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Phase I - Control FundamentalRMT Sales Training - 05 /98
1
Level 1
Fundamentals Training
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Topics: Slide No:
Process Control Terminology 3 - 10
Control Principles 11 - 18
Basic Control Loop 19 - 23
Advance Control Loop 24 - 31
Control Algorithm 32 - 46
Control System 47 - 54
Exercise 55 - 59
Contents
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Any operation or sequence of operations involving achange in the substance being treated.Examples:
A change of energy state - hot to cold, liquid to
gasA change of composition - a chemical reactionA change of dimension - grinding coal
Process Control Terminology
What is a PROCESS ?
Types of PROCESS VARIABLE:
Pressure Specific Gravity of liquid
Flow Density Level Mass
Temperature Conductivity
Liquid Interface CompositionMoles
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A combination of instruments or functions that areinterconnected to measure and control a processvariable with feedback.
Process Control Terminology
What is a CLOSED LOOP ?
PROCESSinput output
A System
withFeedback
FINALCONTROL
ELEMENT
MEASUREMENT
CONTROLLER
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A device that registers a non-electrical parameter (eg.process variable) and outputs a corresponding useableelectrical signal.
Pressure to Capacitance Pressure to Resistance or mV
Temperature to Resistance
Temperature to mV
Example:
Capacitance pressure sensor module
Piezo-resistive pressure sensor module
RTD
Thermocouple
Process Control Terminology
What is a TRANSDUCER
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A device that will translate the transducers interpretationof the measured variable into a standard transmissionsignal.
3 - 15 psi pneumatic signal
4-20 mA dc electrical signal
1-5 V dc electrical signal
Process Control Terminology
What is a TRANSMITTER
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Lower installation cost
simple, twisted pair wiring
Better noise immunity
current vs. voltage
Insensitive to wire resistance
current vs. voltage
Better suited for hazardous locations
intrinsic safety
Process Control Terminology
ADVANTAGE OF 4-20mA CURRENT SIGNAL
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Used to keep a process variable at a desired value (setpoint).
Closed loop vs. Open loop control
Difference: Open loop control has no feedback Control Modes
ON/OFF (Binary)
Proportional (P)
Proportional-plus-Integral (PI) Proportional-plus-Integral-plus-Derivative (PID)
Process Control Terminology
What is a CONTROLLER ?
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9Process Control Terminology
What is a SIGNAL ? An event that conveys data from one point to another.
What is an INDICATOR ?
An instrument which visually shows the value of the variable.
What is a RECORDER ?
An instrument that makes and displays a continuous graphic, acousticor magnetic record of a measured variable.
What is a DCS ?
Distributed Control System consisting of functional integratedsubsystems. The subsystems are connected by a communicationlinkage (eg) data bus,data highway.
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10Process Control Terminology
The last control element in the process control loop
that manipulates the process variable.
Control Valves
modulates flow rate
operated by actuator
Louvers and Dampers
operated by pneumatic actuators
Variable Speed Drives
operated by electronic control signals
4 - 20 mA
What is a FINAL CONTROL ELEMENT?
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11Control Principle
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SP
PV
Control Principle
Control theory can be encapsulated as the matching of ameasured variable (PV) to the plant requirement (SP).
PROCESS
CORRECTINGUNIT
CONTROLLINGUNIT
MEASURINGUNIT
OPERATOR
FEED PRODUCT
Proportional band % = % = x 100%1K Gain
100 IO
O/ P
A controller implements a Control Algorithm so that an output
signal (O/P) activates a correcting unit. The ratio of output signal(O) to input signals (I) is Gain (K).
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13Control Principle
Process Variable (PV) the actual measurement of the state of the process
Set Point (SP) the desired state of the process variable
Control Algorithm the predefined response of the controller to PV-SP
Controller Output (O/P) a signal determined by the control algorithm
Offset the value of PV-SP when the system is in equilibrium
Direct Acting Controllers as the value of the measured variable increases, the
output of the controller increases. Reverse Acting Controllers
as the value of the measured variable increases, theoutput of the controller decreases.
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A plant possesses inherentregulation when, in the absenceof a controller, equilibrium is re-established after a disturbance.
For example, a tank with constantinflow is in equilibrium.
The outflow valve is then openeda little more.
The outflow pressure decreases
as the tank level falls until inflowagain equals outflow.
Manipulation of the outflow valveresult in different, uniqueequilibrium states.
