University of Technology Control and System Engineering Department

Computer and Mechatronics Engineering

Branches

Programmable Logic Controllers

Third year Class

1st Semester

2017 / 2018

Lecture 1

Programmable Logic Controller

Programmable Logic Controller“PLC”

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.”

*NEMA: “National Electrical Manufacturers Association”

1-In 1968 GM Hydra-Matic (the automatic transmission division

of General Motors) issued a request for proposals for an electronic

replacement for hard-wired relay systems based on a white paper

written by engineer Edward R. Clark. The winning proposal came from

Bedford Associates of Bedford, Massachusetts. The first PLC,

designated the 084 because it was Bedford Associates' eighty-fourth

project, was the result.

2-Bedford Associates started a new company dedicated to developing,

manufacturing, selling, and servicing this new product: Modicon,

which stood for MOdular DIgital CONtroller. One of the people who

worked on that project was Dick Morley, who is considered to be the

"father" of the PLC.

3-The Modicon brand was sold in 1977 to Gould Electronics, later

acquired by German Company AEG, and then by French Schneider

Electric, the current owner.

Historical Background

Dick Morley

And

MODICON 084

PLC

Development achieved

• During the past four decades, enormous progress was

made in the development of micro electronics has

greatly influenced PLCs design and programming

methods.

• The range of functions and application fields have

grown considerably.

• Analogue processing, and the use of a PLC in

distributed control systems (DCS) networks is common

in PLC systems.

• Visualisation, which is the representation of machine

statuses such as the control program being executed,

via display or monitor with capability to enter

commands and variables can now be integrated into

many PLC systems.

Subsequent development resulted in a system featuring:

• The simple

connection of binary

signals

• The requirements as

to how these signals

were to be connected

was specified in the

control program

• With the new systems

it became possible for

the first time to plot

signals on a screen

and to store these in

electronic memories

Leading PLC manufacturers list

AMERICAN 1. Allen Bradley

2. Gould Modicon

3. Texas Instruments

4. General Electric

5. Westinghouse

6. Cutter Hammer

7. Square D

EUROPEAN 1. Siemens

2. Klockner & Mouller

3. Festo

4. Telemechanique

JAPANESE 1. Toshiba

2. Omron

3. Fanuc

4. Mitsubishi

PLC Advantages• Flexibility

– In the past, each different electronically controlled production machine required its own

controller; 15 machines might require 15 different controllers.

– Now it is possible to use just one model of a PLC to run any one of the 15 machines.

– Each of the 15 machines under PLC control would have its own distinct program (or a

portion of one running program).

• Implementing Changes and Correcting Errors

– With a wired relay-type panel, any program alterations require time for rewiring of

panels and devices.

– When a PLC program circuit or sequence design change is made, the PLC program can

be changed from a keyboard of a program loader in a matter of minutes.

– No rewiring is required for a PLC-controlled system.

– Also, if a programming error has to be corrected in a PLC control program, a change can

be typed in quickly.

• Large Quantities of Contacts

– The PLC has a large number of contacts for each coil available in its programming.

– Suppose that a panel-wired relay has four contacts and all are in use when a design

change requiring three more contacts is made, time would have to be taken to procure and

install a new relay or relay contact block.

– Using a PLC, however, only three more contacts would be typed in. Contacts are now a

“software” component

PLC Advantages (Continued)

• Lower Cost

– Increased technology makes it possible to condense more functions into smaller and less

expensive packages.

– Now a PLC can be purchased with numerous relays, timers, and counters, a sequencer,

and other functions for a few hundred dollars.

• Pilot Running

– A PLC programmed circuit can be evaluated in the lab. The program can be typed in,

tested, observed, and modified if needed, saving valuable factory time.

• Visual Observation

– A PLC circuit's operation can be seen during operation directly on a screen.

– The operation or mis-operation of a circuit can be observed as it happens.

– Logic paths light up on the screen as they are energized.

– Troubleshooting can be done more quickly during visual observation.

• Reliability and Maintainability

– Solid-state devices are more reliable, in general, than mechanical systems or relays and

timers. Consequently, the control system maintenance costs are low and downtime is

minimal.

• Documentation

– An immediate printout of the true PLC circuit is available in minutes, if required.

– There is no need to look for the blueprint of the circuit in remote files.

– The PLC prints out the actual circuit in operation at a given moment.

– Often, the file prints for relay panels are not properly kept up to date. A PLC printout is the

circuit at the present time; no wire tracing is needed for verification.

PLC Disadvantages

• Fixed Program Applications

– Some applications are single-function applications. It does not pay to use a PLC that

includes multiple programming capabilities if they are not needed.

