PROGRAMMABLE LOGIC

CONTROLLER

Control Systems TypesControl Systems Types

Programmable Logic Controllers Distributed Control System PC- Based Controls

IntroductionIntroduction

The PLC is an assembly of solid state digital logic elements design to make logical decisions and provide outputs.

Programmable Logic Programmable Logic Controllers Controllers

Sequential logic solver PID Calculations. Advanced Subroutines BIT Operations. Data Transfer. Text Handling.

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

Programmable Logic Programmable Logic Controllers Controllers

PLC Types Nano (Small) Micro (Medium) Large

Basic criteria for PLC Types Memory Capacity I/O Range Packaging and Cost per Point

Programmable Logic Programmable Logic Controllers Controllers

Central Processing Unit (CPU) Input Output Modules Power Supply Bus system Programming Device

P L C Components P L C Components

CPU

PROGRAMDEVICE

IN OUT m

MODULEMODULE

It is a micro-controller based circuitary. The CPU consists of following blocks :

Arithmatic Logic Unit (ALU), Program memory Process image memory (Internal memory of CPU) Internal timers and counters Flags CPU performs the task necessary to fulfill the PLC funtions. These

tasks include Scanning, I/O bus traffic control, Program execution, Peripheral and External device communication, special functions or data handling execution and self diagnistics.

P L C : Central Processing P L C : Central Processing Unit Unit

These modules act as interface between real-time status of process variable and the CPU.

Analog input module : Typical input to these modules is 4-20 mA, 0-10 V 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

PLC : Input module PLC : Input module

120 V acL1 L2

L2

L1

1

2

3

4

PB

inputfield

device

Input moduleterminal board

Input statusindicator

PLC : Input module PLC : Input module

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 module PLC : Output module

120 V acL1 L2

L2

L1

1

2

3

4

Output statusindicator

Output field device

Module blown Fuse indicator

Output module Terminal board

PLC : Output module PLC : Output module

I/O SPECIFICATIONI/O SPECIFICATION

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.

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.

P L C : Power Supply P L C : Power Supply

It is path for the transmission of the signal . Bu system is responsible for the signal exchange between processor and I/O modules

The bus system comprise of several single line ie wires / tracks

P L C : Bus System P L C : Bus System

Relay ConnectionRelay Connection

L2

L1

1

2

3

4

L2

L1

1

2

3

4

CR

M

M

CR CL

M

M M M

T1 T2 T3

L1 L2 L3

MOTOR

Advantage of PLC Over Relay Advantage of PLC Over Relay StyleStyle

RELAY PLC 1-Hard wiring 1-Less wiring

2-Changes difficult 2-Easy modification

3-More power 3-Low power

4-More maintenance 4-Solid state reliability

5-Difficult to expand -Ease of expansion

PLC CyclePLC Cycle

Outputs

Machineor

Process

Programmablecontroller

Inputs

Sense the Input Process the Logic Give Output

PLC Signal FlowPLC Signal Flow

Programming Terminal

O:0/7

O:0/7

O:1/5

Output Devices

Output ModulesProcessor MemoryInput Module

Input DevicesLadder 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

Data InputImage Table

OutputImage Table

PLC Architecture EvolutionPLC Architecture Evolution

Mid - 1970s : Discrete Machine Control

ProgrammingTerminal

PLC

I/O

Connection is Point to Point

Programming Language :

- Relay ladder logic - Flexibility in altering Control system operation

Connection is Point to Point

Early - to - Mid 1980 : Discrete and Process Control

PLC Architecture EvolutionPLC Architecture Evolution

Reasonable ComputerRunning PLC

Programming Software

PLC

I/O

Programming Language :

- Ladder Program - PID - Data Storage

MS - DOS

PLC Architecture EvolutionPLC Architecture Evolution

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

TodayToday : : Distributed I/O ModulesDistributed I/O Modules

Distributed I/O modules

PLC

Distributed I/O scanner

Data Communication Bus

PLC Architecture PLC Architecture EvolutionEvolution

Remote I/O Network

SPLITTERS

FIBER OPTIC LINK

TAPS

Remote I/O

Today : Today : Hot Redundant SystemHot Redundant System

PLC Architecture EvolutionPLC Architecture Evolution

Controller ControllerController

Controller

Workstation Workstation Workstation Workstation

Switched Hub

PLC Architecture EvolutionPLC Architecture Evolution

Today : Today : Ethernet Technology in PLCsEthernet Technology in PLCs

RemotePlatform

Wireless Modem

Wireless Modem

PLC

H M I Display

PC

PLC Architecture EvolutionPLC Architecture Evolution

Today : Today : Wireless communicationWireless communication

PLC

PLC Systems of various vendors PLC Systems of various vendors

Siemens S5 -110U, 115U, 135U S7 - 200, 300, 400

Allen Bradley Micrologix 1000, 1200,

1500 SLC 5/01, 5/02, 5/03 PLC 5/10, 5/25 and 5/40

Modicon Nano Micro Premium Quantum

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

PCMCIA memory expansion port

PCMCIA communications port

TSX37-22

Built in display for I/O (in-rack, AS-i) and Diag

I/O Modules

Configuration of PLC : Configuration of PLC : ModiconModicon

Configuration of PLC : Configuration of PLC : SiemensSiemens

CPU

External Power

Supply

I/O Modules

Configuration of PLC : Allen Configuration of PLC : Allen BradleyBradley

CPU

Power Supply I/O Modules

Configuration of PLC : GE FANUCConfiguration of PLC : GE FANUC

CPU

I/O Modules Back plane

PLC Programming StandardsPLC Programming Standards

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

Scan RateScan Rate

The completion of one cycle of the sequence is called- SCAN

Time required for one cycle is called SCAN TIME

Cost of hardware, software, Integration Engineering, Design, Installation, Start-up and Commissioning, Validation documentation and Execution, Training, Spare parts, Maintenance, System service contract and system life cycle.

Reliability, Flexibility, Scalability and Validatability. Ease of Database configuration, Graphics

development, Interlocks and Batch processing. Integration of High-level Application. Control Philosophy for Centralized versus Remote

Operator Console or both. Compliance with an Industry batch standard such as

ISA SP88 and new Communication Protocol.

PLC DCS Selection CriteriaPLC DCS Selection Criteria

Memory TypesMemory Types

ROM (Read Only Memory) RAM (Random Access Memory) PROM (Programmable ROM) EPROM (Erasable PROM) EAROM- Electrically alterable ROM EEPROM-Electrically erasable PROM

Binary System Binary System

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 MSB – Most significant bit or largest

value

1 0234567

8 BIT WORD

LSBMSB

BYTE BYTE

18 BIT WORD

PLC : Terminology PLC : Terminology

INPUT is referred by – Ixxyy OUTPUT is referred by – Qxxyy TIMER is referred by – T xyyzzzz FLAGS are referred by – M xxxx COUNTERS are referred by – C xxxx