2. 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.
Prolific Systems and Technologies Pvt Ltd
3. 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.
Prolific Systems and Technologies Pvt Ltd
4. 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.
Prolific Systems and Technologies Pvt Ltd
5. 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.
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6. 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
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7. CCoonnttrrooll SSyysstteemmss TTyyppeess
Programmable Logic Controllers
Distributed Control System
PC- Based Controls
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8. 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".
Prolific Systems and Technologies Pvt Ltd
9. 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
10. 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
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11. 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
Prolific Systems and Technologies Pvt Ltd
12. 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
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13. 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
Prolific Systems and Technologies Pvt Ltd
14. 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
Prolific Systems and Technologies Pvt Ltd
15. 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
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16. BBaassiicc PPLLCC SScchheemmaattiicc
CPU
Power Supply
Memory
Input Blocks
Output Blocks
Communications
Expansion Connections
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17. 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.
Prolific Systems and Technologies Pvt Ltd
18. 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.
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19. 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.
Prolific Systems and Technologies Pvt Ltd
20. 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.
Prolific Systems and Technologies Pvt Ltd
21. 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
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22. 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.
Prolific Systems and Technologies Pvt Ltd
23. 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
Prolific Systems and Technologies Pvt Ltd
24. PPLLCC :: IInnppuutt mmoodduullee
Transfer of data:-I/P sensor to CPU
Conversion:- 24vdc/230vac to 5vdc
Isolation :- By Opto Coupler
Prolific Systems and Technologies Pvt Ltd
26. 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
Prolific Systems and Technologies Pvt Ltd
27. 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
Prolific Systems and Technologies Pvt Ltd
28. 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 bit resolution the value in the PLC is 0 to 4095
For 12.5 bit resolution the value in the PLC is 0 to 6000
For 13 bit resolution the value in the PLC is 0 to 8192
For 16 bit resolution the value in the PLC is 0 to 32768
Prolific Systems and Technologies Pvt Ltd
31. 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
Prolific Systems and Technologies Pvt Ltd
32. 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
Prolific Systems and Technologies Pvt Ltd
35. 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
Prolific Systems and Technologies Pvt Ltd
36. 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.
Prolific Systems and Technologies Pvt Ltd
37. 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.
Prolific Systems and Technologies Pvt Ltd
38. 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
Prolific Systems and Technologies Pvt Ltd
39. 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
Prolific Systems and Technologies Pvt Ltd
40. 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
Prolific Systems and Technologies Pvt Ltd
42. 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
Prolific Systems and Technologies Pvt Ltd
43. 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
Prolific Systems and Technologies Pvt Ltd
44. PLC AArrcchhiitteeccttuurree EEvvoolluuttiioonn
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
Prolific Systems and Technologies Pvt Ltd
45. PPLLCC AArrcchhiitteeccttuurree EEvvoolluuttiioonn
TTooddaayy :: DDiissttrriibbuutteedd II//OO MMoodduulleess
Distributed I/O modules
PL
C
Distributed I/O scanner
Data Communication Bus
Prolific Systems and Technologies Pvt Ltd
48. Remote
Platform
Wireless Modem / GSM Communication
PLC
Wireless Modem / GSM Communication
H M I
Display
PC
PLC AArrcchhiitteeccttuurree EEvvoolluuttiioonn
TTooddaayy :: WWiirreelleessss ccoommmmuunniiccaattiioonn
PLC
Prolific Systems and Technologies Pvt Ltd
49. 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
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50. Configuration ooff PPLLCC :: SSiieemmeennss
CPU
External Power
Supply
I/O Modules
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51. Configuration ooff PPLLCC :: AAlllleenn BBrraaddlleeyy
CPU
Power Supply
I/O Modules
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53. 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
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54. SSccaann RRaattee
The completion of one cycle of the sequence is called-
SCAN
Time required for one cycle is called SCAN TIME
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55. 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)
Prolific Systems and Technologies Pvt Ltd
56. 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
Prolific Systems and Technologies Pvt Ltd
57. 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
Prolific Systems and Technologies Pvt Ltd
58. 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
Prolific Systems and Technologies Pvt Ltd
59. SSeelleeccttiinngg aa PPLLCC
Number of logical inputs and outputs
Memory
Number of special I/O modules
Expansion Capabilities
Scan Time
Communication
Software
Support
Cost
Prolific Systems and Technologies Pvt Ltd
60. MMaannuuffaaccttuurreess –– MMaajjoorr BBrraannddss
OMRON
Allen Bradley
Schneider
GE Fanuc
Siemens
Automation Direct (Koyo)
Toshiba
Mitsubishi
Hitachi
Keyence
VIPA
Prolific Systems and Technologies Pvt Ltd
61. 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
Prolific Systems and Technologies Pvt Ltd
62. 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
Prolific Systems and Technologies Pvt Ltd
63. 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
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65. LLaaddddeerr LLooggiicc CCoonncceeppttss
Read / Conditional
Instructions
Write / Control
Instructions
|/| | |
True False False
No Logical Continuity
|/| |/|
( )
( )
True True True
Logical Continuity
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66. 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
Prolific Systems and Technologies Pvt Ltd
67. 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
Prolific Systems and Technologies Pvt Ltd
71. 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
Prolific Systems and Technologies Pvt Ltd
72. FFeeww mmoorree IInnssttrruuccttiioonnss
SEQUENCERS
SHIFT REGISTERS
DATA HANDLING
HIGH SPEED COUNTER
SUBROUTINES
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Field input devices provide an electrical signal based on a condition
ON, OFF etc..
The design of the inputs determines the type of electrical signal that can be used.
Different applications, and regions may use different voltages.
Larger rack mount PLC’s typically support a wider range of input voltages
TTL (5Vdc), 12Vdc, 24Vdc/VAC, 48Vdc, 72Vdc, 120Vac, 220Vac etc...
Output module
Terminal board
Field output devices are controlled by electricity being switched by the PLC.
ON, OFF etc..
PLC’s “Switch” electricity, they do not “supply” electricity
The design of the outputs determines the type of electrical “Load” that can be used.
Different applications may require specialized output designs.
Voltage/Current issues include
Higher current - relays
Longer life cycle - solid state (Triacs for AC, MOSFET for DC)
Triacs 120Vac applications 1/2 amp maximum load
MOSFET 24Vdc applications 1 amp maximum load
Isolation issues can be crucial for an application. Typically the more isolation provided between output points the better. (The more individual commons the better) This provides customers greater flexibility in wiring and controlling different loads with the same PLC.
The job description of the PLC when it is the RUN mode
18 BIT WORD
Again, the similarities are virtually identical.
The primary enhancement is that if changes are needed, or if other logic or conditions need to be added, it’s as simple as a few keystrokes on the computer.