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1. Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller
(PLC) (PLC) (PLC) (PLC) (PLC) (PLC) (PLC) (PLC)
Presented By
:
Seminar on Seminar on Seminar on Seminar on Seminar on Seminar on Seminar on Seminar on
Mahesh J. Vadhavaniya(122511)
M. E. –Regular, 2012 –14
NITTTR, Chandigarh
Subject Faculty :
Prof. Ram Murat Singh

2. Objectives : AttheendoftheSessionwewillbeableto:
●DescribethemajorcomponentsofacommonPLC. ●InterpretPLCspecifications.
●Applytroubleshootingtechniques.
●ConvertconventionalrelaylogictoaPLClanguage.
●OperateandprogramaPLCforagivenapplication.

3. Contents :
●HistoryofProgrammableControllers
●RelayLadderLogic
●CentralProcessingUnit
●Input/OutputSystem
●ProgrammingandPeripheralDevices
●ProgrammingConcepts
●Applications
●TroubleshootingandMaintenance

4. 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

5. Why Automation ? Why Automation ? Why Automation ? Why Automation ? Why Automation ? Why Automation ? Why Automation ? Why Automation ?
Higherproductivity Superiorqualityofendproduct Efficientusageofenergyandrawmaterials Improvedsafetyinworkingcondition
etc…

6. 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

7. 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 WhatWhat Whatdoesdoesdoes doesPLCPLCPLCPLCstand stand stand standfor?for?for? for?
•PLC-ProgrammableLogicController •PLCimplementslogiccontrolfunctionsbymeansofa
program

8. Programmable Logic Controllers
( Definition according to NEMA standard ICS3-1978)
A digitallyoperatingelectronic
apparatus whichuses a programming
memory
for
the
internal
storage
of
memory
for
the
internal
storage
of
instructions for implementingspecific
functions suchas logic, sequencing,
timing,countingandarithmetictocontrol
throughdigital or analogmodules,
varioustypesofmachinesorprocess.

9. 1. PLC 1. PLC 1. PLC 1. PLC 1. PLC 1. PLC 1. PLC 1. PLC ----- ---Introduction Introduction Introduction Introduction Introduction Introduction Introduction Introduction
HowHowHowHowdoes doesdoes doesaaaaPLCPLCPLCPLCdiffer differ differ differfrom fromfrom fromaaaacomputer? computer? computer? computer?
•Acomputerisoptimizedforcalculationanddisplaytasks •Acomputerisprogrammedbyspecialists
•APLCisdesignedfor(logic)controlandregulationtasks
•APLCisprogrammedbynon-specialists
•APLCiswelladaptedtoindustrialenvironment

10. PLC Origin PLC Origin
•Developedtoreplacerelaysinthelate1960s •
Costs
dropped
and
became
popular
by
1980
s
•
Costs
dropped
and
became
popular
by
1980
s
•Nowusedinmanyindustrialdesigns

11. Historical Background Historical Background
•The Hydramatic Division of the General Motors
Corporation specified the design criteria for the first
programmablecontrollerin1968
Theirprimarygoal: •Toeliminate thehigh costsassociatedwith inflexible,
relay-controlledsystems.

12. Historical Background Historical Background •Thecontrollerhadtobedesignedinmodularform,so
that sub-assemblies could be removed easily for
replacementorrepair.
•
The
control
system
needed
the
capability
to
pass
data
•
The
control
system
needed
the
capability
to
pass
data
collectiontoacentralsystem. •Thesystemhadtobereusable. •Themethodusedtoprogramthecontrollerhadtobe
simple, so that it could be easily understood by plant
personnel.

