Control [Compatibility Mode]

7/31/2019 Control [Compatibility Mode]

1/59

Phase I - Control FundamentalRMT Sales Training - 05 /98

1

Level 1

Fundamentals Training


2/59

Level 1 - ControlRMT Training - 05 /98

2

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


3/59


3

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


4/59


4

A combination of instruments or functions that areinterconnected to measure and control a processvariable with feedback.


What is a CLOSED LOOP ?

PROCESSinput output

A System

withFeedback

FINALCONTROL

ELEMENT

MEASUREMENT

CONTROLLER


5/59


5

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


What is a TRANSDUCER


6/59


6

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


What is a TRANSMITTER


7/59


7

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


ADVANTAGE OF 4-20mA CURRENT SIGNAL


8/59


8

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)


What is a CONTROLLER ?


9/59


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.


10/59


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?


11/59


11Control Principle


12/59


12

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).


13/59


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.


14/59


14

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


15/59


15

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


16/59


16

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


17/59


17

Connection to Process,Instrument Supply,

or Direct Mechanical Link

Pneumatic Signal

Electric Signal

Signal Types (ISA)

Control Principle


18/59


18Control Principle

Pneumatic

Analog

Digital

Single Loop Controllers Distributed Control System

Fieldbus Control System

Controller Types


19/59


19

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


20/59


20

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


21/59


21

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


22/59


22

I/P LIC

LT

Basic Control Loop

Level Control Loop (Inflow)

Level Loop Issues:

Control At Inflow or OutflowNon-Self Regulating


23/59


23

I/PLIC

LT

Basic Control Loop

Level Control Loop (Outflow)


24/59


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


25/59



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


26/59



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


27/59


27

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


Feedforward

SP


28/59



I/P

TT

FeedforwardLoop

TIC

Steam

ColdWater

HotWater

FT

FFD

FeedforwardEquations

SummingJunction

FeedbackLoop

Implementing Feedforward Control


29/59


29

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.


What is RATIO CONTROL ?

Ratiorelay

Wildflow, A

Controlledflow, B

Remote -set

controllerOutput = A x ratio

SP

Output

Wild flow, A

Controlledflow, B

Ratiocontroller

Output


SP


30/59



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


31/59


31

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.


What is SELECTIVE CONTROL ?

SpeedControl

PICPIC

RS

Low select

PV

Pump

O/PO/P

PV



32/59


32Control Algorithm

On/Off

Multi-step

Proportional

Integral

Derivative


33/59


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


34/59


34

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


35/59


35

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


36/59


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


37/59


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)


38/59


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)


39/59


39

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


40/59


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)


41/59


41

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


42/59


42

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)


43/59


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


44/59


44

I/P

PT

PIC

P

Control Algorithm

P & ID Piping & Instrumentation Drawing

Process Vessel

Fluid Pump

PneumaticControl

Valve

Compressed Air Pipe

ConverterPID

Controller

PressureTransmitter


45/59


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


46/59


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


47/59


47

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.


48/59


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


49/59


49

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


50/59


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


51/59


51

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


52/59


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


53/59


53

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


54/59


54

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


55/59


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. [ ]


56/59


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. [ ]


57/59


57Exercise

9. Identify the components indicated by the Arrows.


58/59


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. [ ]


59/59

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. [ ]

Documents

Control [Compatibility Mode]