What is a PLC?

• PLC is a digitally operating 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 modules, various types of

machine or processes.

PLC History

• More recently electricity has been used for control and early electrical control was based on

relays.

• These relays allow power to be switched on and off without a mechanical switch.

• It is common to use relays to make simple logical control decision.

• The development of low cost computer has brought the most recent revolution the

Programmable Logic Controller (PLC).

• PLC was developed to replace relays in 1960s. Cost dropped and became popular by

1980s.

• The advent of PLC has become the most common choice for manufacturing controls.

How does PLC differs from a personal computer?

• A Programmable Logic Controller (PLC) is a specialized computer, designed to be

used for industrial control.

• Programmable Logic Controllers are sometime called programmable controllers (PC)

but are more commonly called PLCs.

• A PLC looks different from a standard personal computer.

• For a start, a PLC doesn’t have a keyboard or a monitor.

• The following pictures show several PLCs.

Advantages of Using PLCs in Automated Food Industrial

• PLCs have been gaining popularity on the factory floor and will probably remain predominant.

Most of this is because of the advantages they offer.

• Cost effective for controlling complex system.

• Flexible and can be reapplied to control other systems quickly and easily.

• Reliable components make these likely to operate for years before failure.

• Troubleshooting aids make programming easier and reduce downtime.

• Ease to setup and program.

• PLC are tough enough to keep working in even the dirtiest production environment.

Advantages of Using PLCs in Automated Food Industrial

• Programming the PLC is easier than wiring the relay control panel.

• The PLC can be reprogrammed (conventional controls must be rewired).

• Computational abilities allow more sophisticated control.

• PLCs take less floor space than relay control panels.

• Maintenance of the PLC is easier, and reliability is greater.

• The PLC can be connected to the plant computer systems more easily than relays can.

The use of PLC in manufacturing

PLCPLC

Timer and CounterTimer and Counter

SoftwareSoftwareMotor ControlMotor Control

Switches and SensorsSwitches and Sensors

Field IField I//OO

Operator InterfaceOperator Interface CommunicationCommunication

ConnectorConnector

ProcessesProcesses

PLCs

KeyenceKeyence,, JapanJapan

OmronOmron,, JapanJapanMitsubishiMitsubishi,, JapanJapan

Allen BradleyAllen Bradley,, USAUSASiemens AGSiemens AG,, GermanyGermany

SchneiderSchneider,, GermanyGermany

PLC CU PRELUCRARE PE BIT

PLC îndeplinesc sarcini de conducere proprii echipamentelor

de comandă discretă a proceselor industriale, şi au o

funcţionare binară permiţând detectarea schimbărilor de stare

a unor semnale furnizate de elemente de tip:

1. butoane cu menţinere, cu revenire

2. comutatoare basculante

3. limitatoare de cursă

4. detectoare de proximitate

şi prelucrează, în principal logic, informaţiile furnizate de aceste

elemente în vederea emisiei de semnale de ieşire ce comandă

elemente de tip:

1. contactoare

2. relee

3. electroventile

4. ambreiaje

5. elemente de semnalizare

PLC Configuration

PLC’s Component

• Many PLC configurations are available, even from a single vendor.

• But, in each of these are common components and concepts.

• The most essential components are:

• CPU Module:

• Input Modules:

• Output Modules

ANSI/ISA 95 standard

Source: ANSI/ISA–95.00.01–2000

the ANS/ISA standard 95 defines terminology and good practices

Enterprise Resource Planning

Manufacturing Execution System

Control & Command System

Business Planning & LogisticsPlant Production Scheduling

Operational Management, etc.

ManufacturingOperations & Control

Dispatching Production, Detailed ProductScheduling, Reliability Assurance,...

Level 4

Level 3

Levels2,1,0

BatchControl

ContinuousControl

DiscreteControl

PLC Components

PLC Operation

Location of the PLC in the control architecture

Entreprise Network

directly connectedI/O

Control Bus(e.g. Ethernet)

Engineerstation

I/O I/O I/O I/OCP

U

Sensor Bus (e.g. ASI)

Field Bus (proprietary)

gateway

Field Stations

Control Station with Field Bus

direct I/O

I/O

Field DevicesFB

gateway

gateway

I/OI/OI/OI/OCP

UC

OM

I/OI/OI/OCO

M

CP

U

CO

M

CO

M

CO

M

I/O

Field Bus (standard)

CP

U

CO

M 2

I/O I/O I/OCP

UC

OM

1

CO

M 2

I/OCP

U

Operatorstation

PLC

small PLC local intelligence

PLCPLC

CO

M1

CO

M1

SupervisorStation

General PLC architecture

CPUReal-Time

Clockflash

EPROMROM

buffers

signal conditioning

power amplifiers

relayssignal

conditioning

serial portcontroller

Ethernet

parallel bus

ethernetcontroller

RS 232

analog-digital

converters

digitalanalog

convertersDigital Output

DigitalInput

fieldbuscontroller

externalI/Os

extensionbus

field bus direct Inputs and Outputs

CONSOLA DEPROGRAMARE

MEMORIAPROGRAM

UNITATEA CNTRALĂ

MODULESPECIALE

MODULEDE

IEŞŞŞŞIRE

MODULE DE INTRARE

Trad. MAŞŞŞŞINA ELECTRICĂ Contactoare

Busses and processors in industrial plants

PLC nodes(multi-processors)

fieldbus

Operator panelMimic board

plant (Werk, usine)

P

disk

pool

transducers

controlstations

process bus (500m .. 3 km)

valve thermo-couple motor

Process pictures

Process Data Base

Logging

position

station bus

(0,5.. 30 m)

node bus

workstation bus

instrument bus(mimic board)

sensor bus

directly coupled input/output

open network:TCP/IP, ...

station

P P C

I/O MEM I/O

P P C P

MEM BC

station

M

sensor bus

(30m..2 km)

Example: Production management system

transportationcell control

manufacturingcell control

scheduling maintenance quality control

plant network

floor network

productionplanning

robotcontroll

er

enterprise network

millingmachine

rail-guidedvehicle

cell

Example: ABB Industrial IT (redundant system)

3rd partycontrollers,servers etc

Serial, OPCor fieldbus

engineeringworkplace

Field Bus

Firewall

Plant Network / Intranet

Field Bus

Client/server Network

3rd party application server

applicationserver

aspectserver

Workplaces(clients)

Enterprise Optimization

(clients)

MobileOperator

connectivityserver

Control Network

ProgrammableLogic ControllerAC 800C

RedundantAC 800M

touch-screen

plant

Decentralized Control System (DCS)

engineeringworkstation

operatorworkstation

data logger

controller controller controller controller

field bus

control bus

all controllers can communicate as peers (without going through a central master), restricted only by throughput and modularity considerations.

Note: Honeywell's "DCS™" stands for "Distributed Control System", it is not a decentralized control system, but a control system for the process industry.