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It uses a programmable memory to storeinstructions and execute specific functions

/ , , ,that include ON OFF control timing counting, .sequencing arithmetic and data handling

Intro:

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Basic principle of plc:

A Programmable logic controller is acomputer type device used to controlequipment in an industrial facility.

In traditional industry control system, all thedevices are directly wired to each otheraccording to how the system is supposed tooperate but in PLC all devices are wired to itinstead of each other.

Control program inside PLC provideconnection between the devices. Which tellsPLC whats supposed to be going on in thesystem.

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INPUTS

The input screw terminals on a PLCfrom the interface by which fielddevices are connected to the PLC.

The itemsInputsinclude such astool buttons, thumbwheels, limitswitches, selector switches,

proximity sensors and photoelectricsensors

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OUTPUTS

Output circuits operate in a manner similar to i/pcircuits: signals from the CPU pass through anisolation barrier before energizing o/p circuits.PLC use a variety of o/p circuits to energies

their o/p terminals: relays, transistors and triac.

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CENTRAL PROCESSING UNIT

The CPU made up of a microprocessor and a memorysystem, forms the primary component of the PLC

The CPU reads the inputs, executes logics as dictated bythe application program, performs calculations andcontrols the output.

PLC users works with two areas of the CPU: program files and data files.

Program files stores the user application program,subordinate files and the error files.

Data files store data associated with the program such as

input, counter/timer preset and accumulates the valves. Together, these two areas are called application memo0ry

or user memory.

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PLC consists of mainly three components: Central processing unit: CPU is the brain of

plc. It is able to do following operations:

A.Updating inputs and outputs.B.Performing logic n arithmetic operations.

C.Communicating with memory.

D.Scanning application programs.

MEMORY:A.Memory is the component to store memory.

B.The 2 common types of memory used in plcis RAM and ROM.

C.Memory capacities are often expressed forRAM in terms of kilo-bytes.

D.16K memory means there are16*1024=16348 bytes of RAM.

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PLC ADVANTAGES

Flexibility: In the past each different electronically

controlled production machine requiredits own controller. Now it is possible to

use just on model of a PLC to run anyone among a group machines.

Implementing changes and

correcting errors: When a PLC circuit of sequence design

change is made, the PLC program canbe changed from a key board sequencein a matter of minutes. No rewiring is

required for a PLC controlled system.

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Lower Cost: Increased technology makes it

possible more functions into smaller

and less expensive packages.

Visual Observation: A PLC circuits operation can be seen

during operation directly on a CRTscreen.

Speed of Operation: The operational speed for the PLC

program is very fast which a matter ofmilliseconds is.

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DISADVANTAGES

Environmental Considerations: Certain process environments such

as high heat and vibration interface

with electronic devices in PLCswhich limit their use.

o

Fixed Program Applications: Some applications are single

function applications. It does notpay to use a PLC that includes

multiple programming capabilities.

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Key Learning

How the automatic systems controlsthe process in industries?

To interface hardware with software.

Acquired knowledge about theimportance of PLC in daily life.

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Plc was (made) for the

main purpose that is costeffectiveness.

Today, one generallyaccepted rule is that PLCs

become economically

viable in control systemthat requires three to four

or more relays.