8686130 instrument2.es.en
TRANSCRIPT
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Introduction
How to govern a process automatically?
Basics of Control Fundamentals of Instrumentation
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Manual operation of a process
Observe
Compare
DecideAct
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Operating a process
Process
MeasureAct
Dynamic response
Manual or open loop
Changes Replies
Compare
Decide
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Automatic operation
ProcessMeasuAct
Changes Replies
Regulator
Values
Wish
Closed loop operation
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Automatic Operation
LT LC
Measure
Compare
DecideAct
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Components
Process
Variablesto control
Regulator
Values
Wish
Actuator
TransmitterMeasured values
Variables
to act
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Temperature Control
Measure
Compare
Decide
Act
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Index
Control Systems: Terminology
Control Continuous / Discrete
Transmitters
Definitions and types
Level, Pressure, Flow, Temperature ...
Actuators:
Valves
Pumps and Compressors
System Dynamics
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Terminology
Disturbance
Variable
Manipulated
Variable
Controlled Reference
LT LC
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ProcessRegulator
TransmitterControlled Variable
Variable controled CV
Process Variable PV
Output (the process)
Reference
Motto
Set Point SP
Manipulated variable
Manipulated Variable MV
Output to Process OPInput (the process)
w
MV or
and (Europe)
CV and
x
Disturbances
Deviation Variables DV
Block Diagram
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Continuous Control
The controlled variable, taking values in a continuous range, is
measured and continuously acts on a range of values
Actuator
Variable
Manipulated
Variable
Controlled Reference
LT LC
Disturbance
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Discrete control
Peak detector
and minimum height
Solenoid
ON / OFF
Relay
The only variables
support a set
finite state
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Process diagrams P & I
Instruments
Measurement and control
represented by
circles with
numbers and letters
Processing units
and actuators
represented by
special symbols
Connection lines
LT
102
LC
102
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Tools
Indicators
Transmitters
Recorders
Converters
Drivers Actuators
Transducers
Connected by lines
Transmission:
Pneumatic
Power
Digital
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Tools
LRC
128
PT
014
Field Mount
Process connection
or feeding
Pneumatic signal
Panel Mounting
Electrical signal
The number is the same for all instruments of a
same control loop
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Digital Instruments
LRC
128
PT
014
Not normally accessible
to the operator
Accessible to the operator
Shares several features:
display, control, etc..
Software configurable
Network access
The number is the same for all instruments of a
same control loop
DCS controller,
microprocessor
controller, ...
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Digital Instruments
LRC
128
Computer
Unlike a DCS controller
Several functions: DDC,
logging, alarms, etc..
Network access
Connection
software or digital
network
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Digital Instruments
Or sequential logic
controlOr sequences PLC /
DCS logic of a
Accessible to the operator
Not accessible to the operator
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1st letter: measured variable or related
2nd letter: You can qualify to the firstDifferential D
F ratio
S security
Q integration
3 rd ff: Instrument function
I indicator
A record
C Control
T transmitterValve V
And calculation
High H
L under
A analysisDensity D
Voltage E
Flow F
Current IJ Power
L level
M moisture
Pressure P
Speed S
Temperature T
Viscosity V
W Weight
Z position
1st letter
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Tools
PDT LRC PIC
DTT
DT
FY FFC ST
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Warmer
MV
CV
DV
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Transmitters
Sensor: Parent element sensitive to a
physical property related to the variable
being measured. Transmitter: System sensor attached to
converting, conditioning and normalizes the
signal for transmission at a distance. Indicator: combines a sensor and a
measuring system analog or digital.
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Pressure Transmitter
Electronic circuit
Sensor
Piezoelectric
AmplificationFiltered
Calibrated
Power
Normalization
Pressure
Signal
standard
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Transmitters
Pneumatic signal: 0.2 to 1 kg / cm2
3 to 15 psi
Electrical Signal: 4 to 20 mA1 to 5 V dc, ....
