PLC General

PROGRAMMABLE
LOGIC
CONTROLLER
Prolific Systems and Technologies Pvt Ltd

HHiissttoorryy
 Early control systems consisted of huge control boards consisting of
hundreds to thousands of electromechanical relays.
 An engineer would design the system logic, electricians would receive
a schematic outline of logic then implement the logic with relays.
 The schematic was commonly called “Ladder Schematic”
 The ladder displayed all switches, sensors, motors, valves, relays etc in
the system.
 Problems: Long commissioning time, dependency on mechanical
reliance, Any system logic design change required the power to the
control board to be isolated stopping production.

HHiissttoorryy
 General Motors was among the first to recognize a need to replace
the systems “wired control board”
 Hydramatic Division of GM specified the design criteria for the
programmable controller in 1968.
 Goal – Eliminate the high cost associated with inflexible, relay
controlled systems.

HHiissttoorryy
New Controller Specifications:
 Solid State System
 Computer Flexibility
 Operate in Industrial Environment (vibrations, heat, dust etc.)
 Capability of being reprogrammed
 Easily programmed and maintained by electricians and
technicians.

HHiissttoorryy
 In 1969 Gould Modicon developed the first PLC.
 Strength – Programmed with Ladder Logic
 Initially called Programmable Controllers PC’s
 Now - PLC’s, Programmable Logic Controllers
 PLC’s have evolved from simple on/off control to being able to
communicate with other control systems, provide production
reports, schedule production, diagnose machine and process
faults.

Advantage ooff PPLLCC OOvveerr RReellaayy SSttyyllee
RELAY PLC
1-Hard wiring 1-Less wiring
2-Changes difficult 2-Easy modification
3-More power 3-Low power
4-More maintenance 4-Less maintenance
5-Difficult to expand 5-Ease of expansion

CCoonnttrrooll SSyysstteemmss TTyyppeess
 Programmable Logic Controllers
 Distributed Control System
 PC- Based Controls

NNEEMMAA DDeeffiinniittiioonn yyeeaarr 11997788
NNaattiioonnaall EElleeccttrriiccaall MMaannuuffaaccttuurreerrss AAssssoocciiaattiioonn
The PLC, also known as programmable controller is defined by the
National Electrical Manufacturers Association (NEMA) in 1978 as:
"a digitally operating electronic apparatus which uses a programmable
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 input/output, various
types of machines or process".

Programmable LLooggiicc CCoonnttrroolllleerrss
Applications :
 Machine controls, Packaging, Palletizing, Material handling, similar
Sequential task as well as Process control
Advantages of PLC :
 They are fast and designed for the rugged industrial environment.
 They are attractive on Cost-Per-Point Basis.
 These Devices are less Proprietary ( E.g.. Using Open Bus Interface.)
 These Systems are upgraded to add more Intelligence and Capabilities
with dedicated PID and Ethernet Modules.
Disadvantages of PLC :
 PLC were Designed for Relay Logic Ladder and have Difficulty with
some Smart Devices.
 To maximize PLC performance and Flexibility, a number of Optional
Modules must be added
 PLC holds only one copy of program

Programmable LLooggiicc CCoonnttrroolllleerrss
PLC Types
 Nano (Small)
 Micro (Medium)
 Large
Basic criteria for PLC Types
 Memory Capacity
 I/O Range
 Packaging and Cost per Point

SSiizziinngg ooff PPLLCC
Micro PLCs: I/O up to 32 points
Small PLC: I/O up to 128 points
Medium PLC: I/O up to 1024 points
Large PLC: I/O up to 4096 points
Very Large: I/O 4096 Onwards

MMoosstt BBaassiicc ooff PPLLCC SSyysstteemmss
In the most basic of PLC systems, a self contained (shoe box) PLC has 2
terminal blocks, one for Inputs and one for Outputs
Today, most PLC’s in this category are know as Micros. Typically they
provide front panel LED status indication of I/O and Processor states
Inputs
Outputs
CR

