Mechatronics Plc by Nishant

8/6/2019 Mechatronics Plc by Nishant

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Programmable Logic Controller

(PLC)

By

NISHANT V. CHAUDHARI

M.A.E. ALANDI


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PLC

NEMA defines a PROGRAMMABLE LOGICCONTROLLER as:A digitally operating electronic apparatus whichuses a programmable memory for the internalstorage of instructions by implementing specificfunctions such as logic sequencing

timing

Counting arithmetic to control

through digital or analog input/output modules,various types of machines or processes.


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PLC History The Hydramatic Division of the General

Motors Corporation specified the design

criteria for the first programmable

controller in 1968 Their primary goal was to eliminate the

high costs associated with inflexible, relay

controlled systems


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The specifications required a solid-statesystem with computer flexibility able to:

1. Survive in an industrial environment.

2. be easily programmed and maintained by

plant engineers and technicians.

3. be reusable

Such a control system would reduce

machine downtime and provideexpandability for the future


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Some of the initial specifications included the

following: The new control system had to be price competitive with the use

of relay systems.

The system had to be capable of sustaining an industrial

environment.

The input and output interfaces had to be easily replaceable.

The controller had to be designed in modular form, so that

subassemblies could be removed easily for replacement or

repair.

The control system needed the capability to pass data collection

to a central system. The method used to program the controller had to be simple, so

that it could be easily understood by plant personnel.

The system had to be reusable.


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Conceptual Design of PLC

The first programmable controllers were more or lessjust relay replacers.

Their primary function was to perform the sequentialoperations that were previously implemented with relays

These operations included ON/OFF control of machinesand processes that required repetitive operations, suchas transfer lines and grinding and boring machines etc.

These programmable controllers were a vastimprovement over relays

They were easily installed, used considerably less spaceand energy, had diagnostic indicators that aidedtroubleshooting, and unlike relays, were reusable if aproject was scrapped.


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Todays PLC

Many technological advances in the

programmable controller industry continue

today.

These advances not only affect programmable

controller design, but also the philosophical

approach to control system architecture.

Changes include bothh

ardware (physicalcomponents) and software (control program)

upgrades


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The following list describes some recent PLChardware enhancements: Faster scan times are being achieved using new,

advanced microprocessor and electronic technology.

Small, low-cost PLCs, which can replace four to tenrelays, now have more power than their predecessor,

the simple relay replacer. High-density input/output (I/O) systems provide

space-efficient interfaces at low cost.

Intelligent, microprocessor-based I/O interfaces haveexpanded distributed processing.

Typical interfaces include PID (proportional integral-derivative), network, CAN-bus, field-bus, ASCIIcommunication, positioning, host computer, andlanguage modules


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Hardware Components of a PLC

System Processor unit (CPU)

Memory

Input/Output modules Power supply unit

Programming device

Communication modules Remote I/O modules


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PLC Block Diagram


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Major CPU Components


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Input Output Interface


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Functional Interaction of PLC system


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Programming Devices


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Typical Areas Of Application


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Typical Areas Of Application


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Market share

Micro: 15 to 128 I/O pointsMedium: 128 - 512 I/O points

Large: > 512 I/O points

Nano: < 15 I/O points

PC-basedSoftware PLC

Embedded control

32%29%

20%

7%

6%4%

2%

% installed PLCs


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Type of PLCs


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Micro PLC


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Small PLC


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Medium PLC


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Large PLCs


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Large PLCs


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Very Large PLCs


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Global players


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PLC Programming Languages

As Per IEC 61131-3 Standard

Ladder Diagram (LD)

Sequential Function Chart (SFC)

Function Block Diagram (FBD)

Structured Text (ST)

Instruction List (IL)


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Ladder Diagram


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Structured Text

TONR_01.Preset := 500;

TONR_O1.Reset := reset;

TONR_01.TimerEnable :=

limit_switch1;

TONR(TONR_01)

timer_state := TONR_01.DN;

???

TONR_01

TONR ...

Timer On Delay with Reset

TimerEnable

PRE

Reset

ACC0

DN0

?

??

?

??

?

ENDN

Timer On DelayTimer ?Preset ?

A m ?

TON


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I/O connection Diagram


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PLC System


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Local Rack Configuration


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Remote Rack Configuration


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I/O Addressing


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Logic Functions (AND)


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OR Function


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NOT


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Example of hardwiring changes as

opposed to soft wiring changes


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PLC Scan

Read the Data from Sensors

or Input Devices

Execute the users Logic

Program

Update the output Devices or

Actuators


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System Programming and

Implementation


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PLC Panel


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Control System OrganizationIndividual Control


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Centralized Control


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Distributed Control


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Mechatronics Plc by Nishant