User's Manual

Automation and Drives - SCE
T I A Training Document Page 54 of 64 Module
5. SETTING CONTROLLED SYSTEMS
5.1 General
Below, setting controlled systems is discussed, using a PT2 system as an example.
T
u
-T
g
Approximation
The basis for the methods according to Ziegler-Nichols and according to Chien, Hrones and
Reswick is the T
u
-T
g
approximation. With it, the parameters following parameters transfer coefficient
of the system K
S
, delay T
u
und transition time T
g
can be determined from the system step response.
The rules for controller adjustment that are described below were found experimentally, by using
analog computer simulations.
P-T
N
systems can be described with sufficient accuracy with a so-called T
u
-T
g
approximation; that
means, through approximation by means of a P-T
1
-T
L
system.
Starting point is the system step response with the input step height K. The necessary parameters:
transfer coefficient of the system K
S
, delay T
u
and transition time T
g
are ascertained as shown in the
figure below.
This requires measuring the transition function up to the stationary upper range value (K*Ks), so that
the transfer coefficient for system K
S,
required for the calculation, can be determined.
The essential advantage of these methods is that the approximation can also be used if the system
can not be described analytically.
x / %
Preface Fundamentals Discontinuous Action Controller Controller Block (S)FB41 Setting the System Appendix
Figure: T
u
-T
g
Approximation
Wendepunkt
K*K
S
T
g
T
u
Turning Point
t/sec
B3
Issued: 02/2008 Control Engineering with STEP 7