MMoodduullaarr CChhaassssiiss BBaasseedd PPLLCC’’ss
The vast majority of PLC’s installed today are modular chassis based
systems consisting of:
1. Processor Module (CPU)
2. Input & Output Modules
3. Chassis
4. Power Supply

Modular CChhaassssiiss--lleessss PPLLCC SSyysstteemmss
Also available from many vendors are “Chassis less” but still Modular
PLC systems. These systems still require a Processor, I/O Modules, and
Power Supply, but in place of a chassis these components mount
directly onto a panel, din rail, and many use a tongue and grove system
to allow easy insertion and removal

PP LL CC CCoommppoonneennttss
 Central Processing Unit (CPU)
 Input Output Modules
 Power Supply
 Bus system
 Programming Device
IN CPU
OUT m
MODULE MODULE
PROGRAM
DEVICE

BBaassiicc PPLLCC SScchheemmaattiicc
 CPU
 Power Supply
 Memory
 Input Blocks
 Output Blocks
 Communications
 Expansion Connections

PP LL CC :: CCeennttrraall PPrroocceessssiinngg UUnniitt
 It is a micro-controller based circuitary. The CPU consists of
following blocks :
Arithmatic Logic Unit (ALU), Timing / Control ckt, Program
memory, Process image memory (Internal memory of CPU)
Internal timers and counters and Flags, Address stack and
instruction registers
 The Central Processing Unit (CPU) Module is the brain of the
PLC.

CCPPUU MMoodduullee
Self
Check
Scan
Inputs
Execute
Code
PLC Program
Update
Outputs
SCAN
 Primary role to read inputs, execute the control program, update
outputs.
 CPU performs the task necessary to fulfill the PLC functions. These
tasks include Scanning, I/O bus traffic control, Program execution,
Peripheral and External device communication, special functions or
data handling execution and self diagnostics.

MMeemmoorryy
 The memory includes pre-programmed ROM memory containing
the PLC’s operating system, driver programs and application
programs and the RAM memory.
 PLC manufacturer offer various types of retentive memory to save
user-programs and data while power is removed, so that the PLC
can resume execution of the user-written control program as soon as
power is restored.

MMeemmoorryy
 Many PLCs also offer removable memory modules, which are plugged
into the CPU module.
 Memory can be classified into two basic categories: volatile and non-volatile.
Volatile memory loses state (the stored information) when power
is removed.
Nonvolatile memory, maintains the information in memory even
if the power is interrupted.

MMeemmoorryy
Some types of memory used in a PLC include:
 ROM (Read-Only Memory)
 RAM (Random Access Memory)
 PROM (Programmable Read-Only Memory)
 EPROM (Erasable Programmable Read-Only Memory)
 EEPROM (Electronically Erasable Programmable Read-Only
Memory)
 FLASH Memory
 Compact Flash – Can store complete program information, read &
write text files

II//OO MMoodduulleess
 Input and output (I/O) modules connect the PLC to sensors and
actuators.
 Provide isolation for the low-voltage, low-current signals that the PLC
uses internally from the higher-power electrical circuits required by
most sensors and actuators.
 Wide range of I/O modules available including: digital (logical) I/O
modules and Analog (continuous) I/O modules.

PPLLCC :: IInnppuutt mmoodduullee
 These modules act as link between field input sensors and the CPU.
 Analog input module : Typical input to these modules is 4-20 mA,
0-10 V, Ohms, mV
Ex : Pressure, Flow, Level Tx, RTD (Ohm), Thermocouple (mV)
 Digital input module : Typical input to these modules is 24 V DC,
115 V AC, 230 V AC
Ex. : Switches, Pushbuttons, Relays, pump valve on off status

 Transfer of data:-I/P sensor to CPU
 Conversion:- 24vdc/230vac to 5vdc
 Isolation :- By Opto Coupler

