Copyright © 2010 by ISA
+
Process
Feedback
Controller
Manipulated
Input
Disturbance
Input
Multi-loop Control - Feedforward Control
Copyright © 2010 by ISA
Information
needed to
Commission
Feedforward
L/L & DT
Measured
Disturbance (D)
Controlled
Parameter(C)Deadtime
Lead/Lag
+Dynamic
Compensation
Process
Feedback
Controller
Manipulated (M)
C
M
C
D
Feedforward Control Implementation
Copyright © 2010 by ISA
Measured Load
Disturbance
Controlled
Parameter
Manipulated
Input
∆CM ∆CL
∆M
∆L
Time(sec)
Tm Td
63% of
Change
63% of
Change
Measured Load
Disturbance
Controlled
Parameter
Manipulated
Input
Time(sec)
DT1 DT2
Commissioning Dynamic Compensation
Copyright © 2010 by ISA
TC
185
TT
185
50-200 DegF
TT
185A
Workshop – Feedforward Control
Copyright © 2010 by ISA
Secondary
Controller
Manipulated
Disturbance
Disturbance
Process 2Process 1
Primary
Controller
Cascade Control
Copyright © 2010 by ISA
Outlet Steam
Temperature
Controller
Attemp Outlet
Temp Controller
Spray Valve
Steam
generatedFuel
Source
Superheater
Process
Attemperator
ProcessOutlet Steam
Temperature
Steam
Temp
Superheater Tubes
Boiler Drum
Spray Valve
Attemperator
TT
186TT
187
Example – Boiler Steam Temperature
Copyright © 2010 by ISA
Cascade Control Implementation
Selecting
FRSI_OPT for
dynamic reset
in primary loop
and Use PV for
BKCAL_OUT in
secondary loop
can often
improve
dynamic
response.
Copyright © 2010 by ISA
Workshop – Cascade Control
Copyright © 2010 by ISA
Manipulated
Controller
Information Needed to Tune
Controllers
Override
Controller
<
Max Value
Process
Constraint
Override Control
Copyright © 2010 by ISA
White Liquor
Clarifier
SC
190
FY
190
FC
190
AC
191
FT
190
AT
191
<
Density
Example – Override Control
Copyright © 2010 by ISA
Override Control Implementation
Copyright © 2010 by ISA
Workshop – Override Control
Copyright © 2010 by ISA
Controller Process
One(1) Controlled
ParameterTwo(2) Manipulated
Parameters
FY
Disturbance
Override Control
Copyright © 2010 by ISA
Split Range Control Implementation
Copyright © 2010 by ISA
Splitter SP
0 1000
100
0
100
0
100
100
100
0
0
OUT_1
OUT_2
LOCK_VAL “holds ”
LOCK_VAL “is zero ”
OUT_ARRAY
0 100 0 100
IN_ARRAY
0 100 0 100
OUT_ARRAY
100 0 0 100
IN_ARRAY
0 40 35 100
OUT_ARRAY
0 100 0 100
IN_ARRAY
0 40 35 100
Split Range Setup
Copyright © 2010 by ISA
400# Header
1475# Header
Boiler
Turbo
Generator
FY
196
PC
196
PT
196
BA
Example – Split Range Control
Copyright © 2010 by ISA
Workshop – Split Range Control
TT
197
TC
197
HeaterCooler
FY
197
Steam
Cooling
Water
BA
Copyright © 2010 by ISA
pH Process
Fine Valve
Coarse Valve
I-Only Controller
SP= Target
Valve
Position
Time
pH
Fine Valve
Coarse Valve
Target Valve
Position
AT
201
AC
201
ZC
201
Valve Position Control
Copyright © 2010 by ISA
PID configured for I-Only control
Valve Position Control Implementation
Copyright © 2010 by ISA
Low BTU – Waste Fuel
HI BTU Fuel
Boiler
BTU Demand
ZC
205
FT
205A
FT
205B
FC
205
FY
205
Example – Valve Position Control
Copyright © 2010 by ISA
Small
Valve
Big Valve
FT
215
FC
215
ZC
215
Workshop – Valve Position Control
Copyright © 2010 by ISA
Input = SP or PV of
independent loop
SP
SP= (Ratio * Independent Loop Input )
FT
220
FC
220
FT
221
FC
221
RC
221
Ratio Control
Copyright © 2010 by ISA
Ratio Control Implementation
Copyright © 2010 by ISA
FT
230
FC
230
FT
231
FC
231
AC
232
AT
232
RC
231
Example – Ratio Control
In this example
the ratio setpoint
is adjusted using
feedback control
based on a
downstream
analysis of the
blended material
Copyright © 2010 by ISA
Static Mixer
Main Flow
Blend Flow
% Solids
FC
251
FT
250
FC
250
AT
252
AC
252
RC
251
FT
251
Workshop – Ratio Control