ion & Control Eng'g

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Instrumentation engineeringInstrumentation engineering

Instrumentation engineeringInstrumentation engineering is theis the

engineering specialization focused on theengineering specialization focused on the

principle and operation of measuringprinciple and operation of measuring

instruments which are used in design andinstruments which are used in design and

configuration of automated systems inconfiguration of automated systems inelectrical, pneumatic domains etc. Theyelectrical, pneumatic domains etc. They

typically work for industries withtypically work for industries with automatedautomated

processes, such asprocesses, such as chemicalchemical or or manufacturingmanufacturing plants, with the goal of plants, with the goal of

improving systemimproving system productivityproductivity, reliability,, reliability,

safety, optimization, and stability.safety, optimization, and stability.



Applications of Instrumentation to Measurement Applications of Instrumentation to Measurement

Instrumentation is used to measure manyInstrumentation is used to measure manyparameters (physical values). These parametersparameters (physical values). These parameters

include:include:

PressurePressure, either , either differentialdifferential or or staticstatic

FlowFlow

TemperatureTemperature

LevelsLevels of liquids etc.of liquids etc.

DensityDensity

ViscosityViscosity

Other mechanical properties of materialsOther mechanical properties of materials

FrequencyFrequency

CurrentCurrent



Applications of Instrumentation in Measurement Applications of Instrumentation in Measurement

VoltageVoltage InductanceInductance

CapacitanceCapacitance

ResistivityResistivity Chemical compositionChemical composition

Chemical propertiesChemical properties

Properties of lightProperties of light

VibrationVibration

WeightWeight



Example: Control Panel of a Steam TurbineExample: Control Panel of a Steam Turbine



Instrumentation EngineeringInstrumentation Engineering

Instrumentation engineeringInstrumentation engineering deals with thedeals with thedesign of devices to measure physicaldesign of devices to measure physical

quantities such asquantities such as pressure, flow andpressure, flow and

temperaturetemperature. The design of such. The design of suchinstrumentation requires a goodinstrumentation requires a good

understanding of understanding of physicsphysics that often extendsthat often extends

beyondbeyond electromagnetic theoryelectromagnetic theory. For . For

example,example, thermocouplesthermocouples use theuse the Peltier Peltier--SeebeckSeebeck effecteffect to measure the temperatureto measure the temperature

difference between two points.difference between two points.




Often instrumentation is not used by itself,Often instrumentation is not used by itself,

but instead as thebut instead as the sensorssensors of larger of larger

electrical systems. For example, aelectrical systems. For e

xample, athermocouple might be used to help ensurethermocouple might be used to help ensure

a furnace's temperature remains constant.a furnace's temperature remains constant.

For this reason, instrumentation engineeringFor this reason, instrumentation engineering

is often viewed as the counterpart of controlis often viewed as the counterpart of controlengineeringengineering




An instrument is a device that measures An instrument is a device that measures

and/or regulates process variables such asand/or regulates process variables such as

flow, temperature, level, or pressure.flow, temperature, level, or pressure.Instruments include many variedInstruments include many varied

contrivances which can be as simple ascontrivances which can be as simple as

valvesvalves andand transmitterstransmitters, and as complex as, and as complex as

analyzersanalyzers. Instruments often comprise. Instruments often comprisecontrol systems of varied processes such ascontrol systems of varied processes such as

refineries, factories, and vehicles.refineries, factories, and vehicles.




The control of processes is one of the mainThe control of processes is one of the main

branches of applied instrumentation.branches of applied instrumentation.

The control of the parameters in a processThe control of the parameters in a processor in a particular system, are made possibleor in a particular system, are made possible

by using devices such as microprocessors,by using devices such as microprocessors,

microcontrollers or PLCs, but their ultimatemicrocontrollers or PLCs, but their ultimate

aim is to control the parameters of a system.aim is to control the parameters of a system.




Output instrumentation includes devices such asOutput instrumentation includes devices such assolenoidssolenoids,, valvesvalves,, regulatorsregulators,, circuit breakerscircuit breakers, and, and

relaysrelays. These devices control a desired output. These devices control a desired output

variable, and provide either remote or automatedvariable, and provide either remote or automated

control capabilities. These are often referred to ascontrol capabilities. These are often referred to asfinal control elements when controlled remotely or final control elements when controlled remotely or

by aby a control systemcontrol system..

Control Instrumentation plays a significant role inControl Instrumentation plays a significant role in

both gathering information from the field andboth gathering information from the field and

changing the field parameters, and as such are achanging the field parameters, and as such are a

key part of key part of control loopscontrol loops..




TransmittersTransmitters are devices which produce an outputare devices which produce an outputsignal, often in the form of a 4signal, often in the form of a 4± ±2020 m Am A electricalelectrical

currentcurrent signal, although many other options usingsignal, although many other options using

voltagevoltage,, frequencyfrequency,, pressurepressure, or , or ethernetethernet areare

possible. This signal can be used for informationalpossible. This signal can be used for informationalpurposes, or it can be sent to apurposes, or it can be sent to a PLCPLC,, DCSDCS,, SC AD ASC AD A

system, or other type of computerized controller,system, or other type of computerized controller,

where it can be interpreted into readable values andwhere it can be interpreted into readable values and

used to control other devices and processes in theused to control other devices and processes in thesystem.system.




A A programmable logic controller programmable logic controller ((PLCPLC) or ) or programmable controller programmable controller is ais a digital computer digital computer used for used for

automationautomation of of electromechanicalelectromechanical processes, such asprocesses, such as

control of machinery on factorycontrol of machinery on factory assembly linesassembly lines,,

amusement rides, or lighting fixtures. Unlike generalamusement rides, or lighting fixtures. Unlike general--

purpose computers, the PLC is designed for multiple inputspurpose computers, the PLC is designed for multiple inputs

and output arrangements, extended temperature ranges,and output arrangements, extended temperature ranges,

immunity to electrical noise, and resistance to vibration andimmunity to electrical noise, and resistance to vibration and

impact. Programs to control machine operation areimpact. Programs to control machine operation are

typically stored in batterytypically stored in battery--backed or backed or nonnon--volatile memoryvolatile memory. A . A PLC is an example of aPLC is an example of a real timereal time system since outputsystem since output

results must be produced in response to input conditionsresults must be produced in response to input conditions

within a bounded time, otherwise unintended operation willwithin a bounded time, otherwise unintended operation will

result.result.




ProgrammingProgramming

PLC programs are typically written in aPLC programs are typically written in a

special application on a personal computer,special application on a personal computer,

then downloaded by a directthen downloaded by a direct--connectionconnectioncable or over a network to the PLC. Thecable or over a network to the PLC. The

program is stored in the PLC either inprogram is stored in the PLC either in

batterybattery--backedbacked--upup R AMR AM or some other nonor some other non--

volatilevolatile flash memoryflash memory. Often, a single PLC. Often, a single PLC

can be programmed to replace thousands of can be programmed to replace thousands of

relaysrelays..




IEC 61131IEC 61131--3 currently defines five programming3 currently defines five programminglanguages for programmable control systems:languages for programmable control systems:

FBD (FBD (Function block diagramFunction block diagram), LD (), LD (Ladder Ladder

diagramdiagram), ST (), ST (Structured textStructured text, similar to the, similar to the PascalPascal

programming languageprogramming language), IL (), IL (Instruction listInstruction list, similar , similar toto assembly languageassembly language) and SFC () and SFC (SequentialSequential

function chartfunction chart). These techniques emphasize). These techniques emphasize

logical organization of operations.logical organization of operations. While the fundamental concepts of PLC programming are common toWhile the fundamental concepts of PLC programming are common to

all manufacturers, differences in I/O addressing, memory organizationall manufacturers, differences in I/O addressing, memory organization

and instruction sets mean that PLC programs are never perfectlyand instruction sets mean that PLC programs are never perfectly

interchangeable between different makers. Even within the sameinterchangeable between different makers. Even within the same

product line of a single manufacturer, different models may not beproduct line of a single manufacturer, different models may not be

directly compatible.directly compatible.



Digital andDigital and analoganalog signalssignals

Digital or discrete signals behave as binaryDigital or discrete signals behave as binaryswitches, yielding simply an On or Off signal (1 or switches, yielding simply an On or Off signal (1 or

0, True or False, respectively). Push buttons, limit0, True or False, respectively). Push buttons, limit

switches, andswitches, and photoelectric sensorsphotoelectric sensors are examplesare examples

of devices providing a discrete signal. Discreteof devices providing a discrete signal. Discrete

signals are sent using either signals are sent using either voltagevoltage or or currentcurrent,,

where a specific range is designated aswhere a specific range is designated as OnOn andand

another asanother as Off Off . For example, a PLC might use 24. For example, a PLC might use 24

V DC I/O, with values above 22 V DC representingV DC I/O, with values above 22 V DC representing

OnOn, values below 2VDC representing, values below 2VDC representing Off Off , and, and

intermediate values undefined. Initially, PLCs hadintermediate values undefined. Initially, PLCs had

only discrete I/O.only discrete I/O.



