Training - Control

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Level 1 - Fundamental Training Control

Power Point Presentation Handouts

1Phase I - Control Fundamental

Level 1

Fundamentals TrainingFundamentals Training

Level 1 - Control

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

ContentsContents





Level 1 - Control

3

Any operation or sequence of operations involving a

change in the substance being t reated.

Examples:

A change of energy state - hot to cold, liquid to

gas

A change of composi tion - a chemical reaction

A change of dimens ion - grinding coal

Process Control TerminologyProcess Control Terminology

What is a PROCESS ?What is a PROCESS ?

Types of PROCESS VARIABLE:Types of PROCESS VARIABLE:

Pressure Specific Gravity of liquid

Flow Density

Level Mass

Temperature ConductivityL iquid In ter face Compos it ion

Moles

Level 1 - Control

4

A combination of instruments or functions that are

interconnected to measure and control a process

variable with feedback.


What is a CLOSED LOOP ?What is a CLOSED LOOP ?

PROCESSinput output

A SystemSystem

withithFeedbackeedback

FINALCONTROL

ELEMENTMEASUREMENT

CONTROLLER





Level 1 - Control

5

• A device that registers a non-electrical parameter (eg.

process variable) and outputs a corresponding useable

electrical 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 TRANSDUCERWhat is a TRANSDUCER

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6

• A device that will translate the transducers interpretation

of the measured variable into a standard transmission

signal.

– 3 - 15 psi pneumatic signal

– 4-20 mA dc electrical signal

– 1-5 V dc electrical signal


What is a TRANSMITTERWhat is a TRANSMITTER





Level 1 - Control

9Process Control TerminologyProcess Control Terminology

What is a SIGNAL ?What is a SIGNAL ?

• An event that conveys data from one point to another.

What is an INDICATOR ?What is an INDICATOR ?

• An instrument which visually shows the value of the variable.

What is a RECORDER ?What is a RECORDER ?

• An instrument that makes and displays a continuous graphic, acoustic

or magnetic record of a measured variable.

What is a DCS ?What is a DCS ?

• Distributed Control System consisting of functional integrated

subsystems. The subsystems are connected by a communication

linkage (eg) data bus,data highway.

Level 1 - Control

10


• 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?What is a FINAL CONTROL ELEMENT?





Level 1 - Control

11Control PrincipleControl Principle

Level 1 - Control

12

SPPV

Control PrincipleControl Principle

Control theory can be encapsulated as the matching of a

measured variable (PV) to the plant requirement (SP).

PROCESS

CORRECTING

UNIT

CONTROLLING

UNIT

MEASURING

UNIT

OPERATOR

FEED PRODUCT

Proportional band % = % = x 100%1

K Gain

100 IO

O/P

A controller implements a Control Algorithm so that an outputsignal (O/P) activates a correcting unit. The ratio of output signal

(O) to input signals (I) is Gain (K).





Level 1 - Control

13Control PrincipleControl 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.

Level 1 - Control

14

• A plant possesses inherent

regulation when, in the absence

of a controller, equilibrium is re-

established after a disturbance.

– For example, a tank with constant

inflow is in equilibrium.

– The outflow valve is then opened

a little more.

– The outflow pressure decreasesas the tank level falls unti l inflow

again equals outflow.

– Manipulation o f the outflow valve

result in different, unique

equilibrium states.

Inherent RegulationInherent Regulation






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15

Example Instruments

TT

FIC

TE

Temperature Transmitter

Flow Indicating Controller

Temperature Element

(Thermocouple, RTD)

I/P Current-to-Pressure

Transducer

Pressure Transmitter

Pressure-to-Pressure

Transducer

PT

P/P

Local

Mounting

Panel Front

Mounting

Panel Rear,

or Rack Mounting

Instrument Location

Instrument SymbolsInstrument Symbols


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16

First Letter Succeeding LettersMeasured or InitiatingVariable

Modi fier Readout or PassiveFunction

OutputFunction

A Analysis AlarmC User's Choice ControlD User's Choice DifferentialF Flow Rate Ratio

(Fraction)I Current

(Electrical)Indicate

L Level Light

P Pressure,Vacuum

Point (TestConnection)