IInnppuutt DDeevviicceess
 Pushbuttons
 Selector Switches
 Limit Switches
 Level Switches
 Photoelectric Sensors
 Proximity Sensors
 Motor Starter Contacts
 Relay Contacts
 Thumbwheel Switches

DDiiggiittaall IInnppuuttss MMoodduulleess
The list below shows typical ranges for input voltages.
 5 Vdc – used when Microcontroller based sensors are used as I/P
 12 Vdc Now not much used
 24 Vdc – Widely used (Standard for I/P)
 48 Vdc - Was used high power devices pneumatic / hydraulic cylendors /
limit switches
 12 Vac not being used
 24 Vac discontinued
 120 Vac Sensors are at long distance from controller
 240 Vac – Not much used

SOURCING vvss.. SSIINNKKIINNGG DDCC IInnppuuttss
DC
Power
Supply
Field
Device
DC
Input
Module
+
- DC COM
IN1
C
VDC
IN1
DC
Input
Module
Field
Device
+
DC
Power
Supply
-
+VDC
IN1
SINK SOURCE

AAnnaalloogguuee IInnppuuttss//OOuuttppuuttss
 Analogue input cards convert continuous signals via a A/D
converter into discrete values for the PLC
 Analogue output cards convert digital values in then PLC to
continuous signals via a D/A converter.
 Resolution can be important in choosing an applicable card
 Example, for a temperature input of 0 to 100 degrees C
For 8 bit resolution the value in the PLC is 0 to 255
For 12.5 bit resolution the value in the PLC is 0 to 6000

AAnnaalloogguuee CCaarrddss
Typical Analogue Input
signals are:
 Flow sensors
 Humidity sensors
 Load Cells
 Potentiometers
 Pressure sensors
 Temperature sensors
 Vibration
Analogue Output signals
control:
 Analogue Valves
 Actuators
 Chart Recorders
 Variable Speed Drives
 Analogue Meters
Typical Analogue Signal Levels
 4-20mA
 1-5 Vdc
 0-10 Vdc
 -10 – 10Vdc

PPLLCC :: OOuuttppuutt mmoodduullee
 These modules act as link between the CPU and the output devices
in the field.
 Analog output module : Typical output from these modules is 4-20
mA, 0-10 V
Ex : Control Valve, Speed, Vibration
 Digital output module : Typical output from these modules is 24 V
DC, 115 V AC, 230 V AC
Ex. : Solenoid Valves, lamps, Actuators, dampers, Pump valve on
off control

PLC : Output mmoodduullee -- TTyyppeess
 Relay type -For AC or DC
 Transistor Type Logic(TTL) - For DC
 Triac (Triode AC) type - For AC
 Isolated common type -For different device

PPLLCC :: OOuuttppuutt mmoodduullee

OOuuttppuutt DDeevviicceess
 Valves
 Motor Starters
 Solenoids
 Control Relays
 Alarms
 Lights
 Fans
 Horns
 Relays
 120 VAC/VDC
 240 VAC
 24 VAC/VDC
 Triac
 120/230 VAC
 Transistor MOSFET
 24 VDC

RReellaayyss
The most important consideration when selecting relays, or relay
outputs on a PLC, is the rated current and voltage.
For transistor outputs or higher density output cards relay terminal
blocks are available.
Advantage of individual standard replaceable relays

II//OO SSppeecciiffiiccaattiioonnss
 INPUT VOLTAGE – Magnitude and type of voltage
 ON-STATE INPUT VOLTAGE RANGE – voltage at which signal is
recognized
 Nominal current per input – Min. current to operate input circuit
 AMBIENT TEMP RATING – Max temp of surrounding the I/O
module
 INPUT DELAY – Time duration for input signal to be on before
known as valid input. ( 9-ms to 25ms)
 NOMINAL OUTPUT VOLTAGE – It is min and max o/p operating
voltage.e.g. Rated 120 v ac o/p ckt. Works in 92 to 138 v range.
 MAX O/P CURRENT RATING – Max current a single o/p or
module can safely carry under load
 OFF –STATELEAK CURRENT PER O/P – Max value of leak current
flows through the o/p in OFF position
 ELECTRICAL ISOLATION – Max volts between I/o and logic ckt.