Digital andDigital and analoganalog signalssignals

Analog Analog signals are like volume controls, with a range of signals are like volume controls, with a range of values between zero and fullvalues between zero and full--scale. These are typicallyscale. These are typically

interpreted as integer values (counts) by the PLC, withinterpreted as integer values (counts) by the PLC, with

various ranges of accuracy depending on the device andvarious ranges of accuracy depending on the device and

the number of bits available to store the data. As PLCsthe number of bits available to store the data. As PLCs

typically use 16typically use 16--bit signed binary processors, the integer bit signed binary processors, the integer

values are limited betweenvalues are limited between --32,768 and +32,767. Pressure,32,768 and +32,767. Pressure,

temperature, flow, and weight are often represented bytemperature, flow, and weight are often represented by

analoganalog signals.signals. Analog Analog signals can usesignals can use voltagevoltage or or currentcurrent

with a magnitude proportional to the value of the processwith a magnitude proportional to the value of the processsignal. For example, ansignal. For example, an analoganalog 00 -- 1010 V input or V input or 44--2020 m Am A

would bewould be convertedconverted into an integer value of 0into an integer value of 0 -- 32767.32767.



Example: PLC ApplicationExample: PLC Application

As an example, say a facility needs to store water As an example, say a facility needs to store water in a tank. The water is drawn from the tank byin a tank. The water is drawn from the tank by

another system, as needed, and our exampleanother system, as needed, and our example

system must manage the water level in the tank.system must manage the water level in the tank.

-- Using only digital signals, the PLC has two digitalUsing only digital signals, the PLC has two digitalinputs frominputs from float switchesfloat switches (Low Level and High(Low Level and High

Level). When the water level is above the switch itLevel). When the water level is above the switch it

closes a contact and passes a signal to an input.closes a contact and passes a signal to an input.

The PLC uses a digital output to open and closeThe PLC uses a digital output to open and closethe inletthe inlet valvevalve into the tank.into the tank.




-- When the water level drops enough so thatWhen the water level drops enough so that

the Low Level float switch is off (down), thethe Low Level float switch is off (down), the

PLC will open the valve to let more water in.PLC will open the valve to let more water in.

Once the water level rises enough so thatOnce the water level rises enough so thatthe High Level switch is on (up), the PLC willthe High Level switch is on (up), the PLC will

shut the inlet to stop the water fromshut the inlet to stop the water from

overflowing. This rung is an example of overflowing. This rung is an example of sealseal--in (latching) logic. The output is sealedin (latching) logic. The output is sealed

in until some condition breaks the circuit.in until some condition breaks the circuit.




Ladder DiagramLadder Diagram

Low LevelLow Level High Level Fill ValveHigh Level Fill Valve

--------------------------------------------[/][/]------------------------------------------------[/][/]----------------------------------------(OUT)(OUT)----------------

Fill ValveFill Valve

----------------------------------------------[ ][ ]----------------------



Considerations:Considerations:

An An analoganalog system might use a water system might use a water pressure sensor pressure sensor or aor aload cellload cell, and an adjustable (throttling) dripping out of the, and an adjustable (throttling) dripping out of the

tank, the valve adjusts to slowly drip water back into the tank.tank, the valve adjusts to slowly drip water back into the tank.

In this system, to avoid 'flutter' adjustments that can wear outIn this system, to avoid 'flutter' adjustments that can wear out

the valve, many PLCs incorporate "the valve, many PLCs incorporate "hysteresishysteresis" which" whichessentially creates a "essentially creates a "deadbanddeadband" of activity. A technician" of activity. A technician

adjusts thisadjusts this deadbanddeadband so the valve moves only for aso the valve moves only for a

significant change in rate. This will in turn minimize the motionsignificant change in rate. This will in turn minimize the motion

of the valve, and reduce its wear.of the valve, and reduce its wear.

A real system might combine both approaches, using float A real system might combine both approaches, using floatswitches and simple valves to prevent spills, and a rateswitches and simple valves to prevent spills, and a rate

sensor and rate valve to optimize refill rates and preventsensor and rate valve to optimize refill rates and prevent

water hammer water hammer . Backup and maintenance methods can make. Backup and maintenance methods can make

a real system very complicated.a real system very complicated.




A A distributed control systemdistributed control system (DCS) refers to a(DCS) refers to a controlcontrolsystemsystem usually of ausually of a manufacturing systemmanufacturing system,, processprocess or anyor any

kind of kind of dynamic systemdynamic system, in which the, in which the controller controller elementselements

are not central in location (like theare not central in location (like the brainbrain) but are distributed) but are distributed

throughout the system with each component subthroughout the system with each component sub--systemsystem

controlled by one or more controllers. The entire system of controlled by one or more controllers. The entire system of

controllers is connected by networks for communicationcontrollers is connected by networks for communication

and monitoring.and monitoring.

DCS is a very broad term used in a variety of industries, to monitor andDCS is a very broad term used in a variety of industries, to monitor and

control distributed equipment:control distributed equipment:E

lectrical power gridsE

lectrical power grids andand electricalelectricalgenerationgeneration plants, Environmental control systems,plants, Environmental control systems, Traffic signalsTraffic signals, radio, radio

signals, Water management systems, Oilsignals, Water management systems, Oil refiningrefining plants,plants, ChemicalChemical

plantsplants,, PharmaceuticalPharmaceutical manufacturing,manufacturing, Sensor networksSensor networks, Dry cargo and, Dry cargo and

bulk oil carrier bulk oil carrier shipsships



Example: DCS applied to Building AutomationExample: DCS applied to Building Automation




SCADASCADA stands for stands for supervisory cont rol and d at a acquisi t ionsupervisory cont rol and d at a acquisi t ion..It generally refers to industrial control systems: computer It generally refers to industrial control systems: computer

systems that monitor and control industrial, infrastructure, or systems that monitor and control industrial, infrastructure, or

facilityfacility--based processes:based processes:

--Industrial processes include those of Industrial processes include those of manufacturingmanufacturing,, productionproduction,, power power generationgeneration,, fabricationfabrication, and, and refiningrefining, and may run in continuous, batch,, and may run in continuous, batch,

repetitive, or discrete modes.repetitive, or discrete modes.

-- Infrastructure processes may be public or private, and includeInfrastructure processes may be public or private, and include water water

treatmenttreatment and distribution, wastewater collection andand distribution, wastewater collection and treatmenttreatment, oil and, oil and

gas pipelines, electrical power transmission and distribution,gas pipelines, electrical power transmission and distribution, WindWind

farmsfarms,, civilcivil defensedefense sirensiren systems, and large communication systems.systems, and large communication systems.

--Facility processes occur both in public facilities and private ones,Facility processes occur both in public facilities and private ones,

including buildings, airports, ships, and space stations. They monitor including buildings, airports, ships, and space stations. They monitor

and controland control HV ACHV AC, access, and energy consumption., access, and energy consumption.



SCADA schematic overviewSCADA schematic overview



What is Control Engineering?What is Control Engineering?

engineeringengineering discipline that focuses on thediscipline that focuses on themathemat ical mathemat ical mod eli ng mod eli ng systems of a diversesystems of a diverse

nature, analyzing their dynamic behavior,nature, analyzing their dynamic behavior,

and usingand using cont rol theory cont rol theory to make a controller to make a controller

that will cause the systems to behave in athat will cause the systems to behave in a

desired manner.desired manner.

Control engineering is closely related toControl engineering is closely related to

electrical engineeringelectrical engineering, as electronic circuits, as electronic circuitscan often be easily described using controlcan often be easily described using control

theory techniques.theory techniques.



What is meant by Control?What is meant by Control?

ControlControl ± ± the process in a system in whichthe process in a system in which

one or several input variables influenceone or several input variables influence

other output variables as a result of the lawsother output variables as a result of the lawspertaining to the system. Controlling ispertaining to the system. Controlling is

characterized by thecharacterized by the openopen--looploop sequence of sequence of

actions via the single transfer element or theactions via the single transfer element or the

control chain.control chain. (accor d i ng t o DIN 19226)(accor d i ng t o DIN 19226)



As shown in the As shown in the Fig.1Fig.1, the input variables, the input variables xe xe «..acting on«..acting on

this system are linked in a self this system are linked in a self-- contained box andcontained box and

issued as output variablesissued as output variables xa xa«.. and these variables«.. and these variables

now act on the energy flow or mass flow to be controlled.now act on the energy flow or mass flow to be controlled.Fig 1.1Fig 1.1

x x e1e1

x x e2e2 x x a1a1

x x e3e3 x x a2a2

In general:In general: xaxa = f (= f ( xexe ))

The term ³control´ is often applied to the complete systemThe term ³control´ is often applied to the complete systemin which controlling takes place, not only to the controlin which controlling takes place, not only to the control

operation itself.operation itself.



