Appendix; Control Algorithm - Beckhoff TwinCAT 3 Manual

Appendix

7 Appendix
7.1

Control Algorithm

The heart of the TwinCAT Temperature Controller is a standard PID controller. This controller kernel also
supports anti-reset windup measures to limit the I-component if the control value is subjected to limiting.
Since the controller has been designed to minimise disturbances using the adjusting procedure according to
Chien, Hrones and Reswick, overshoot is possible when the set point is changed. In order to reduce such
overshoot, a pre-controller can be inserted to handle changes in the set point. The pre-regulator has a D-T1
characteristic, and reduces ringing in the controller as a whole. Since the D component of the pre-controller
has the effect of "roughening" the control value, the use of a pre-controller must be considered very carefully.
The pre-controller is switched off when the actual value enters within a certain range of the set value and
remains there for some length of time. The pre-controller is switched off by ramping it down over a
considerable period of time. To minimise oscillation of the control value, it is optionally possible to follow the
main controller with a filter. P-T1 and moving average filters are available for this purpose.
Requirements
Development environment
TwinCAT 3.1.4006
44
target platform
PC or CX (x86)
Version: 1.1
PLC libraries to include
Tc2_TempController
TC3 Temperature Controller