Siemens SIPART DR21, Manual

Page: 63 / 242

3 Functional description of the structure switches
3.4 Controller types (S1, S42 to S45)
Manual
SIPART DR21
C73000-B7476-C143-08
63
D
SPC-controls
Here a process computer takes over command of the setpoint during computer operation
RC = Int
∧
CB = 1. In the case of computer failure (CB from 1
!
0) the controller takes over
either the last computer setpoint (tracked wi) or the safety setpoint SH (selection via S44).
D
Cascade controls
A command controller, e.g. a fixed setpoint controller (with the main controlled variable)
feeds the external setpoint of a slave controller with its manipulated variable (with the auxili-
ary controlled variable) and this the final control element. This gives faster control of the
main controlled variable in the event of changes in the auxiliary controlled variable, e.g. fur-
nace temperature control (furnace temperature, main controlled variable) with different flow
of the medium to be heated (auxiliary controlled variable).
D
Slave controls
A command controller feeds several synchronized controllers simultaneously whose individ-
ual setpoints can be set in a ratio to each other by the constants c4 and c5 and then drag
the controlled variables accordingly (controlled variable synchronization).
D
Control signals for the setpoint switching
The setpoint switching takes place via the logic link RC = Int
∧
CB and its negation (see table
3-4, page 65 and table 3-5, page 66). Both control signals can be set statically to 1 or 0 (int
via S49, CB via S24) in addition to their normal functions as Shift key or control signal with
the states 1 and 0, see fig. 3-2, page 52 and fig. 3-3, page 53.
The factory setting is Int = 1 (S42 = 0) and CB=1 (S23 = 8), so that the internal setpoint
wi is always active and cannot be switched in the factory setting
With this setting option it is possible to make the setting only dependent on Int (S42=2,
S23= 8) or only dependent on CB (S42=1, S23=1 to 7) as a slave controller with Internal/Exter-
nal-switching. If the switching option is blocked in External position (S42=1, S23=8), the con-
troller operates as a slave controller without Internal/External-switching.