plc-131022133632-phpapp02.pdfNBCvNVhbig knobh

Objectives :
At the end of the Session we will be able to:
● Describe the major components of a common PLC.
● Interpret PLC specifications.
● Apply troubleshooting techniques.
● Convert conventional relay logic to a PLC language.
● Operate and program a PLC for a given application.

Contents :
● History of Programmable Controllers
● Relay Ladder Logic
● Central Processing Unit
● Input/Output System
● Programming and Peripheral Devices
● Programming Concepts
● Applications
● Troubleshooting and Maintenance

Process
Process
Process
Process
Process
Process
Process
Process Control
Control
Control
Control
Control
Control
Control
Control & Automation
& Automation
& Automation
& Automation
& Automation
& Automation
& Automation
& Automation
Process control
Process control
Process control
Process control
Recognizing
the status
Process the
Information
Actuate the
control elements
the status Information control elements
Rules &
guidelines

Why Automation ?
Why Automation ?
Why Automation ?
Why Automation ?
Why Automation ?
Why Automation ?
Why Automation ?
Why Automation ?
Higher productivity
Superior quality of end product
Efficient usage of energy and raw materials
Improved safety in working condition
etc…

History of
History of
History of
History of
History of
History of
History of
History of Process Control
Process Control
Process Control
Process Control
Process Control
Process Control
Process Control
Process Control &
&
&
&
&
&
&
& Automation
Automation
Automation
Automation
Automation
Automation
Automation
Automation
Electronics Control
PLC Control
Manual Control
Hard-Wire Control

1. PLC
1. PLC
1. PLC
1. PLC
1. PLC
1. PLC
1. PLC
1. PLC -
-
-
-
-
-
-
- Introduction
Introduction
Introduction
Introduction
Introduction
Introduction
Introduction
Introduction
What
What
What
What does
does
does
does PLC
PLC
PLC
PLC stand
stand
stand
stand for?
for?
for?
for?
• PLC - Programmable Logic Controller
• PLC implements logic control functions by means of a
program

Programmable Logic Controllers
( Definition according to NEMA standard ICS3-1978)
A digitally operating electronic
apparatus which uses a programming
memory for the internal storage of
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.

1. PLC
1. PLC
1. PLC
1. PLC
1. PLC
1. PLC
1. PLC
1. PLC -
-
-
-
-
-
-
- Introduction
Introduction
Introduction
Introduction
Introduction
Introduction
Introduction
Introduction
How
How
How
How does
does
does
does a
a
a
a PLC
PLC
PLC
PLC differ
differ
differ
differ from
from
from
from a
a
a
a computer?
computer?
computer?
computer?
• A computer is optimized for calculation and display tasks
• A computer is programmed by specialists
• A PLC is designed for (logic) control and regulation tasks
• A PLC is programmed by non-specialists
• A PLC is well adapted to industrial environment

PLC Origin
PLC Origin
• Developed to replace relays in the late 1960s
• Costs dropped and became popular by 1980s
• Costs dropped and became popular by 1980s
• Now used in many industrial designs

Historical Background
• The Hydramatic Division of the General Motors
Corporation specified the design criteria for the first
programmable controller in 1968
Their primary goal :
• To eliminate the high costs associated with inflexible,
relay-controlled systems.

• The controller had to be designed in modular form, so
that sub-assemblies could be removed easily for
replacement or repair.
• The control system needed the capability to pass data
• The control system needed the capability to pass data
collection to a central system.
• The system had to be reusable.
• The method used to program the controller had to be
simple, so that it could be easily understood by plant
personnel.

Programmable Controller Development
1968 Programmable concept developed
1969 Hardware CPU controller, with logic
instructions, 1 K of memory and 128 I/O
points
1974 Use of several (multi) processors within a
1974 Use of several (multi) processors within a
PLC - timers and counters; arithmetic
operations; 12 K of memory and 1024 I/O
points
1976 Remote input/output systems introduced
1977 Microprocessors - based PLC introduced

1980 Intelligent I/O modules developed
Enhanced communications facilities
Enhanced software features
(e.g. documentation) Use of personal
(e.g. documentation) Use of personal
microcomputers as programming aids
1983 Low - cost small PLC’s introduced
1985 Networking of all levels of PLC, computer
and machine using SCADA software.
onwards