13. Programmable Controller Development Programmable Controller Development
1968OProgrammableconceptdeveloped
1969OHardwareCPUcontroller,withlogic
instructions,1Kofmemoryand128I/O
points
1974
O
Use
of
several
(multi)
processors
within
a
1974
O
Use
of
several
(multi)
processors
within
a
PLC-timersandcounters;arithmetic
operations; 12 K of memory and 1024 I/O
points
1976ORemoteinput/outputsystemsintroduced
1977OMicroprocessors-basedPLCintroduced

14. 1980OIntelligentI/Omodulesdeveloped
Enhancedcommunicationsfacilities
Enhancedsoftwarefeatures
(e
.
g
.
documentation)
Use
of
personal
Programmable Controller Development Programmable Controller Development
(e
.
g
.
documentation)
Use
of
personal
microcomputersas programmingaids
1983OLow-costsmallPLC’sintroduced
1985ONetworking of all levels of PLC, computer
andmachineusingSCADAsoftware. onwards

15. INTRODUCTION TO PLCS INTRODUCTION TO PLCS
Advantages of PLCs :
•Lesswiring.
•Wiring between devices and relay contacts are done
inthePLCprogram.
•Easierandfastertomakechanges.
•Trouble shooting aids make programming easier
andreducedowntime.
•Reliablecomponentsmaketheselikelytooperatefor
yearsbeforefailure.

16. INTRODUCTION TO PLCS INTRODUCTION TO PLCS
Advantages of PLCs :
•Theyarecost-effective
•Theyareflexible,reliableandcompact
•
They
have
significant
advantages
over
traditional
•
They
have
significant
advantages
over
traditional
controlsystemsbasedonrelayorpneumatics

17. 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
undertakenwithrelaysorpneumatics)
•In addition, PLCs can performa variety of
calculation,communicationandmonitoringtasks

18. Leading Brands Of PLC 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

19. JAPANESE:
1. Toshiba
2. Omron
3.
Fanuc
Leading Brands Of PLC Leading Brands Of PLC
3.
Fanuc
4. Mitsubishi

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

21. PLC Size : PLC Size :
Small:
•It covers units with up to 128 I/O’s and memories
upto2Kbytes.
•These PLC’s are capable of providing simple to
advancelevelsormachinecontrols.
Medium:
•Have up to 2048 I/O’s and memories up to 32
Kbytes.
Large:
•ThemostsophisticatedunitsofthePLCfamily.
•They have up to 8192 I/O’s and memories up to 750
Kbytes.
•Can control individual production processes or
entireplant.

22. Major Components of a Common PLC 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.

23. Major Components of a Common PLC Major Components of a Common PLC
Power Supply:
•Provides the voltage needed to run the primary PLC
components
I/O Modules:
•Provides signal conversion and isolation between the
internallogic- level signals inside the PLC and the field’s
highlevelsignal.

24. Processor :
•Provides intelligence to command and govern the activities
of
the
entire
PLC
systems
.
Major Components of a Common PLC Major Components of a Common PLC
of
the
entire
PLC
systems
.
Programming Device :
•Used to enter the desired programthat will determine the
sequence of operation and control of process equipment or
drivenmachine.

25. I/O Module I/O Module
•The I/O interface section of a PLC connects it to external fiel d
devices.
•The main purpose of the I/O interface is to condition the
various signals received fromor sent to the external input
andoutputdevices.
•Inputmodulesconvertssignalsfromdiscreteoranaloginput
devicestologiclevelsacceptabletoPLC’sprocessor.
•Output modules converts signal fromthe processor to levels
capable of driving the connected discrete or analog output
devices.

26. 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
effects of electrical noise
Current
Limiting
Resistor
FROM
INPUT
DEVICE
Buffer,
Filter,
hysteresi
s Circuits
TO
PROCESSOR

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

29. 29

31. IS NEEDED TO:
•Prevent voltage
transients from
damaging the
processor.
•Helps reduce the
effects of electrical
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

33. 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
motorstarters.
•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
timewithoutfailure.

34. 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. N oise
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
indicationofinputsturningonoroffbecauseofnoise.

