Process reaction curve

Process reaction curve This can be obtained from the forward-path transfer function... 

Figure 4.34 shows the response to a unit step, or the process reaction curve. 

From the R and D values obtained from the process reaction curve, using the Zeigler-Nichols PID controller settings given in Table 4.2... 

Fig. 4.34 Process reaction curve for the temperature control system shown in Figure 4.33.

Figure 2.34. Process reaction curve for the Ziegler-Nichols Method.

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. 

Allow the tank to achieve steady-state operation in the absence of control (Kc = 0). Use the resulting process reaction curve to estimate combined proportional and integral control parameters. Then use the obtained steady-state values as the initial values for a following sequence of runs. 

Controller settings based on process reaction curve... 

To make use of empirical tuning relations, one approach is to obtain the so-called process reaction curve. We disable the controller and introduce a step change to the actuator. We then measure the open-loop step response. This practice can simply be called an open-loop step test. Although we disconnect the controller in the schematic diagram (Fig. 6.1), we usually only need to turn the controller to the manual mode in reality. As shown in the block diagram, what we measure is a lumped response, representing the dynamics of the blocks Ga,... 

Gp, and Gm. We denote the lumped function as GPRC, the process reaction curve function ... 

The real time data (the process reaction curve) in most processing unit operations take the form of a sigmoidal curve, which is fitted to a first order with dead time function (Fig. 6.2) 1... 

Empirical tuning with open-loop step test Measure open-loop step response, the so-called process reaction curve. Fit data to first order with dead-time function. 

From Problem 7.17, the open-loop transfer function for generation of the process reaction curve is given by ... 

Repeat Exercise 1 for step changes in inlet temperature (set stepflow=0 and steptemp = 1). From the response curve determine TL and K from the process reaction curve as described in Chapter 2. 

The controller is placed on manual control (i.e. effectively removing it from the control loop) and the response of the measured variable to a small step change in the manipulated variable is recorded as shown in Fig. 7.58a(21). This response is called the process reaction curve. A tangent is drawn to this curve at the point of inflexion (Fig. 7.586). The intercept of this tangent on the abscissa is termed the apparent dead time (rad) of the system. The gradient of the tangent is given by ... 

Fig. 7.58. Cohen-Coon method (a) block diagram (b) process reaction curve...

Workers at Louisiana State University2 have used the minimisation of these error criteria to produce controller settings from the process reaction curve. Values of controller parameters based upon the ITAE criterion are based upon a tuning relation of the form ... 

Kr Steady-state gain of process reaction curve (in Cohen-Coon procedure) ... 

The tuning settings based on the process reaction curves obtained by the open-loop tuning method, in addition to the Ziegler-Nichols method (Table 2.38), can also be selected by other methods. Figure 2.39 compares the load responses and Figure 2.40 compares the set point responses of these methods. 

Figure 9 Process reaction curve (Cohen-Coon) method...

Process Reaction Curve Method (Cohen-Coon Tuning). For some processes, it may be difficult or hazardous to operate with continuous cycling, even for short periods. The process reaction curve method obtains settings based on the open loop response and thereby avoids the potential problem of closed loop instability. The procedure is as follows ... 

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