bem4843 ch1 industrial control

8/8/2019 BEM4843 Ch1 Industrial Control

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Engr. Hairulazwan [email protected]
mailto:[email protected]:[email protected]:[email protected]


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Chapter 1 Introduction to

industrial control

system

Chapter 2 Interfacing

devices

Chapter 3 Thyristor


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Industrial Control Classification

Elements of Open-Loop and Closed-Loop Systems

Feedback Control

Practical Feedback Application

Dynamic Response of a Closed-Loop System

Feed-Forward Control


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Motioncontro

l an automatic control system thatcontrols the physical motion orposition of an object.

also referred to as servos, or

servomechanisms.

Eg: industrial robot arm which

performs welding operations and

assembly procedures.

Other eg: CNC machine toolequipment, printing presses, office

copiers, packaging equipment, and

electronics parts insertion machines

that place components onto a PCB. Proce

sscontro

l one or more variables are regulatedduring the manufacturing of aproduct.

Variables such as temperature,

pressure, flow rate, liquid and solid

level, pH, or humidity.

2 categories i.e batch and

continuous.


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a sequence of timedoperations executed on theproduct beingmanufactured

Figure 1-1 shows anindustrial machine thatproduces various types ofcookies.


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one or more operations arebeing performed as theproduct is being passedthrough a process.

Raw materials arecontinuously entering andleaving each process step.

Figure 1-2: Producingpaper.


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The purpose of any industrial system is tomaintain one or more variables in aproduction process at a desired value.

Industrial control systems are also classifiedby how they control variables, either manuallyin an open-loop system or automatically in aclosed-loop system.


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The simplest way to controla system.

Figure 1-3 shows a systemcomposed of a storagetank.

Manually controlled thevalve and an outlet pipe.

Ideally, the flow controlvalve setting and the size ofthe outlet pipe are exactlythe same and hence thewater level in the tankremains the same.

Process reaches a steady-state condition (balanced.)

Problem occur when anychange or disturbance will

upset the balance. Eg. substantial rainfall may

cause overflow.

Require operatorperiodically inspects the

tank.


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Antenna will rotateclockwise andanticlockwise depending onthe output signal, negativeor positive.

Antenna will stationary ifthe input signal is 0v.

When the antenna isapproaching the desiredangle or position, the inputsignal must approach 0v.

It can be conclude that thecontrol action isindependent of the output.


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Some manufacturingapplications requirecontinuous monitoring andself-correcting action of theoperation for long periods

of time withoutinterruption.

The automatic closed-loopconfiguration performs theself-correcting function.

This automatic systememploys a feedback loop tokeep track of how well theoutput actuator is doing the

job it was commanded to

do.

Replacing the manual valvewith an adjustable valve

connected to a float. The valve, the float, and the

linkage mechanism providethe feedback loop.


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From diagram, if0= ithen V0 =Vi so the errorsignal, Ve = Vi V0 = 0V

If the V0 not equal Vi ,Vegreater or less than 0V, theantenna will rotateclockwise, anticlockwise(depends on Ve polarity).

The antenna will continuerotating until V0 = Vi .

In this example, the systemautomatically corrects theoutput when the system isdisturbed. This system isknown as automatic

control system.


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Elements of Open-

and Closed-Loop

Systems

Controlled

variableMeasured

variable

Measurement

device

Feedback

signal

Set

point

Error

detectorError

signal

Controller

Actuator

Manipulated

variable

Manufacturing

process

Disturbance


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Closed-loop block diagram that showselements, input/output signals, and

signal direction


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the actual variable being monitored and maintained at a desired value.Eg. (process control): temperature, pressure, and flow rate.

Eg. (motion control): position or velocity.

Eg. (water reservoir): the water level is the controlled variable.

Controlled

Variable.

The condition of the controlled variable at a specific point in time.Various methods are used for measurements.Eg. (water level): measure the pressure at the bottom of a tank. Thepressure that represents the controlled variable is taken at the instant of

measurement.

Measured

Variable.