35. I/O I/O Circuits Circuits
4. Analog I/O :
•Circuitsofthistypesenseordriveanalogsignals.
•Analog inputs come fromdevices, 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
.
•StandardAnalogInputsignals:4-20mA;0-10V
•Analog outputs can be used to drive devices such as
voltmeters, X-Y recorders, servomotor drives, and valves
throughtheuseoftransducers.
•StandardAnalogOutputsignals:4-20mA;0-5V;0-10V

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

37. INPUTS
OUTPUTS
MOTOR
CONTACTOR
PLC
LAMP
CONTACTOR
PUSH BUTTONS

38. INPUT DEVICES:
Thumbwheel SW Limit Switch
Push Button
Level SW Flow SWThumbwheel SW

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

40. L1L2
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 1A161A16 1A161A16 1A161A16 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

41. 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

42. 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. I n 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

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

44. An analog input is an input signal that has a continuous
signal.Typical inputs may vary from0 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 th e
PLC can either increase or decrease as the level increases
or decreases.
Analog Input
IN
PLC
Analog
Input
Module
Tank
Level Transmitter

45. OUT
A discrete output is either in an ON or OFF condit ion. Solenoids,
contactors coils, lamps are example of devices conn ected 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

46. OUT
An analog output is an output signal that has a continu ous
signal. Typical outputs may vary from 0 to 20mA, 4 to 2 0mA
or 0 to10V.
Analog Output
Electric to pneumatic transducer
OUT
PLC
Analog
Output
Module
E
P
Pneumatic control valve
Supply air
0 to 10V

47. 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
.

48. 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 c ontrol
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 compo sed of
specific control functions such as logic, sequencin g, timing,
counting, and arithmetic.
•System memory is generally built from read-only me mory
devices.
APPLICATION
•The application memory is divided into the data ta ble area
and user program area.
•The data table stores any data associated with the user’s
control program, such as system input and output st atus data,
and any stored constants, variables, or preset valu es. 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 a pplication
control program.
•Data Table
•User Program

49. Memory Designs VOLATILE.
A volatile memory is one that loses its stored informatio n when power is
removed.
Even momentary losses of power will erase any informatio n 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 th e memory can be
retrieved or read, while write indicates that the user can program or write
information into the memory.

50. Memory Designs The words random accessrefer 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.

51. 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.

52. Memory Designs NON-VOLATILE
Has the ability to retain stored information when pow er is removed,
accidentally or intentionally. These memories do not re quire battery back-up.
Common Type of Non-Volatile Memory
ROM, Read Only Memory
Read only indicates that the information stored in mem ory 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 th e PLC.

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

54. Memory Designs EPROM, Erasable Programmable Read Only Memory
Ideally suited when program storage is to be semi-perma nent or additional
security is needed to prevent unauthorized program change s.
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 rem oved and the
circuitry exposed to ultra violet light, the memory cont ent can be erased. circuitry exposed to ultra violet light, the memory cont ent can be erased. The EPROM chip is also referred to as UVPROM.

55. Memory Designs EEPROM, Electrically Erasable Programmable Read Only
Memory
Also referred to as E
2
PROM, 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.

56. Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller Programmable Logic Controller
Input
CPU
Output
Power
supply
Input
module
CPU
Program memory
Output module
Field Control
Input
Elements
Process / Machine

57. PLC Operating Principle PLC Operating Principle PLC Operating Principle PLC Operating Principle PLC Operating Principle PLC Operating Principle PLC Operating Principle PLC Operating Principle
Self test Self test Self test Self test
InInIn In----put scan put scan put scan put scan
Start Start Start Start
Self test Self test Self test Self test
OutOutOutOut----put scan put scan put scan put scan
Communication Communication Communication Communication

58. PLC Operation Basic Function of a Typical PLC
Read all field input devices via the input interfaces, ex ecute the user
program stored in application memory, then, based on w hatever 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.

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

60. 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 t he inputs
•
The application program is executed using the status of t he inputs
PHASE 3– Logic Solve/Program Execution
•Once the program is executed, the CPU performs diagnostics and
communication tasks

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

62. 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 g enerally depends
on the amount of memory taken by the control program and type of
instructions used in the program. The time to make a sing le scan can vary instructions used in the program. The time to make a sing le scan can vary from 1 ms to 100 ms.

63. 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 Oper ator Interface Units
(OIUs).

