Fundamentals Training Think About Control · PDF fileP & ID Piping & Instrumentation Drawing...

1

Fundamentals TrainingThink About Control

Terminology Control

Control Fundamental - Con't

Eko Harsono

[email protected];

Contents

2

Topics: Slide No:• Advance Control Loop 3 - 10• Control Algorithm 11 - 25• Control System 26 - 32• Exercise 33 - 38


Advance Control Loop

3

Consist of one controller (primary, or master) controlling thevariable that 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 controlvalve.

What is CASCADE CONTROL ?What is CASCADE CONTROL ?

FBC FBC

Secondary Process

Primary Process

Secondary controller

Primary controller

Disturbancer1 r2 m

c1 c2

Multi-Variable Control



4

The temperature of the liquid in the vessel is controlled by regulating the steam pressure in the jacket around the vessel.

Example of CASCADE CONTROLExample of CASCADE CONTROL

Temperature transmitter

Temperature controller

Measurement

Output

SteamValve

Jacket

IN

OUT

SINGLE-LOOP CONTROL

Pressure transmitter

Measurement Pressure controller

Cascade Control LoopControl Fundamental - Con't


5

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 HeaderPressure

SteamHeader

FT

FC

RSP_

Implementing Cascade Control Implementing Cascade Control



6

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.

Level indicating controller

Flow controller

Boiler

FeedwaterFT

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

FT LT

Steam

SP

PV O/P


Feed forwardSP



7

I/P

TT

FeedforwardLoop

TIC

Steam

ColdWater

HotWater

FT

FFD

FeedforwardEquations

SummingJunction

FeedbackLoop

Implementing Feedforward ControlImplementing Feedforward Control



8

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 whichwould be located between the wild flow transmitter and the flowcontroller set point. Flow B is controlled in a preset ratio to flow A.

What is RATIO CONTROL ?What is RATIO CONTROL ?

Ratio relay

Wild flow, A

Controlled flow, B

Remote -set

controller

Output = A x ratio

SP

Output

Wild flow, A

Controlled flow, B

Ratio controller

Output


SP



9

Example of RATIO CONTROLExample of RATIO CONTROL

Other Application : Fuel/air ratio control system on combustion equipment, e.g. boilers.

Acid supply

Magnetic flowmeter

Pickle tank

Flow transmitter

FT FC

Control valve

Flow BFlow AWater

Manual water regulator

MeasurementSet

Pickling Process



10

The more important condition between two or more candidatesis selected. They are used mainly to provide protection to apiece of equipment which could suffer damage as a result ofabnormal operating conditions.

O/P

What is SELECTIVE CONTROL ?What is SELECTIVE CONTROL ?

Speed ControlPIC

PIC

RSLow select

PV

Pump

O/PO/P

PV



Control Algorithm

11

•• On/Off On/Off

•• MultiMulti--stepstep

•• ProportionalProportional

•• IntegralIntegral

•• DerivativeDerivative


Control Algorithm

12

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 ControlOff Control

differentialMeasured variable

Controller output

Time


Control Algorithm

13

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

1234

75

80

85


Control Algorithm

14

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 modeControl Fundamental - Con't

Control Algorithm

15

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.

Proportional Action (P)Proportional Action (P)The Algorithm is :

O/P - (PV - SP)Proportional

Band

Constant= +

S - PV

O/P %100

(Constant is normally 50% )

50

Tan = Gain = 100 / Proportional Band

Time

SP

Time

Recovery time Offset

Many controllers have a ‘manual reset’. This enables the operators to manipulate the ‘constant’ term of the algorithm to eliminate offset.

PV


Control Algorithm

16

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)Low Proportional Gain: (Closed Loop)


Control Algorithm

17

0 1 2 3 4 5 6 7 8 9Time

100

90

80

70

60

50

40

30

20

10

%

SPPV

Output

higain

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


Control Algorithm

18

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

% Output

Time

Set Point

a=b

RT

RT = Reset Time min./rpta {b {

Integral mode Proportional plus Integral mode

Open-loop response


Control Algorithm

19

0 1 2 3 4 5 6 7 8 9Time

100

90

80

70

60

50

40

30

20

10

%

SP

PV

ProportionalPlus IntegralOutput

ProportionalResponse

Integral Action: (Closed Loop)Integral Action: (Closed Loop)


Control Algorithm

20

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-loop response

Proportional + Derivative

Proportional only


Control Algorithm

21

0 1 2 3 4 5 6 7 8 9Time

100

90

80

70

60

50

40

30

20

10

%

SP

PV PID Output

PID Action: (Closed Loop)PID Action: (Closed Loop)


Control Algorithm

22

PID ControlPID Control

A

B

80

60

40

20% S

cale

Ran

geC

ontro

ller O

utpu

tor

Valv

e P

ositi

onMeasurement

Proportional

Time - minutes

Open-loop response of three-mode controller

Proportional + Integral + Derivative

Proportional + Integral


Control Algorithm

23

I/P

PT

PIC

P

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

Process Vessel

Fluid Pump

PneumaticControlValve

Compressed Air Pipe

ConverterPID

Controller

PressureTransmitter


Control Algorithm

24

Controller SelectionController Selection

Can offset be tolerated ?

