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 | | From: | Barp | | Subject: | Re: verify transfer function | | Date: | Thu, 20 Jan 2005 16:40:55 -0600 (CST) |
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 | Hi,
Before I answer, let me review something here, so we are talking=
the same thing. To be able to simulate continuous systems in a computer, w=
e use differential equation solvers that numerically try to come with a sol=
ution for the equation. These techniques are easily encounter in the litera=
ture, but, in general you would see solvers that are fixed step size, as Ru=
nge-Kutta 1 (Euler) which is a single-step explicit
Runge-Kutta ODE solv=
er of first order, or variable step size, as Runge-Kutta 45 which is a sing=
le-step explicit Runge-Kutta ODE solver of fifth order, which uses the Dorm=
and-Prince coefficients.
In Simulink, you don't need to specify dT b=
ecause it uses an algorithm to identify those coefficients "auto". Also, th=
ey have the variable step size as defaut. In the case of the Advanced Contr=
ol Vis, those are VIs that are ONLY based on the Runge-Kutta 1 (Euler) Inte=
grator, and it needs also the dT, since it does not calculate this paramete=
r for you.
The best guess for dT CAN NOT be only twice the sampling=
time, because the Euler Integrator will only have 1 point to calculate the=
derivative and if try to apply a signal with sharp corners, must probably =
you will be unstable. The dT must by much higher (than the dynamic of the s=
ystem and, in general, 10 times is good enough.
If you are really lo=
oking to simulate dynamic system in LabVIEW, you should look into the Simul=
ation Module. It allows similar functionality as Simulink and also allows y=
ou to choose Variable Step size for the integrator. Look into: http://www.n=
i.com/realtime/control_design.htm OR http://sine.ni.com/apps/we/nioc.vp?cid=
=3D13852&lang=3DUS for more information about this and other new tools for =
Control Design and Simulation in LabVIEW.
Hope this help. If not, fi=
ll free to reply back.
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