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Programmable Logic ControllerProgrammable Logic Controller - digital computer similar to a PC at itscore ,used for the automation of electro-mechanical processes, such as machinecontrol systems on factory assembly lines, amusement rides, or lighting fixtures.

i dustri l put ri dustri l put r - B ilt t wit sta v ry ars vir ts.Unlik neral- r se c ters, t e L is esi ned f r lti le inputs and utput arrangements, extended temperature ranges, immunity t electricalnoise,

and resistance to vi ration and impact.

Siemens 314 -2 t



Allen- radley P C installed in a control panel

a device that a user can program to perform aseries or sequence of events.Programs to control machine operation are

typically stored in battery-backed or non-volatilememory.A P C is an example of a real time system sinceoutput results must be produced in response toinput conditions ithin a bounded time, other iseunintended operation ill result.

A plc ill continually loop through its user defined program aiting for inputsand giving outputs at the specific programmed times.

This language hich is used to program the Programmable ogic Controllercan be used in three formats, ladder, instruction list and logic symbol.



net ork binary inputs

binary outputs

analog inputs / outputs



go ay back to the 60s- time of INVENTION. relay controlled machines

Before the P C, control, sequencing, and safety interlock logic for manufacturingautomobiles as accomplished using hundreds or thousands of relays, cam timers,

and drum sequencers and dedicated closed-loop controllersWe can think of a relay as an electromagnetic switch.Apply a voltage to the coil and a magnetic field is generated-pulls the contacts of the relay in, causing them to make a connection.



Here we are using a dc relay tocontrol an AC circuit. When the switch isopen no current can flow through the coil of

the relay.As soon as the switch is closed, however,current runs through the coil causing amagnetic field to build up.This magnetic field causes the contacts of the relay to close.Now AC current flows through the bell and

we hear it.



gave rise to severalgave rise to severalproblemsproblems--

they failed often as theyere mechanical.

coil failure and contactear ere difficult to

diagnose and replace

if changeover as neededthat called for re iring of each and every relaytimeconsuming & expensive

relays consumed loads of po er



Richard D. MorleyRichard D. Morley of BedfordAssociates, inventedthe first Programmable Logic Controller as aconsultation project for the General ElectricCompany in 1968.BedfordAssociates changed their name after some

time to Modicon P C and eventually became thesupplier of P Cs. The Modicon brand as sold in1977 to Gould Electronics, and later acquired byGerman Company AEG and then by FrenchSchneider Electric, the current o ner.

Note: Programmable ogic Controllers first came about as a replacement for automatic control systems

that used tens and hundreds (maybe even thousands) of hard ired relays, motor driven cam timersand rotary sequencers.

More often then not, a single P C can be programmed to replace thousands of relays and timers. TheseProgrammable ogic Controllers ere first befriended by the automotive manufacturing industry, this

enabled soft are revision to replace the laborious re- iring of control panels hen a ne production

model as introduced.



PLCADVANTAGES

Cost effective for

controlling complexsystems.Flexible & can be reappliedto control other systems

quickly & easily.Computational abilitiesallo more sophisticatedcontrol.Troubleshooting abilities

make programming easier &reduce do ntime.Reliable componentsmake these likely to operate

for years before failure.



HOW P Cs WORK.

THE COMPONENTS THAT MAKE A

MODULAR PLC WORK CAN BE DIVIDEDINTO FOUR CORE AREAS.

THE BACKPLANE OR RACK AND POWER

SUPPLY.

THE CENTRAL PROCESSING UNIT (CPU).

THE INPUT/OUTPUT (I/O) SECTION.

THE PROGRAM SECTION.



The rack above

is a Mitsubishi'A' series rack

with eight I/O

slots and a

power supply

unit (PSU) slot.



Here it is

again with the

PSU slotted in

place.



The CPU - Central Processing Unit.

Ho P Cs ork is do n to the CPU, the CPU is the P Cpart hich is the brain of the hole P C. This moduletypically lives in the slot beside the po er supply or isincorporated ith a po er supply.

The CPU itself has a fe different operating modes. Programming Mode. Run Mode.

Stop Mode. Reset Mode.



Below is the basic flow chart of how PLCs work through and process the I/O, theirprogram operation and error checks, know as the Scan process. The Scan-time is howlong it takes the PLC to loop around the whole process back to the start, and can changedepending on how much the Scan process has to do.