PP LL CC :: PPoowweerr SSuuppppllyy
 The power supply gives the voltage required for electronics
module (I/O Logic signals, CPU, memory unit and peripheral
devices) of the PLC from the line supply.
 The power supply provides isolation necessary to protect the solid
state devices from most high voltage line spikes.
 As I/O is expanded, some PLC may require additional power
supplies in order to maintain proper power levels.

PP LL CC :: BBuuss SSyysstteemm
 It is path for the transmission of the signal . Bus system is
responsible for the signal exchange between processor and I/O
modules
 The bus system comprise of several single line ie wires / tracks
 Types of Bus
Address bus - Location
Data
bus - Carries Data
Control
bus - Synchronization

SSppeecciiaall MMoodduulleess
RF ID
Voice
Gas Flow Calculation
Weigh Cell
Hydraulic Servo
ASCII
Fuzzy Logic
Temperature Sensor
Temperature Control
Heat/Cool Control
Field Bus Cards
DeviceNet, Profibus etc
Lonworks, BACNet
Fast Response (Interrupt)
PID
Loop Controller
BASIC Cards
RS232 Comm’s
Modbus ASCII/RTU
Ethernet Comm’s
High Speed Counters
Position Control Cards
Peer to Peer Comm’s
Controller Link
DH+
Modbus Plus

Input Scan
PPLLCC OOppeerraattiinngg CCyyccllee
Housekeeping
START
The status of external inputs
(terminal block voltage) is written to
the Input image (“Input file”).
Internal checks on
memory, speed and
operation. Service any
communication requests,
etc.
Output Scan Program Scan
Each ladder rung is scanned using
the data in the Input file. The
resulting status (Logic being
solved) is written to the Output
file (“Output Image”).
The Output Image data is
transferred to the external
output circuits, turning the
output devices ON or OFF.
This scan cycle can be interrupted if required using interrupts

PPLLCC SSiiggnnaall FFllooww
Input Module Processor Memory Output Modules
Programming Terminal
O:0/7
O:0/7
O:1/5
Output Devices
Input Devices
Ladder Program
O:0/7
O:1/5
I:0/6
I:1/4
O:1/5
I:0/6
I:1/4
I:0/6
I:1/4
Input Data
Image Table
Output
Image Table

PPLLCC AArrcchhiitteeccttuurree EEvvoolluuttiioonn
Mid - 1970s : Discrete Machine Control
Programming
Terminal
Connection is Point to Point
PLC
I/O
Programming Language :
- Relay ladder logic
- Flexibility in altering
Control system operation

PLC AArrcchhiitteeccttuurree EEvvoolluuttiioonn
Early - to - Mid 1980 : Discrete and Process Control
Reasonable Computer
Running PLC
Programming Software
PLC
I/O
Programming Language :
- Ladder Program
- PID
- Data Storage
MS - DOS

Late 1980’s to early 1990’s : Discrete and Process
Control
PC running
PLC Programming Software
PLC
I/O
Connection in networked allowing
Multiple PLC
PLC became a part of the
developing enterprise resource
system
Windows
PLC

TTooddaayy :: DDiissttrriibbuutteedd II//OO MMoodduulleess
Distributed I/O modules
PL
C
Distributed I/O scanner
Data Communication Bus

Remote
I/O Network
SPLITTERS
TTooddaayy :: HHoott RReedduunnddaanntt SSyysstteemm
FIBER OPTIC LINK
LLeevveell ooff rreedduunnddaannccyy
PPoowweerr SSuuppppllyy
CCPPUU
II//OO
CCoommmmuunniiccaattiioonn
TAPS
Remote I/O