– Their operational sequence is seldom or never changed, so the reprogramming available

with the PLC would not be necessary.

• Fail-Safe Operation

– In relay systems, the stop button electrically disconnects the circuit; if the power fails, the

system stops.

– This, of course, can be programmed into the PLC; however, in some PLC programs, you

may have to apply an input voltage to cause a device to stop. These systems may not be

fail-safe.

There are seven distinct characteristics in a PLC system, these are:

1. It is field programmable by the user. This characteristic allows the user to write and

change programs in the field without rewiring or sending the unit back to the

manufacturer for this purpose.

2.It contains preprogrammed functions. PLCs contain at least logic, timing, counting,

and memory functions that the user can access through some type of control-oriented

programming language.

3.It scans memory and inputs and outputs (I/O) in a deterministic manner. This critical

feature allows the control engineer to determine precisely how the machine or process

will respond to the program.

4.It provides error checking and diagnostics. A PLC will periodically run internal tests

of its memory, processor, and I/O systems to ensure that what it is doing to the machine

or process is what it was programmed to do.

5.It can be monitored. A PLC will provide some form of monitoring capability, either

through indicating lights that show the status of inputs and outputs, or by an external

device that can display program execution status.

6.It is packaged appropriately. PLCs are designed to withstand the temperature,

humidity, vibration, and noise found in most factory environments.

7.It has general-purpose suitability. Generally a PLC is not designed for a specific

application, but it can handle a wide variety of control tasks effectively.

Characteristics of a PLC System

Types of PLC Construction:

• Compact PLC- it covers units with up to 128 I/O’s and

memories up to 2 Kbytes.

- Capable of providing simple to advance levels

or machine controls

• Modular PLC-The most sophisticated units of the PLC family.

They have up to 8192 I/O and memories up

to 750 Kbytes.

- Can control individual production processes or

entire plant.

Basic Elements of a PLC

•Power Supply

•Processor (CPU)

•Memories

•Input/output modules

•Programming Port

•PLC Bus

•Expansion Models

Power Supply

The basic function of the power supply is to

convert the field power into a form more suitable

for Use electronic devices that comprise the PLC

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.

•It is typically non-redundant. Hence a

failure of the PLC power supply can

cause the entire control system to fail.

Power Supply Features and Specifications

Useful guidelines when considering the power supply of a PLC include the following:

1. The power supply should be packaged properly so that the heat generated by the

power supply can be removed in order to prevent overheating. This will increase reliability.

If the power supply cabinet is hot to the touch at room temperature in an office

environment, it will be hotter still when locked in a control panel or located on the factory

floor. Care, of course, must always be taken to avoid touching any exposed power terminals.

2. The power supply should be tested by a certification agency, such as Underwriters

Laboratories ( ) or the Canadian Standards Association ( ). These agencies perform

temperature testing and electrical isolation testing on power supply components. A UL or

CSA mark on the PLC power supply will indicate that the power supply was tested to

comply with some basic minimum standards.

3. The power supply should meet at least one reputable standard for noise immunity.

Two of these standards are NEMA ICS 2-230 (a showering arc noise test) and IEEE Std.

472 (a high-voltage impulse test). Some noise testing may also be performed by certification

agencies, such as UL and CSA. The power supply should also be capable of withstanding

line-voltage variations such as dropouts, brownouts, and surges, which are common to

industrial facilities.

•It will typically contain high-voltage

components. Hence an isolation failure can

create the potential for serious injury or fire.

Processor Module

ProcessorModule

This module is the prime essence of a PLC system

It consists of a microprocessor which is

sometimes specially designed for the

purpose of being implemented in a PLC

system design for implementing the

logic, and controlling the

communications among the modules.

The processor module accepts input data

from various sensing devices via Input

modules, executes the stored user program,

and sends appropriate output commands

to control devices via output modules.

Processor Module Details A detailed block diagram of the processor section of a

PLC is shown in Figure below.

This section consists of four major elements: (1) power

supply, (2) memory, (3) central processing unit (CPU), and

(4) I/O interface.

Memories

•The program memory receives and holds the downloaded

program instructions from the programming device

-This memory is usually an EEPROM (electrically erasable

programmable ROM) or a battery-backup RAM, both of which are

capable of retaining data

Data memory is RAM memory used as a “scratch pad” by the

processor to temporarily store internal and external program-

generated data

For example, it would store the present status of all switches

connected to the input terminals and the value of internal counters

and timers.

20

Memory Designs

VOLATILE.