INTRODUCTION TO PLCS
Advantages of PLCs :
• 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 :
• They are cost-effective
• They are flexible, reliable and compact
• They have significant advantages over traditional
• They have significant advantages over traditional
control systems based on relay or pneumatics

1. PLC
1. PLC
1. PLC
1. PLC
1. PLC
1. PLC
1. PLC
1. PLC -
-
-
-
-
-
-
- Introduction
Introduction
Introduction
Introduction
Introduction
Introduction
Introduction
Introduction
What tasks do PLC perform ?
• The logic control tasks such as interlocking,
sequencing, timing and counting (previously
sequencing, timing and counting (previously
undertaken with relays or pneumatics)
• In addition, PLCs can perform a variety of
calculation, communication and monitoring tasks

Leading Brands Of PLC
AMERICAN: 1. Allen Bradley
2. Gould Modicon
3. Texas Instruments
4. General Electric
5. Westinghouse
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
3. Fanuc
4. Mitsubishi

Areas of Application :
Areas of Application :
• Manufacturing / Machining
• Food / Beverage
• Metals
• Metals
• Power
• Mining
• Petrochemical / Chemical

PLC Size :
PLC Size :
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.
Medium: • Have up to 2048 I/O’s and memories up to 32
Kbytes.
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.

Major Components of a Common PLC
POWER
SUPPLY
I M
N O
P D
O M
U O
T D
PROCESSOR
P D
U U
T L
E
T D
P U
U L
T E
PROGRAMMING
DEVICE
From
SENSORS
Pushbuttons,
contacts,
limit switches,
etc.
To
OUTPUT
Solenoids,
contactors,
alarms.
Motors
etc.

Power Supply:
• Provides the voltage needed to run the primary PLC
components
I/O Modules:
• Provides signal conversion and isolation between the
internal logic- level signals inside the PLC and the field’s
high level signal.

Processor :
• Provides intelligence to command and govern the activities
of the entire PLC systems.
of the entire PLC systems.
Programming Device :
• Used to enter the desired program that will determine the
sequence of operation and control of process equipment or
driven machine.

I/O Module
I/O Module
• The I/O interface section of a PLC connects it to external field
devices.
• The main purpose of the I/O interface is to condition the
various signals received from or sent to the external input
and output devices.
• Input modules converts signals from discrete or analog input
devices to logic levels acceptable to PLC’s processor.
• Output modules converts signal from the processor to levels
capable of driving the connected discrete or analog output
devices.

IS NEEDED TO:
• Prevent voltage
transients from
damaging the
processor.
•Helps reduce the
effects of electrical
USE TO
DROP THE
VOLTAGE
TO LOGIC
LEVEL
I/O Module
I/O Module
DC Input Module
OPTO-
-
-
-
ISOLAT
OR
noise
Current
Limiting
Resistor
FROM
INPUT
DEVICE
Buffer,
Filter,
hysteresi
s Circuits
TO
PROCESSOR

IS NEEDED TO:
• Prevent voltage
transients from
damaging the
processor.
•Helps reduce the
CONVERTS THE
AC INPUT TO DC
AND DROPS THE
VOLTAGE TO
LOGIC LEVEL
I/O Module
I/O Module
AC Input Module
OPTO-
-
-
-
ISOLAT
OR
noise
Rectifier,
Resistor
Network
FROM
INPUT
DEVICE
LOGIC LEVEL
Buffer,
Filter,
Hysteresis
Circuits
TO
PROCESSOR

plc-131022133632-phpapp02.pdfNBCvNVhbig knobh

IS NEEDED TO:
• Prevent voltage
transients from
damaging the
processor.
•Helps reduce the
noise
I/O Module
I/O Module
DC/AC Output Module
OPTO-
-
-
-
ISOLA
TOR
FROM
PROCESSOR
TTL
Circuits
Amplifier
RELAY
TRIAC
X’SISTO
R
TO
OUTPUT
DEVICE

I/O
I/O Circuits
Circuits
DIFFERENT TYPES OF I/O CIRCUITS
1. Pilot Duty Outputs :
• Outputs of this type typically are used to drive high-current
electromagnetic loads such as solenoids, relays, valves, and
motor starters.
• These loads are highly inductive and exhibit a large inrush
current.
• Pilot duty outputs should be capable of withstanding an
inrush current of 10 times the rated load for a short period of
time without failure.

