1. CBE 491 (CBE 433)
Review II: Fall 2012

2. Controller Block Feedback Control Loop
measure some property
compare to setpoint
decide what to do
change another property
Loads
Flowrate
Temp or Level
Process
Action
Measure
Feedback Control Loop
error
Decision
Compare SP

3. Controller Block c(t) = CV or PV or TO m error c Decision CompareSP m c
e = r - c
(-)
Control
algorithm
(+) r
m = output of controller (MV or CO)

4. Control Algorithms 1. ON/OFF Control Direct controller (ac = +1)
If e > 0 Then m = 0%
If e < 0 Then m = 100%
OFF ON
Reverse controller (ac = -1)
If e > 0 Then m = 100%
If e < 0 Then m = 0% ON
OFF

5. Example: P Control Loop on BZ Flash
aT = +1 AC
aC = -1
av = -1
aP = -1
Reverse controller (ac = -1)
If e > 0 Then m = 100%
If e < 0 Then m = 0%

6. Example: P Control Loop on BZ Flash
aT = +1 AC
aC = +1
av = -1
aP = -1
What IF: Direct controller (ac = +1)
If e > 0 Then m = 0%
If e < 0 Then m = 100%

7. Example: Graph Signals
Pressure = c
r - c = e
100% m m 0%
100%
Flow  VP 0% t

8. On / Off Control Okay for Some Systems

36. P & PI Algorithms: Open & Closed Loop Responses
OPEN LOOP: analysis of controller …. Only
CLOSED LOOP: analysis of controller …. In the control loop
P-Only t c r
r - c = e m
Flow (qo)
100% 0% qi
OPEN
LOOP

37. P & PI Algorithms: Open & Closed Loop Responses
OPEN LOOP: analysis of controller …. Only
CLOSED LOOP: analysis of controller …. In the control loop
P-Only t c r
r - c = e m
Flow (qo)
100% 0% qi
CLOSED
LOOP

38. P & PI Algorithms: Open & Closed Loop Responses
Proportional & Integral PI t c r
r - c = e m
Flow (qo)
100% 0% qi
OPEN
LOOP

39. P & PI Algorithms: Open & Closed Loop Responses
Proportional & Integral PI t c r
r - c = e m
Flow (qo)
100% 0% qi
CLOSED
LOOP

40. Problem solving exercises
Homework