Look at the open loop response. What are the ZN open loop settings for this process?
From the open loop response it is possible to evaluate:
Hence the open loop ZN controller settings are:
Now try these settings with different setpoints. Comment on your results.
First try above values at a Setpoint of 0. The response here is quite good with not a lot of oscillation although the process does not return to the setpoint very quickly. This is due to the large reset time which in turn is accounted for in this method by the long delat time (hence undesirable).
However by simply moving the Setpoint to 0.1 it can be seen that the response differs (improves?). Now there is a little more oscillation but this is damped quickly and the process returns to it's setpoint.
At a Setpoint of 0.2 it can be seen that the oscillations increase and the process does not settle out.
From a Setpoint of 0.4 and upwards the process starts to oscillate wildly and the oscillations increase in amplitude until they reach the upper and lower bounds of the process.
Since the response changes when control is added, depending on the setpoint, the controller will have to be tuned using the ZN closed loop method. What controller settings do you evaluate for setpoints of 0, 0.5 and 1.0? Find optimal values for the setpoints above.
This gives a smooth response but does not quite get back to the setpoint quickly enough. Could solve this problem by decreasing the reset time.
These settings show a nice damping effect eventually reaching the setpoint. Need to eliminate the small amount of oscillation by reducing the gain and reset.
There is some oscillation and the response does not reach the setpoint. Again try reducing the above values.
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