I/O
I/O Circuits
Circuits
2. General Purpose Outputs :
• These are usually low- voltage and low-current and are used
to drive indicating lights and other non-inductive loads. Noise
suppression may or may not be included on this types of
modules.
3. Discrete Inputs :
• Circuits of this type are used to sense the status of limit
switches, push buttons, and other discrete sensors. Noise
suppression is of great importance in preventing false
indication of inputs turning on or off because of noise.

I/O
I/O Circuits
Circuits
4. Analog I/O :
• Circuits of this type sense or drive analog signals.
• Analog inputs come from devices, such as thermocouples,
strain gages, or pressure sensors, that provide a signal
voltage or current that is derived from the process variable.
voltage or current that is derived from the process variable.
• Standard Analog Input signals: 4-20 mA; 0-10V
• Analog outputs can be used to drive devices such as
voltmeters, X-Y recorders, servomotor drives, and valves
through the use of transducers.
• Standard Analog Output signals: 4-20 mA; 0-5V; 0-10V

I/O
I/O Circuits
Circuits
5. Special Purpose I/O :
• Circuits of this type are used to interface PLCs to very specific
types of circuits such as servomotors, stepping motors PID
(proportional plus integral plus derivative) loops, high-speed
pulse counting, resolver and decoder inputs, multiplexed
displays, and keyboards.
• This module allows for limited access to timer and counter
presets and other PLC variables without requiring a program
loader.

INPUTS
OUTPUTS
MOTOR
CONTACTOR
PLC
LAMP
CONTACTOR
PUSH BUTTONS

INPUT DEVICES:
Thumbwheel SW
Limit Switch
Push Button
Level SW
Flow SW
Thumbwheel SW

Motor
Solenoid
LED Display
OUTPUT DEVICES:
LED Display
Heater Coil
Lamp

L1 L2
P. B SWITCH
I:2
0
I= Input
Module
slot # in rack
Module
Terminal #
Allen
Allen
Allen
Allen
Allen
Allen
Allen
Allen-
-
-
-
-
-
-
-Bradley 1746
Bradley 1746
Bradley 1746
Bradley 1746
Bradley 1746
Bradley 1746
Bradley 1746
Bradley 1746-
-
-
-
-
-
-
-1A16
1A16
1A16
1A16
1A16
1A16
1A16
1A16
INPUT MODULE
WIRING DIAGRAM
LADDER PROGRAM
Terminal #
Address
Address
Address
Address I:2.0/0
I:2.0/0
I:2.0/0
I:2.0/0

N.
O
C
L2
L1
L1
L2
OUTPUT MODULE
MOTOR
CONTACTOR
FIELD
WIRING
•SOLENOI
D
•VALVES
•LAMP
•BUZZER
OUTPUT MODULE
WIRING
O:4
0
CONTACTOR
LADDER PROGRAM
L1
L2

Discrete Input
A discrete input also referred as digital input is an input that is either
ON or OFF are connected to the PLC digital input. In the ON condition
it is referred to as logic 1 or a logic high and in the OFF condition
maybe referred to as logic o or logic low.
Normally Open Pushbutton
Normally Closed Pushbutton
Normally Closed Pushbutton
Normally Open switch
Normally Closed switch
Normally Open contact
Normally closed contact

OFF
Logic 0
IN
PLC
Input
Module
24 V dc
OFF
Logic 1
IN
PLC
Input
Module
24 V dc

An analog input is an input signal that has a continuous
signal. Typical inputs may vary from 0 to 20mA, 4 to 20mA
or 0 to10V. Below, a level transmitter monitors the level of
liquid in the tank. Depending on the level Tx, the signal to the
PLC can either increase or decrease as the level increases
or decreases.
Analog Input
IN
PLC
Analog
Input
Module
Tank
Level Transmitter

OUT
A discrete output is either in an ON or OFF condition. Solenoids,
contactors coils, lamps are example of devices connected to the
Discrete or digital outputs. Below, the lamp can be turned ON or OFF by
the PLC output it is connected to.
Digital Output
OUT
PLC
Digital
Output
Module
Lamp

OUT
An analog output is an output signal that has a continuous
signal. Typical outputs may vary from 0 to 20mA, 4 to 20mA
or 0 to10V.
Analog Output
Electric to pneumatic transducer
OUT
PLC
Analog
Output
Module
E
P
Pneumatic control valve
Supply air
0 to 10V