A volatile memory is one that loses its stored

information when power is removed.

Even momentary losses of power will erase any

information stored or programmed on a volatile

memory chip.

Common Type of Volatile Memory

RAM. Random Access Memory(Read/Write)

Read/write indicates that the information stored in the

memory can be retrieved or read, while write

indicates that the user can program or write

information into the memory.

21

Memory Designs

Several Types of RAM Memory:

1.MOS

2.HMOS

3.CMOS

The CMOS-RAM (Complimentary Metal Oxide Semiconductor) is

probably one of the most popular. CMOS-RAM is popular because

it has a very low current drain when not being accessed

(15microamps.), and the information stored in memory can be

retained by as little as 2Vdc.

NON VOLATILE.

A non volatile memory is one that does not lose its stored information when

power is removed.

•EPROM, Erasable Programmable Read Only Memory

Ideally suited when program storage is to be semi-permanent or additional

security is needed to prevent unauthorized program changes.

The EPROM chip has a quartz window over a silicon material that contains the

electronic integrated circuits. This window normally is covered by an opaque

material, but when the opaque material is removed and the circuitry exposed to

ultra violet light, the memory content can be erased.

The EPROM chip is also referred to as UVPROM.

Memory Designs

23

Memory Designs

NON VOLATILE

EEPROM, Electrically Erasable

Programmable Read Only Memory

Also referred to as E2PROM, is a chip that can be programmed

using a standard programming device and can be erased by the

proper signal being applied to the erase pin.

EEPROM is used primarily as a non-volatile backup for the normal

RAM memory. If the program in RAM is lost or erased, a copy of

the program stored on an EEPROM chip can be down loaded into

the RAM.

Battery backed CMOS RAM can

also be classified as non-volatile

I/O Section

Consists of input modules

and output modules.

Input module connects to :

Field sensors: switches, flow, level, pressure, temp.

transmitters, etc.

Output modules connect to:

Field output devices: motors, valves, solenoids, lamps, or

audible devices

I/O Section

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

Output Module

Forms the interface

by which output field

devices are connected

to the controller.

PLCs employ a relay

or an optical isolator

which uses light to

electrically isolate the

internal components

from the input and

output terminals.

Programming Device

PC with appropriate

software

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

The software allows users to create, edit, document,

store and troubleshoot programs.

The computer monitor is used to display the logic on

the screen. The personal computer communicates with the PLC

processor via a serial or parallel data communications

link.

If the programming unit is not in use, it may be unplugged

and removed. Removing the programming unit will not

affect the operation of the user program.

Programming Device

Hand-held unit

with display

•Hand-held programming devices are sometimes used to program small PLCs.

•They are compact, inexpensive, and easy to use, but

are not able to display as much logic on screen as a

computer monitor.

Hand-held units are often used on the factory floor for

troubleshooting, modifying programs, and transferring

programs to multiple machines.

PLC

-operates in the industrial

environment

-is programmed in relay

ladder logic

-has no keyboard, CD drive,

monitor, or disk drive

-has communications ports,

and terminals for input and

output devices

PLCs Versus Personal Computers

Same basic architecture

PC

-capable of executing several

programs simultaneously, in

any order

-some manufacturers have

software and interface cards

available so that a PC can do

the work of a PLC

PLC Size Classification

Criteria

- number of inputs and outputs (I/O count)

- cost

- physical size

Nano PLC

- smallest sized PLC

- handles up to 16 I/O points

Micro PLC

- handles up to

32 I/O points

Allen-Bradley SLC-500 Family

- handles up to 960 I/O points

Allen-Bradley PLC-5

Family

- handles several

thousand I/O points

31

Areas of Application

Manufacturing / Machining

Food / Beverage

Metals

Power

Mining

Petrochemical / Chemical

End of Lecture 1

University of Technology Control and System Engineering Department

Computer and Mechatronics Engineering

Branches

Programmable Logic Controllers

Third year Class

1st Semester

2017 / 2018

Lecture 2

PLC Programming

Devices Connecting to PLC I/O Modules

•Devices connecting to PLC input modules

- Pushbuttons momentary contact:

•Toggle switches:Throw - number of states

Pole - number of connecting moving parts

(number of individual circuits).