Inherent Regulation
Control Principle
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Example Instruments
TT
FIC
TE
Temperature Transmitter
Flow Indicating Controller
Temperature Element
(Thermocouple, RTD)
I/P Current-to-PressureTransducer
Pressure Transmitter
Pressure-to-Pressure
Transducer
PT
P/P
Local
Mounting
Panel Front
Mounting
Panel Rear,
or Rack Mounting
Instrument Location
Instrument Symbols
Control Principle
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First Letter Succeeding LettersMeasured orInitiatingVariable
Modifier Readout orPassiveFunction
OutputFunction
A Analysis Alarm
C User's Choice ControlD User's Choice DifferentialF Flow Rate Ratio
(Fraction)I Current
(Electrical)Indicate
L Level LightP Pressure,
Vacuum
Point (Test
Connection)Q Quantity Integrate,
TotalizeR Radiation RecordT Temperature TransmitV Vibration Valve, Damper,
Louver
Letter DesignationsInstrument Symbols
Control Principle
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Connection to Process,Instrument Supply,
or Direct Mechanical Link
Pneumatic Signal
Electric Signal
Signal Types (ISA)
Control Principle
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18Control Principle
Pneumatic
Analog
Digital
Single Loop Controllers Distributed Control System
Fieldbus Control System
Controller Types
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I/P
PT
PIC Pressure Loop Issues:May be a Fast Process
Liquid Small Volume
May Require Fast Equipment
Basic Control Loop
Pressure Control Loop
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Steam
ColdWater
HotWater
LoadDisturbance
Basic Control Loop
Temperature Control Loop Temperature Loop Issues:
Fluid response slowly to change in input heatRequires advanced control strategies
Feedforward Control
TT
TIC
I/P
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I/P FIC
TTFT
Basic Control Loop
Flow Control Loop Flow Loop Issues:
May be a Very Fast Process Noise in Measurement Signal
May Require Filtering May Require Fast-Responding Equipment
Typically Requires Temperature Compensation
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I/P LIC
LT
Basic Control Loop
Level Control Loop (Inflow)
Level Loop Issues:
Control At Inflow or OutflowNon-Self Regulating
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I/PLIC
LT
Basic Control Loop
Level Control Loop (Outflow)
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24Advance Control Loop
Consist of one controller (primary, or master) controlling the variablethat is to be kept at a constant value, and a second controller(secondary, or slave) controlling another variable that can causefluctuations in the first variable. The primary controller positions theset point of the secondary, and it, in turn, manipulates the control
valve.
What is CASCADE CONTROL ?
FBC FBC
SecondaryProcess
PrimaryProcess
Secondarycontroller
Primarycontroller
Disturbancer1 r2 m
c1 c2
Mult i-Var iable Cont r ol
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25Advance Control Loop
Example of CASCADE CONTROLThe temperature of the liquid in the vessel is controlled byregulating the steam pressure in the jacket around the vessel.
Temperaturetransmitter
Temperature
controller
Measurement
Output
SteamValve
Jacket
IN
OUT
SI N GLE- LOOP CON T ROL
Pressuretransmitter
Measurement Pressure
controller
Cascade Cont r ol Loop
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26Advance Control Loop
TemperatureProcess
Steam FlowProcess
Load A(Demand)
TIC
FT
TT
FC
Load B(Header Pressure)
SP RSP
__
I/P
TT
TIC
Steam
ColdWater
HotWater
Condensate
Major Load A:
Outflow Rate(Demand)
Major Load B:Steam Header
Pressure
Steam
Header
FT
FC
RSP
_
Implementing Cascade Control
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Levelindicatingcontroller
Flowcontroller
Boiler
FeedwaterFT
Applies to a system in which a balance between supply anddemand is achieved by measuring both demand potential anddemand load and using this data to govern supply. It gives asmoother and stable control than feedback control.
Advance Control Loop
What is FEED FORWARD CONTROL ?
FT LT
Steam
SP
PV O/P
Mult i-Var iable Cont r ol
Feedforward
SP
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28Advance Control Loop
I/P
TT
FeedforwardLoop
TIC
Steam
ColdWater
HotWater
FT
FFD
FeedforwardEquations
SummingJunction
FeedbackLoop
Implementing Feedforward Control
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An uncontrolled flow determines a second flow so that a desired ratiois maintained between them.
The ratio factor is set by a ratio relay or multiplying unit which would belocated between the wild flow transmitter and the flow controller setpoint. Flow B is controlled in a preset ratio to flow A.
Advance Control Loop
What is RATIO CONTROL ?
Ratiorelay
Wildflow, A
Controlledflow, B
Remote -set
controllerOutput = A x ratio
SP
Output
Wild flow, A
Controlledflow, B
Ratiocontroller
Output
Mult i-Var iable Cont r ol
SP
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30Advance Control Loop
Example of RATIO CONTROL
Other Application : Fuel/air ratio control system oncombustion equipment, e.g. boilers.