64. PLC Communications Serial Communications PLC communications facilities normally provides serial tran smission 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.

65. PLC Communications Local Area Network (LAN) Local Area Network provides a physical link between all de vices plus
providing overall data exchange management or protocol, ensuring that each
device can “talk” to other machines and understand data re ceived 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 seve ral users to
share costly software packages and peripheral equipment such as printers
and hard disk storage.

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

67. 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

68. Specifications Several factors are used for evaluating the quality and performance of
programmable controllers when selecting a unit for a pa rticular application.
These are listed below.
NUMBER OF I /O PORTS
This specifies the number of I/O devices that can be connecte d 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 expa nsion.

69. 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

70. PLC Programming PLC Programming PLC Programming PLC Programming PLC Programming PLC Programming PLC Programming PLC Programming
PLCissoftwaredrivenequipmentlike computer WorkingofPLC(process)isdecidedbyuserthroughprogram. Depending on process requirement program(set of instruction) is
prepared.
CPU sequentially read these instruction and operates control
elementsbasedoninputsignalsandprograminstruction.
ProgrammingcanbedoneOn-lineorOff-line. Normallyprogramming /change in programis done in memory of
programming unit and then simply this change is loaded in CPU
memoryofPLC

71. Addressing Inputs & Outputs Addressing Inputs & Outputs Addressing Inputs & Outputs Addressing Inputs & Outputs Addressing Inputs & Outputs Addressing Inputs & Outputs Addressing Inputs & Outputs 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
CPUCPUCPUCPU

72. PROGRAMMING
Normally Open
(NO)
Normally Closed
(NC)
Power flows through these contacts when they are closed. T he
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 con tact is 0.

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

74. 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.

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

76. 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).

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

78. Writing Program Writing Program Writing Program Writing Program Writing Program Writing Program Writing Program Writing Program
• Ladder Diagram (LAD) Ladder Diagram (LAD) Ladder Diagram (LAD) Ladder Diagram (LAD)
– Use relay logic symbols to formulate the Use relay logic symbols to formulate the 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) 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 Use digital graphical symbols to formulate
–
Use digital graphical symbols to formulate 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) Statement List (STL) Statement List (STL)
– Use mnemonic abbreviation in Use mnemonic abbreviation in Use mnemonic abbreviation in Use mnemonic abbreviation in
programming. programming. programming. programming.
&

79. 1. PLC -Introduction
Data Flow in the PLC

80. 1. PLC -Introduction
nOne of the advantages of PLC is that it can be prog rammed by
non-specialists
nProgram can be written either in the form of a
statement list: a set of mnemonic instructions repr esenting a statement list: a set of mnemonic instructions repr esenting a statement list: a set of mnemonic instructions repr esenting a statement list: a set of mnemonic instructions repr esenting a statement list: a set of mnemonic instructions repr esenting a statement list: a set of mnemonic instructions repr esenting a statement list: a set of mnemonic instructions repr esenting a statement list: a set of mnemonic instructions repr esenting 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 ladder diagram: a graphical language resembling the electrical ladder diagram: a graphical language resembling the electrical ladder diagram: a graphical language resembling the electrical
relay diagrams relay diagrams relay diagrams relay diagrams

81. 1. PLC -Introduction statement list statement list statement list statement list

82. 1. PLC -Introduction Ladder diagram Ladder diagram Ladder diagram Ladder diagram

83. 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) Ladder Diagram (LAD) Ladder Diagram (LAD) 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 4.1Q 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

84. 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) Control System Flowchart (CSF) Control System Flowchart (CSF) 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

85. 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) Statement List (STL) Statement List (STL) 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
OOOO
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
OOOOA 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

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

87. Ladder Logic (2)
01
02
03
50
relay coil
(bobine)
break contact
make contact
(contact travail) origin:
electrical
circuit
0102
50
03
break contact
(contact repos)
corresponding
ladder diagram
50
05
44
rung rungrung rung
"coil" 50 is used to move
other contact(s)

88. Ladder logic (3) The contact plan or "ladder logic" language allows an e asy 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 a re 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