S - single, D - double

- There are special purpose input modules that can be

connected directly to special sensing devices like shaft

encoders and analogue sensors like thermocouples *IEC: International Electrotechnical Commission

Devices Connecting to PLC I/O Modules continued- Other types of switches:

Limit switch

Liquid

level

(float)

switch

Pressure switch

Temperature

actuated switch

Devices Connecting to PLC I/O Modules continued

-Proximity

switches / sensors:

Inductive

proximity switch /

sensorsFor ferrous and

ferromagnetic objects

Reed switch

Devices Connecting to PLC I/O Modules continued

-Proximity switches / sensors:Optical proximity switch / sensors

•Through beam

•Reflective

•Retro-reflective

Reflective scan

•Devices connecting to PLC output modules

Devices Connecting to PLC I/O Modules continued

-There are Several output devices that

ca be controlled through the output

modules of the PLC system, the symbols

of these devices are shown next to this

text. In general these can be categorized

as follows:

Indicators and Alarm.

Relays and contactors.

Solenoids and solenoid valves.

Motors.

heaters.

-There are special output modules that

can drive special output devices like

stepper motors and analogue metering

devices.

Devices Connecting to PLC I/O Modules continued

Solenoid: construction and operation.

Solenoid valve: construction and

operation. Relay: construction

Devices Connecting to PLC I/O Modules continued

Relay: Operation and symbol

Contactor: Construction and symbol

PLC Programming Languages

PLC- Programming languages - IL

• IL: Instruction List

• Fastest possible logic execution.

• Low level language

• Similar to assembly language

PLC- Programming languages - ST

• ST: Structured Text

• High level language

• Equations, table manipulation

• Complex algorithms (If/Then)

PLC- Programming languages - LD

• Traditional ladder logic is an easy-to-use

graphical programming language that

implements relay-equivalent symbol.

• Intuitive.

• LD in old PLCs had limited functionalities.

• LD Functionality has been greatly improved in

modern PLCs

PLC- Programming languages - FBD

• FBD : Function Block Diagram

• Easy way of programming

• Easy way of debugging

• Limited for complex algorithms

PLC- Programming languages - SFC

• SFC : Sequential Function Chart –

• A graphical method of representing a sequential

control system (stepper).

• Siemens : Simatic Step7 v5.5– Modular

– Wide range of functionalities

– Diagnostic tools

– Network configuration

• LSis/GLOFA: GMWIN for GM4 and GM6 v4.18– Supports the international language (IEC61131-3)

IL, LD, SFC

– Simulation Program test and debugging without PLC

– Editing, monitoring, debugging using symbol and variable name

– Automatic memory allocation support

Compiler sets a variable location automatically

– Optimization (PLC code) by compiler method

– User-defined function/function block support

PLC- Programming software tools

Creating a new LD project using GMWIN package.

Defining the labels to be in an LD program.

Creating an LD program for GLOFA GM6 PLC.

Converting the created LD program into an

executable sequence program (Compiling).

Correcting the program if any error occurs in

execution.

PLC Programming Process

Programming PLC Using LD (Ladder Diagram)

Language

The ladder diagram consists of two vertical lines representing the power

rails. Circuits are connected as horizontal lines, i.e., the rungs of the

ladder, between these two verticals

LD language convention:

1. The vertical lines of the diagram

represent the power rails between which

circuits are connected. The power flow is

taken to be from the left-hand vertical across

a rung.

2. Each rung on the ladder defines one

operation in the control process.

3. A ladder diagram is read from left to

right and from top to bottom, the figure

on the right shows the scanning motion

employed by the PLC. The top rung is read

from left to right. Then the second rung down

is read from left to right and so on.

LD language convention: Continued

4. When the PLC is in its run mode, it goes through the entire ladder

program to the end, the end rung of the program being clearly denoted, and then

promptly resumes at the start. This procedure of going through all the rungs of the

program is termed a cycle. The end rung might be indicated by a block with the

word END or RET for return, since the program promptly returns to its beginning.

5. Each rung must start with an input or inputs and must end with at least

one output. The term input is used for a control action, such as closing the contacts

of a switch, used as an input to the PLC. The term output is used for a device

connected to the output of a PLC, e.g., a motor.

6. Electrical devices are shown in their normal condition. Thus a switch,

which is normally open until some object closes it, is shown as open on the

ladder diagram. A switch that is normally closed is shown closed.

7. A particular device can appear in more than one rung of a ladder. For

example, a relay that switches on might be used on one or more devices. The same

letters and/or numbers are used to label the device in each situation.

8. The inputs and outputs are all identified by their addresses, the notation

used depending on the PLC manufacturer. This is the address of the input or

output in the memory of the PLC.

Types of PLC Control Action

• Temporal -- control based in time

• State -- control based in state level

• Hybrid – both temporal and state

Functions of PLC Systems

1) on-off control,

2) sequential control,

3) feedback control, and

4) motion control

Basic symbols of LD Language

PLC Programming Using GMWIN Software

in LD Language

General form of an LD Rung.