What is meant by Control?What is meant by Control?

The field of control withinThe field of control within chemicalchemical

engineeringengineering is often known asis often known as processprocess

controlcontrol. It deals primarily with the control of . It deals primarily with the control of variables in a chemical process in a plant. Itvariables in a chemical process in a plant. It

employs many of the principles in controlemploys many of the principles in control

engineering, and is a wellengineering, and is a well--established fieldestablished field

in its own right.in its own right.



Process ControlProcess Control (process control(process control

engineering):engineering):

an engineering discipline that deals withan engineering discipline that deals with

architecture, mechanisms, and algorithmsarchitecture, mechanisms, and algorithms

for controlling the output of a specificfor controlling the output of a specificprocess.process.

uses analog sensors to monitor realuses analog sensors to monitor real--worldworld

signals and digital computers to do thesignals and digital computers to do theanalysis and controlling; makes extensiveanalysis and controlling; makes extensive

use of analog/digital and digital/analoguse of analog/digital and digital/analog

conversion.conversion.



In practice, process control systems can beIn practice, process control systems can be

characterized as one or more of the following forms:characterized as one or more of the following forms:

Discr eteDiscr ete ± ± Found in many manufacturing,Found in many manufacturing,

motion and packaging applications, discretemotion and packaging applications, discrete

process control systems use a device calledprocess control systems use a device calledaa progr ammable l ogic cont roller progr ammable l ogic cont roller (PLC) to(PLC) to

read a set of digital and analog inputs, applyread a set of digital and analog inputs, apply

a set of logic statements, and generate a seta set of logic statements, and generate a set

of outputs. Robotic assembly, such as thatof outputs. Robotic assembly, such as thatfound in automotive production, can also befound in automotive production, can also be

characterized as discrete process control.characterized as discrete process control.





Bat chBat ch ± ± Some applications require thatSome applications require that

specific quantities of raw materials bespecific quantities of raw materials be

combined in specific ways for particular combined in specific ways for particular duration to produce an intermediate or endduration to produce an intermediate or end

result. One example is the production of result. One example is the production of

adhesives and glues, which normally requireadhesives and glues, which normally require

the mixing of raw materials in a heatedthe mixing of raw materials in a heatedvessel for a period of time to form a quantityvessel for a period of time to form a quantity

of end product.of end product.





C ont inuousC ont inuous ± ± Often, a physical system isOften, a physical system is

represented though variables that arerepresented though variables that are

smooth and uninterrupted in time. Thesmooth and uninterrupted in time. Thecontrol of the water temperature in a heatingcontrol of the water temperature in a heating

jacket, for example, is an example of jacket, for example, is an example of

continuous process control.continuous process control.

Hy brid Hy brid -- applications having elements of applications having elements of

discrete, batch and continuous processdiscrete, batch and continuous process

controlcontrol



W hat is a C ont rol S y stem? W hat is a C ont rol S y stem?

a device or set of devices that manage thea device or set of devices that manage thebehavior of other devices.behavior of other devices.

an interconnection of componentsan interconnection of components(mechanical, electrical, optical, thermal or (mechanical, electrical, optical, thermal or

hydraulic) connected or related in such ahydraulic) connected or related in such a

manner as to command, direct, or regulatemanner as to command, direct, or regulate

itself or another system to maintain aitself or another system to maintain a

desired output.desired output.



W hat is a Cont roller?W hat is a Cont roller?

aa com ponent com ponent of aof a syst emsyst em that makesthat makes i t i t

operate within desired limits.operate within desired limits.

a device that attempts to control thea device that attempts to control the st at esst at esor or out put sout put s of aof a d y namic syst emd y namic syst em. Generally, it. Generally, it

accomplishes this usingaccomplishes this using f eedback f eedback to correctto correct

disturbances to the system; known asdisturbances to the system; known as

c l osed c l osed- - l oo pl oo p controlcontrol..



Example 1.1:Example 1.1:If the output of an air compressor is controlled by the quantityIf the output of an air compressor is controlled by the quantity

drawn in, then:drawn in, then: The opening and closing of the valve is theThe opening and closing of the valve is the cont rol operat ioncont rol operat ion

The valve, whose setting affects the quantity drawn in, is theThe valve, whose setting affects the quantity drawn in, is thecont rol element cont rol element

The opening provided by the valve is theThe opening provided by the valve is the cont rolled variablecont rolled variabley.y.

TheThe handwheelhandwheel with which the valve is actuated is thewith which the valve is actuated is thecont rol d evicecont rol d evice..

The varying load on the compressed air system caused byThe varying load on the compressed air system caused by

the users that affects the control system is thethe users that affects the control system is the d ist ur banced ist ur bancez z . This also applies to speed fluctuations or variations in the. This also applies to speed fluctuations or variations in thedegree of efficiency caused by the compressor. On thedegree of efficiency caused by the compressor. On theaccount of the open action loop of the control system, it isaccount of the open action loop of the control system, it isnot possible to compensate for such disturbance variablnot possible to compensate for such disturbance variables.es.



Types of control loops:Types of control loops:

openopen--loop loop controller controller does not usedoes not use feedbackfeedback toto

controlcontrol statesstates or or outputsoutputs of aof a dynamic systemdynamic system. Open. Open--

loop control is used for systems that are sufficientlyloop control is used for systems that are sufficiently

well characterized to predict whatwell characterized to predict what inputsinputs areare

necessary to achieve the desired states or outputs.necessary to achieve the desired states or outputs.

E.g. the velocity of aE.g. the velocity of a motor motor may be well characterizedmay be well characterized

for thefor the voltagevoltage fed into it, in which case feedback mayfed into it, in which case feedback may

not be necessary.not be necessary.

closedclosed--loop loop controller controller usesuses feedbackfeedback to controlto control

statesstates or or outputsoutputs of aof a dynamic systemdynamic system..



Fig. 1.2 shows the block diagram representing an openFig. 1.2 shows the block diagram representing an open--

loop control itself together with the system to be controlled.loop control itself together with the system to be controlled.

Fig. 1.2Fig. 1.2

DisturbanceDisturbance z1z1

Energy/MassEnergy/Mass

FlowFlow

Controller OutputController Output

yy Sequence of ActionsSequence of Actions

( Action Loop)( Action Loop)

DisturbanceDisturbance z2z2

Controlled

System

Controller



Controller

Sequence

of Actions

Controlled System

Controller Output

(Error) y

Energy/

Mass Flow

Command Variable w

Disturbance z2

Disturbance z1 Controlled

Variable x

Controller

Fig. 1.3 Closed-Loop Controller



AutomaticAutomatic controlcontrol

ProcessProcess inin whichwhich thethe cont rolled cont rolled variablevariable isiscontinuouslycontinuously measuredmeasured andand comparedcompared withwith another another variable,variable, thethe command command variable,variable, thethe processprocess beingbeinginfluencedinfluenced accordingaccording toto thethe resultresult of of thisthis comparisoncomparisonbyby modifyingmodifying toto matchmatch thethe command command variablevariable..

TheThe sequencesequence of of actionsactions resultingresulting fromfrom thisthis takestakesplaceplace inin aa closedclosed loop,loop, thethe cont rol cont rol looploop.. TheThe purposepurposeof of thethe closed closed looploop controlcontrol isis toto matchmatch thethe valuevalue of of thethecontrolledcontrolled variablevariable toto thethe valuevalue specifiedspecified byby thethe

commandcommand variablevariable eveneven if if perfectperfect equalizationequalization isis notnotattainedattained under under thethe prevailingprevailing circumstancescircumstances.. (according(accordingtoto DINDIN 1922619226))



Terms and Definitions:Terms and Definitions: Controlled SystemControlled System ± ± the part of the total system to bethe part of the total system to be

influenced.influenced.

Actuator Actuator ± ± element that acts on the mass flow or energyelement that acts on the mass flow or energy

flow to be controlled and is located at the input to theflow to be controlled and is located at the input to the

controlled system.controlled system.

Actuating pathActuating path ± ± path along which the actions determiningpath along which the actions determininga control operation are transmitted.a control operation are transmitted.