Frequency: pulse / time
Other: RTD, Contacts, ...
Digital signal: HART, Fieldbus, RS-232 ...
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4-20 mA
The current signal is the same in any point of the line
You can differentiate a fault or break in line of range
lower measurement
You can connect a maximum number of loads or instruments
Transmitter
mA
FC
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Pulse / Frequency
Transmitter FCCounter
Pulse
The number of voltage pulses received
per unit time is proportional to
value of the measured quantity
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Feeding
TransmittermA
Transmitter
mA
220 V ac
24 V dc
Consumption
Connectors
Working conditions
Protections
Mounting
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Connection
XT
Protection
and isolation Filtered
Tomas
auxiliaryConditioningXC
SP
CV
MV
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Shielding
Transmitter
mA
FC
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Wiring, Reliability, ...
Control
Room TT
FT
DT
Wiring costs
Noise
Reliability of equipment
Calibration, maintenance, ...
Distance
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Fieldbus
PLC
Computer
Digital Bus 1101 ...
Microprocessor
Module A / D and
Communications
TT FT
DT
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Intelligent Instrumentation
It incorporates a
microprocessor
This gives youcomputing power and
storage of information:
Instrument Data
Dynamic Data
Provides a digital
communications
system which may bebidirectional
Provide new features
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Intelligent Instrumentation
Fully digital fieldbus
Communications
between all elementsconnected to the bus,
instruments and
control systems
Hybrid: combines
analog transmission
and digital HARTprotocol
Communications
between transmitters
and control systems
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Fieldbus
Save wiring
Noise Rejection
New features: Remote setting rank, test, documentation, ....
More elaborate information
Architectures and Protocols
PLC
Computer
Digital Bus
1101 ...
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Fieldbuses
Foundation Fieldbus (H1 and H2 levels)
Profibus DP, PA
WorldFIP
CAN
DeviceNet
.....
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HART
UnitHART RS-232
LT
PT
FT
Superimposed digital communicationto the signal 4-20mA
Allows test, calibration. Etc.
from your computer or handheld module
4-20 mA
1011 ..
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Serial interface
Analyzer
Point to point RS-232, RS-422
RS-485 Bus
A / DCommunication protocol
11010 ...
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Terminology (SAMA)
Rank
Span
Dynamic error
Accuracy
Sensitivity
Repeatability
Dead zone and hysteresis
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Transmitters
Range: 20 - 80 C
Span: 80-20 = 60 C
20 mA
4 mA
20 C 80 th C
Calibrated:
read = f (actual value)
Zero and Span Adjustme
mA = 0.2667 C - 1.3333
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Transmitters
20 mA
4 mA
20 C 80 th C
Calibrated:
read = f (actual value)
Zero and Span Adjustme
mA = 0.2667 C - 1.3333
Zero
Span
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Transmitters
20 mA
4 mA
20 C 80 th C
Linearity error
Due to the
nonlinearity of theactual calibration curve
% Span
Value indicated
Actual value
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TransmittersDead Zone:
Change in variable
As not alter
reading.
% Of span
20 mA
4 mA
20 C 80 th C
Area
dead
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Transmitters
Repeatability
20 mA
4 mA
20 C 80 th C
Repeatability:
Ability to obtain the same reading to read the same value
of the variable measured in the same direction of change.
% Of span
Hysteresis:
The same but in different directions of change.
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Transmitters
20 mA
4 mA
20 C 80 th C
Actual value
dynamic error
value indicated
Accuracy:
Maximum Limit
possible error
by linearity,hysteresis, etc. ....
% Of span
% Of reading
Direct value ...
