P L C General

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PROGRAMMABLE LOGIC

CONTROLLER

Control Systems Control Systems TypesTypes

Programmable Logic ControllersDistributed Control SystemPC- Based Controls

PLCPLC

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

PLC is programmed interface between input sensor &output device.

Programmable Logic Programmable Logic ControllersControllers

Sequential logic solverPID Calculations.Advanced SubroutinesBIT Operations.Data Transfer.Text Handling.

Applications : Machine controls, Packaging, 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 more Capabilities with dedicated

PID and Ethernet Modules.

Disadvantages of PLC : PLC one time cost is high To maximize PLC performance a number of IO Modules to be

added. PLC hold only one copy of program.

Programmable Logic Programmable Logic Controllers Controllers

Central Processing Unit (CPU) Input Modules Output Modules Power Supply Bus system Rack(Rail)

P L C P L C Components(Hardware)Components(Hardware)

POWER SUPPLY

I/Pmod

O/Pmod m

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

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

functions. i.e. Scanning I/O bus traffic control, Program execution, Peripheral and External device communication, data handling and self diagnostics.

Central Processing UnitCentral Processing 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

Input moduleInput 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 Digital output module : Typical output from these

modules is 24 V DC, 115 V AC, 230 V AC Ex. : Solenoid Valves, lamps, Actuators, Pump valve on

off control

Output module Output module

I/O MODULE SPECIFICATIONI/O MODULE SPECIFICATION

COST INPUT VOLTAGE ON-STATE INPUT VOLTAGE RANGE AMBIENT TEMP RATING INPUT DELAY – NOMINAL OUTPUT VOLTAGE MAX O/P CURRENT ELECTRICAL ISOLATION –

The power supply gives the voltage required for electronics module (I/O, CPU, memory unit) 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.

Power SupplyPower Supply

It is path for the transmission of the signal between power supply module,processor and I/O modules.

The bus comprise of several single line i.e. wires /tracks

Bus SystemBus System

Advantage of PLC Over Advantage of PLC Over RelayRelay

RELAY PLC 1-More wiring 1-Less wiring

2-Changes difficult 2-Changes easy

3-More power 3-Low power

4-More maintenance 4-Solid state reliability

5-Difficult to expand 5 -Easy to expand

PLC CyclePLC Cycle

OutputsCPUInputs

Sense the Input Process the Logic Give Output

PLC Signal FlowPLC Signal Flow

Programming Terminal

Output Devices

Output ModulesProcessor MemoryInput Module

Input DevicesLadder Program

Data I/pImage Table

OutputImage Table

PLC Architecture EvolutionPLC Architecture Evolution

1970s : Discrete Machine Control

ProgrammingTerminal

Connection is Point to Point

Programming Language :

- Relay ladder logic - Flexibility in altering Control system operation

Connection is Point to Point

1985 : Discrete and Process Control

Reasonable ComputerRunning PLC

Programming Software

Programming Language :

- Ladder Program - PID - Data Storage

MS - DOS

1990’s : Discrete and Process Control

PC running PLC Programming Software

Connection in networked allowing Multiple PLC

PLC became a part of the developing enterprise resource system

Windows

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

Distributed I/O modules

Distributed I/O scanner

Data Communication Bus

PLC Architecture PLC Architecture EvolutionEvolution

Remote I/O Network

SPLITTERS

FIBER OPTIC LINK

Remote I/O

Today : Today : Hot Redundant SystemHot Redundant System

Controller ControllerController

Controller

Workstation Workstation Workstation Workstation

Switched Hub

PLC Architecture PLC Architecture EvolutionEvolutionToday : Today : Ethernet Technology in PLCsEthernet Technology in PLCs

RemotePlatform

Wireless Modem

H M I Display

Today : Today : Wireless communicationWireless communication

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 LOGIX PLATFORM

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

External Power

Supply

I/O Modules

Configuration of PLC : Allen Configuration of PLC : Allen BradleyBradley

Power Supply I/O Modules

Configuration of PLC : GE FANUCConfiguration of PLC : GE FANUC

I/O Modules Back plane

PLC Programming StandardsPLC Programming Standards

Ladder Diagram Function Block Diagram Sequential Function Chart Structured Text Language

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, I/O requirement CPU memory Spare parts& Maintenance, Reliability, Flexibility& Integration of High-level Application. Compatible Protocol

PLC Selection CriteriaPLC 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 i.e.0 or1

BYTE – Group of 8 bits WORD = Two bytes=16 bits DOUBLE WORD =Two word

=4bytes=32bits 1 0234567

8 BIT WORD

BYTE BYTE

16 BIT WORD

PLC : Terminology PLC : Terminology

INPUT is referred by – I OUTPUT is referred by – Q or O TIMER is referred by – T FLAGS are referred by – M or B COUNTERS are referred by – C

PLC : Protocol PLC : Protocol

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) Ethernate Controlnet

P L C General

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