Siemens SIPART DR22 Manual page 80

1 Technical Description
1.5 Functional description of the structure switches
1.5.4 Controller types (S1, S49 to S53)
- Example: Core temperature control with maximum casing temperature limiting
The core temperature of a reactor is to be controlled without the cooled casing of the reactor
exceeding a specific temperature (limiting setpoint Sb).
In error-free operation the main controller (Controller I) controls the core temperature to the
set setpoint w . Since the casing temperature is below the critical limiting setpoint Sb, the
core
limiting controller (Controller II) has a positive control difference. The manipulated variable of
the main controller is fed -- increased by 1% -- to the limiting controller as a maximum limiting
variable and forms its maximum manipulated variable. The limiting controller is driven to this
limit by the positive control difference.
Its manipulated variable is also fed to the main controller as a maximum manipulated
variable limit but remains ineffective because it is an increase of 1% above the manipulated
variable of the main controller.
In this situation the main controller can set its manipulated variable totally independently of
the limiting controller and control the core temperature of the reactor.
Sb=w
case
x
+
case +
--
w
core
+
+
--
x
core
Figure 1-42 Core temperature control with max. casing temperature limiting
If the casing temperature rises above the set limiting value Sb, e.g. due to failure of the
cooling water, the limiting controller gets a negative control difference. As a result its
manipulated variable is released from the forced limit and the heating performance is
reduced. The limiting controller then forces the reduced manipulated variable on the main
controller as a maximum manipulated variable limit. Due to the reduced heating performance
the main controller receives a positive control difference which drives it to the manipulated
variable limit. Now the limiting controller controls the process to constant casing
temperature.
When the cooling is reinstated, the casing temperature drops. The limiting controller will now
increase the heating performance and maintain the casing temperature. With increasing
heating performance the core temperature also increases and the control difference of the
main controller becomes negative.
78
YE
Casing temperature controller
(Limiting controller)
Controller II
S1=8
YE
Controller I
Core temperature controller
(Main controller)
y
Manual
SIPART DR22 6DR2210
C79000-G7476-C154-03