Processor
The processor module contains the PLC’s microprocessor, its supporting
circuitry, and its memory system.
The main function of the microprocessor is to analyze data coming from
field sensors through input modules, make decisions based on the user’s
defined control program and return signal back through output modules to
the field devices. Field sensors: switches, flow, level, pressure, temp.
transmitters, etc. Field output devices: motors, valves, solenoids, lamps, or
transmitters, etc. Field output devices: motors, valves, solenoids, lamps, or
audible devices.
The memory system in the processor module has two parts: a system
memory and an application memory.

Memory Map Organization
SYSTEM
•System memory includes an area called the EXECUTIVE,
composed of permanently-stored programs that direct all
system activities, such as execution of the users control
program, communication with peripheral devices, and other
system activities.
•The system memory also contains the routines that
implement the PLC’s instruction set, which is composed of
specific control functions such as logic, sequencing, timing,
counting, and arithmetic.
•System memory is generally built from read-only memory
devices.
APPLICATION
•The application memory is divided into the data table area
and user program area.
•The data table stores any data associated with the user’s
control program, such as system input and output status data,
and any stored constants, variables, or preset values. The
data table is where data is monitored, manipulated, and
changed for control purposes.
•The user program area is where the programmed
instructions entered by the user are stored as an application
control program.
•Data Table
•User Program

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.

Memory Designs
The words random access refer to the ability of any location (address) in
the memory to be accessed or used. Ram memory is used for both the
user memory (ladder diagrams) and storage memory in many PLC’s.
RAM memory must have battery backup to retain or protect the stored
program.

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.

Memory Designs
NON-VOLATILE
Has the ability to retain stored information when power is removed,
accidentally or intentionally. These memories do not require battery back-up.
Common Type of Non-Volatile Memory
ROM, Read Only Memory
Read only indicates that the information stored in memory can be read only
and cannot be changed. Information in ROM is placed there by the
and cannot be changed. Information in ROM is placed there by the
manufacturer for the internal use and operation of the PLC.

Memory Designs
Other Types of Non-Volatile Memory
PROM, Programmable Read Only Memory
Allows initial and/or additional information to be written into the chip.
PROM may be written into only once after being received from the PLC
manufacturer; programming is accomplish by pulses of current.
The current melts the fusible links in the device, preventing it from being
The current melts the fusible links in the device, preventing it from being
reprogrammed. This type of memory is used to prevent unauthorized
program changes.

Memory Designs
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.
circuitry exposed to ultra violet light, the memory content can be erased.
The EPROM chip is also referred to as UVPROM.

Memory Designs
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
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.

Input CPU Output
Power
supply
Input
module
CPU
Program memory
Output
module
Field Control
Input
Elements
Process / Machine

PLC Operating Principle
Self test
Self test
Self test
Self test
In
In
In
In-
-
-
-put scan
put scan
put scan
put scan
Start
Start
Start
Start
Self test
Self test
Self test
Self test
Out
Out
Out
Out-
-
-
-put scan
put scan
put scan
put scan
Communication
Communication
Communication
Communication

PLC Operation
Basic Function of a Typical PLC
Read all field input devices via the input interfaces, execute the user
program stored in application memory, then, based on whatever control
scheme has been programmed by the user, turn the field output devices on
or off, or perform whatever control is necessary for the process application.
This process of sequentially reading the inputs, executing the program in
This process of sequentially reading the inputs, executing the program in
memory, and updating the outputs is known as scanning.

While the PLC is running, the scanning process includes the following four
phases, which are repeated continuously as individual cycles of operation:
PHASE 2
Program
PHASE 1
Read Inputs
Scan
Program
Execution
PHASE 3
Diagnostics/
Comm
PHASE 4
Output
Scan

PHASE 1 – Input Status scan
• A PLC scan cycle begins with the CPU reading the status of its inputs.
PHASE 2– Logic Solve/Program Execution
• The application program is executed using the status of the inputs
• The application program is executed using the status of the inputs
PHASE 3– Logic Solve/Program Execution
• Once the program is executed, the CPU performs diagnostics and
communication tasks

PHASE 4 - Output Status Scan
•An output status scan is then performed, whereby the stored output
values are sent to actuators and other field output devices. The cycle
ends by updating the outputs.

