On Off Control 2 Poles
One of the simplest nonlinearities occurs in on off control. The applet below shows a second order system with on off control illustrating
the cycling of the output.
In this case there are 2 time constants 1/a and 1/b.
Compared with the first order system, the second order system can overshoot the
set value and this occurs here also.
When controlling these systems a and b are usually fixed
and control is achieved by the changing the upper and lower levels Ul and Ll to get an
acceptable frequency and amplitude of the on off cycling. However to control
the overshoot, L may also have to be adjusted.
Gif image below shows how applet should appear.
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COPYRIGHT © 2006 Cuthbert Nyack.