plc fundamentals

KARMAVEER BHAURAO PATIL POLYTECHNIC,

SATARA

Rayat Shikshan Sanstha’s

Department Of Electronics And Telecommunication Engineering

PLC Fundamentals

Control System and PLC

Amit NevaseLecturer,

Department of Electronics & Telecommunication Engineering, Karmaveer Bhaurao Patil Polytechnic, Satara

EJ5G Subject Code: 17536 Third Year Entc

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Objectives

The student will be able to:

Understand classifications of control system.

Understand Steady state, time response, and frequency

response analysis.

Analyze the Stability of control system using RH criteria.

Understand the fundamentals and diff. Hardware parts of

PLC.

Draw ladder diagrams to program PLC

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Teaching & Examination Scheme

Two tests each of 25 marks to be conducted as per the schedule given by MSBTE.

Total of tests marks for all theory subjects are to be converted out of 50 and to be entered in mark sheet under the head Sessional Work (SW).

Teaching Scheme Examination Scheme

TH TU PR PAPERHRS TH PR OR TW TOTAL

03 -- 02 03 100 50# --- 25@ 175

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Module I – Introduction to Control System Introduction to Control systems (4 Marks)

Control System – Definition and Practical Examples Classification of Control System : Open Loop and Closed Loop Systems –

Definitions, Block diagrams, practical examples, and Comparison, Linear and Non-linear Control System, Time Varying and Time In-varying Systems

Servo System : Definition, Block Diagram, Classification (AC and DC Servo System), Block diagram of DC Servo System.

Laplace Transform and Transfer Function (4 Marks) Laplace Transform : Signifiance in Control System Transfer Function : Definition, Derivation of transfer functions for Closed loop

Control System and Open Loop Control System, Differential Equations and transfer functions of RC and RLC Circuit

Block Diagram Algebra (8 Marks) Order of a System : Definition, 0,1,2 order system Standard equation, Practical

Examples Block Diagram Reduction Technique: Need, Reduction Rules, Problems

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Module II – Time Response Analysis Time Domain Analysis (4 Marks)

Transient and Steady State Response Standard Test Inputs : Step, Ramp, Parabolic and Impulse, Need, Significance

and corresponding Laplace Representation Poles and Zeros : Definition, S-plane representation

First and Second order Control System (8 Marks) First Order Control System : Analysis for step Input, Concept of Time Constant Second Order Control System : Analysis for step input, Concept, Definition and

effect of damping Time Response Specifications (8 Marks)

Time Response Specifications ( no derivations ) Tp, Ts, Tr, Td, Mp, ess – problems on time response specifications Steady State Analysis – Type 0, 1, 2 system, steady state error constants,

problems

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Module III – Stability

Introduction to Stability (4 Marks)Definition of Stability, Analysis of stable, unstable, critically stable

and conditionally stable Relative StabilityRoot locations in S-plane for stable and unstable system

Routh’s Stability Criterion (8 Marks) Routh’s Stability Criterion : Different cases and conditionsStatement MethodNumericals Problems

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Module IV – Control Actions

Process Control System (4 Marks)Process Control System – Block diagram, explanation of each block

Control Actions (8 Marks) Discontinuous Mode : On-Off Controller, Equation, Neutral Zone Continuous modes: Proportional Controller (offset, proportional

band), Integral Controllers, Derivative Controllers – output equations, corresponding Laplace transforms, Response of P, I, D controllers

Composite Controllers : PI, PD, PID Controllers – output equations, response, comparison

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Module V – PLC Fundamentals Introduction (4 Marks)

Evolution of PLC in automation, need and benefits of PLC in automation

Block Diagram of PLC (12 Marks) Block diagram and description of different parts of PLC - CPU Function, Scanning cycle, speed of execution, Power supply

function, Memory – function , organization of ROM and RAM Input modules – function, different input devices used with PLC

and their usesOutput modules – function, different output devices used with

PLC and their uses Fixed and Modular PLCs

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Module VI – PLC Hardware and Programming

PLC Hardware (8 Marks) Discrete Input Modules – Block diagram, typical wiring details, Specifications of

AC input modules and DC input modules. Sinking and sourcing concept in DC input modules

Discrete Output Modules – Block diagram, typical wiring details, Specifications of AC output modules and DC output modules.

