Question

Can a controller be both a servo and regulator?

Answer 1

The basic type of controller is the Feedback Controller.

In feedback control constantly measures variable required to be controlled. This measurement value is compared with a given set point. The controller considers this error and determines what action the modified variable must take to compensate for the error and thus eliminate it.

This type of control has the advantage that it is easy to implement. The action of feedback control is completely empirical. The control system should remove the effect of an external disturbance as long as an adjustment is made in the correct sense.

The downside is that before it is removed, the disruption has to reach and interrupt the system.

A feedback control loop can have one of two objectives.

1. A servo control loop is one that reacts to a change in setpoint. The setpoint can be modified as a function of time (batch processes are characteristic of this), so the managed variable will obey the setpoint.

Figure 1. Servo control

2. A regulatory control loop is one that responds to a change in some input value that returns the system to a stable state. Regulatory control is much more common in process industries than servo control.

  

Figure 2. Regulatory control