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Transmitters
1 unit
20 mA
4 mA
20 C 80 th C
Sensitivity
Sensitivity:
Change in reading
corresponding
to a unit change
in the variable
% Of span
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Temperature Transmitters
Bulb
RTD (Pt100 0 C 100 )
Thermistors (Semiconductors)
Thermocouples E, J, K, RS, T
Pyrometers (high temperature, radiation)
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Pt-100
0 C 100
The electrical
resistance changes
with temperature
Electrical bridge
for conversion to
electric voltage
signal
Range of use: -200 500 C Sensitivity: 0.4 / C
Accuracy: 0.2%
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Bridge
V
R R
RRt
Pt100
When the bridge is balanced, the voltage V
is zero. If you change Rt the voltage V is
changed.
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Three-wire connection
V
R R
RRt
Pt100
The length of the connecting wires is important as the third
line makes the same resistance is added to each branch and
offset imbalance in the bridge
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Thermocouples
T1T2
I
At the juncture of certain
metals is generated emf if
the ends are at different
temperatures. The f.e.m.depends on the
temperature difference
Thermocou
ple
T
M
Measure: Opposes a
known voltage to the
thermocouple to the output
of amp. differential is zero
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Thermocouples
Type Range Accuracy
T -200 250 C 2%
J 0 750 C 0.5%
K 0 1300 C 1%
R / S 0 1600 C 0.5%
W 0 2800 C 1%
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Pressure Transmitters
Absolute pressure
Pressure gauge
Differential pressure
Measures based on:
DisplacementGauges
Piezoelectricity
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Sensor
displacement
Capacity
Induction
Potentiometer
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Pressure
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Piezoelectric sensor
Quartz crystal
Force
Metal plate
+
-
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Gauges / Hall Effect
N
S
Current
Force
Hall Effect
Strain gagesThe
deformation
varies R
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Pressure Transmitter
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Level Transmitters
Displacement
Float
Force: Archimedes Principle
Differential pressure
Capacitive
Ultrasound
Radar
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Level: differential pressure
LT
(P0+gh) - p0
Measuring the
pressure difference
between bothbranches
It is assumed
constant density
Condensation in the
tubes
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Capacitive
Between the electrode
and the shell wall is
formed a capacitorwhose capacity depends
on the level of liquid
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Level: Ultrasound
The time between
transmission andreception of high
frequency waves is
proportional to the
level
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Flow Transmitters
Differential pressure
Electromagnetic
Turbine
Vortex
Doppler Effect
Mass (Coriolis) .....
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Orifice plates
P1 P2
D
d)PP(g2
4
D
1Cq 21
2
4
2
Based on the
differential pressure
measurement
Dd
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S
Electromagnetic flowmeters
N
S
B
In the conductor
(liquid) flowing at
a rate within thefield B induces an
EMF proportional
to speed, which is
collected at theelectrodesN
-
+
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Actuators
Final control elements. Altering the
manipulated variable of the process
according to the control signal.Valves
Engines
Variable speed pumpsPower amplifiers
....
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Valves
Device for varying the flow rate through a
driving modifying the pressure drop across
it by a variable shutter.
Manual closing
Retention
Security
On / Off
Regulation
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Regulating valves
Structure and function
Types of valves
Calculation Formulas Static characteristics
Cavitation
Installed Features A valve dynamics
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Pneumatic seat
Air
Fluid
Shutter
Seat
Flanges
Membrane
StemSpring
Top
Indicator
Body
ServomotorTire
Electric
3 -15 psi
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Regulating valves
Air Seat or balloon
Double seat
Needle
Saunders
GateButterfly
Camflex II
2 -3 waysSealing
Maximum pressure
Flow capacity
Fluid type
Fluid
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Butterfly
Body
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Air open / close
Air
Air
Air closesOpen
air
Air
close
s
Open
air
/
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I / P
3-15 psi air
IP4 to 20
mA
Low accuracy in
positioning the rod
Air and electric power
P iti
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Positioner
Positioner
Air Supply
Air
Control signal
4 to 20 mA
P D
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Pressure Drop
pa C
qv
1
2 2
2
pressure drop pflow q
a fraction of opening
Coefficient C
density
q
p
to
p1 p2
C l l ti F l
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Calculation Formulas
qaC pv v116.
