Suggestions For Tuning Loops; Standard Pid Algorithm; Dynamic Pid Algorithm - Siemens SIMATIC 505 User & Programmers Manual

5.11

Suggestions for Tuning Loops

5.11.1
Standard PID
Algorithm
5.11.2
Dynamic PID
Algorithm
5-22 Selected Functions
These suggestions assume that you have some knowledge of PID
terminology and are familiar with the operation of the TurboPlastic module.
Use them as guidelines in tuning a loop, but understand that each
application has its own characteristics.
Understanding of the PID loops available in the TurboPlastic module, as
well as how the loops react, is helpful. There are two user-selectable loops in
the TurboPlastic module. Either can be selected to control velocity and/or
pressure loops. Since one algorithm is not superior to the other, experiment
with both while adjusting the process. The different characteristics of the
two algorithms may make one algorithm more suitable to the particular
machine being run.
The standard PID loop was modeled on the 505 system controller loop
algorithm. Within this loop, the setpoint can be forced into the loop bias
term each time there is a change in setpoint. Since the setpoint is output at
the first loop calculation, the control on this loop is taken instantaneously
around the setpoint, the PID algorithm reaction does not need to be quick.
Gain and reset are almost always used in tuning this loop. This algorithm is
used more frequently for controlling pressure loops.
The dynamic PID loop was modeled on the TMS320C25 chip algorithm with
some minor adaptations. Within this loop, the calculation starts by reading
a new error term and calculating a new output. Each subsequent output is
biased by the previous output. This is a quicker reaction loop than the
standard algorithm, therefore, the setpoint is not forced into the equation in
order to react to changes in the setpoint. Gain alone is used in most cases to
tune this loop. This algorithm is used more frequently for controlling
velocity loops.