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Instruction Manual
IM-106-880C, OI
September 2009
7-47
Hazardous Area OCX 8800
Figure 7-18. PID Function Block Diagram for Feedfoward Control
Cascade Control with Master and Slave Loops
Situation
A slave loop is added to a basic PID control configuration to measure and
control steam flow to the steam heater. Variations in the steam pressure
cause the temperature in the heat exchanger to change. The temperature
variation will later be sensed by TT101. The temperature controller will
modify the valve position to compensate for the steam pressure change.
The process is slow and causes variations in the product temperature.
Figure 7-19 illustrates the process instrumentation diagram.
Figure 7-19. PID Function Block
Cascade Control Example
Outlet
Temperature
Input
Inlet
Temperature
Input
BKCAL_IN
BKCAL_OUT
OUT
OUT
OUTOUT
IN
CAS_IN
FF_VAL
AI
Function
Block
AI
Function
Block
PID
Function
Block
AO
Function
Block
TT101
TC101
TCV101
TT100
38740098
38740099
Steam
Supply
FC
101
Steam Heater
Condensate
TC
101
TT
101
FT
101
TT
100
TCV
101