Emerson Oxymitter 5000, Инструкция по эксплуатации

Страница: 218 / 226

Oxymitter 5000
E-14
Instruction Manual
IM-106-350, Rev 2.2
July 2008
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 E-8
illustrates the correct function block configuration.
Figure E-8. PID Function Block
Diagram for Cascade Control
Example
Cascade Control with
Override
You can use the PID function block with other function blocks for complex
control strategies. Figure C-9 illustrates the function block diagram for
cascade control with override.
When configured for cascade control with override, if one of the PID function
blocks connected to the selector inputs is deselected, that PID block filters the
integral value to the selected value (the value at its BKCAL_IN). The selected
PID block behaves normally and the deselected controller never winds up. At
steady state, the deselected PID block offsets its OUT value from the selected
value by the proportional term. When the selected block becomes
output-limited, it prevents the integral term from winding further into the limited
region.
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
38730137