Process Control: Modeling, Design, and Simulation

M6.2. Closed-Loop Time-Domain Simulation

Here, we begin by using the SIMULINK diagram shown in Figure M6-1.

Figure M6-1. Simulink diagram. For best results, choose a stiff integrator, such as ode15s (stiff/NDF), from the “parameters” pull-down menu.

The system is on the verge of instability when k_c = 3.8 %/°C, as shown in Figure M6-2; the ultimate proportional gain is then k_cu = 3.8 %/°C. The period of oscillation (ultimate period, P_u) is approximately 17.2 minutes. Both of these values can be obtained from frequency-response analysis, as shown in Section M6.3. Notice that the manipulated variable action is constant from t = 1 to t = 6 minutes. ...