Siemens SIMATIC S7-1200 Function Manual page 26

Principles for control
2.4 Pulse controller
Three-step controllers
Three-step controllers are used for heating / cooling. These controllers have two switching
points as their output. The control-action results are optimized through electronic feedback
structures. Fields of applications for such controllers are heating, low-temperature, climatic
chambers and tool heating units for plastic-processing machines.
The following diagram shows the characteristic of a three-step controller
y
x
w
x
Sh
26
Output value, e.g.
y11 = 100% heating
y12 = 0% heating
y21 = 0% cooling
y22 = 100% cooling
Physical quantity of the process value, e.g., temperature in° C
Setpoint
Distance between Switching Point 1 and Switching Point 2
Function Manual, 03/2017, A5E35300227-AC
PID control