Controller Controller ± ± part of the actuating path causing thepart of the actuating path causing the

controlled system to be influenced by the actuator; thecontrolled system to be influenced by the actuator; the

control or automatic control proper whose elements link thecontrol or automatic control proper whose elements link theinput signals in accordance with the respective laws.input signals in accordance with the respective laws.

Disturbance pointDisturbance point -- point at which a factor acts that is notpoint at which a factor acts that is not

influenced by the system and which disturbs the conditioninfluenced by the system and which disturbs the condition

to be maintained.to be maintained.



Variables and their ranges in the actuatingVariables and their ranges in the actuating

path:path:

Controller outputController output y y ± ± output from the controller andoutput from the controller and

at the same time input variable to the controlat the same time input variable to the control

system.system.

Controller output rangeController output range y y hh ± ± range within which therange within which theoutput maybe adjusted.output maybe adjusted.

Desired valueDesired value x x A A ± ± value to be acted upon by thevalue to be acted upon by the

controlcontrol

Control rangeControl range x x Ah Ah ± ± range within which the desiredrange within which the desiredvalue may be when the control is operatedvalue may be when the control is operated

properly.properly.



Variables and their ranges in the actuatingVariables and their ranges in the actuating

path:path:

Command variableCommand variable w w ± ± value introduced from thevalue introduced from theoutside to the control chain or to the control loopoutside to the control chain or to the control loop

whose output value is to follow in a predeterminedwhose output value is to follow in a predetermined

manner (manner (ieie.. setpointsetpoint device in close loop control,device in close loop control,

input signal in open loop control.)input signal in open loop control.)w w hh ± ± range of command variablerange of command variable

Disturbance variableDisturbance variable z z ± ± variable acting from thevariable acting from the

outside that influences the intended action of theoutside that influences the intended action of the

control.control.

z z hh ± ± range within which the disturbance variable mayrange within which the disturbance variable may

be allowed without adversely affecting thebe allowed without adversely affecting the

operability of the control.operability of the control.



Example 2: House heating/ Air Example 2: House heating/ Air--conditioning systemconditioning system

In this example:In this example:

TheThe ther

most at ther

most at acts as theacts as the cont roller cont roller which directswhich directsthe activities of the heater.the activities of the heater.

heater or the air heater or the air--conditioner is the processor thatconditioner is the processor that

warms or cools the air inside the house.warms or cools the air inside the house.

thethe air air comi ng comi ng into the heater or air into the heater or air--conditioner is theconditioner is thei n put i n put ..

thethe air g oi ng out air g oi ng out of the heater of the heater or air conditioner is itsor air conditioner is its

out put out put ..

thethe air air t em perat ure read i ng st em perat ure read i ng s inside the house are theinside the house are the

f eedback f eedback s.s.

and finally, theand finally, the househouse is theis the environment environment in which thein which the

heating/air heating/air--conditioning system operatesconditioning system operates



W hat is feed back ? W hat is feed back ?

In cybernetics and control theory, feedback isIn cybernetics and control theory, feedback isa process whereby some proportion or ina process whereby some proportion or in

general, function, of the output signal of ageneral, function, of the output signal of a

system is passed (fed back) to the input.system is passed (fed back) to the input.

Often this is done intentionally, in order toOften this is done intentionally, in order to

control the dynamic behavior of the system.control the dynamic behavior of the system.

Feedback may be:Feedback may be:

neg at iveneg at ive, which tends to reduce output, or , which tends to reduce output, or

posi t ive posi t ive, which tends to increase output., which tends to increase output.



Example 3Example 3P rocess:P rocess: cooling a roomcooling a room

Desired out come:Desired out come: reach/ maintain a definedreach/ maintain a definedtemperature constant over temperature constant over

time, say 20time, say 20 oo CC

Cont rolled variableCont rolled variable:: temperaturetemperature

I n put variable:I n put variable: temperature, since it is measuredtemperature, since it is measured

by a thermometer and is used toby a thermometer and is used to

decide whether to cool or notdecide whether to cool or not

Set poi nt Set poi nt :: 2020oo

CCManipulat ed variable:Manipulat ed variable: state of the cooler (the settingstate of the cooler (the setting

of the valve allowing chilled water to flow throughof the valve allowing chilled water to flow through

it)it)



SignalsSignals

Signals represent information, theSignals represent information, the

representation may refer to the value or therepresentation may refer to the value or the

change in values of a physical dimensionchange in values of a physical dimension

and may refer to transmission, processing or and may refer to transmission, processing or

storage of information.storage of information.

In abstract considerations, signal refers toIn abstract considerations, signal refers to

values or change in value of mathematicalvalues or change in value of mathematicalquantities.quantities.



Types of SignalsTypes of Signals

Analog Analog ± ± information is assigned continuouslyinformation is assigned continuously

point by point to a range of values.point by point to a range of values.

DigitalDigital ± ± the range to be considered is dividedthe range to be considered is divided

into a finite number of separate value ranges,into a finite number of separate value ranges,

and one specific item of information is assignedand one specific item of information is assigned

to each range of values.to each range of values.

The digital group includes theThe digital group includes the binary signalbinary signal,,also known as analso known as an onon--off signaloff signal, representing, representing

two items of information.two items of information.



Types of SignalsTypes of Signals

Digital signals are used more frequently inDigital signals are used more frequently incontrol engineering and the digital signals arecontrol engineering and the digital signals are

mainly in the form of binary signals.mainly in the form of binary signals.

These binary signals are of considerableThese binary signals are of considerablesignificance for information processing becausesignificance for information processing because

they can easily be produced by equipment (e.g.they can easily be produced by equipment (e.g.

switches) and can also be processed simply.switches) and can also be processed simply.

In practice, it is essential to clearly define theIn practice, it is essential to clearly define the

relationship between range of values and signalrelationship between range of values and signal

in the case of binary signalsin the case of binary signals



Analog Analog/Digital Signals illustrated/Digital Signals illustrated

If a continuously changeable pressure from 0If a continuously changeable pressure from 0

to 600kPa is considered, each intermediateto 600kPa is considered, each intermediate

value of the range maybe assigned a specificvalue of the range maybe assigned a specific

signal.signal. If the pressure is indicated on a BourdonIf the pressure is indicated on a Bourdon

pressure gauge, each intermediate valuepressure gauge, each intermediate value

corresponds to a specific position of thecorresponds to a specific position of thepointer. The position of the pointer representspointer. The position of the pointer represents

anan analoganalog signal.signal.



Analog Analog/Digital Signals illustrated/Digital Signals illustrated

If the dial is now divided into separate valueIf the dial is now divided into separate valueranges, say in pressure steps of 50ranges, say in pressure steps of 50 kPakPa andand

if each range is assigned a specific item of if each range is assigned a specific item of

information:information:

50 . . .50 . . . 100100 kPakPa,, value =1value =1100 . . .100 . . . 150150 kPakPa,, value = 1.5value = 1.5

150 . . .150 . . . 200kPa,200kPa, value =2,value =2,

Then, we are dealing with digitalThen, we are dealing with digitalsignals!signals!



Signal Flow DiagramSignal Flow Diagram

The Symbolic representation of theThe Symbolic representation of theeffective relationships between the signalseffective relationships between the signals

in a system.in a system. Block and line of actionBlock and line of action

XXe1e1

Linkage pointsLinkage points xxa1a1

XXe2e2

Branch pointsBranch points

X

X

X

X



Representation of a closed loop in the signal flow diagram

Xe1

Xe2 = y

y

X

W

Xd = W - X

_

+



Breakdown of the Control ChainBreakdown of the Control Chain

In the preceding sections, the controller hasIn the preceding sections, the controller hasbeen represented as a self been represented as a self--contained blockcontained block

which can be broken down even further. A which can be broken down even further. A

control can always be broken down by thecontrol can always be broken down by the

same method to show the arrangement of thesame method to show the arrangement of theindividual components; at the same timeindividual components; at the same time

showing the signal flow.showing the signal flow.

The control chain is thus characterized by aThe control chain is thus characterized by asignal flow from signal input via signalsignal flow from signal input via signal

processing to signal output/execution of processing to signal output/execution of

instruction.instruction.



Breakdown of the control chain:

Actuating Device

Processing Element

Input Element

Signal output/ execution

of instruction

Signal Processing

Signal input

Hardware breakdown Signal Flow

H d tH d t



Hardware terms:Hardware terms:

Actuating mechanism

Actuating mechanism ± ± element that has direct effect on aelement that has direct effect on acontrolled system, moves the final control element whencontrolled system, moves the final control element when

mechanically actuated.mechanically actuated.

Actuating device Actuating device ± ± consists of actuating mechanism and finalconsists of actuating mechanism and final

control element.control element.