As soon as Phase 4 are completed, the entire cycle begins again with
Phase 1 input scan.
The time it takes to implement a scan cycle is called SCAN TIME. The scan
time composed of the program scan time, which is the time required for
solving the control program, and the I/O update time, or time required to
read inputs and update outputs. The program scan time generally depends
on the amount of memory taken by the control program and type of
instructions used in the program. The time to make a single scan can vary
instructions used in the program. The time to make a single scan can vary
from 1 ms to 100 ms.

PLC Communications
Common Uses of PLC Communications Ports
Changing resident PLC programs - uploading/downloading from a
supervisory controller (Laptop or desktop computer).
Forcing I/O points and memory elements from a remote terminal.
Linking a PLC into a control hierarchy containing several sizes of PLC
Linking a PLC into a control hierarchy containing several sizes of PLC
and computer.
Monitoring data and alarms, etc. via printers or Operator Interface Units
(OIUs).

PLC Communications
Serial Communications
PLC communications facilities normally provides serial transmission of
information.
Common Standards
RS 232
RS 232
Used in short-distance computer communications, with the majority of
computer hardware and peripherals.
Has a maximum effective distance of approx. 30 m at 9600 baud.

PLC Communications
Local Area Network (LAN)
Local Area Network provides a physical link between all devices plus
providing overall data exchange management or protocol, ensuring that each
device can “talk” to other machines and understand data received from them.
LANs provide the common, high-speed data communications bus which
interconnects any or all devices within the local area.
LANs are commonly used in business applications to allow several users to
share costly software packages and peripheral equipment such as printers
and hard disk storage.

PLC Communications
RS 422 / RS 485
Used for longer-distance links, often between several PCs in a
distributed system. RS 485 can have a maximum distance of about 1000
meters.

PLC Communications
Programmable Controllers and Networks
Dedicated Network System of Different Manufacturers
Manufacturer Network
Allen-Bradley Data Highway
Allen-Bradley Data Highway
Gould Modicon Modbus
General Electric GE Net Factory LAN
Mitsubishi Melsec-NET
Square D SY/NET
Texas Instruments TIWAY

Specifications
Several factors are used for evaluating the quality and performance of
programmable controllers when selecting a unit for a particular application.
These are listed below.
NUMBER OF I /O PORTS
This specifies the number of I/O devices that can be connected to the
controller. There should be sufficient I/O ports to meet present requirements
controller. There should be sufficient I/O ports to meet present requirements
with enough spares to provide for moderate future expansion.

Working of PLC
Working of PLC
Working of PLC
Working of PLC
Working of PLC
Working of PLC
Working of PLC
Working of PLC
CPU
•User Program memory
•Internal timers
•Internal counters
Input
Module
Output
Module
I/O Bus I/O Bus
II
IV
•Internal counters
Module Module
PII PIQ
Field
signals
Field
Controls
I III

PLC Programming
PLC Programming
PLC Programming
PLC Programming
PLC Programming
PLC Programming
PLC Programming
PLC Programming
PLC is software driven equipment like computer
Working of PLC (process) is decided by user through program.
Depending on process requirement program (set of instruction) is
prepared.
CPU sequentially read these instruction and operates control
elements based on input signals and program instruction.
Programming can be done On-line or Off-line.
Normally programming / change in program is done in memory of
programming unit and then simply this change is loaded in CPU
memory of PLC

Addressing Inputs & Outputs
Slot
Slot
Slot
Slot numbers
numbers
numbers
numbers
0 1 2 3 4 ---------------- 30 31
0
1
2
3
Channel Nos.
Channel Nos.
Channel Nos.
Channel Nos.
CPU
2
5
7
6
CPU
CPU
CPU
CPU

PROGRAMMING
Normally Open
(NO)
Normally Closed
(NC)
Power flows through these contacts when they are closed. The
normally open (NO) is true when the input or output status bit
controlling the contact is 1. The normally closed (NC) is true
when the input or output status bit controlling the contact is 0.

Coils
Coils represent relays that are energized when power flows to
them. When a coil is energized it causes a corresponding
output to turn on by changing the state of the status bit controlling
output to turn on by changing the state of the status bit controlling
the output to 1. That same output status bit maybe used to control
normally open or normally closed contact anywhere in the program.

