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S T I R R E D-T A N K H E A T E R
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WHY PROCESS TO BE CONTROLLED?
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Safety
Environmental friendly
Operator friendly
To improve product quality
To increase production rate
Highly integrated plant with small
surge capacities
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Tougher competition
To make profitable
Reduced raw material cost
Extended equipment life
Most economical operating
conditions
Reduced energy consumption
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Typical Response to a step change in load variable
0 Time
PV
No control
P control
PIPI
PID
0 Time
Increasing Kc
No control (Kc= 0)
Typical process responses P control: effect of KC
Time0
Increasing TI
Time0
Increasing kc
PI control : effect of TI
PV
PVPV
PI control : effect of KC
SPSP
SP SP
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Typical Response to a step change in load variable
Time0
TDIncreasing
PID Control: effect of TD
PV SP
Increasing TDfrom zero
Improves speed of response by Reducing
maximum deviationresponse time
oscillation
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LV Simple PID Position Algorithm
Algorithm: Parallel PID controller
DnInpnn mmmm
t
t
Ip dt
deTdtte
TteKtm
D
0
)()(
1)()(
11
nnD
n
k
kI
nn eet
Te
T
tem
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LV Simple PID Position AlgorithmCont.
Controller Inputs
PV = Process Variable
SP = Set Point
tn = Most recent sampling start instant
nt
t
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LV Simple PID Position AlgorithmCont.
Controller Tuning Parameters
P= Kp =Proportional component
I = 1
/TI
=Integral component
D= TD=Derivative component
mmax
= Upper limit of controller output
mmin= Lower limit of controller output
nt
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LV Simple PID Position Algorithm Cont.
Error
nnn PVSPe
Deviation Error
1_nnn
eee
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LV , P--- Controller
nnppn ePeKm
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LV, I Controller
n
k
k
I
In eT
tm1
n
I
nIIn e
T
tmm
)1(
I
n
nIIn
T
temm
)1(
teImmnnInI
)1(
WhereI
TI
1
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LV, D Controller
t
eTm nDDn
t
eDm nDn
WhereDTD
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LV Simple PID Controller Cont
DnInpnn mmmm
Controller Output
Controller Output Limiting
minmmnIf Then minmmn
If maxmmn Then maxmmn
nn mm
Otherwise
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LV Simple PID Controller Cont
Normalization of Output
IfThen
Otherwise
minmax mm
maxm
mm
n
n
minm
mm
n
n
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LV Simple PID Position Algorithm
A
1_nnn ttt
Input Parameters : PV, SP, tn
Tuning Parameters: P, I, D, mmax,mminParameter Initialization:
mI0=0,mD0=0
IS1msect
1msect
+ +
A
No Yes
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LV Simple PID Position AlgorithmCont.
nnn PVSPe
nppn eKm
teImm nnInI )1( 1_nnn eee
t
eDm n
Dn
nDnInpn mmmm
A
B
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LV Simple PID Position Algorithm Cont.
Controller Output Limiting
IS
No
Yes
IS
No
B
minmmn
maxmmn minmmn
Yes
maxmm
n
+ +
+
BBB
C
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LV Simple PID Position Algorithm Cont.
Normalization of Output
No IS
B
Yes
+ +
BBC
minmax mm
maxm
m
m n
n
minm
mm nn
