Installing Basic Controllers

Let us go through the details of installing a level controller on the base of the column. Go to the Exploring window, click on Dynamics under Simulation, and select Control Models. A long list of alternative controller types and dynamic elements is displayed, as shown in Figure 7.9. We will use several of these extensively: Dead_time, Lag_1, Multipy, PID, and PIDIncr.

For simple level controllers, which should be proportional only, the PID model is used. Place the cursor on the PID icon, press and hold the left mouse button, and drag the cursor to the flowsheet window. Releasing the mouse button places a circle on the flowsheet, which is labeled "B2" (see Fig. 7.10). This can be renamed by clicking the circle, right-clicking, selecting Rename block, and typing in the desired label "LC11."

Now the control signals must be connected. The process variable signal PV is the variable to be controlled. For this level controller, it is the liquid level on the last stage of the column (stage 32). We go back to the Exploring window and click on Stream Types under Dynamics, as shown in Figure 7.11.

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