Boxes
Boxes represent various instructions or functions that are
Executed when power flows to the box. Some of these
Functions are timers, counters and math operations.

AND OPERATION
Each rung or network on a ladder program represents
a logic operation. In the rung above, both inputs A and B
Rung
A B C
a logic operation. In the rung above, both inputs A and B
must be true (1) in order for the output C to be true (1).

OR OPERATION
Rung
A
B
C
In the rung above, it can be seen that either input A or B
is be true (1), or both are true, then the output C is true (1).

NOT OPERATION
In the rung above, it can be seen that if input A is be true (1),
Rung
A C
In the rung above, it can be seen that if input A is be true (1),
then the output C is true (0) or when A is (0), output C is 1.

Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
• Ladder Diagram (LAD)
Ladder Diagram (LAD)
– Use relay logic symbols to formulate the
Use relay logic symbols to formulate the
control task
control task
control task
control task
• Control System Flowchart (CSF)
Control System Flowchart (CSF)
– Use digital graphical symbols to formulate
Use digital graphical symbols to formulate
– Use digital graphical symbols to formulate
the control task
the control task
the control task
the control task
• Statement List (STL)
Statement List (STL)
– Use mnemonic abbreviation in
Use mnemonic abbreviation in
programming.
programming.
programming.
programming.
&

1. PLC - Introduction
Data Flow in the PLC

n One of the advantages of PLC is that it can be programmed by
non-specialists
n Program can be written either in the form of a
statement list: a set of mnemonic instructions representing a
function of the CPU
function of the CPU
function of the CPU
function of the CPU
or a
ladder diagram: a graphical language resembling the electrical
relay diagrams
relay diagrams
relay diagrams
relay diagrams

statement list
statement list
statement list
statement list

Ladder diagram
Ladder diagram
Ladder diagram
Ladder diagram

Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
• Circuit Diagram
Circuit Diagram
Circuit Diagram
Circuit Diagram • Ladder Diagram (LAD)
I 1.0
I 1.0
I 1.0
I 1.0
I 1.1
I 1.1
I 1.1
I 1.1
I 1.2
I 1.2
I 1.2
I 1.2
I 1.3
I 1.3
I 1.3
I 1.3
I 1.1
I 1.1
I 1.1
I 1.1
I 1.0
I 1.0
I 1.0
I 1.0 Q 4.1
Q 4.1
Q 4.1
Q 4.1
I 1.1
I 1.1
I 1.1
I 1.1 I 1.3
I 1.3
I 1.3
I 1.3
Q 4.1
Q 4.1
Q 4.1
Q 4.1
I 1.3
I 1.3
I 1.3
I 1.3
I 1.2
I 1.2
I 1.2
I 1.2

Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
• Circuit Diagram
Circuit Diagram
Circuit Diagram
Circuit Diagram • Control System Flowchart (CSF)
I 1.0
I 1.0
I 1.0
I 1.0
I 1.1
I 1.1
I 1.1
I 1.1
I 1.2
I 1.2
I 1.2
I 1.2
I 1.3
I 1.3
I 1.3
I 1.3
&
I 1.0
I 1.0
I 1.0
I 1.0
I 1.1
I 1.1
I 1.1
I 1.1
I 1.1
I 1.1
I 1.1
I 1.1 I 1.3
I 1.3
I 1.3
I 1.3
Q 4.1
Q 4.1
Q 4.1
Q 4.1
>=1
=
&
I 1.2
I 1.2
I 1.2
I 1.2
I 1.3
I 1.3
I 1.3
I 1.3
Q 4.1
Q 4.1
Q 4.1
Q 4.1

Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
Writing Program
• Circuit Diagram
Circuit Diagram
Circuit Diagram
Circuit Diagram • Statement List (STL)
A I 1.0
A I 1.0
A I 1.0
A I 1.0
A I 1.1
A I 1.1
A I 1.1
A I 1.1
O
O
O
O
I 1.0
I 1.0
I 1.0
I 1.0
I 1.1
I 1.1
I 1.1
I 1.1
I 1.2
I 1.2
I 1.2
I 1.2
I 1.3
I 1.3
I 1.3
I 1.3
O
O
O
O
A I 1.2
A I 1.2
A I 1.2
A I 1.2
A I 1.3
A I 1.3
A I 1.3
A I 1.3
= Q 4.1
= Q 4.1
= Q 4.1
= Q 4.1
I 1.1
I 1.1
I 1.1
I 1.1 I 1.3
I 1.3
I 1.3
I 1.3
Q 4.1
Q 4.1
Q 4.1
Q 4.1

Ladder logic (1)
The ladder logic is the oldest programming language for PLC
it bases directly on the relay intuition of the electricians.
it is widely in use outside Europe.
It is described here but not recommended for new projects.
(Kontaktplansprache, langage à contacts)
It is described here but not recommended for new projects.

