cbe / met 433
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CBE / MET 433. 22 Feb 12 (Transfer functions and Block Diagrams). Professor Douglas Cooper, author Loop Pro-Trainer. What are Valve Characteristics Inherent Characteristics. The three most common valve characterizations are equal percentage, linear, and quick opening . - PowerPoint PPT PresentationTRANSCRIPT
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CBE / MET 43322 Feb 12
(Transfer functions and Block Diagrams)
Professor Douglas Cooper, author Loop Pro-Trainer
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What are Valve CharacteristicsInherent Characteristics
• The three most common valve characterizations are equal percentage, linear, and quick opening
2Professor Douglas Cooper, author Loop Pro-Trainer
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What are Valve CharacteristicsInstalled Characteristics
• In many process applications the pressure drop across a valve varies with the flow. In these instances an equal percentage valve will act to linearize the process.
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Equal percentage valves are the most commonly used control valves. • How do you know what inherent valve characteristic to choose to get a
linear installed characteristic?– The correct selection of valve characteristic to linearize the process
gain will ease the tuning process and make for a robust system.– Most times this selection is through experience, guesswork or the
valve manufacturer’s recommendation.Professor Douglas Cooper, author Loop Pro-Trainer
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Feedback Block DiagramTransmitter
Transducer
Valve
Energy Transfer Controller
Process
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Feedback Block Diagram
11s
11
sK
s+
+
si
sQ
sWVK
sMcK sM y-
sE+ sR
TK sC
sMor T
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Feedback Block Diagram (simplified)
11s
1
sK
s+
+
si
sWVK
sMcK
-
sE+ sR
TK sC
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Closed Loop Transfer Function (let R(s)=0)
11s
1
sK
s+
+
si
sWVK
sMcK
-
sE+ sR
TK sC
sKKKsKs
ss TcVi
11
1
TcVi KKK
sK
sss
11
11
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Closed Loop Transfer Function (let R(s)=0)
11s
1
sK
s+
+
si
sWVK
sMcK
-
sE+ sR
TK sC
TcV
i KKKsK
sss
11
11
looptheinblocksallouputtoinputfrompathdirectonblocksall
ss
input
output
1
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Open Loop vs Closed Loop
Transfer Function (R(s)=0)
11s
1
sK
s
++
si
sWVK
sMcK
-
sE+ sR
TK sC
TcVi KKK
sK
sss
11
11
Open Loop:
Closed Loop:
11ss
s
i
TcV KKKKs
11
11
11
sKKKK
KKKK
TcV
TcV
1*
*
sK
*
* 1K tt
evse *
t
eAt 1
*1*
teAKt
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0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
0 1 2 3 4 5
time (t)
Y(t)
Open - loop
Closed - loop
t
time
AK *
A
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Transfer Functions (Chap 3-5)
11s
1
sK
s
++
si
sWVK
sMcK
-
sE+ sR
TK sC
11
s
GL
Define:
For heated, stirred tank:
..FTG
)()(ss
i
VV KG
1
sKGP
cc KG
TT KG
11s
1
sK
s
++
si
sWVK
sMcK
-
sE+ sR
TK sC
LG
PGVGcG
TG
)()(sRs
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11s
skgsW C
LG sTo
11s
skg
s sW C
sG sTo
11s
CsTi
C
iTG sTo
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sRSPG
sT seto
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)(sWsTo
)(sTsT
i
o
)(sT
sTseto
o