A further reflection on this 'saga' led me to take a second look at the simulations I've so far done on this problem.
Taking the steps outlined in my preceding post I obtain the first step response shown as an attachment.
Then I applied the Z-N heuristic approach of disabling the integral term in the PI block and 'winding up' the proportional gain until a steady-state oscillation is obtained.
Per the prescribed heuristic methodology I note the required gain to achieve oscillation [Ku] and the actual period of oscillation [Pu]
From these I derive the estimated values [per the literature] of
Kc=Ku/2.2=0.253/2.2=0.115
&
Ti=Pu/1.2=0.23/1.2=0.192 sec
Plugging these values into my simulation I obtain the second slightly less oscillatory response.
It's worth noting this distinction - I would suggest the Z-N method based on the second 'heuristic' approach produces a slightly 'better' response than the 'formula' method.
Taking the steps outlined in my preceding post I obtain the first step response shown as an attachment.
Then I applied the Z-N heuristic approach of disabling the integral term in the PI block and 'winding up' the proportional gain until a steady-state oscillation is obtained.
Per the prescribed heuristic methodology I note the required gain to achieve oscillation [Ku] and the actual period of oscillation [Pu]
From these I derive the estimated values [per the literature] of
Kc=Ku/2.2=0.253/2.2=0.115
&
Ti=Pu/1.2=0.23/1.2=0.192 sec
Plugging these values into my simulation I obtain the second slightly less oscillatory response.
It's worth noting this distinction - I would suggest the Z-N method based on the second 'heuristic' approach produces a slightly 'better' response than the 'formula' method.
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