Analog Input and output modules : Block diagram, typical wiring details and specifications

PLC Programming (16 Marks) I/O Addressing in PLC PLC Instruction Set : Relay instructions, timer instructions, counter instructions,

data handling instructions, logical and comparison instructions PLC programming examples based on above instruction using Ladder

programming

Module-VPLC Fundamentals

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Specific Objectives

Explain the basics of PLC.

Draw functional block diagram of PLC.

Examples of PLCs

Manufacturing of Bubble Gum

Water Treatment Plant

Wood Industry

Color Mixing

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What is a Programmable Logic Controller?

A programmable logic controller (PLC) is a digital

computer used for automation of

electromechanical processes, such as control of

machinery on factory assembly lines,

amusement rides, or lighting fixtures.

PLCs are used in many industries and machines.

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Less wiring.

Wiring between devices and relay contacts are done

in the PLC program.

Easier and faster to make changes.

Trouble shooting aids make programming easier and

reduce downtime.

Reliable components make these likely to operate for

years before failure.

Advantages of PLCs

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Advantages of PLCs

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Eliminates much of the hard wiring that was associated with conventional relay control circuits.

The program takesthe place of much of the external wiringthat would be requiredfor control of a process.

Advantages of PLCs

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Increased Reliability: Once a program has been written and tested it can be downloaded to other PLCs.

Since all the logic is containedin the PLC’s memory, there is no chanceof making a logic wiringerror.

Advantages of PLCs

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More Flexibility: Original equipment manufacturers (OEMs) can provide system updates for a process by simply sending out a new program.

It is easier tocreate and changea program in a PLCthan to wire andrewire a circuit.End-users can modifythe program in the field.

Advantages of PLCs

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Lower Costs: Originally PLCs were designed to replace relay control logic. The cost savings using PLCs have been so significant that relay control is becoming obsolete, except for power applications.

Generally, if an applicationrequires more than about 6 control relays, it willusually be less expensiveto install a PLC.

Advantages of PLCs

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Communications Capability: A PLC can communicate with other controllers or computer equipment.

They can be networked to perform such functionsas: supervisory control, datagathering, monitoring devices and process parameters, and downloading and uploading of programs.

Advantages of PLCs

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Faster Response Time: PLCs operate in real-time which means that an event taking place in the field will result in an operation or output taking place.

Machines that process thousands of items per second and objects that spend only a fraction of a second in front of a sensor require the PLC’s quick response capability.

Advantages of PLCs

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Easier To Troubleshoot: PLCs have resident diagnostic and override functions that allows users to easily trace and correct software and hardware problems.

The control programcan be watched in real-time as it executes to find and fix problems

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Developed to replace relays in the late 1960s

Costs dropped and became popular by 1980

Now used in many industrial designs

Origin of PLCs

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Evolution of PLCs

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1968 Programmable Concept Developed

1969 Hardware CPU Controller with logic instructions, 1K of memory and 128 I/O points

1974 Use of several (multi) processors within a PLC, timers and counters, arithmetic operations, 12K of memory and 1024 I/O points

1976 Remote Input/output system introduced

1977 Microprocessor based PLC introduced

Evolution of PLCs

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1980 Intelligent I/O modules developed, Enhanced communication facilities, Enhanced software features, (e.g. documentation), Use of personal microcomputers as programming aids

1983 Low cost small PLC’s introduced

1985 on Networking of all levels of PLC, Computer and machine using SCADA software

(Definition according to NEMA standard ICS3-1978)

A digitally operating electronic apparatus which uses a

programming memory for the internal storage of instructions

for implementing specific functions such as logic,

sequencing, timing, counting and arithmetic to control

through digital or analog modules, various types of machines

or process.