Signal transducer Signal transducer ± ± device transform an input signal as clearlydevice transform an input signal as clearly

as possible into an associated output signal, where necessaryas possible into an associated output signal, where necessary

using auxiliary energy. Among others, this group of devicesusing auxiliary energy. Among others, this group of devices

includes amplifiers and signal converters.includes amplifiers and signal converters.

Signal amplifier Signal amplifier ± ± device using auxiliary energy for power device using auxiliary energy for power amplification.amplification.

Signal Converter Signal Converter ± ± devices in which input and output signalsdevices in which input and output signals

have different structurehave different structure

Examples of Hardware ElementsExamples of Hardware Elements



Examples of Hardware ElementsExamples of Hardware Elements Signal elements:Signal elements: limit switch with cam and roller limit switch with cam and roller

operation, proximity switches,operation, proximity switches,light barriers, reflex sensors,light barriers, reflex sensors,

push buttons, manual switches,push buttons, manual switches,

etc.etc.

Processing elements:Processing elements: Electronic logic elements,Electronic logic elements,contactors, relays, valvescontactors, relays, valves

released by pneumatic logic, etc.released by pneumatic logic, etc.

Final control elements:Final control elements: Power contactors, pneumaticPower contactors, pneumatic

and hydraulic (directional control)and hydraulic (directional control)valves, etc.valves, etc.

Drive elements:Drive elements: Electric motors, pneumatic/Electric motors, pneumatic/

hydraulic motors, cylinders, etc.hydraulic motors, cylinders, etc.



Types of controlsTypes of controls visvis aa visvis power requirement:power requirement:

Control without auxiliaryControl without auxiliary ± ± power requirement topower requirement to

adjust the final control element is provided by theadjust the final control element is provided by theinput element of the control.input element of the control.

Control with auxiliary energyControl with auxiliary energy ± ± power required topower required to

adjust the final control element is supplied entirely or adjust the final control element is supplied entirely or

in part through a source of auxiliary energy.in part through a source of auxiliary energy.

It is possible to operate with different levels of It is possible to operate with different levels of

energy within the control chain, thus it is necessaryenergy within the control chain, thus it is necessary

to distinguish theto distinguish the working energyworking energy ± ± the energythe energyrequired to operate the actuating device, from therequired to operate the actuating device, from the

control energycontrol energy that supplies the signal input andthat supplies the signal input and

signal processing.signal processing.



Based on these considerations, an extended controlBased on these considerations, an extended control

chain can be drawn up as follows:chain can be drawn up as follows:

Input Element

Processing element

Transducer

Actuating

Device

Controlled System

Execution of

Instruction

Signal Output

Processing element

Signal element

Controller

Operative part

Examples of hardware used for Electrical and Pneumatic Systems



Actuating Mechanism

Final Control Elements

Electric Motor

Solenoid

Linear motor

Power contactors

Pneumatic cylinder

Air motor

Directional control valves

Processing Elements Auxiliary Contactors

Relays

Directional control valves

Non-return valves

Pressure control valves

Flow Control valves

Input Elements Switches

Push buttons

Limit switches

Program generators

Proximity signallers

Switches

Push buttons

Limit switches

Program generators

Proximity signallers

Electrical Systems Pneumatic Systems

Examples of hardware used for Electrical and Pneumatic Systems

Ex Control with the same form of energy for theEx Control with the same form of energy for the



Ex. Control with the same form of energy for theEx. Control with the same form of energy for the

operative and control partoperative and control part

II I

Controlled System

Actuating

Mechanism

Final controlelement

Signal

processing

Signal input

1.31.2

1.51.1



Types of energy for operative and control partTypes of energy for operative and control part

By means of suitable devices (signal transformers/By means of suitable devices (signal transformers/

transducers) it is possible to convert one type of transducers) it is possible to convert one type of energy into signals of another type of energyenergy into signals of another type of energy ± ± inin

control engineering, one can work within the controlledcontrol engineering, one can work within the controlled

system with different types of energy.system with different types of energy.

In practice however, it is not always easy to select theIn practice however, it is not always easy to select the

³right control system´. Apart from the immediate³right control system´. Apart from the immediate

requirements of the problem, therequirements of the problem, the auxiliaryauxiliary

requirementsrequirements in particular (place of installation,in particular (place of installation,

environmental influences, etc.) determine the solution.environmental influences, etc.) determine the solution.

These auxiliary often conflict with the simple solutionThese auxiliary often conflict with the simple solution

to the problem that can make project engineeringto the problem that can make project engineering

more difficult.more difficult.




If a system uses different types of energy for theIf a system uses different types of energy for the

operative and control parts, one refers to aoperative and control parts, one refers to a mixedmixedtechnologytechnology ± ± which is being used to an increasingwhich is being used to an increasing

extent in control design.extent in control design.

Working Media:-Mechanical

-Electrical

-Hydraulics

-Pneumatics

Criteria for system selection:-Force

-Displacement

-Type of motion

-Speed-Physical size

-Life

-Sensitivity

-Working safety

Ch i i f ki diCh i i f ki di



Characteristics of working media:Characteristics of working media:

Electrical:Electrical:

Energy storage difficult, transmission fast, costs low.Energy storage difficult, transmission fast, costs low.Creation of straight line motion complex andCreation of straight line motion complex and

expensive, as it is necessary either to convert byexpensive, as it is necessary either to convert by

mechanical means or short displacements possiblemechanical means or short displacements possible

with lifting magnets and only small forces possiblewith lifting magnets and only small forces possiblewith linear motors.with linear motors.

Creation of rotary motion at very high efficiency,Creation of rotary motion at very high efficiency,

large physical size, speed limited, speed torquelarge physical size, speed limited, speed torque

regulation difficult and elaborateregulation difficult and elaborate

Elements not overloadElements not overload--proof, not intrinsicallyproof, not intrinsically

explosionexplosion--proof.proof.





HydraulicsHydraulics

Storage of energy only to a limited degree, limitedStorage of energy only to a limited degree, limitedand slow energy transmission, high energy cost.and slow energy transmission, high energy cost.

Creation of straight line motion is very simple,Creation of straight line motion is very simple,

working speed not too high (up to 0.5m/s max.), veryworking speed not too high (up to 0.5m/s max.), very

small dimensions, large to very large forces can besmall dimensions, large to very large forces can beachieved.achieved.

Creation of rotary motion is simple, however at notCreation of rotary motion is simple, however at not

very high speed, speeds constant even at lowvery high speed, speeds constant even at low

range, high efficiency, high torquerange, high efficiency, high torque

Elements are overloadElements are overload--proof, line installation difficultproof, line installation difficult

and expensive and must be insured that system isand expensive and must be insured that system is

completely sealed.completely sealed.




PneumaticsPneumatics

Energy storage presents no problem, limited andEnergy storage presents no problem, limited andslow energy transmission, high energy costsslow energy transmission, high energy costs

Creation of straight line motion simple and cheap,Creation of straight line motion simple and cheap,

high working speeds (1high working speeds (1--2m/s), stroke length limited2m/s), stroke length limited

up to 2m depending on the design, force obtainableup to 2m depending on the design, force obtainableis limited up 40000N max., small dimensions.is limited up 40000N max., small dimensions.

Creation of rotary motion simple and cheap, highCreation of rotary motion simple and cheap, high

operating costs due to poor efficiency, high speedsoperating costs due to poor efficiency, high speeds

(up to 500,000m/min), torque obtainable not too high(up to 500,000m/min), torque obtainable not too high

Elements are over Elements are over--load proof, intrinsically explosionload proof, intrinsically explosion--

proof, very simple regulation of speed, torque, force.proof, very simple regulation of speed, torque, force.




Control Media:Control Media: Criteria for system selection:Criteria for system selection:

-- MechanicalMechanical -- Signal speedSignal speed

-- ElectricalElectrical -- Switching times of Switching times of elementselements

-- ElectronicsElectronics -- Working safety of elementsWorking safety of elements

-- Low pressure pneumaticsLow pressure pneumatics -- LifeLife

-- Normal pressure pneumaticsNormal pressure pneumatics -- Sensitivity to environmentalSensitivity to environmental

influencesinfluences

-- HydraulicsHydraulics -- Space requirementSpace requirement

-- Ease of maintenanceEase of maintenance



Electrical Electronics Normal-pressure

pneumatics

Low-pressure

pneumaticsSignal speed Very high,

approx speed of

sound

Very high,

approx speed of

sound

Approx 40-70 m/s 100-200m/s

normal, to some

extent speed of

light

Distance w/c can

be covered

Practically

unlimited

Practically

unlimited

Limited by speed of

signal

Limited by speed of

signalSwitching times

of elements

Greater than 10

ms

Less than 1 ms Greater than 10 ms Greater than 10 ms

Reliability Sensitive to envi

influences

Very sensitive to

envi influences

Insensitive to envi

influences

Insensitive to envi

influences

Space

requirement

large Very small Very large small

Main type of

signal processing

digital Digital, analog digital Digital, analog

Components Contactors,

relays

Electronic

valves,

transistors

Directional control

valves

Static, dynamic

elements

Characteristics of Control media:

Diff ti ti h t i ti f t lDiff ti ti h t i ti f t l



Differentiating characteristics of controlsDifferentiating characteristics of controls

Controls can be classified according to:Controls can be classified according to: Control energy usedControl energy used

Mode of operation with respect to signal processingMode of operation with respect to signal processing

Combined controlsCombined controls ± ± a certain combination of a certain combination of input signals is always associated with ainput signals is always associated with a

combination of combination of output signals. These signalsoutput signals. These signals

operate without timeoperate without time behavior behavior..