Q Quantity Integrate,Totalize

R Radiation RecordT Temperature TransmitV Vibration Valve, Damper,

Louver

Letter Designations

Instrument SymbolsInstrument Symbols






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17

Connection to Process,Instrument Supply,or Direct Mechanical Link

Pneumatic Signal

Electric Signal

Signal Types (ISA)Signal Types (ISA)


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18


• Pneumatic

• Analog

• Digital

– Single Loop Controllers

– Distributed Control System

– Fieldbus Control System

Controller TypesController Types





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19

I/P

PT

PIC • Pressure Loop Issues: – May be a Fast Process

» Liquid

» Small Volume

– May Require Fast Equipment

Basic Control LoopBasic Control Loop

Pressure Control LoopPressure Control Loop

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20

Steam

ColdWater

HotWater

Load

Disturbance

Basic Control LoopBasic Control LoopTemperature Control LoopTemperature Control Loop

• Temperature Loop Issues: – Fluid response slowly to change in input heat

– Requires advanced control strategies

» Feedforward Control

TT

TIC

I/P





Level 1 - Control

21

I/P FIC

TTFT


Flow Control LoopFlow 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

Level 1 - Control

22

I/P LIC

LT

Basic Control LoopBasic Control LoopLevel Control Loop (Inflow)Level Control Loop (Inflow)

• Level Loop Issues: – Control At Inflow or Outflow

– Non-Self Regulating





Level 1 - Control

23

I/PLIC

LT


Level Control Loop (Outflow)Level Control Loop (Outflow)

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24

Advance Control Loop Advance Control Loop

Consist of one controller (primary, or master) controlling the variable

that is to be kept at a constant value, and a second controller

(secondary, or slave) controlling another variable that can cause

fluctuations in the first variable. The primary controller positions the

set point of the secondary, and it, in turn, manipulates the control

valve.

What is CASCADE CONTROL ?What is CASCADE CONTROL ?

FBC FBC

Secondary

ProcessPrimary

Process

Secondary

controller

Primary

controller

Disturbancer 1 r 2 m

c1 c2

Multi-Variable Control





Level 1 - Control

25 Advance Control Loop Advance Control Loop

Example of CASCADE CONTROLExample of CASCADE CONTROL

The temperature of the liquid in the vessel is controlled by

regulating the steam pressure in the jacket around the vessel.

Temperature

transmitter Temperature

controller Measurement

Output

SteamValve

Jacket

IN

OUT

SINGLE-LOOP CONTROL

Pressure

transmitter

Measurement Pressure

controller

Cascade Control Loop

Level 1 - Control


Temperature

Process

Steam Flow

Process

Load A

(Demand)

TIC

FT

TT

FC

Load B

(Header Pressu re)

SP RSP

_ _

I/P

TT

TIC

Steam

ColdWater

Hot

Water Condensate

Major Load A:Outflow Rate(Demand)

Major Load B:Steam Header

Pressure

Steam

Header

FT

FC

RSP

_

Implementing Cascade ControlImplementing Cascade Control





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27

Levelindicating

controller

Flow

controller

Boiler

Feedwater FT

Applies to a system in which a balance between supply and

demand is achieved by measuring both demand potential and

demand load and using this data to govern supply. It gives a

smoother and stable control than feedback control.


What is FEED FORWARD CONTROL ?What is FEED FORWARD CONTROL ?

FT LT

Steam

SP

PV O/P


Feed

forwardSP

Level 1 - Control


I/P

TT

FeedforwardLoop

TIC

Steam

ColdWater

HotWater

FT

FFD

FeedforwardEquations

SummingJunction

FeedbackLoop

ImplementingImplementing FeedforwardFeedforward ControlControl





Level 1 - Control

29

An uncontrolled flow determines a second flow so that a desired ratio

is maintained between them.

The ratio factor is set by a ratio relay or multiplying unit which would be

located between the wild flow transmitter and the flow controller set

point. Flow B is controlled in a preset ratio to flow A.


What is RATIO CONTROL ?What is RATIO CONTROL ?

Ratio

relayWild

flow, A

Controlled

flow, B

Remote -

set

controller

Output = A x ratio

SP

Output

Wild flow, A

Controlled

flow, B

Ratio

controller

Output


SP

Level 1 - Control

30


Example of RATIO CONTROLExample of RATIO CONTROL

Other Application : Fuel/air ratio control system on

combustion equipment, e.g. boilers.

