08/24/1706 / 09 / 2007

PLC 1

INDUSTRIAL AUTOMATION USING PROGRAMABLE LOGIC CONTROLLER (PLC)

By: Saumya Ranjan Behura

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transfer of control from man to machine

machine intelligence interface between hardware and

software

AUTOMATION : what is it?

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PLC advantages:

Flexibility Fast implementation Low cost V.D.U. display More reliable Reduces space Energy saving Ease of maintainance Economical

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PLC HARDWARE STRUCTURE (in modules)

Power supply module C.p.u./ controller Input/output module Counter module Rack/back plane Communication module

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Power supply module:

Calculation of total power before selection of power module.

Selection of proper voltage range. Regulation of 5v,12v for operation of

electronic components. Proper ground connection.

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CPU / CONTROLLER :

Controlling of the logic,logging of data,fault & history.

Consists of processor,some memory chips & a math processor.

Processor collects the status of input and writes to PII

Writes the result in PIQ.

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RAM :

Programme memory Timers Counters Flags Process i/o image tables System data alu

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INPUT MODULES :

Acts as a interface between field control inputs & c.p.u.

Volage/current generated by sensors transducers etc. are applied to the terminal of input module.

Converts field signal into a standard control signal for processing by plc.

Sends one input at a time to c.p.u.

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OUTPUT MODULES: Acts as a link b/w C.P.U. & output

devices located in the field. Filed devices could be

relays,contactors,actuators etc. Converts the signal delivered by cpu

into an appropiate voltage level suitable for output field devices.

Both input & output modules can be analog or digital.

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DIGITAL I/O MODULE :

Mounted on the rack Connected with c.p.u.(ribbon cable) Connected with c.p.u. in a serial bus. Capacity : 8,16,32 i/p Voltage :24 V d.c.,110 V a.c.,240 V

a.c. Module must match with field device

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ANALOG I/O MODULE : Used for analog signals Two modes of operation- 4-20 mA /

0-10 V. Analysing a continuously changing

output through a transducer like temperature,pressure,speed / distance.

Converts analog signal to digital values that c.p.u. can process.

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BUSSES IN PLC:

Address bus Data bus Control bus

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BLOCK DIAGRAM OF PLC:

POWER SUPPLY MODULE

INPUT MODULES CPUPROGRAM MEMORY

OUTPUT MODULES

FIELD INPUTS CONTROL [RELAYS, LAMPS ETC]

PROCESS OR MACHINE

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INSTALLATION : Mount the power supply module near c.p.u. Communication must be mounted in the

third slot. Maximum 8 no. of modules can be mounted

in one tier. Slot no. starts from right of the c.p.u. &

ends at the interface module. Power supply & chassis should be grounded

properly. Module should only be removed when the

load voltage is off.

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WORKING PRINCIPLE OF P.L.C. :

Bringing the input signal status to the internal memory of the c.p.u.

Processing the signal using programme. The result of user programmes scans are

then stored in internal memory of c.p.u. (PIQ)

At the end of the programme scan c.p.u. transfers the signal states of the process image output to the output module & further to field controls.

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Layout Of PLC System:

FieldSignals

INPUT MODULES

CENTRAL PROCESSINGUNIT

INPUTIMAGETABLE

OUTPUTIMAGETABLE

I/OBUS

USER PROGRAM MEMORY INTERNAL TIMERS

INTERNALCOUNTERS

INTERNALFLAG BITS

OUT PUT MODULES

IO BUS

FIELD DEVICES

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AB PLC PROCESSOR :SPECIFICATION SLC5/01

1747-L511,L514

SLC 5/021747-L532

SLC 5/041747-L541

SLC 5/041747-L542

SLC 5/041747-L543

PROGRAMMEMORY

1K OR 4KISTRUCTIONS

4K INSTRUCTIONS

12KWORDS

28K WORDS

60K WORDS

MAX.I/O CAPACITY 256 480 960 960 960

TYPICALSCAN TIME 8MS/K 8 4.8 1 0.9 0.9

PROGRAMMING INSTRUCTIONS

52 71 99 99 99

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Programming of PLC :

Software driven equipment Control process is decided by user

program. The program is stored in user

memory or program memory. C.P.U. sequentially executes the

instruction & operates the control elements.

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PLC SOFTWARE & LADDER PROGRAMMING :

AB software- RS logix-5000 Siemens PLC-SEMANTIC-S7 Types of programming language: (1) STL (2) FBD (3)LADDER LOGIC

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LADDER LOGIC : LADDER ELEMENTS : Power Rail:two thick lines drawn in the diagram.

Rung :a horizontal which sequences the order of ladder logic execution.

Rung comment :description written above the rung.

Instruction :codes that evaluate the data & perform computation.

Instruction comment:the desrciptive text for an instruction.

Branch :separate path on a rung.

Loops :are given to tempararily bypass a portion of rung.

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Ladder logic diagram :

XIO OTE

XIC - Examine In ClosedXIO – Examine if openOTE – Output energizeOTL – Output latch

xic

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LADDER DIAGRAM 2 :

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REAL TIME APPLICATION :

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AB & SIEMENS S7 :

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CASE STUDY :

APPLICATION OF PLC IN ROLLING MILLS FOR PIPE MAKING.

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QUESTIONAIRE

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