Area Of Application - Siemens SIMATIC Manual

3.3

Area of Application

Transient Response
The process must have a stable, asymptotic transient response with time lag.
After a step change in the manipulated variable, the process variable must change
to a steady state. This therefore excludes processes that have an oscillating
response without control and processes that are not self-regulating (integrator in
the process).
Linearity and Operating Range
The process must have a linear response over the operating range. A non-linear
response occurs, for example, when the state of a unit is changed. The tuning must
take place in a linear part of the operating range.
This means that both during tuning and during normal controlled operation, non-
linear effects within the operating range must be insignificant. It is, however
possible to retune the process when the operating point changes if the tuning is
repeated in the close vicinity of the new operating point and providing that the non-
linearity does not occur in the range covered during tuning.
If certain static non-linearities (for example valve characteristics) are known, it is
always advisable to compensate these with a polyline curve to linearize the
process behavior.
Disturbances in Temperature Processes
Disturbances such as the transfer of heat to neighboring zones must not affect the
overall temperature process too much. For example, when tuning the zones of an
extruder, all zones must be heated at the same time.
For information on measurement noise and low-frequency interference, refer to
Section 3.11, Page 3-12.
PID Temperature Control
A5E00125039-02
Controller Tuning in FB 58 "TCONT_CP"
3-3