User's Manual

Automation and Drives - SCE

T I A Training Document Page 26 of 64 Module

2.7.3.4 Derivative Action Controllers (D-Controller)

The D-controller generates its controller output from the rate of change of the system deviation, and

not -like the P-controller- from its amplitude. For that reason, it still responds considerably faster than

the P-controller. Even if the system deviation is small, it generates -in anticipation, as it were- large

margins of the manipulated variable as soon as the amplitude changes. On the other hand, the D-

controller does not know a lasting system deviation; because, regardless of how large it is, its rate of

change equals zero. In practice, the D-controller is used rarely by itself for that reason. Rather, it is

used together with other control elements, usually in connection with a proportional component.

2.7.3.5 PID Controllers

If we expand a PI controller with a D-component, we enhance the universal PID controller. As in the

case of the PD controller, adding the D-component has the effect that, if laid out correctly, the

controlled variable reaches its setpoint sooner and enters the steady state faster.

Block Diagram

with

Preface Fundamentals Discontinuous Action Controller Controller Block (S)FB41 Setting the System Appendix

Issued: 02/2008 Control Engineering with STEP 7