Presentation on PLCs and PACs

By Bipin Likhar

PLCA Programmable Logic Controller

(PLC) is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, control of amusement rides, or control of lighting fixtures.

History of PLCPLC was introduced in late 1960’s to remove relay’s based

system.First commercial & successful Programmable Logic

Controllers was designed and developed by Modicon as a relay replacer for General Motors.

Earlier, it was a machine with thousands of electronic parts.Later ,in late 1970’s,the microprocessor became reality &

greatly enhanced the role of PLC permitting it to evolve form simply relay to the sophisticated system as it is today.

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Major Components of a Common PLC

PROCESSOR

POWERSUPPLY

I MN O P D U UT L E

O M U OT DP UU LT E

PROGRAMMING DEVICE

From SENSORS

Pushbuttons,contacts,

limit switches,etc.

ToOUTPUT

Solenoids, contactors,

alarmsetc.

Major Components of PLCPOWER SUPPLY

Provides the voltage needed to run the primary PLC components

I/O MODULES Provides signal conversion and isolation between the

internal logic level signals inside the PLC and the field’s high level signal.

 PROCESSOR Provides intelligence to command and govern the activities

of the entire PLC systems.PROGRAMMING DEVICE Used to enter the desired program that will determine the

sequence of operation and control of process equipment or driven machine.

PLC Operation

Programming a PLCLadder LogicFunctional block diagramStructural text(similar to Pascal)Instruction list(similar to assembly language)

Why PLC ?....• The controller is designed in modular form, so

that sub-assemblies could be removed easily for replacement or repair.

• A PLC can work in the harsh and extreme conditions of the industry where other systems such as a Micro-Controller cannot.

• The system becomes reusable.

• The method used to program the controller is simple, so that it can be easily understood by plant personnel.

Programmable Automation Controller

PACPAC stands for Programmable Automation

Controller.PLC is best suited for machine control but

has limited memory and a focus on discrete I/O with on/off control.

On the other hand , a PAC is geared more toward complex automation system architectures composed of a number of PC-based software applications

Features of PACComposed of a number of PC-based software

applicationsIncluding HMI (human machine interface)

functionsArchitecture based on Ladder logicProvide greater flexibility in programmingLarger memory capacity

Advantages of PACs over PLCsMore open architectureModular designMore analog I/O optionsBetter process control capabilitiesMore built in communication portsProgramming over USB portsTag based programming (one software

package capable of programming multiple models )

Thank You