TTooddaayy :: EEtthheerrnneett TTeecchhnnoollooggyy iinn PPLLCCss
Workstation Workstation Workstation Workstation
Controller Controller
Controller
Controller
Switched Hub

Remote
Platform
Wireless Modem / GSM Communication
PLC
Wireless Modem / GSM Communication
H M I
Display
PC
TTooddaayy :: WWiirreelleessss ccoommmmuunniiccaattiioonn
PLC

8 Analog Inputs 1
Analog Output
Up/Down Fast
Counter
Up Counter
Programming Terminal PC Connection
Unitelway Port for connection
of up to 5 Slaves
TSX37-22
PCMCIA communications port
PCMCIA memory expansion port
Built in display for I/O
(in-rack, AS-i) and Diag
I/O Modules
CCoonnffiigguurraattiioonn ooff PPLLCC :: MMooddiiccoonn

Configuration ooff PPLLCC :: SSiieemmeennss
CPU
External Power
Supply
I/O Modules

Configuration ooff PPLLCC :: AAlllleenn BBrraaddlleeyy
CPU
Power Supply
I/O Modules

CCoonnffiigguurraattiioonn ooff PPLLCC :: GGEE FFAANNUUCC
CPU
I/O Modules Back plane

PPLLCC PPrrooggrraammmmiinngg SSttaannddaarrddss
The open, manufacturer-independent programming
standard for automation is IEC 61131-3. You can thus choose
what configuration interface you wish to use when writing your
application :
 Ladder Diagram
 Statement List
 Instruction List
 Function Block Diagram
 Sequential Function Chart
 Structured Text

SSccaann RRaattee
 The completion of one cycle of the sequence is called-
SCAN
 Time required for one cycle is called SCAN TIME

BBiinnaarryy SSyysstteemm
BIT – Each digit of a binary number
BYTE – Group of 8 bit
WORD – Group of one or more byte
LSB – Least significant bit or smallest
value
7 6 5 4 3 2 1 0
MSB – Most significant bit or largest
value
8 BIT ( 1 BYTE )
MSB LSB
BYTE BYTE
16 BIT (1 WORD)

PPLLCC :: TTeerrmmiinnoollooggyy
 INPUT is referred by – I
 OUTPUT is referred by – Q / O
 TIMER is referred by – T
 FLAGS are referred by – M /B
 COUNTERS are referred by – C

PPLLCC :: CCoommmmuunniiccaattiioonn PPrroottooccooll
It is a set of rules for data transmission when PLC is connected to
network
 RS-232 (Recommended standard)
 RS-485
 MPI(Multi point Interface)
 Profibus
 DH(Data Highway)
 Ethernet
 Controlnet
 Devicenet

Baud rraattee ((CCoommmmuunniiccaattiioonn SSppeeeedd))
 It is rate of data transmission on network Unit is bits/second
Range:-
120 bits /sec
to
100 Mega bits per second

SSeelleeccttiinngg aa PPLLCC
 Number of logical inputs and outputs
 Memory
 Number of special I/O modules
 Expansion Capabilities
 Scan Time
 Communication
 Software
 Support
 Cost

MMaannuuffaaccttuurreess –– MMaajjoorr BBrraannddss
 OMRON
 Allen Bradley
 Schneider
 GE Fanuc
 Siemens
 Automation Direct (Koyo)
 Toshiba
 Mitsubishi
 Hitachi
 Keyence
 VIPA

PPLLCC SSttaannddaarrddiizzaattiioonn
 IEC 61131
Based on IEC 1131 (1992) standard, developed to be a
common and open framework for PLC architecture.
 IEC 61131-1 Overview
 IEC 61131-2 Requirements Test Procedures
 IEC 61131-3 Data Types Programming
 IEC 61131-4 User Guidelines
 IEC 61131-5 Communications
 IEC 61131-7 Fuzzy Control
 IEC 61131-7 Guidelines for the application and implementation
of programming languages

