Use for example the VI "Derivative x(t).vi" located in the
Analyze>>Signal Processing>>Time Domain palette. The VI processes your
Y(t) array. Remember to enter the dt value (the one you specified for
the Spline interpolation). You can also enter an appropriate initial
value condition to the VI to avoid mis-leading result values at the
beginning, or you can choose to ignore the first few points of your
differentiated result. (same considerations with final conditions
and/or ignoring the last few points)