Ladder Logic (2)
01
02
03 50
relay coil
(bobine)
break contact
make contact
(contact travail)
origin:
electrical
circuit
01 02
50
03
break contact
(contact repos)
corresponding
ladder diagram
50 05
44
rung
rung
rung
rung
"coil" 50 is used to move
other contact(s)

Ladder logic (3)
The contact plan or "ladder logic" language allows an easy transition from the
traditional relay logic diagrams to the programming of binary functions.
It is well suited to express combinational logic
It is not suited for process control programming (there are no analog
elements).
The main ladder logic symbols represent the elements:
The main ladder logic symbols represent the elements:
make contact
break contact
relay coil
contact travail
contact repos
bobine
Arbeitskontakt
Ruhekontakt
Spule

Ladder logic (4)
Binary combinations are expressed by series and parallel relay contact:
+ 01 02
50
Coil 50 is active (current flows) when 01 is active and 02 is not.
01
02
50
Series
ladder logic representation “logic" equivalent
+ 01
40
02
Coil 40 is active (current flows) when 01 is active or 02 is not.
Parallel
01
02 40

Ladder logic (5)
The ladder logic is more intuitive for complex binary expressions than literal languages
50
1 2 3 4
5 6
!N 1 & 2 STR 3 & N 4 STR N 5
& 6 / STR & STR = 50
textual expression
50
0 1 4 5
6 7
2 3
10 11
12
!0 & 1 STR 2 & 3 / STR STR 4
& 5 STR N 6 & 7
/ STR & STR STR 10
& 11 / STR & 12 = 50

Ladder logic (6)
Ladder logic stems from the time of the relay technology.
As PLCs replaced relays, their new possibilities could not be expressed any
more in relay terms.
The contact plan language was extended to express functions:
literal expression:
!00 & 01 FUN 02 = 200
200
FUN 02
01
00
!00 & 01 FUN 02 = 200
The intuition of contacts and coil gets lost.
The introduction of «functions» that influence the control flow itself, is problematic.
The contact plan is - mathematically - a functional representation.
The introduction of a more or less hidden control of the flow destroys the
freedom of side effects and makes programs difficult to read.

Ladder logic (7)
Ladder logic provides neither:
• sub-programs (blocks), nor
• data encapsulation nor
• structured data types.
It is not suited to make reusable modules.
IEC 61131 does not prescribe the minimum requirements for a compiler /
IEC 61131 does not prescribe the minimum requirements for a compiler /
interpreter such as number of rungs per page nor does it specifies the minimum
subset to be implemented.
Therefore, it should not be used for large programs made by different persons
It is very limited when considering analog values (it has only counters)
→ used in manufacturing, not process control