Sequential controlsSequential controls ± ± controls containingcontrols containingelements with timeelements with time behavior behavior (e.g. Timing(e.g. Timing

elements, storage devices, etc.elements, storage devices, etc.




According to the type of operating sequence According to the type of operating sequence

CONTROL

Pilot Control Memory Control Program Control

Time-schedule

control

Coordinated

motion control

Sequence control




Pilot ControlPilot Control ± ± establishes always a uniqueestablishes always a unique

relationship between the command variablerelationship between the command variable

and output variable.and output variable.

Examples:Examples:

1.1. Copying on machine toolsCopying on machine tools ± ± the movements of the movements of the tracer pin are uniquely related to thethe tracer pin are uniquely related to the

movement of the cutting toolmovement of the cutting tool

2.2. Brightness controlBrightness control ± ± the brightness of the lamp isthe brightness of the lamp is

at all times uniquely related to the position of theat all times uniquely related to the position of the

resistor or of the transformer.resistor or of the transformer.




Memory controlMemory control ± ± after removing or taking back theafter removing or taking back the

command variable, the value reached by the outputcommand variable, the value reached by the outputvariable is retained until an opposing signal isvariable is retained until an opposing signal is

presented.presented.

Example:Example: SwitchSwitch--on and switch off of an electric motor on and switch off of an electric motor

by means of a pressure switchby means of a pressure switchRo

³ OFF´ b2

³ON´ b1

c1

Mp

3 ± 380 V

RST

M



1.31.2

1.1

Example: Controlling the advance and return movement of a double-

acting cylinder by manual switch.

Here, the condition obtained by the output variable is retained after the

command variable has been removed, until the opposing signal ispresented.





TimeTime--schedule controlschedule control

Command variables are supplied by a timeCommand variables are supplied by a time--dependentdependentprogram transmitter (program storage device) and aprogram transmitter (program storage device) and a

timetime--dependent operating sequence of the program.dependent operating sequence of the program.

Centrally stored program; usually compactCentrally stored program; usually compact

constructionconstruction

TimeTime--constant program execution; executionconstant program execution; execution

insensitive to disturbing factors and independent/noinsensitive to disturbing factors and independent/no

check of operating sequence, hence no sequencecheck of operating sequence, hence no sequencereliability. Disturbances in the operating sequencereliability. Disturbances in the operating sequence

have no effect on program execution.have no effect on program execution.





Coordinated motion controlCoordinated motion control

The command variables are provided by a programThe command variables are provided by a programtransmitter, the output variables of w/c aretransmitter, the output variables of w/c are

dependent on the distance covered (displacement or dependent on the distance covered (displacement or

position of a movable part of the controlled system.position of a movable part of the controlled system.

Program is defined by the arrangement of limitProgram is defined by the arrangement of limitswitches/ signal elements, hence the layout is notswitches/ signal elements, hence the layout is not

clearly arranged and is not easy to serviceclearly arranged and is not easy to service

Operating sequence reliability is provided byOperating sequence reliability is provided by

displacementdisplacement--dependent sequence, disturbances independent sequence, disturbances in

the operating sequence can be registered, programthe operating sequence can be registered, program

execution maybe interruptedexecution maybe interrupted





A A program transmitter program transmitter maybe:maybe:

-- camshaft, cam disk, program belt, punchcamshaft, cam disk, program belt, punch

card/tape, etc.card/tape, etc.

Example: A piano displays the characteristicsExample: A piano displays the characteristics

of a timeof a time--schedule control. The program isschedule control. The program iscontained in a program transmitter, which incontained in a program transmitter, which in

this case maybe a drum and is run throughthis case maybe a drum and is run through

on a timeon a time--dependent basis (constant speeddependent basis (constant speedof program transmitter drive motor)of program transmitter drive motor)

Example ± Coordinated motion control



Example Coordinated motion control

Movement of a double-acting pneumatic cylinder: The advance motion is

tripped by operating ST ART button 1.2, the return motion being effected by a

limit switch1.3 after a certain length of travel, depending on the position of LS

1.3

1.31.2

1.1

1.3 1.0





Sequence controlSequence control

The operating sequence program is stored in aThe operating sequence program is stored in aprogram transmitter w/c runs through a ³stepprogram transmitter w/c runs through a ³step--byby--

step´ program in accordance w/ the conditionstep´ program in accordance w/ the condition

reached at any one time by the controlled system.reached at any one time by the controlled system.

Is identified by having a program transmitter and anIs identified by having a program transmitter and anequipment w/c is capable of ³interrogating´ theequipment w/c is capable of ³interrogating´ the

conditions prevailing in the system, has theconditions prevailing in the system, has the

advantage of ³check the momentary machineadvantage of ³check the momentary machine

status´ (operating sequence reliability and isstatus´ (operating sequence reliability and ispossible to advance the program transmitter steppossible to advance the program transmitter step--

byby--step (stepping motor).step (stepping motor).

M f ti tiM f ti ti



Means of representing motionMeans of representing motion

sequences and switching conditions:sequences and switching conditions:

Movement sequences and switching conditionsMovement sequences and switching conditions

of working and control elements must beof working and control elements must be

represented in a clear fashion. As we mayberepresented in a clear fashion. As we maybe

confronted with a more difficult problem, theconfronted with a more difficult problem, therelationships can be identified quickly and withrelationships can be identified quickly and with

certainty only if a suitable form of certainty only if a suitable form of

representation can be selected.representation can be selected.Only neat representation allows largeOnly neat representation allows large--scalescale

projects to be understood clearly.projects to be understood clearly.

Means of representing motion sequences andMeans of representing motion sequences and



Means of representing motion sequences andMeans of representing motion sequences and

switching conditions:switching conditions:

Writing down in chronological sequenceWriting down in chronological sequence

Tabular formTabular form

Vector diagramVector diagram

Graphical representation in graphical form,Graphical representation in graphical form,

commonly referred to ascommonly referred to as Function DiagramFunction Diagram,,consisting of:consisting of:

1.1. Motion DiagramMotion Diagram ± ± records conditions relating torecords conditions relating to

working elements and componentsworking elements and components2.2. Control DiagramControl Diagram ± ± provides informationprovides information

concerning the condition of individual controlconcerning the condition of individual control

elementselements



Motion diagrams:Motion diagrams:

DisplacementDisplacement--step diagramstep diagram ± ± The operating sequenceThe operating sequence

of a working element is represented in a manner suchof a working element is represented in a manner suchthat the displacement is recorded in relation to thethat the displacement is recorded in relation to the

various steps or change in condition of anyvarious steps or change in condition of any

component. If a control has several working elements,component. If a control has several working elements,

each is represented in the same manner and each iseach is represented in the same manner and each is

drawn one beneath the other.drawn one beneath the other.

Displacement

Steps

Forward (1)

Rear (0)

1 2 3 4 5=1

Cylinder A

Recommendations for layout when drawingRecommendations for layout when drawing




displacementdisplacement--step diagram:step diagram:

The steps should be drawn (when possible) linearly andThe steps should be drawn (when possible) linearly andhorizontally.horizontally.

If possible, the displacement should not be drawn to scale, butIf possible, the displacement should not be drawn to scale, but

of equal size for all components.of equal size for all components.

If the condition of the system changes during motion,If the condition of the system changes during motion,intermediate steps maybe introduced.intermediate steps maybe introduced.

The steps may be numbered as required.The steps may be numbered as required.

The designation of the condition may be optional, binary digitsThe designation of the condition may be optional, binary digits

may be used, say 0 for rear end position and 1 for forward endmay be used, say 0 for rear end position and 1 for forward end

position.position.

The designation of the unit must be written on the left side of The designation of the unit must be written on the left side of

the diagram.the diagram.