PPLLCC PPrrooggrraammmmiinngg
 The purpose of a PLC Program is to control the state of PLC
outputs based on the current condition of PLC Inputs
 Different PLC’s support different languages, but the most
popular PLC language is know as “Ladder Logic”.
 PLC Ladder Logic purposely resembles Relay Logic

IIEECC 6611113311--33
 IL (Instruction List) – mnemonic programming
 LD (Ladder Diagram) – Relay logic
 ST (Structured Text) – A BASIC like programming language
 FDB (Functional Block Diagram) – Graphical dataflow
programming language
 SFC (Sequential Flow Chart) – Graphical method for structured
programs

LLaaddddeerr LLooggiicc CCoonncceeppttss
Read / Conditional
Instructions
| |
| | |/|
Write / Control
Instructions
| | |/|
| |
| | |/|
| |
( )
( )
( )
( )
| | |/| ( )
Start (Rung #1)
End (Rung #5)

LLaaddddeerr LLooggiicc CCoonncceeppttss
Read / Conditional
Instructions
Write / Control
Instructions
|/| | |
True False False
No Logical Continuity
|/| |/|
( )
( )
True True True
Logical Continuity

LLooggiiccaall AANNDD CCoonnssttrruuccttiioonn
IF input 4 AND input 5 have power
THEN energize output 0
I/4
| |
I/5
| |
O/0
( )
T T T
Logical Continuity
On

LLooggiiccaall OORR CCoonnssttrruuccttiioonn
IF input 4 OR input 5 have power
THEN energize output 0
I/4
I/5
I/4
| |
I/5
| |
O/0
O/0
( )
Logical Continuity
F
T
On
| |
| |
( )
Logical Continuity
T
F
On

TTyyppiiccaall CCoonnssttrruuccttiioonn
I/1
I/7
I/3
I/11
|/|
I/4
I/5
| |
|/|
I/0
I/1
|/|
| |
I/2
| |
| |
|/|
| |
I/9
| |
I/8
|/|
I/1
| |
O/0 | |
( )
I/10

AAddddrreessssiinngg EExxaammpplleess
L1 L2
PB1 LS1 PS2 SOL6
DEVICE
PB1
LS1
PS2
SOL6
I/5 I/6 I/7 O/0
| | | | | | ( )
ADDRESS
HHP
I/5
I/6
I/7
O/0
Logix
I:0/5
I:0/6
I:0/7
O:0/0

PB1 LS1 SOL2
I/4 I/6 O/0
| | | | ( )
I/7 I/5 B/0
| | | | ( )
B/0
INPUT Address Assignment:
PB1- I/4 PB2- I/5
LS1- I/6 LS2- I/7
LS3- I/8 LS4- I/9
OUTPUT Address Assignment:
SOL2- O/0 M1- O/1
LS1 PB2
|/|
CR3
LS3
CR3 LS4
M1
I/8
O/1
| |
|/|
( )
RReellaayy LLooggiicc ttoo LLaaddddeerr LLooggiicc
I/9
| |

AAvvaaiillaabbllee IInnssttrruuccttiioonnss
 Sequence
Input
Output
Control
 Logic
 Timer and Counters
 Comparison
 Range Comparison
 Data Movement
 Data Shift
 Step / Step Next
 Serial Communications
 Text String Processing
 File Manipulation
 Increment/Decrement
 Conversion
ASCII
Number Systems
 Math
 Floating Point Math
 Statistics
 Scaling
 PID
 PID with Auto tune
 Clock / Date
 Block Processing
IF,THEN,ELSE,LOOP
Table Processing
LIFO, FIFO

FFeeww mmoorree IInnssttrruuccttiioonnss
 SEQUENCERS
 SHIFT REGISTERS
 DATA HANDLING
 HIGH SPEED COUNTER
 SUBROUTINES

TThhaannkkss ……..

PLC General

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