Siemens SIMATIC S7-1200 Function Manual page 19

PT2 controlled systems
In a PT2 controlled system, the process value does not immediately follow a step change of
the output value, i.e., it increases in proportion to the positive rate of rise and then
approaches the setpoint at a decreasing rate of rise. The controlled system shows a
proportional response characteristic with second order delay element.
Examples:
● Pressure control
● Flow rate control
● Temperature control
Non-self-regulating controlled systems
Non-self-regulating controlled systems have an integral response. The process value
approaches an infinite maximum value.
Example:
● Liquid flow into a container
Controlled systems with dead time
A dead time always represents the runtime or transport time that has to expire before a
change to the system input can be measured at the system output.
In controlled systems with dead time, the process value change is delayed by the amount of
the dead time.
Example:
Conveyor
PID control
Function Manual, 03/2017, A5E35300227-AC
Principles for control
2.2 Controlled systems
19