89. Ladder logic (4)
Binary combinations are expressed by series and parallel rel ay contact:
+
0102
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 i s not.
Parallel
01
02
40

90. Ladder logic (5) The ladder logic is more intuitive for complex binary exp ressions 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
1011
12
!0 & 1 STR 2 & 3 / STR STR 4
& 5 STR N 6 & 7
/ STR & STR STR 10
& 11 / STR & 12 = 50

91. Ladder logic (6)
Ladder logic stems from the time of the relay technology.
As PLCs replaced relays, their new possibilities could not b e expressed any
more in relay terms.
The contact plan language was extended to express function s:
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 contr ol flow itself, is problematic. The contact plan is - mathematically - a functional represen tation.
The introduction of a more or less hidden control of th e flow destroys the
freedom of side effects and makes programs difficult to re ad.

92. 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 ma de by different persons
It is very limited when considering analog values (it has o nly counters)
→used in manufacturing, not process control

94. Criteria for selecting a PLC Criteria for selecting a PLC Criteria for selecting a PLC Criteria for selecting a PLC Criteria for selecting a PLC Criteria for selecting a PLC Criteria for selecting a PLC Criteria for selecting a PLC
• HowHowHowHowmany manymany manycontrol control control controlinputs inputs inputs inputstototo tobebebe beprocessed processed processed processed––––NosNosNosNos....ofofof ofInput Input Input Input
• HowHowHowHowmany manymany many output output output output devices devices devices devices ororor or controlling controlling controlling controlling elements elements elements elements areareareare
controlled controlled controlled controlled––––NosNosNosNos....ofofof ofOutput Output Output Output....
• WhatWhatWhat What memory memory memory memory capacity capacity capacity capacity isisis is needed needed needed needed tototo to store store store store thethethethe `user `user `user `user
program’ program’ program’ program’????
• WhatWhatWhat What speed speed speed speed ofofof of processing processing processing processing andandandand operational operational operational operational capabilities capabilities capabilities capabilities
desire? desire? desire? desire? desire? desire? desire? desire?
• WhatWhatWhat Whatarearearearethethethethecommunication communication communication communicationrequirements requirements requirements requirements????
• AreAreAreAre there there there there anyanyanyany special special special special ororor or specific specific specific specific requirements requirements requirements requirements including including including including
that thatthat thatofofof ofsafety, safety, safety, safety,reliability, reliability, reliability, reliability,expandability expandability expandability expandabilityetcetcetcetc....
• System System System Systemvoltage voltage voltage voltageavailable available available availableforforforforauxiliary auxiliary auxiliary auxiliarysupply supply supply supplyofofof ofPLCPLCPLCPLC....
OnOnOnOn getting getting getting getting this thisthis this information information information information check check check check forforforfor thethethethe specification specification specification specification of ofof of
thethethetheavailable available available availablePLCs PLCsPLCs PLCs....

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

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

97. Specifications Several factors are used for evaluating the quality and performance of
programmable controllers when selecting a unit for a pa rticular application.
These are listed below.
NUMBER OF I /O PORTS
This specifies the number of I/O devices that can be connecte d 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 expa nsion.

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

99. Specifications MEMORY CAPACITY The amount of memory required for a particular appli cation is related to the
length of the program and the complexity of the contr ol system. Simple
applications having just a few relays do not require sign ificant amount of
memory. Program length tend to expand after the syste m have been used
for a while. It is advantageous to a acquire a controlle r that has more
memory than is presently needed. memory than is presently needed.

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

101. 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.

102. 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 manu al.)

103. 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

104. Summary
• Overview
– A dedicated computer for rapid processing of simple logi c
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/progr ams
– Few limitations for its function
– Main known vendors: Honeywell, Rockwell, Sharp, Unitronics
– Standards: IEC 61131. Trying to standardize PLC prog rams
• Application examples
– Modeling Programs and Diagnosable functions for PLCs
– Useful in planning and determining structure and diag ram
– Parking garage video
– Design your own street light system
– End of the line