Bode stability demonstration in Simulink

I'm trying to create a demonstration of the Bode stability "thought experiment" using Simulink. What I'd like to do is have an input to an open-loop feedback control system be a sine wave, then some time later have that input changed to a constant value and the loop closed.

Any thoughts on how to do this?

Answer 1

[Swarooph]

Have you thought about using something like a switch? Have a look at this demo 'sldemo_zeroxing' that shows input changing as a function of simulation time. You could use a similar switch to make the open loop/closed loop connections.

Another approach could be to use an enabled subsystem:

http://www.mathworks.com/help/releases/R2011b/toolbox/simulink/ug/f4-84107.html

Answer 2

[Robert]

Thanks for your suggestion. Adding switches allowed me to do exactly what I wanted. Thanks!

[maamouri maamouri]

please can you help me how to analyse the stability of a model using simulink ( wich block you used ???)

thank you