Control Engineering - A guide for beginners - Chapter 4 pps

JUMO, FAS 525, Edition 02.04 63

4 Control loops with continuous controllers

4.1 Operating methods for control loops with continuous controllers

The previous chapters dealt with the individual elements of a control loop, the process and the

controller. Now we consider the interaction between these two elements in the closed control loop.

Amongst other things, the stable and unstable behavior of a control loop should be examined, to￾gether with its response to setpoint changes and disturbances. In the section on “Optimization”,

we will come across the various criteria for adjusting the controller to the process.

We also often refer to the static and dynamic behavior of the control loop. The static behavior of a

control loop characterizes its steady state on completion of all dynamic transient effects, i.e. its

state long after any earlier disturbance or setpoint change. The dynamic behavior, on the other

hand, shows the behavior of the control loop during changes, i.e. the transition from one state of

rest to another. We have already discussed this kind of dynamic behavior in Chapter 2 “The pro￾cess”.

When a controller is connected to a process, we expect the process variable to follow a course like

that shown in Fig. 42.

Fig. 42: Transition of the process variable in the closed control loop