q aC p p pv v 72 4 1 2.( )q t / hp bars
to both a
q m3 / h
p bars
densityonto both a
Saturated steam
Liquids
q
p
to
p1 p2
Flow coefficient Cv
St ti h t i ti
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Static characteristics
% Of position
rod
% Area of
Seat 100%
% Of peak flow
in cond. nominaltoconstant p
Linear
Isoporcentuales
Quick opening
ButterflyCamflex
0% 100%
0%
St ti h t i ti
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0% 100%
0% Butterfly
Quick
opening
Linear
Equal
percentage
Static characteristics
R bilit
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Rangeability
0% 100%
0%
maximum controllable flo
R = -------------------------------
minimum controllable flow
% Position of the rod
Flow
uncontrollable
R = 50 ... 20
Ca itation
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Cavitation
length
pressure p1
p2
length
pressure p1
p2
Steam pressureSteam pressure
Vapor Pressure:
Pressure at which boiling
liquid at room
work
Cavitation
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Cavitation
qaC pv v116.
Cavitation
incipient
pv
q
Maximum pto regulate flow
Critical flow
p K p pv c v ( )1
Kc Coefficient
incipient cavitation
p C p pp
pM f v
v
c
2
1096 028( . . )
p Maxima caida de presion admisibleM
CF Flow factor
critical
pc pressure
critical point
Calculation Formulas
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Calculation Formulas
qa C C p y y
y
C
p
p
f v
f
v
1
3
1
0148
54 5
16315
( . )
.
..
gas
y
q t / h
p bars
qa C C p y y
qa C C p
f v
f v
1
3
1
0148
837
837
( . )
.
.
vapor saturado
flujo critico
Installed Features
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Installed Features
qaC pv v116.
q
pv
to
p1 p2
h
qp gh
Ka C
L
v
1
116 1
0
2 2
.
p p K q ghv L02
p0
Installed Features
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Installed Features
qp gh
Ka C
L
v
1
116 1
0
2 2
.
% Position of the rod
% Q
Smart Valves
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Smart Valves
Positioner +
Microprocessor
Air
Fieldbus
Characterizatio
n
DiagnosticsAlarms
Control blocks,
etc..
Pumps
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Pumps
Positive Displacement
Centrifuges
Installation
Power and performance
Characteristic curves
Cavitation
Positive Displacement
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Positive Displacement
Piston, diaphragm, ...
Centrifuges
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Centrifuges
Engine
AsynchronousImpeller
Electric power Mechanical energy
Centrifugal pumps
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Centrifugal pumps
p aw bqb 2 2
P p q P P
P W
b
36 022. otencia suministrada
W Potencia absorvida
P kw
q m3 / hp bars
Increased energy = energy supplied - losses
Characteristic curves
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Characteristic curves
pb
q
1
22 > 1
Operating point
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Operating point
pb
q
q
pv
to h
p p p K q gh
pa C
K q gh p
b v L
b
v
L
0
2
2 2
20
1
( )
p0pb
Variable speed pumps
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Variable speed pumps
M Drive
4 to 20 mA
Compressors
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Compressors
pb
q
1
2 2 > 1
Pumping line (surge)
Electric motors
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Electric motors
N
S
B
F
F
Electric motors AC / DC
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Electric motors AC / DC
MAmplifier
CC
4 to 20 mA
Feeding
M Drive
4 to 20 mA
DC
Motor
ACinduction
motor
THE PROBLEM OF
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CONTROL
ProcessControllerorw and
SP CV
v
MV
DV
Drivers
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Drivers
Generate a control signal to the actuator
normalized according to the measured value
of the variable to be controlled and itsdesired value.