Acidsupply

Magneticflowmeter

Pickle tank

Flowtransmitter

FT FC

Control valve

Flow BFlow AWater

Manualwater regulator

MeasurementSet

√

Pickling Process





Level 1 - Control

31

O/P

The more important condition between two or more candidates is

selected. They are used mainly to provide protection to a piece of

equipment which could suffer damage as a result of abnormal

operating conditions.


What is SELECTIVE CONTROL ?What is SELECTIVE CONTROL ?

Speed

ControlPIC

PIC

RS

Low select

PV

Pump

O/PO/P

PV


Level 1 - Control

32

Control AlgorithmControl Algorithm

•• On/Off On/Off

•• MultiMulti--stepstep

•• ProportionalProportional

•• IntegralIntegral

•• DerivativeDerivative





Level 1 - Control

33Control AlgorithmControl Algorithm

It is a two-position control, merely a switch arranged to be off

(or on as required) when the error is positive and on (or off as

required) when the error is negative. Ex.. Oven & Alarm control.

OnOn--Off Contro lOff Control

differentialMeasured

variable

Controller

output

Time

Level 1 - Control

34

A controller action that may initiate more than two positioning of

the control valve with respect to the respective predetermined

input values.


MultiMulti--Step ActionStep Action

Multi-step actionTime

Time

V a l v e

p o s i t i o n

I n p u t

1234

7

5

8

0

8

5





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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).


Proportional Action (P)Proportional Action (P)

Process

Load

Controller

Output

SP

PV

Open-loop response of proportional mode

Level 1 - Control

36


Proportional Action (P)Proportional Action (P)

When a disturbance alters the process away from the set-point, the

controller acts to restore initial conditions. In equilibrium, offset (PV-

SP = constant) results.

The Algorithm is :

O/P- (PV - SP)

ProportionalBand

Constant= +

S - PV

O/P %100

(Constant is normally 50% )

50θ

Tan θ = Gain = 100 / Proportional Band

Time

SP

Time

Recovery timeOffset

Many controllers have a ‘manual

reset’. This enables the operators

to manipulate the ‘constant’ term

of the algorithm to eliminate offset.

PV





Level 1 - Control


0 1 2 3 4 5 6 7 8 9

Time

100

90

80

70

60

50

40

30

20

10

%

SP

PV

Output

E1E0 E2 E3 E4

prop

Low Proport ional Gain: (Closed Loop)Low Proport ional Gain: (Closed Loop)

Level 1 - Control


0 1 2 3 4 5 6 7 8 9

Time

100

90

80

70

60

50

40

30

20

10

%

SP

PV

Output

High Proportional Gain: (Closed Loop)High Proportional Gain: (Closed Loop)





Level 1 - Control

39

Whilst PV ≠ SP, the controller operates to restore equality. As long as the measurement remains at the set point, there is no

change 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 by

Proportional Action alone.


Integral Action (I)Integral Action (I)

Time

Set

Point

%

Measurement

% OutputTime

Set

Point

a=b

RT

RT = Reset Time min./rpta {

b {

Integral mode Proportional plus Integral mode

Open-loopresponse

Level 1 - Control


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

Proportional

Response

Integral Act ion: (Closed Loop)Integral Action: (Closed Loop)





Level 1 - Control

41

As the PV changes, the controller resists the change.

The controllers output is proportional to the rate at which the

difference between the measured and desired value changes.

The derivative time is an indication of this action. It is the time that

the open-loop P+D response is ahead of the response due to P only.


Derivative Action (D)Derivative Action (D)

Time

Set

Point

%

Measurement

% Output

(I/D)

Derivative mode

Time

Set

Point

DT

DT = Derivative Time (min)

Proportional plus Derivative mode

Open-loopresponseProportional + Derivative

Proportional only

Level 1 - Control

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 AlgorithmControl AlgorithmPID Action: (Closed Loop)PID Action: (Closed Loop)





Level 1 - Control


PID ControlPID Control

A

B

80

60

40

20 % S

c a l e R a n g e

C o n t r o l l e r O u t p u t

o r

V a l v e P o s i t i o n

Measurement

Proportional

Time - minutes

Open-loop response of three-mode controller

Proportional + Integral +

Derivative

Proportional +

Integral

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44

I/P

PT

PIC

P


P & ID Piping & Instrumentation DrawingP & ID Piping & Instrumentation Drawing

Process Vessel

Fluid Pump

Pneumatic

Control

Valve

Compressed Air Pipe

Converter PID

Controller

Pressure

Transmitter





Level 1 - Control


Controller SelectionController Selection

Can offset be

tolerated ?