M ti DiM ti Di



Motion Diagram:Motion Diagram:

DisplacementDisplacement--time diagramtime diagram ± ± The displacementThe displacement

of a component is drawn in relation to time; theof a component is drawn in relation to time; thetime is drawn linearly and establishes thetime is drawn linearly and establishes the

relationship (motion/displacement) between therelationship (motion/displacement) between the

individual components.individual components.

Displacement Time t

0

1

Cylinder A

1

0Cylinder B





displacementdisplacement--step diagram:step diagram:

The rules for drawing the diagram are roughly the same asThe rules for drawing the diagram are roughly the same asfor the displacementfor the displacement--step diagram; the relationships to thestep diagram; the relationships to the

displacementdisplacement--step diagram are indicated by the broken linesstep diagram are indicated by the broken lines

(step lines), although the distance between them is not drawn(step lines), although the distance between them is not drawn

to scale.to scale.

Whereas the displaceWhereas the displace--step diagram allows the relationshipsstep diagram allows the relationships

to be seen more clearly, overlaps and varying speeds can beto be seen more clearly, overlaps and varying speeds can be

shown better in the displacementshown better in the displacement--time diagramtime diagram

In case of rotating elements, the changes in condition withIn case of rotating elements, the changes in condition with

respect to time are no longer accounted for, i.e. in therespect to time are no longer accounted for, i.e. in thedisplacementdisplacement--step diagram, a change in condition (e.g.step diagram, a change in condition (e.g.

Switching of an electric motor) does not extend over theSwitching of an electric motor) does not extend over the

whole step but is entered directly on the step linewhole step but is entered directly on the step line

Control DiagramControl Diagram



Control DiagramControl Diagram

In the control diagram, the switching condition of In the control diagram, the switching condition of

control element is shown in relation to the steps or control element is shown in relation to the steps or the times, the switching time itself not beingthe times, the switching time itself not being

considered, for example the condition of a relayconsidered, for example the condition of a relay b1b1

being opened:being opened:

Note that relay b1 pulls up at step 2 and drops off Note that relay b1 pulls up at step 2 and drops off

again at step 5.again at step 5.

Condition

Steps

Open

Closed

b1

1 2 3 4 5 6=1

Function Diagram Example:



Function Diagram, Example:

0

1 A

1

0B

1 2 3 4 5=1

1.1

2.1

2.2

The control diagram shows the conditions of the directional control valves 1.1

which controls cylinder A, 2.1 which controls cylinder B and limit switch 2.2

which is installed at the front end position of cylinder A.

Working out a control problemWorking out a control problem




Step 1Step 1 -- Problem definition, determination of Problem definition, determination of

conditionsconditionsRight at the start, the problem and specifically theRight at the start, the problem and specifically the

objectives must be clearly defined. Also, it is veryobjectives must be clearly defined. Also, it is very

important to list theimportant to list the auxiliary conditionsauxiliary conditions withwith

respect to:respect to:

-- functional sequencefunctional sequence: as start conditions,: as start conditions,

setting up conditions, safety conditionssetting up conditions, safety conditions

-- auxiliary conditions for operating influencesauxiliary conditions for operating influences::environmental influences, place of environmental influences, place of

installation, supply, personnelinstallation, supply, personnel

-- reliability of performancereliability of performance





Possible auxiliary conditions for the functionalPossible auxiliary conditions for the functional

sequence:sequence:Start and setting up conditions:Start and setting up conditions:

-- Automatic operation: Automatic operation: AUT AUT

-- Single cycleSingle cycle-- Continuous cyclingContinuous cycling

-- Jogging operationJogging operation

-- Manual operation:Manual operation: M ANM AN

Setting up: each element can be operated in anySetting up: each element can be operated in any

sequencesequence

Setting: by operating the ³set´ button, the system isSetting: by operating the ³set´ button, the system is

brought into a defined positionbrought into a defined position





Possible auxiliary conditions for thePossible auxiliary conditions for the

functional sequence:functional sequence:

Safety conditions:Safety conditions:

EMERGENCY STOP: the position of theEMERGENCY STOP: the position of the

working elements assumed when this conditionworking elements assumed when this condition

applies must be clearly definedapplies must be clearly defined

EMERGENCY STOP unlocking: the system isEMERGENCY STOP unlocking: the system isagain released for reagain released for re--start and continuance of start and continuance of

operationoperation





Step 2Step 2 ± ± Determination of the sequence of Determination of the sequence of

operationsoperationsStep 3Step 3 ± ± Selection of the type of control and controlSelection of the type of control and control

energyenergy

Step 4Step 4 ± ± Selection of the type of control and controlSelection of the type of control and control

energyenergy

Step 5Step 5 ± ± Draw the positional sketchDraw the positional sketch

Step 6Step 6 ± ± Draw the circuit diagramDraw the circuit diagram

What are the common types of control systems?



W hat ar e t he common t y pes of cont rol sy stems?

The common types of controllers, with manyThe common types of controllers, with many

variations and/ or combinations of whichvariations and/ or combinations of which

are:are:

Logic controlsLogic controls

Pure logic controls were historicallyPure logic controls were historically

implemented by electricians with networksimplemented by electricians with networks

of relays, and designed with a notationof relays, and designed with a notation

calledcalled ladd er l ogic ladd er l ogic .. Nowadays, most suchNowadays, most suchsystems are constructed withsystems are constructed with prog rammable prog rammable

log ic cont rollerslog ic cont rollers..

L i C t llL i C t ll



Logic ControllersLogic Controllers

Logic controllers usually respond toLogic controllers usually respond to

switches or photoelectric cells, and causeswitches or photoelectric cells, and cause

the machinery to perform some operation.the machinery to perform some operation.

Logic systems are great for sequencingLogic systems are great for sequencingmechanical operations in places likemechanical operations in places like

elevators and factories, but notably poor atelevators and factories, but notably poor at

managing continuous process controls inmanaging continuous process controls insuch places as oil refineries and steel mills.such places as oil refineries and steel mills.

L i C t llL i C t ll



Logic ControllersLogic Controllers

Logic systems are quite easy to design, andLogic systems are quite easy to design, and

can handle very complex operations. Logiccan handle very complex operations. Logic

systems may be designed with a systemsystems may be designed with a system

similar tosimilar to Boolean log ic Boolean log ic .. ( ( Log ic Log ic gates thatgates that

are primarilyare primarily electronicallyelectronically--controlled butcontrolled but

can also be constructed fromcan also be constructed from

electromagneticelectromagnetic relaysrelays, electronic, electronic d iod esd iod es,,f lui d icsf lui d ics,, opt ical opt ical or evenor even mec hanical mec hanical

elements, are commonly employed.elements, are commonly employed.

Li f db k t lLi f db k t l



Linear or feedback controlsLinear or feedback controls

Linear controls use negativeLinear controls use negative f eedback f eedback totokeep some desired process within ankeep some desired process within an

acceptable range. For example, aacceptable range. For example, a

thermostat is a simple negative feedbackthermostat is a simple negative feedback

control; when the temperature goes below acontrol; when the temperature goes below a

threshold, control starts. Systems thatthreshold, control starts. Systems that

include feedback are prone toinclude feedback are prone to hunt i ng hunt i ng ,,

which iswhich is oscillat ionoscillat ion of output resulting fromof output resulting fromimproperly tuned inputs of first positive thenimproperly tuned inputs of first positive then

negative feedback.negative feedback.

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In the furnace example, the valve may open andIn the furnace example, the valve may open and

shut indefinitely in a cycle as the furnace heats, andshut indefinitely in a cycle as the furnace heats, and

then overruns the target temperature. This is badthen overruns the target temperature. This is bad

because it stresses the system. In a furnace, thebecause it stresses the system. In a furnace, theconstantly turning valve will quickly wear out. Moreconstantly turning valve will quickly wear out. More

expensively, the fluctuating temperature causesexpensively, the fluctuating temperature causes

expansion and contraction all through the furnace,expansion and contraction all through the furnace,

causing unnecessary, very expensive mechanicalcausing unnecessary, very expensive mechanicalwear. Most systems have similar problems.wear. Most systems have similar problems.

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Linear or Linear or feedback controlsfeedback controls

Often, if the response of the system isOften, if the response of the system isslowed down enough to prevent oscillation,slowed down enough to prevent oscillation,

the system doesn't respond fast enough tothe system doesn't respond fast enough to

work in normal situations. To resolve thework in normal situations. To resolve theproblems, the most common feedback loopproblems, the most common feedback loop

scheme has mathematical extensions toscheme has mathematical extensions to

cope with the future and the past. This typecope with the future and the past. This type

of loop is called aof loop is called a P ropor t ional P ropor t ional --I nt eg ral I nt eg ral --Derivat ive LoopDerivat ive Loop, or , or P ID loopP ID loop..