Reference
Controlled variable
4-20 mA
Error
+-
Variable
manipulated
4-20 mACalculation and
normalization
Drivers
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Drivers
Technologies:
Pneumatics
Electronics
Digital
Loop controllers (PID)
PLCs (PLC)
Distributed Control Systems (DCS)
Control Computer (PC)
Controller
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SP 45
45.5 PV
4-20 mA
transmitter
4-20 mA to
actuator
MV
38%
Governor Signs
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g
ProcessRegulator
Transmitter
Actuatorw
The input and output signals to the controller are
normalized signals, usually 4-20 mA
or and
4-20 mA
4-20 mA
THE PID CONTROLLER
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THE PID CONTROLLER
signal based controllerDoes not incorporate
explicit knowledge of the process
3 tuning parameters Kp, Ti, Td
Various modifications
e t w t y t
u t K e tT
e d Tde
dtp
i
d
( ) ( ) ( )
( ) ( ) ( )
1
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Two options
ProcessR
w or
ProcessRw or
Mr.
mAMr.
Mr.
Mr.
mA
Mr. %
%
mAa
n
d
a
n
d
mA
%
+
-
+
-
%
Kp % /%
Kp % / Eng
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Analysis of the regulator
GpR
100/span
Actuator
W
The input and output signals to the controller usually
expressed in% of the span of the transmitter and the actuatorrespectively.
The conversion of the regulator should correspond to
Transmitter Calibration
U
%
%%
+
-
And
100/span
PID parameters
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p
Kp gain / proportional term
% Span control /% controlled variable span
proportional band PB = 100 / Kp Ti Full time / full term
minutes or sg. (By repetition) (reset time)
replicates per min = 1 / Ti Td Derivative time / term derivative
minutes or sg.
Proportional action
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p
u t K e t biasp( ) ( )
and
t
or
t
An error of x% causes a control actionofKp x% of the actuator
bias = manual reset (CV = SD)
Direct / reverse action
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LT
Direct acting controller Kp 0
u (t) = Kp(W-y) if u increases and decreases with Kp
positive
consider the type of
valve
LCLT
LC
Proportional action
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M
Kpw or
Mr.
Ampl.a
n
d 30%
+
-
1500rpm
1500
rpm
u (t) = Kp e (t) + 30You can only reach an
equilibrium with zero error
Integral action (Automatic reset)
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a
n
d
a
n
d
w w
t t
or
t
or
t
A regulator does not eliminate P
stationary error
self-regulating processes
Integral action continues
changing or until the
error is zero
K
Ted
p
i
Integral Action
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M
Kp
w or
Mr.
Ampl.
a
nd
+-
1500
rpm
K
Ted
p
i
1500rpm
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Derivative action
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a
n
d
an
d
w w
t t
or
t
or
t
A P controller with gain
high for rapid response
may cause oscillations
for u too
The derivative action accelerates
or if the moderates and grows and
decreases, preventing oscillations
)td
edTe(K)t(u dp
Derivative action
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u t K Td e
d tp d( )
and
t
and
t
KpTdtoIf e = a t
Td
Kpand
With e varying linearly, the derivative givessame or that the proportional give Td sg. later
Anticipatory action
Not influence the steady state
PD
Derivative action
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u t K Td e
d tp d( )
and
t
and
t
KpTdtoIf e = a t
Td
K Td e
d tK T a K at t Tp d p d p d
Td time taken for the
derivative action in match
proportional action
if e = HV
Kpand
PID tuning methods
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Trial and error methods
Methods based on experiments
Estimate certain dynamic characteristics of the process
with an experiment Calculate the controller parameters using tables or
formulas derived on the basis of the dynamic
characteristics estimated
Analytical methods based on models Minimization of error indices
Phase margins and / or gain
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Dynamic response
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Change
step
variable
manipulated
time
level
Dynamic response
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Process
MV
or
time
CV
and
time
ExperimentationMathematical model
Dynamic response
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Stationary
time
or
and
Transient
Types of processes
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Self-regulated No self-regulated
or Integrators
time
or
and
time
or
and
Types of processes
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Minimum phase Non-minimum phase
