Cascade Control With Pid_Temp; Introduction - Siemens SIMATIC S7-1200 Function Manual

6.4

Cascade control with PID_Temp

6.4.1

Introduction

In cascade control, several control loops are nested within each other. In the process, slaves
receive their setpoint (Setpoint) from the output value (OutputHeat) of the respective higher-
level master.
A prerequisite for establishing a cascade control system is that the controlled system can be
divided into subsystems, each with its own measured variable.
Setpoint specification for the controlled variable is carried out at the outmost master.
The output value of the innermost slave is applied to the actuator and thus acts on the
controlled system.
The following major advantages result from the use of a cascade control system in
comparison with a single-loop control system:
● Thanks to the additional subordinate control loops, disturbances which occur there are
corrected quickly. Their influence on the controlled variable is reduced considerably. The
disturbance behavior is thus improved.
● The subordinate control loops act in linearizing form. The negative effects of such non-
linearities on the controlled variable are thus moderated.
PID_Temp offers the following functionality especially for use in cascade control systems:
● Specification of a substitute setpoint
● Exchange of status information between master and slave (for example, current operating
mode)
● Different Anti-Wind-Up modes (response of the master to limitation of its slave)
PID control
Function Manual, 03/2017, A5E35300227-AC
Using PID_Temp
6.4 Cascade control with PID_Temp
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