If the error curve is graphed over time, the past isIf the error curve is graphed over time, the past is

considered by adding a number proportional to theconsidered by adding a number proportional to thearea under the curve over a certain amount of timearea under the curve over a certain amount of time

in the past (this is the "integration" part). Thein the past (this is the "integration" part). The

future is considered by the adding a number future is considered by the adding a number

proportional to the slope of a line tangent to theproportional to the slope of a line tangent to theerror's curve at the present time (this is theerror's curve at the present time (this is the

"differential" part). A PID loop always adds its"differential" part). A PID loop always adds its

result to the current output, so that it effortlesslyresult to the current output, so that it effortlessly

floats to a new steady output level.floats to a new steady output level.

W hat is PI D? W hat is PI D?



A A ProportionalProportional--IntegralIntegral--Derivative controller Derivative controller or or

PIDPID is a standardis a standard f eedback f eedback loop component inloop component ini nd ust rial cont rol applicat ionsi nd ust rial cont rol applicat ions. It measures an. It measures an

"output" of a process and controls an "input", with a"output" of a process and controls an "input", with a

goal of maintaining the output at a target value,goal of maintaining the output at a target value,

which is called the "which is called the "setpointsetpoint". A

n example of a PID".

An e

xample of a PIDapplication is the control of a process temperature,application is the control of a process temperature,

although it can be used to control any measurablealthough it can be used to control any measurable

variable which can be affected by manipulatingvariable which can be affected by manipulating

some other process variable. For example, it can besome other process variable. For example, it can beused to control pressure, flow rate, chemicalused to control pressure, flow rate, chemical

composition, force, speed or a number of other composition, force, speed or a number of other

variables.variables.




The basic idea is that the controller reads aThe basic idea is that the controller reads a sensor sensor ..

Then it subtracts the measurement from a desiredThen it subtracts the measurement from a desired

""setpointsetpoint" to determine an "error"." to determine an "error". The error is thenThe error is then

treated in three different ways simultaneously:treated in three different ways simultaneously:

ProportionalProportional -- To handle the present, the error is multiplied byTo handle the present, the error is multiplied by

a negative proportional constanta negative proportional constant PP, and sent to the output., and sent to the output. PP

represents the band over which a controller's output isrepresents the band over which a controller's output is

proportional to the error of the system. E.g. for a heater, aproportional to the error of the system. E.g. for a heater, a

controller with a proportional band of 10degC and acontroller with a proportional band of 10degC and a setpointsetpoint

of 20deg C would have an output of 100% at 10 deg C, 50%of 20deg C would have an output of 100% at 10 deg C, 50%

at 15 Deg C and 10% at 1.9 deg C. Adding the change to theat 15 Deg C and 10% at 1.9 deg C. Adding the change to theoutput makes the output self output makes the output self--adjusting. For example, if theadjusting. For example, if the

burner were to get dirty, decreasing the heater's efficiency,burner were to get dirty, decreasing the heater's efficiency,

the baseline output would just drift upwards a bit, and thenthe baseline output would just drift upwards a bit, and then

rere--stabilize.stabilize.

What is PID?What is PID?




I ntegr al I ntegr al -- To handle the past, the error is integratedTo handle the past, the error is integrated

(or averaged, or summed) over a period of time,(or averaged, or summed) over a period of time,

and then multiplied by a constantand then multiplied by a constant II, and added to, and added to

the proportional output.the proportional output. II represents the steadyrepresents the steady

state error of the system. Using the Proportionalstate error of the system. Using the Proportional

term alone it is not possible to reach a steady setterm alone it is not possible to reach a steady set

point temperature. Real world processes are notpoint temperature. Real world processes are not

perfect and are subject to a number of perfect and are subject to a number of

environmental variables. As these variables areenvironmental variables. As these variables are

often constant they, can be measured andoften constant they, can be measured and

compensated for.compensated for.





Using the Proportional example above; at 19.9Using the Proportional example above; at 19.9deg C the controller output is 1%, at thisdeg C the controller output is 1%, at this

temperature environmental losses through heattemperature environmental losses through heat

transmission are 3%. In this scenario the systemtransmission are 3%. In this scenario the system

controller will never be able to reachcontroller will never be able to reach setpointsetpoint,,however it can be corrected by introducing anhowever it can be corrected by introducing an

Integral termIntegral term, which will attempt to remove errors, which will attempt to remove errors

that last for some time. In practice, the Integralthat last for some time. In practice, the Integral

term of a controller only considers a relativelyterm of a controller only considers a relativelyshort history of the controller.short history of the controller.





Deriv at iv eDeriv at iv e -- To handle the future, the firstTo handle the future, the firstderivative of the error (its rate of change) isderivative of the error (its rate of change) is

calculated with respect to time, and multiplied bycalculated with respect to time, and multiplied by

another constantanother constant DD, and summed with the, and summed with the

proportional and integral terms. The derivativeproportional and integral terms. The derivativeterm is used to govern a controller's response to aterm is used to govern a controller's response to a

change in the system. The larger the derivativechange in the system. The larger the derivative

term the more rapidly the controller will respond toterm the more rapidly the controller will respond to

changes in the process value. This is a good thingchanges in the process value. This is a good thingto reduce when trying to dampen a controller'sto reduce when trying to dampen a controller's

response to short term changes.response to short term changes.





The genericThe generic t ransf er f unc t iont ransf er f unc t ion for a PIDfor a PIDcontroller is:controller is:

H( s) = ( DsH( s) = ( Ds2 2 + P s + I )/ ( s + C ); + P s + I )/ ( s + C ); withwith C C being a constant (typically .01 or being a constant (typically .01 or

.001)..001).





Most real feedback loops are concernedMost real feedback loops are concerned

about wearing out control machinery likeabout wearing out control machinery like

valves, by adjusting them many times per valves, by adjusting them many times per

second. Therefore, they often have asecond. Therefore, they often have ad ead band d ead band , a region around the current, a region around the current

value in which no control action occurs. Invalue in which no control action occurs. In

commercial controls, thecommercial controls, the deadbanddeadband isisprogrammable.programmable.





Another common method is to Another common method is to f il t er f il t er thethe

feedback loop. A filter eliminatesfeedback loop. A filter eliminates

undesirable frequencies (cycles) from theundesirable frequencies (cycles) from the

system under control, which perfectlysystem under control, which perfectlyeliminates oscillations. Many systemseliminates oscillations. Many systems

oscillate at just one frequency. By filteringoscillate at just one frequency. By filtering

out that frequency, one can use very "stiff"out that frequency, one can use very "stiff"feedback and the system can be veryfeedback and the system can be very

responsive without shaking itself apart.responsive without shaking itself apart.





Some feedback controls operate through complex Some feedback controls operate through complex

indirect effects. For example, in an airplane'sindirect effects. For example, in an airplane's

aut opilot aut opilot , the flight plan determines the desired, the flight plan determines the desired

numbers (where to move) that drives everything.numbers (where to move) that drives everything.Each mechanical control has aEach mechanical control has a d i ff erent ial d i ff erent ial

equat ionequat ion that takes the desired movement in six that takes the desired movement in six

different axes (roll, pitch, yaw, forward, back anddifferent axes (roll, pitch, yaw, forward, back and

up), and calculates the control's position. Usuallyup), and calculates the control's position. Usuallyeach input and output number is filtered for each input and output number is filtered for

particular oscillations of the aircraft or the controlparticular oscillations of the aircraft or the control

part.part.





The most complex linear control systemsThe most complex linear control systems

developed to date are in oil refineries (developed to date are in oil refineries (Mod el Mod el

P red ic t ive Cont rol P red ic t ive Cont rol ). The chemical reaction paths). The chemical reaction paths

and control systems are normally designedand control systems are normally designed

together using specialized computer together using specialized computer--aidedaided--designdesignsoftware. When the automated controlsoftware. When the automated control--systemsystem

design techniques pioneered by oil refinerydesign techniques pioneered by oil refinery

controls were applied to aircraft control systems,controls were applied to aircraft control systems,

they caused a revolution, speeding design timesthey caused a revolution, speeding design timesby a hundredby a hundred--fold or more. Now, the core codes of fold or more. Now, the core codes of

many modern aircraft autopilots are actuallymany modern aircraft autopilots are actually

themselves coded by computer programs.themselves coded by computer programs.





Feedback loops can be combined andFeedback loops can be combined and

modified in many ways. Usually if a systemmodified in many ways. Usually if a system

has several measurements to be controlled,has several measurements to be controlled,

a feedback loop will be present for each of a feedback loop will be present for each of them.them.

ion & Control Eng'g

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