The eye of the system.It senses the measured variable and produces an output signal thatrepresents the status of the controlled variable.

Eg. (process control): use thermistor to measure temperature or a

humidity detector to measure moisture.

Eg. (motion control): use optical device to measure position or a

tachometer to measure rotational speed.

Eg. (water reservoir): use float.

Other terms used are detector, transducer, and sensor.

Measurement

Device.


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The output of the measurement device.Feedback Signal.

The prescribed input value or desired condition of the controlled variable.

May be manually set by operator, automatically set by an electronic

device/programming.Eg. (water reservoir): position at which the float is placed along rod A.

Other terms used are command, or reference.

Set Point.

Compares the set point to the feedback signal.

Produces an output signal that is proportional to the difference between

them.

Eg. (water reservoir): the entire linkage mechanism.

Other terms used are comparator or comparer and summing junction.

Error Detector.

The output of the error detector.

If signal are not equal, an error signal proportional to their difference

develops.

When equal, the error signal goes to zero.

Eg. (reservoir): the angular position of member B of the linkage

mechanism.

Other terms used are difference signal and deviation.

Error Signal.


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Operation performed by the actuator to

control a physical variable.

Manufacturing

Process.

A factor that upsets the manufacturing

process being performed, causing a change in

the controlled variable.

Eg. (reservoir): the rainfall and evaporation

that alter the water level.

Disturbance.


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The basic concept of feedback control is that an error

must exist before some corrective action can be made.

An error can develop in one of three ways:

The set point is changed.

A disturbance appears.

The load demand varies.


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Feedback system is a system that maintains a relationship between the output

and some reference input by comparing them and using the difference as a

means of control.

Feedback is used to reduce the error between reference and the system output .

Feedback effect on performance characteristic:

Stability

Overall gain

Sensitivity

External disturbances


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Open-Loop Closed-Loop

The output is

not measured.

Control system

is independent

of the output.

System cannot

compensate for

disturbance.

Eg.: toaster,

washingmachine, fan

System hasfeedback and

output is

measured.

System output has

an effect on the

control action.

System can

compensate for

disturbance.

Eg.:air

conditioner, robot

(arm)


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Open-Loop Closed-Loop

Advantages

Low cost

More reliable

Easier to build/maintain.

Stability is not major problem

Disadvantages

Not accurate (depends on equipments

calibration)

Slow system response (small bandwidth)

Limitations on application.No error correction by a controller.

Advantages

High accuracy

Fast system response

More complex

Disadvantages

Cost expensive

Less reliable

Difficult to maintain

Stability problem, which may tend to

overcorrect errors that can cause

oscillations of constant.


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Step 1Transform

requirements

into a physical

system

Step 2Draw a

functional

block diagram

and schematic

Step 3Develop a

mathematical

model (block

diagram)

Step 4Reduce the

block diagram

Step 5Analyze and

design

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Determine physical system and specification fromrequirements

First of all, the design requirements of the system which

are desired transient response and steady state error

are determined.

Step 1Functional block diagram and schematicBased on the systems requirements, a functional block

diagram is drawn. Based on the block diagram, aschematic of the system is obtained. This schematic can

be in a form of electrical model, mechanical model or

both.

Step 223


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Mathematical representation A mathematical model of the system is obtained

from schematic using physical laws such as

Kirchoff's Voltage Law, Kirchoff's Current Law

and Newton's Law

Step 3 Reduction of block diagram Initial block diagram might be too complicated.

Therefore, it is reduced to simple block in orderto get Simple equations that represent the

systemStep 424


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Analyze and design Once the simple representation of the system

is obtained, it is easier to analyze the system.The system is analyzed to see whether the

transient response specification, steady state

error and stability requirements are met. If

the requirements are not met, then the

controller is designed to meet the

specification.

Step525


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Find the home appliance which appliedclosed-loop system. Identify the following: System operation

Element of system (such as set point, controller,

actuator, manipulated variable, process,disturbance etc.)

Block diagram


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bem4843 ch1 industrial control

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