or inverse response
time
or
and
time
or
and
Stability
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0 2 4 6 8 10-0.5
0
0.5
1
1.5
2
open loop response
0 2 4 6 8 10-0.5
0
0.5
1
1.5
2
open loop response
Stable Unstable
A limited entry is for a limited output
or
and and
Damping
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0 2 4 6 8 10-0.5
0
0.5
1
1.5
2
open loop response
0 2 4 6 8 10-0.5
0
0.5
1
1.5
2
open loop response
Overdamped Underdampedor
and and
Dynamic response
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time
+5% Of final value
or
and
Retardation
time
settlement
dynamic response
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Overshoot in% = 100 Mp /and
Gain = and /or
or
andand
or
Mp
time
Gain
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Positive gain Negative gain
or conversely
time
or
and
time
or
and
dynamic response
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or
and
time
period
oscillation
Rise time
90%s
10%s
ands final valu
Mathematical model
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Process
or
time
and
time
Model
andm
time
Discrete Event Systems
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Many processes are not continuous
Its variables support only a finite number of
values The values of the variables change
continuously over time, but in certain
moments. Control problems and sequential logic
Discrete states
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Engine:
Running or
stopped
Deposit:
With fluid or
vacuum
Valve:
Open or
closed
Instrumentation
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Closed
circuit
Open
circuit
Minimum level
detector: when
the level drops
the minimumvalue is set / or
off the sensor
signal
Instrumentation
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Process
PS
TS
Thermostat:
When the
temperatureexceeds a limit
on / off sensor
Pressure
Instrumentation
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Presence
detector
Transmi
tter
Receiver
Limit
Instrumentation
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On / off valve
Solenoid
Motor starter
~
Combinational Systems
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Associated alarms or logical operation
The answers depend only on the inputs
through logic functions and, or, not IF (logical conditions)
THEN (action)
Combinational logic
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AND 1 0
1 1 0
0 0 0
OR 1 0
1 1 1
0 1 0
NOT 1 0
0 1AND A.B
A + B ORA NOT
BAB.A
B.A)BA(
MorganLaw
Logic gates
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&A
B
1A
B
A.B
A +
B
1A A
DIN
nomenclature
Logical expressions may be equated to electrical circuits inwhich the conditions are true or false in the presence or
absence of signal and the conclusion is expressed in terms
of the output signal
Logic circuits
-
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& 1
B
C (C + B).A
1&
A
B
D&
C
A.B + C.D
1A A
Contact diagrams
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Normally open contact Normally closed contact
Logical expressions may be equated to electrical circuitsthat true or false conditions correspond to closed or open
contacts and the conclusion is expressed in terms of current
flows or not
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Contact diagrams
-
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A
B
C D
+ -
Logical function: (A + B). C.D
Relays
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A device that can implement logical actions and
act on physical elements
~Load
S1
S2
IF (S1 and S2 = closed = closed)THEN load driven
coil
Ladder diagram
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relay coil
S1 S2
X1
Normally open push
NC button
Other items:
timers, counters,buttons, etc..
+ -
Example
X2
S2
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M ~
relay
S1 P1
X1
+ -
S1P1
X1
X1 X2
X2
S2
Sequential Processes
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AB
Discharge
Succession of stages
of operation with
specific actions andtransition conditions
including
1 Wait 2 Load 3
Operation 4Download
M
State transition graphs
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State transition graphs
A BM
1
2
3
4
Start
Full tank
Operation
terminated
Empty
tank
States
Transitions
Waiting
Load
Operation
Discharge
PLCs
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Programmable devices designed to
implement sequential logic functions
and connected to a process
CPU
Communications
I / O
Feeding
Architecture
Modicon TSX Nano
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PC + PLC + Process
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