Start

Use

P-only

Yes

Use

P+I

Yes

No

Is dead time

excessive ?

No

Use

PID

Yes

Is noise

present ?

No Reaction curve

of measured

variable

CapacityDead Time

C

63.2

%

Time (sec)

Step change in

valve travel

Level 1 - Control

46


Controller AdjustmentController Adjustment

Time

C o n t r o l l e d V a r i a b l e

Period

P-only

PID

PI

Control loop Proportional band Time constant Derivative

Flow 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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47

An automatic control scheme in which the controller is programmed

to evaluate its own effectiveness and modify its own control

parameters to respond to dynamic conditions occurring in or to the

process which affect the controlled variables.

Control SystemControl System

Adaptive Control Adaptive Control

Ex) Digital Controller

- Sensors are run to the computer’s input.

- Servomechanisms are connected to the computer’s output.

- Future changes don’t require re-wiring.

- Changing control functions (P,I, and D) and configurations

(between cascade mode and feedforward mode) will be

made on the computer’s program and not necessarily to anyhardware.

Level 1 - Control

48


A control strategy where the process control computer performs

system control calculations and provides its output to the setpoints

inputs of conventional analog controllers. These analog controllers

actually control the process actuators, not the main-control

computer.

Supervisory ControlSupervisory Control

M.I.SSupervisory

Control

A

S

Controller

S

AController

S

AController

⇒SP1

⇒SP2

⇒SP3





Level 1 - Control

49

Measurement

HW andSoftware

Filtering

I/O Rack

Coax

Controller Tools for Process

Anal ysi s, Diagnosti cs.

Sampled

Value

Tools for Process Anal ysi s, Diagnosti cs.

Controller I/O Rack


Today’s DCS SystemToday’s DCS System

Level 1 - Control

50Control SystemControl System

Definition...

Control room

operator 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 ?What is a FIELDBUS ?

P

T

L

F





Level 1 - Control

51

Gateway HSE

H1

H1

H1

H1

BridgeH2

H1

H1

124

Devices

Work

Systems

H1 - 31.25 Kbit/sHSE - 100 M bit/s

(Fast Ethernet)

(due to address limits) .

Total of approximately 35,000 devices

FieldbusFieldbus Control SystemControl System

Controller

32 Devices

32

Devices


Level 1 - Control

52Control SystemControl System

AI AI

PIDPID

AI AI AO AO

PIDPID

DCS

4 -20 mA 4 -20 mA 4 -20 mA

ADVANCED CONTROL OPTIMIZATION

•• Control in the control roomControl in the control room

Proprietary BusProprietary Bus





Level 1 - Control

53

PIDIN

OUT

BKCAL_INFIELDVUE

AO

BKCAL_OUT

CAS_IN

AIOUT

Delta V

Valve

Transmitter


ControlControl

AnywhereAnywhere

Built Built-- In In

FunctionFunction

BlocksBlocks

FoundationFoundation FieldbusFieldbus DevicesDevices

•• Control in the field withControl in the field with fieldbusfieldbus

Level 1 - Control

54

FCS

Loop 1 Loop 2

Digital

PIDPID

DCS

Loop 1 Loop 2

Digital

PID

Anal og

DDC

Anal og

PID

Loop 1 Loop 2

Central

Control Loop

Local Control

Loop

Control in

the field

Control in the

device itself

Look at how the CONTROL migrateLook at how the CONTROL migrate





Level 1 - Control

55ExerciseExercise

Which defined term is closest to the description or encompasses the

example 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. [ ]

Level 1 - Control

56

ExerciseExercise

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 pneumaticsignal to an industry standard hydraulic signal. [ ]





Level 1 - Control

57ExerciseExercise

9. Identify the components indicated by the Arrows.

Level 1 - Control

58

ExerciseExercise

Which defined term is closest to the description or encompasses theexample given.

A. Cascade control F. GainB. Control algorithm G. OffsetC. Control valve H. Proprietary BusD. Feed-forward control I. Smart DeviceE. 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 controller’s output to input. [ ]

13. It is a final control element operated by an actuator. [ ]




Level 1 - Control

59ExerciseExercise

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. [ ]

Training - Control

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