Criteria for selecting a PLC
• How
How
How
How many
many
many
many control
control
control
control inputs
inputs
inputs
inputs to
to
to
to be
be
be
be processed
processed
processed
processed –
–
–
– Nos
Nos
Nos
Nos.
.
.
. of
of
of
of Input
Input
Input
Input
• How
How
How
How many
many
many
many output
output
output
output devices
devices
devices
devices or
or
or
or controlling
controlling
controlling
controlling elements
elements
elements
elements are
are
are
are
controlled
controlled
controlled
controlled –
–
–
– Nos
Nos
Nos
Nos.
.
.
. of
of
of
of Output
Output
Output
Output.
.
.
.
• What
What
What
What memory
memory
memory
memory capacity
capacity
capacity
capacity is
is
is
is needed
needed
needed
needed to
to
to
to store
store
store
store the
the
the
the ùser
ùser
ùser
ùser
program’
program’
program’
program’ ?
?
?
?
• What
What
What
What speed
speed
speed
speed of
of
of
of processing
processing
processing
processing and
and
and
and operational
operational
operational
operational capabilities
capabilities
capabilities
capabilities
desire?
desire?
desire?
desire?
desire?
desire?
desire?
desire?
• What
What
What
What are
are
are
are the
the
the
the communication
communication
communication
communication requirements
requirements
requirements
requirements ?
?
?
?
• Are
Are
Are
Are there
there
there
there any
any
any
any special
special
special
special or
or
or
or specific
specific
specific
specific requirements
requirements
requirements
requirements including
including
including
including
that
that
that
that of
of
of
of safety,
safety,
safety,
safety, reliability,
reliability,
reliability,
reliability, expandability
expandability
expandability
expandability etc
etc
etc
etc.
.
.
.
• System
System
System
System voltage
voltage
voltage
voltage available
available
available
available for
for
for
for auxiliary
auxiliary
auxiliary
auxiliary supply
supply
supply
supply of
of
of
of PLC
PLC
PLC
PLC.
.
.
.
On
On
On
On getting
getting
getting
getting this
this
this
this information
information
information
information check
check
check
check for
for
for
for the
the
the
the specification
specification
specification
specification of
of
of
of
the
the
the
the available
available
available
available PLCs
PLCs
PLCs
PLCs.
.
.
.

Selecting a PLC
Criteria
• Number of logical inputs and outputs.
• Memory
• Number of special I/O modules
• Scan Time
• Communications
• Communications
• Software

A Detailed Design Process
1. Understand the process
2. Hardware/software selection
3. Develop ladder logic
4. Determine scan times and memory requirements

Specifications
OUTPUT-PORT POWER RATINGS
Each output port should be capable of supplying sufficient voltage and
current to drive the output peripheral connected to it.
SCAN TIME
This is the speed at which the controller executes the relay-ladder logic
This is the speed at which the controller executes the relay-ladder logic
program. This variable is usually specified as the scan time per 1000 logic
nodes and typically ranges from 1 to 200 milliseconds.

Specifications
MEMORY CAPACITY
The amount of memory required for a particular application is related to the
length of the program and the complexity of the control system. Simple
applications having just a few relays do not require significant amount of
memory. Program length tend to expand after the system have been used
for a while. It is advantageous to a acquire a controller that has more
memory than is presently needed.
memory than is presently needed.

PLC Status Indicators
•Power On
•Run Mode
•Programming Mode
•Fault
•Fault

Troubleshooting
1. Look at the process
2. PLC status lights
HALT - something has stopped the CPU
RUN - the PLC thinks it is OK (and probably is)
ERROR - a physical problem has occurred with the PLC
3. Indicator lights on I/O cards and sensors
4. Consult the manuals, or use software if available.
5. Use programming terminal / laptop.
5. Use programming terminal / laptop.

List of items required when working with PLCs:
1. Programming Terminal - laptop or desktop PC.
2. PLC Software. PLC manufacturers have
their own specific software and license key.
3. Communication cable for connection from Laptop
to PLC.
4. Backup copy of the ladder program (on diskette, CDROM,
hard disk, flash memory). If none, upload it from the PLC.
5. Documentation- (PLC manual, Software manual, drawings,
5. Documentation- (PLC manual, Software manual, drawings,
ladder program printout, and Seq. of Operations manual.)

Examples of PLC Programming Software:
1. Allen-Bradley – Rockwell Software RSLogix500
2. Modicon - Modsoft
3. Omron - Syswin
4. GE-Fanuc Series 6 – LogicMaster6
5. Square D- PowerLogic
6. Texas Instruments – Simatic
6. Telemecanique – Modicon TSX Micro

Summary
• Overview
– A dedicated computer for rapid processing of simple logic
instructions in a defined time
– Used in automated processes (rollercoaster)
– Used a lot in automated industry
– Logic control and sequencing approaches
– Cost: $60-$400
– Machine vision commonly used as supporting technology
– Dr. Red = Good reference
– Dr. Red = Good reference
• Use in Industry
– Applications include simple and, or, not diagrams/programs
– Few limitations for its function
– Main known vendors: Honeywell, Rockwell, Sharp, Unitronics
– Standards: IEC 61131. Trying to standardize PLC programs
• Application examples
– Modeling Programs and Diagnosable functions for PLCs
– Useful in planning and determining structure and diagram
– Parking garage video
– Design your own street light system
– End of the line

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