Acidsupply
Magneticflowmeter
Pickle tank
Flow
transmitter
FT FC
Control valve
Flow BFlow AWater
Manualwaterregulator
MeasurementSet
Pickling Process
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O/P
The more important condition between two or more candidates isselected. They are used mainly to provide protection to a piece ofequipment which could suffer damage as a result of abnormaloperating conditions.
Advance Control Loop
What is SELECTIVE CONTROL ?
SpeedControl
PICPIC
RS
Low select
PV
Pump
O/PO/P
PV
Mult i-Var iable Cont r ol
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32Control Algorithm
On/Off
Multi-step
Proportional
Integral
Derivative
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33Control Algorithm
It is a two-position control, merely a switcharranged to be off(or on as required) when the error is positive and on (or off asrequired) when the error is negative. Ex.. Oven & Alarm control.
On-Off Control
differentialMeasuredvariable
Controlleroutput
Time
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A controller action that may initiate more than two positioning ofthe control valve with respect to the respective predeterminedinput values.
Control Algorithm
Multi-Step Action
Multi-step actionTime
Time
1234
75
8
0
85
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It is the basis for the 3-mode controller. The controller output (O/P)is proportional to the difference between Process Variable (PV)and the Set Point (SP).
Control Algorithm
Proportional Action (P)
Process
Load
Controller
Output
SP
PV
Open-loop response of proportional mode
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36Control Algorithm
Proportional Action (P)
When a disturbance alters the process away from the set-point, thecontroller acts to restore initial conditions. In equilibrium, offset (PV-SP = constant) results.
The Algorithm is :
O/ P- (PV - SP)
Pr opor t ionalBand
Const ant= +
S - PV
O/P %100
(Constant is normally 50% )
50
Tan = Gain = 100 / Proportional Band
Time
SP
Time
Recovery timeOffset
Many controllers have a manualreset. This enables the operatorsto manipulate the constant termof the algorithm to eliminate offset.
PV
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37Control Algorithm
0 1 2 3 4 5 6 7 8 9Time
100
90
80
70
60
50
40
30
20
10
%
SP
PV
Output
E1E0 E2 E3 E4
prop
Low Proportional Gain: (Closed Loop)
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38Control Algorithm
0 1 2 3 4 5 6 7 8 9Time
100
90
80
70
60
50
40
30
20
10
%
SP
PV
Output
hi a in
High Proportional Gain: (Closed Loop)
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Whilst PV SP, the controller operates to restore equality.As long as the measurement remains at the set point, there is nochange in the output due to the integral mode in the controller.The output of the controller changes at a rate proportional to the offset.The integral time gives indication of the strength of this action. It is the
time taken for integral action to counter the offset induced byProportional Action alone.
Control Algorithm
Integral Action (I)
Time
SetPoint
%Measurement
% Output
Time
SetPoint
a=b
RT
RT= Reset Time min./rpta{
b{
Integral mode Proportional plus Integral mode
Open- loopr esponse
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40Control Algorithm
0 1 2 3 4 5 6 7 8 9
Time
100
90
80
70
60
50
40
30
20
10
%
SP
PV
Proportional
Plus Integral
Output
ProportionalResponse
Integral Action: (Closed Loop)
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As the PV changes, the controller resists the change.The controllers output is proportional to the rate at which thedifference between the measured and desired value changes.The derivative time is an indication of this action. It is the time thatthe open-loop P+D response is ahead of the response due to P only.
Control Algorithm
Derivative Action (D)
Time
SetPoint
%Measurement
% Output(I/D)
Derivative mode
Time
SetPoint
DT
DT= Derivative Time (min)
Proportional plus Derivative mode
Open- loopr esponse
Proportional + Derivative
Proportional only
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0 1 2 3 4 5 6 7 8 9Time
100
90
80
70
60
50
40
30
20
10
%
SP
PV PID Output
Control Algorithm
PID Action: (Closed Loop)
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43Control Algorithm
PID Control
A
B
80
60
40
20%ScaleRange
Con
trollerOutput
or
Va
lvePosition
Measurement
Proportional
Time - minutes
Open-loop response of three-mode controller
Proportional + Integral +Derivative
Proportional +Integral
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I/P
PT
PIC
P
Control Algorithm
P & ID Piping & Instrumentation Drawing
Process Vessel
Fluid Pump
PneumaticControl
Valve
Compressed Air Pipe
ConverterPID
Controller
PressureTransmitter
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45Control Algorithm
Controller Selection
Can offset betolerated ?
Start
UseP-only
Yes
UseP+I
Yes
No
Is dead timeexcessive ?
No
UsePID
Yes
Is noisepresent ?