Start

UseP-only

Yes

UseP+I

Yes

No

Is dead time excessive ?

No

UsePID

Yes

Is noise present ?

No Reaction curve of measured

variable

CapacityDead Time

C

63.2%

Time (sec)

Step change in valve travel


Control Algorithm

25

Controller AdjustmentController Adjustment

Time

Con

trolle

d Va

riabl

e Period

P-only

PID

PI

Control loop Proportional band Time constant DerivativeFlow High (250%) Fast (1 to 15 sec) NeverLevel Low Capacity dependent RarelyTemperature Low Capacity dependent UsuallyAnalytical High Usually slow SometimesPressure Low Usually fast SometimesControl Fundamental - Con't

Control System

26

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.

Adaptive ControlAdaptive 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 any hardware.


Control System

27

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.S Supervisory Control

A

S

Controller

S

AController

S

AController

SP1

SP2

SP3


28

Control System

Measurement

HW andSoftwareFiltering

I/O Rack

Coax

ControllerTools for Process Analysis, Diagnostics.

SampledValue

Tools for Process Analysis, Diagnostics.

ControllerI/O Rack

Today’s DCS SystemToday’s DCS System


Control System

29

Definition...

Control roomoperator stations

Control systems(DCS or PLC)

A digital, two-way, multi-drop communication link among intelligent field devices and automation systems.

Fieldbus (Only Digital Signals)

What is a FIELDBUS ?What is a FIELDBUS ?

P

T

L

F


Control System

30

Gateway HSE

H1H1H1H1

BridgeH2

H1

H1

124Devices

Work Systems

H1 - 31.25 Kbit/sHSE - 100 M bit/s(Fast Ethernet)

(due to address limits) .Total of approximately 35,000 devices

Fieldbus Control SystemFieldbus Control System

Controller

32 Devices

32DevicesControl Fundamental - Con't

Control System

31

AI

PID

AI AO

PID

DCS

4 -20 mA 4 -20 mA4 -20 mA

ADVANCED CONTROL OPTIMIZATION

•• Control in the control roomControl in the control room

Proprietary BusProprietary Bus


Control System

32

PIDIN OUT

BKCAL_IN FIELDVUE

AO

BKCAL_OUT

CAS_IN

AIOUT

Delta V

Valve

Transmitter

Control Control AnywhereAnywhere

BuiltBuilt--InInFunction Function BlocksBlocks

Foundation Fieldbus DevicesFoundation Fieldbus Devices

•• Control in the field with fieldbusControl in the field with fieldbusControl Fundamental - Con't

Look at how the CONTROL migrate

33

FCS

Loop 1 Loop 2

Digital

PID PID

DCS

Loop 1 Loop 2

Digital

PID

Analog

DDC

Analog

PID

Loop 1 Loop 2

Central Control Loop

Local Control Loop

Control in the field

Control in the device itself


Exercise

34

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. [ ]


Exercise

35

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. [ ]


Exercise

36

9. Identify the components indicated by the Arrows.


Exercise

37

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

A. Cascade control F. GainB. Control algorithm G. OffsetC. Control valve H. Proprietary BusD. 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 controller’s output to input. [ ]

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


Exercise

38

14. Involves master & slave controllers. [ ]

15. The output of the loop drives the input. [ ]

16. A digital communication based control network with control action in the controller only. [ ]

17. A digital communication based control network that allow control in the field. [ ]

18. A device that provide both analog & communication signal in its loop wire pair. [ ]


Reference A Smith-Corripio [1997]. Principles and Practice

of Automatic Process Control 2nd Edition, John Willey & Sons

Ogata [2010]. Modern Control Engineering 5th

Edition, Prentice Hall Rosemont [2002]. Fundamental Control Training http://www.isa.org

39 Control Fundamental - Con't

Date post:	10-Feb-2018
Category:	Documents
Upload:	vuongnguyet
View:	217 times
Download:	2 times

Fundamentals Training Think About Control · PDF fileP & ID Piping & Instrumentation Drawing...

Documents