Controller Type (2-Step, 3-Step Controllers) - Siemens SIMATIC S5 Manual

Notes on Controller Settings
Most controller systems are so-called self-regulating systems (see Fig. 4.1/1). The dynamic
response can be approximated by the variables delay time T , response time T and maximum
u g
value X . These values are determined by placing a tangent to the response curve which
max
intersects the maximum and minimum values. The transient response must in many cases not be
allowed to reach the maximum value, since the controlled variable must not exceed certain values.
The rate of rise v is therefore used to define the controlled system.
max
Characteristic values of important temperature-controlled systems

4.2 Controller Type (2-step, 3-step controllers)

2-step controller without feedback
2-step controllers have the switching states "ON" and "OFF". This corresponds to 100% or 0%
power. This action produces a continuous oscillation of the controlled variable x round the
setpoint w.
The amplitude and the period of oscillation increases with the ratio of delay time (T ) to response
u
time T of the controlled system and with the hysteresis X of the controller. These controllers are
g Sd
mainly used for simple temperature controls, e.g. electric directly heated ovens or as limit value
detectors.
IP244
4–124
C79000–B8576–C860–02