No Reaction curveof measured
variable
Capacity
Dead Time
C
63.2%
Time (sec)
Step change invalve travel
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46Control Algorithm
Controller Adjustment
Time
Controlled
Variable
Period
P-only
PID
PI
Control loop Proportional band Time constant DerivativeFlow High (250%) Fast (1 to 15 sec) Never
Level Low Capacity dependent Rarely
Temperature Low Capacity dependent Usually
Analytical High Usually slow Sometimes
Pressure Low Usually fast Sometimes
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An automatic control scheme in which the controller is programmedto evaluate its own effectiveness and modify its own controlparameters to respond to dynamic conditions occurring in or to theprocess which affect the controlled variables.
Control System
Adaptive Control
Ex) Digital Controller- Sensors are run to the computers input.- Servomechanisms are connected to the computers output.- Future changes dont require re-wiring.
- Changing control functions (P,I, and D) and configurations(between cascade mode and feedforward mode) will bemade on the computers program and not necessarily to anyhardware.
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48Control System
A control strategy where the process control computer performssystem control calculations and provides its output to the setpointsinputs of conventional analog controllers. These analog controllersactually control the process actuators, not the main-controlcomputer.
Supervisory Control
M.I.SSupervisory
Control
A
S
Controller
S
AController
S
AController
SP1
SP2
SP3
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Measurement
HW andSoftwareFiltering
I/O Rack
Coax
ControllerTools for Process
Analysis, Diagnostics.
SampledValue
Tools for ProcessAnalysis, Diagnostics.
ControllerI/O Rack
Control System
Todays DCS System
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50Control System
Definition...
Control roomoperator stations
Control systems(DCS or PLC)
A digital, two-way, multi-drop communication link amongintelligent field devices and automation systems.
Fieldbus (Only Digital Signals)
What is a FIELDBUS ?
P
T
L
F
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Gateway HSE
H1
H1
H1
H1
BridgeH2
H1
H1
124Devices
WorkSystems
H1 - 31.25 Kbit/sHSE - 100 M bit/s(Fast Ethernet)
(due to address limits) .Total of approximately 35,000 devices
Fieldbus Control System
Controller
32 Devices
32
Devices
Control System
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52Control System
AI
PID
AI AO
PID
DCS
4 -20 mA 4 -20 mA4 -20 mA
ADVANCED CONTROL OPTIMIZATION
Control in the c ontrol room
Proprietary Bus
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PIDIN
OUT
BKCAL_INFIELDVUE
AO
BKCAL_OUT
CAS_IN
AIOUT
Delta V
Valve
Transmitter
Control System
Control
Anywhere
Built-In
Function
Blocks
Foundation Fieldbus Devices
Control in the field with fieldbus
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FCS
Loop 1 Loop 2
Digital
PIDPID
DCS
Loop 1 Loop 2
Digital
PID
Analog
DDC
Analog
PID
Loop 1 Loop 2
CentralControl Loop Local ControlLoop Control inthe field
Control in thedevice itself
Look at how the CONTROL migrate
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55Exercise
Which defined term is closest to the description or encompasses theexample given?
A. Controller F. Primary element
B. Converter G. Signal
C. Instrument H. Transducer
D. Point of measurement I. Transmitter
E. Process
1. Process temperature increases the measurable
resistance in a monitored electrical circuit. [ ]
2. Pulsed output from a turbine meter. [ ]
3. Heat-injected plastic molding. [ ]
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56Exercise
4. Temperature transmitter. [ ]
5. Device which adjusts the measured value of the
process to the requirements of the operator. [ ]
6. Element, flow transmitter, controller and correcting unit. [ ]
7. A pipe piece is tapped for a sample fluid. [ ]
8. A device changes an industry standard pneumatic
signal to an industry standard hydraulic signal. [ ]
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57Exercise
9. Identify the components indicated by the Arrows.
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58Exercise
Which defined term is closest to the description or encompasses theexample given.
A. Cascade control F. Gain B. Control algorithm G. Offset C. Control valve H. Proprietary Bus D. Feed-forward control I. Smart Device E. Foundation Fieldbus
10. The predefined response of the controller to PV-SP. [ ]
11. The value of PV-SP when the system is in equilibrium. [ ]
12. The ratio of controllers output to input. [ ]
13. It is a final control element operated by an actuator. [ ]
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C
59Exercise
14. Involves master & slave controllers. [ ]
15. The output of the loop drives the input. [ ]
16. A digital communication based control networkwith control action in the controller only. [ ]
17. A digital communication based control network thatallow control in the field. [ ]
18. A device that provide both analog & communicationsignal in its loop wire pair. [ ]