Settings for controls

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G. D. Anderson s article recommends initial controller settings for those control loops set on automatic rather than manual for a plant startup. For liquid level, the settings depend upon whether the sensor is a displacer type or differential pressure type, or a surge tank (or other surge) is installed in the process ... 

Control problem Given the system parameters, the control problem is to determine the controller settings for K, T and T. This will be undertaken using the Zeigler-Nichols process reaction method described in Section 4.5.5(a). 

With another drive (such as a turbine), with control set for constant-speed operations. 

Obtain the process reaction curve for the process with disconnected controller, as explained in Sec. 2.3.3. Analyse this curve to obtain the parameters for the Ziegler-Nichols Method. Use Table 2.2 to obtain the best controller settings for P and PI control. Try these out in a simulation. 

Example 5.7B What would be the PID controller settings for the dye mixing problem if we use IMC-based tuning relations ... 

Determine the open-loop response of the output of the measuring element in Problem 7.17 to a unit step change in input to the process. Hence determine the controller settings for the control loop by the Cohen-Coon and ITAE methods for P, PI and PID control actions. Compare the settings obtained with those in Problem 7.17. 

The Bode plot of is given in Fig. 13.20 for D = 0.5. The ultimate gain is 3.9 (11.6 dB), and the ultimate frequency is 3.7 radians per minute. The ZN controller settings for P and PI controllers and the corresponding phase and gain margins and log moduli are shown in Table 13.2 for several values of deadtime D. Also shown are the values for a proportional controller that give +2-dB maximum closedloop log modulus. 

There are a couple of simple empirical approaches for estimating the optimum controller settings for a particular process. Both approaches require data on the response of the existing process to simple stimuli one the open-loop response to a step the other the behavior of the closed-loop at the condition of ultimate gain. 

IV.45 Select the controller settings for the PID controller of the feedback loop shown in Figure PIV.3b. Use the Cohen-Coon tuning technique. In a graph paper display the actual process reaction curve and its first-order plus dead time approximation. 

Figure 3 Approximate contour plots of optimal proportional controller settings for consecutive reactions (from Millman and Katz [13]).

Controllers with non-adjustable parameters are not well suited to extrusion operations where changes in temperature are very rapid (water cooling, blown film, etc.) or very slow combined with long dead times, as may occur in very large machines. Typical controller settings for pre-tuned controllers are shown in Table 4.6. 

The controller settings for various controllers can now be calculated from Table 32.1. 

Table 35.4. PID controller settings for basic control scheme.

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