The input/output (I/O) section.

Above is a simple PLC wiring diagram (called a

schematic), in this example you can see the PLC is a

24V DC supply type.



PLC PROGRAMMING CABLE SPLC PROGRAMMING CABLE S



THIS ABOVE IS THE SIMPLEST OF PROGRAMS THAT CAN

BE WRITTEN FOR A PLC, THAT I MIGHT ADD, WILL

ACTUALLY WORK. A DIGITAL INPUT, LIKE A PUSHBUTTON CONNECTED TO THE FIRST INPUT POSITION ON

THE CARD. WHEN THE INPUT IS MADE (THE GAP

BRIDGED) IT TURNS ON THE OUTPUT, WHICH SUPPLIES

POWER TO ENERGIZE AN INDICATOR LIGHT OUTSIDE THE

PLC.



THE COMPLETED PROGRAM LOOKS SOMETHING LIKE THIS



Video demonstration of plc programming



Every system or machine has a controller. Depending on the type of technology used, controllers can be divided into pneumatic, hydraulic,electrical and electronic controllers. Frequently, a combination of differenttechnologies is used. Furthermore, differentiation is made bet¡ eenhard- ¡ ired programmable (e.g. ¡ iring of electro-mechanical or electroniccomponents) and programmable logic controllers. The first is used primarily

in cases, ¡ here any reprogramming by the user is out of thequestion and the job size ¡ arrants the development of a special controller.Typical applications for such controllers can be found in automatic

¡ ashing machines, video cameras, and cars.

Ho ¡ ever, if the job size does not ¡ arrant the development of a specialcontroller or if the user is to have the facility of making simple or independentprogram changes, or of setting timers and counters, then theuse of a universal controller, ¡ here the program is ¡ ritten to an electronic

memory, is the preferred option. The P

¢

C represents such a universalcontroller. It can be used for different applications and, via the

program installed in its memory, provides the user ¡ ith a simple meansof changing, extending and optimising control processes.

Example of a

PLC application



Aerospace- Water tank quenching system

Example

As an example, say a facility needs to store ater in a tank. The ater is dra n from the tank by another

system, as needed, and our example system must manage the ater level in the tank.

Using only digital signals, the P C has t o digital inputs from float s itches ( o evel andHigh evel).

When the ater level is above the s itch it closes a contact and passes a signal to an input. The P C usesa digital output to open and close the inlet valve into the tank.

When the ater level drops enough so that the o evel float s itch is off (do n), the P C ill open

the valve to let more ater in. Once the ater level rises enough so that the High evel s itch is on (up),

the P C ill shut the inlet to stop the ater from overflo ing. This rung is an example of seal-in

(latching) logic. The output is sealed in until some condition breaks the circuit.

| |

| Low Level High Level Fill Valve |

|------[/]------|------[/]----------------------(OUT)---------|

| | |

| | |

| | |

| Fill Valve | |

|------[ ]------| |

| |

| |



Man fact ring In stry- ead acid battery plant, complete manufacturing system- Extruder factory, silo feeding control system

T ravel In stry- Escalator operation, monitored safety control system- ift operation, monitored safety control system

Agric lt re- Glasshouse heating, ventilation & atering system

Fo n ry- Overhead transportation system from casting process

to shotblasting machine

Leis re- Roller coaster ride and effects control system- Greyhound track 'Rabbit' drive system



Printing In stry- Offset eb press print register control system- Multi stage screen ashing system

Foo In stry- Filling machine control system- Main factory feed ater pump duty changeover system

T extile In stry- Indutrial batch ashing machine control system- Closed loop textile shrinkage system

Hos itals- Coal fired boiler fan change-over system

Film In stry- Servo axis controlled camera positioning system

Corr gating- Main corrugator machine control system-BOBST platten press drive and control system

Plastics In stry- Extruder factory, silo feeding control system- Injection moulding control system



A few more applications

Plc programming in laser printing Internet communication



INTERNET NETWORK



*7 SEGMENT DISPLAY * VENTILATION

*LASER PRINTING



www.wikipedia.org/wiki/Programmable_logic_controller

www.machine-informationsystem.com

www.P CS.net

www.ieee.org

www.plcmanual.com

plc final full

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