Owner's manual

FOUNDATION
TM
Fieldbus Blocks Manual
A-14
Solution If the flow is controlled, steam pressure variations will be compensated
before they significantly affect the heat exchanger temperature. The
output from the master temperature loop is used as the setpoint for the
slave steam flow loop. The BKCAL_IN and BKCAL_OUT connections
on the PID blocks are used to prevent controller windup on the master
loop when the slave loop is in Manual or Automatic mode, or it has
reached an output constraint. Figure A-17 illustrates the correct
function block configuration.
Figure A-17. PID Function Block
Diagram for Cascade Control Example
Outlet
Temperature
Input
AI
Function
Block
PID
Function
Block
AI
Function
Block
Steam
Flow
Input
PID
Function
Block
AO
Module
Block
OUT
IN
OUT
IN
OUT
IN
CAS_IN
BKCAL_OUT
BKCAL_IN
BKCAL_OUT
BKCAL_IN
OUT
FT 101
FC 101
TCV 101
TT 101
TC 101
FIELDBUS-FBUS_19A