delay equal to some fraction of the drive period.

For example, you could detect an extremum of the drive (acceleration changes sign), what half of a period, and then sample with frequency equal to the drive frequency.

---

[Arthuruuuuuu]

Sorry Ben,

I have done exactly the same on you recommended me but i cant find Phase Locked in the "ctrl+space" options.

[Ben]

It is part of the Modulation Toolkit.

A cut-n-paste of the help reads..

"

Attempts to track the unknown phase of an input complex exponential tone by means of a feedback control system. At steady state, when the phase-locked loop (PLL) has acquired a lock to the input signal, the PLL estimates the offset of the input signal carrier phase and carrier frequency from the reference phase and frequency. The polymorphic instances of this VI accept either a complex baseband waveform or a real passband waveform.

Use the pull-down menu to select an instance of this VI.

"

I hope that helps,

Ben

[Arthuruuuuuu]

Hey Darink, sorry to be late. 

Here are attached my main VI and Sub VIs i am using.

as you can see, I am acquiring 4 signals (displacement, voltage, force and acceleration). 

To plot the Phase Space, i use the derivative tool of labview to get the tip velocity and plot toguether with displacement. 

To plot the Poincare section now, i have to divide the period in a integer number (N) and store (save) position and velocity every time my N is set.

Have a look and tell me how can you help. Thanks a lot,

Arthur.