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Definition of PLC

Leading Brands of PLC

AMERICAN 1. Allen Bradley2. Gould Modicon3. Texas Instruments 4. General Electric5. Westinghouse6. Cutter Hammer7. Square D

EUROPEAN 1. Siemens2. Klockner & Mouller3. Festo 4. Telemechanique

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Leading Brands of PLC

JAPANESE 1. Toshiba

2. Omron

3. Fanuc

4. Mitsubishi

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Areas of Applications of PLC

Manufacturing/Machining

Food/Beverage

Metals

Power

Mining

Petrochemical/Chemical

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Role of PLC in Automation

In an automated system, PLC is commonly regarded as the

heart of control system.

With a control application program stored within the

memory of PLC in execution, PLC constantly monitors the

state of the system.

PLC provides easy and economical solution for many

automation tasks such as logic/sequence control, PID

control & computing, co-ordination and communication,

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Role of PLC in Automation

Any manufacturing application, which involves repetitive or

discreet operation for that application PLC, can be used.

Intelligence of an automated system is greatly depending

on the ability of a PLC to read in the signal from various

types of automatic sensing and manual input devices.

An automatic system is also depending on the ability of the

PLC to control various output field devices like motor,

solenoid valve etc.

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Block Diagram of PLC

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Block Diagram of PLC

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Power Supply

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Supplies DC power to other modules that plug into the rack.

In large PLC systems, this power supply does not normally supply power to the field devices.

In small and micro PLC systems, the power supply is also used to power field devices.

Processor

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ProcessorModule

Is the “brain” of the PLC. Consists of a microprocessor for implementing the logic, and controlling the communications among the modules.

Designed so the desired circuit can be entered in relay ladder logic form.

The processor accepts input data from various sensing devices, executes the stored user program, and sends appropriate output commands to control devices.

I/O Section

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Consists of input modulesand output modules.

I/O Section

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Input Module

Forms the interface by which input field devices are connected to the controller.

The terms “field” and “real world” are used to distinguish actual external devices that exist and must be physically wired into the system.

I/O Section

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Output Module

Forms the interface by which output field devices are connected to the controller.

PLCs employ an optical isolator which uses light to electrically isolate the internal components from the input and output terminals.

Programming Device

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PC with appropriate software

A personal computer (PC) is the most commonly used programming device.

The personal computer communicates with the PLC processor via a serial or parallel data communications link.

The computer monitor is used to display the logic on the screen.

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Memory in PLC

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PLC Scan Cycle

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PLC Size

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Sr. No. Size Description

1 Small - It covers units with up to 128 I/O’s and memories up to 2 Kbytes.- These PLC’s are capable of providing simple to advance levels or machine controls.

2 Medium - It have up to 2048 I/O’s and memories up to 32 Kbytes.

3 Large - the most sophisticated units of the PLC family. - They have up to 8192 I/O’s and memories up to

750 Kbytes.- can control individual production processes or

entire plant.

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Types of PLC

Fixed PLC:

A Fixed PLC has all of its components-the input section, CPU and associated memory, power supply, and output section-built into one self-contained unit.

All input and output terminals are built into the PLC package and are fixed, not removable. 05/01/2023 Nevase A M 48

Types of PLC

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Fixed I/O

Is typical of small PLCs

Comes in one package, with no separate removable units.

The processor and I/O are packaged together.

Lower in cost – but lacks flexibility.

Types of PLC

Modular PLC:

The modular PLC comes as separate pieces. A modular PLC is purchased piece by piece.

There may be two or three power supplies to choose from, a handful of different processors (CPUs), many separate input and output cards or modules, and selection of assemblies, called racks, chassis, or base plates to hold the pieces together.05/01/2023 Nevase A M 50

Types of PLC

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Modular I/O

Is divided by compartmentsinto which separate modulescan be plugged.

This feature greatly increasesyour options and the unit’s flexibility. You can choosefrom all the modules availableand mix them in any way you desire.

Types of PLC

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Modular I/O

When a module slides into the rack,it makes an electrical connection with a series of contacts - called the backplane. The backplane is located at the rear of the rack.

Selection Criteria of PLC To determine the most suitable PLC to be used in the automation

task, there are several basic considerations to be made

Necessary input/output capacity;

Types of I/O required;

Size of memory required;

Speed and power required of the CPU and instruction

set

Manufacturer's support and backup.