GLOFA GMWIN form of an LD Rung.

LADDER DIAGRAM

A ladder diagram (also called contact symbology) is a

means of graphically representing the logic required in a

relay logic system.

A

R1

PB1 PB2

R1

R1

start emergency stop

Rail

Rung

PLC Instructions

1) Relay,

2) Timer and counter,

3) Program control,

4) Arithmetic,

5) Data manipulation,

6) Data transfer, and

7) Others, such as sequencers.

RelayA Relay consists of two parts, the coil and the contact(s).

Contacts:

a. Normally open -| |-

b. Normally closed -|/|-

Coil:

a. Energize Coil -( )-

b. De-energize -(/)-

c. Latch -(L)-

d. Unlatch -(U)-

( )

Logic States

ON : TRUE, contact closure, energize, etc.

OFF: FALSE, contact open , de-energize, etc.

The internal relay and program should not be confused with the externalswitch and relay. Internal symbols are used for programming.External devices provide actual interface.

AND and OR LOGIC

AND

OR

Combined AND & OR

R1 = PB1 .OR. (PB2 .AND. PB3)

Logic for Ladder Solution

Relay wiring diagram PLC with I/O wiring

The sequential task is as follows:

1. Start button is pressed.

2. Table motor is started.

3. Package moves to the position of the limit

switch and automatically stops

An Example of a Sequential Task

End of Lecture 2

University of Technology Control and System Engineering Department

Computer and Mechatronics Engineering

Branches

Programmable Logic Controllers

Third year Class

1st Semester

2017 / 2018

Lecture 3

Examples on PLC Programming Using

Ladder Language to Solve Automation

Problems

Writing a Ladder Logic Program Directly from a

Narrative Description

In most cases, it is possible to prepare a ladder logic program directly from

the narrative description of a control process.

Some of the steps in planning a program are as follows:

• Define the process to be controlled.

• Draw a sketch of the process, including all sensors and manual controls

needed to carry out the control sequence.

• List the sequence of operational steps in as much detail as possible.

• Write the ladder logic program to be used as a basis for the PLC program.

• Consider different scenarios where the process sequence may go astray and

make adjustments as needed.

• Consider the safety of operating personnel and make adjustments as

needed.

The following are examples of ladder logic programs derived from narrative

descriptions of control processes.

Experiment 1

The figure to the left shows

the sketch of a drilling

process that requires the

drill press to turn on only if

there is apart present and

the operator has one hand

on each of the start

switches. This precaution

will ensure that the

operator’s hands are not in

the way of the drill. The

sequence of operation

requires that switches 1 and

2 and the part sensor all be

activated to make the drill

motor operate. The next

figure shows the ladder logic

program required for the

process implemented using

a GLOFA GM6 PLC.

Experiment 2

A motorized overhead garage door is to be operated automatically to preset open and

closed positions. The field devices include one of each of the following:

• Reversing motor contactor for the up and down directions.

• Normally open down limit switch to sense when the door is fully closed.

• Normally open-held closed up limit switch to sense when the door is fully opened.

• Normally open door up button for the up direction.

• Normally open door down button for the down direction.

• Normally closed door stop button for stopping the door.

• Red door ajar light to signal when the door is partially open.

• Green door open light to signal when the door is fully open.

• Yellow door closed light to signal when the door is fully closed.

The sequence of operation requires that:

• When the up button is pushed, the up motor contactor energizes and the door travels

upward until the up limit switch is actuated.

• When the down button is pushed, the down motor contactor energizes and the door

travels down until the down limit switch is actuated.

• When the stop button is pushed, the motor stops. The motor must be stopped before it

can change direction.

The figure below shows the ladder logic program required for the operation

implemented using a GLOFA GM6 PLC.

EXPERIMENT 3

The figure below shows the sketch of a continuous filling operation.

This process requires that boxes moving on a conveyor be automatically

positioned and filled. The sequence of operation for the continuous filling

operation is as follows:

• Start the conveyor when the start button is momentarily pressed.

• Stop the conveyor when the stop button is momentarily pressed.

• Energize the run status light when the process is operating.

• Energize the standby status light when the process is stopped.

• Stop the conveyor when the right edge of the box is first sensed by the

photo-sensor.

• With the box in position and the conveyor stopped, open the solenoid valve

and allow the box to fill. Filling should stop when the level sensor goes true.

• Energize the full light when the box is full. The full light

should remain energized until the box is moved clear of the photo-sensor.

The figure after shows the ladder logic program required for the operation.

End of Lecture