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C-15
PID Function Block
If the instrument connected to the AI block fails, you can place the AI
block in Manual mode and set the output to some nominal value for use
in the Integrator function block. In this case, IN at the slave PID block
is constant and prevents the integral term from increasing
or decreasing.
Figure C-9. Function Block Diagram for
Cascade Control with Override.
PID
Function
Block
AO
Function
Block
PID
Function
Block
Control
Selector
Function
Block
PID
Function
Block
PID
Function
Block
AI
Function
Block
Configured for High Selection
Master Controller
Slave Controller
Master Controller
OUT
OUT
OUT
OUT
OUT
IN_1
CAS_IN
CAS_IN
IN
SEL_1
SEL_2
BKCAL_SEL_2
BKCAL_SEL_1
BKCAL_OUT
BKCAL_IN
FIELDBUS-FBUS_20A