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PC Vs PLCSr. No. Parameter PLC Systems Computer System

1 Price per function LOW HIGH

2 Physical size Very Compact Fairley compact

3 Operating speed Fast Fairley fast

4Electrical noiseImmunity

Good Quite good

5Installation Simple to program and

installProgramming extremely time consuming

6Capable of complicatedOperations

YES YES

7Ease of changingFunctions

Very Simple Quite Simple

8Ease of maintenance Good- few standard cards Poor- Several custom boards

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Input Modules

Input modules serve as the link between field devices and the

PLC’s CPU.

Each input module has a terminal block for attaching input

wiring from each individual field input device.

Typically input modules have either 8, 16 or 32 input terminals.

The main function of an input module is to take the field device

input signal, convert it to a signal level that the CPU can work

with, electrically isolate it, and send the signal, by the way of the

backplane board, to the CPU.

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Input Module Connections

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The same input field devices are used.

These devices are wired to the input module according to the manufacturer’s labeling scheme.

Input Devices

Mechanical Switches:

A mechanical switch generates an on/off signal or

signals as a result of some mechanical input causing

the switch to open or close.

Such a switch might be used to indicate the

presence of a work piece on a machining table, the

work piece pressing against the switch and so

closing it.

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Proximity Switches:

Proximity switches are used to detect the presence of an item without making contact with it.

There are a number of forms of such switches, some being suitable only for metallic objects.

The eddy current type of proximity switch has a coil that is energized by a constant alternating current and produces a constant alternating magnetic field.

When a metallic object is close to it, eddy currents are induced in it.

Input Devices

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Photoelectric Sensors and Switches: (LED, Photodiode, Photo transistor):

Photoelectric switch devices can either operate as

transmissive types, in which the object being

detected breaks a beam of light, usually infrared

radiation, and stops it reaching the detector, which

shows a U-shaped form in which the object breaks

the light beam; or reflective types, in which the

object being detected reflects a beam of light onto

the detector.

Input Devices

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Encoders: (Absolute encoder, incremental encoder):

The term encoder is used for a device that provides

a digital output as a result of angular or linear

displacement.

An incremental encoder detects changes in angular

or linear displacement from some datum position;

an absolute encoder gives the actual angular or

linear position.

Input Devices

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Temperature Sensors: (RTD, Thermister,

Thermocouple):

A simple form of temperature sensor that can be

used to provide an on/off signal when a particular

temperature is reached is the bimetal element.

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Input Devices

Position/Displacement Sensors: (Rotary/Linear

Potentiometer)

The term position sensor is used for a sensor that

gives a measure of the distance between a reference

point and the current location of the target, while a

displacement sensor gives a measure of the distance

between the present position of the target and the

previously recorded position.

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Input Devices

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Output Modules

Output modules serve as the link between the PLC’s

microprocessor and hardware field devices.

Each output module has a terminal block for attaching output

wiring to go to each individual field output device.

Typical output modules have either 8, 16 or 32 output terminals.

The output signal once received from the CPU, must be stored

before being sent to each output module’s output screw

terminals.

The storage area for output signals is called the output status

file.05/01/2023 Nevase A M 65

Output Module Connections

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Same output field device is used and wired to the output module. Triac

Triac switches motor ON and OFF in accordance with the control signal from the processor.

Relay:

For a relay connected to the output of a PLC, when

the output switches on, the solenoid magnetic field

is produced, and this pulls on the contacts and so

closes a switch or switches.

The result is that much larger currents can be

switched on. Thus the relay might be used to switch

on the current to a motor.

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Output Devices

Directional Control Valves:

Another example of the use of a solenoid as an

actuator is a solenoid operated valve.

The valve may be used to control the directions of

flow of pressurized air or oil and so used to operate

other devices, such as a piston moving in a cylinder.

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Output Devices

Motors

Stepper Motors

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Output Devices

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References

Programmable Logic

Controllers – F. D. Petruzella

Introduction to

Programmable Logic

Controllers – Gary Dunning

Programmable Logic

Controllers – Jhon Hackworth,

Federic Hackworth

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Thank You

Amit Nevase