plc

IEEE HIT STUDENT BRANCH

Workshop on PLC and SCADA

Presentation By: DEBAYON SAHA

What is PLC?

• PLC – Programmable Logic Controller • PLC is a digital computer designed for controlling

multiple inputs and output arrangements, extended temperature ranges, immunity to electrical noise, and resistance to vibration and impact.

• A PLC is an example of a real time system. • PLC works on the principle of Relay Logic.

History of PLC

PLC was introduced in late 1960’sFirst 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.

Leading Brand of PLC• Siemens - Germany• AB (Allen Bradley) – US• Schneider Electric (Modicon) – France• Mitsubishi – Japan.• ABB – Germany.• SAIA – Switzerland• GE Fanuc – US.• B&R (Bernecker & Reiner) – Austria.• Teco – Czech Republic.

Types of PLC• NANO PLC: Latest and smallest plc Consist of less than 10 input & Output ports

• MICRO PLC: Smaller PLC Consists of15-20 input & 10-12 output ports

• MINI PLC: Medium size Consists of 100-200 input & output ports

• RACK PLC: Large size Consists of 1000 of input & output ports

PARTS OF PLC

PLC

HARDWARE SOFTWARE

HARDWARES & SOFTWARES OF PLC

MAKER’S NAME HARDWARE SOFTWARE

SIEMENS S7-300, S7-200, S7-400 etc.

Siematic Manager, Logo

Allen Bradley MicroLogicx LogicxPro

ABB AC500, S500 AC500, S500

MAJOR COMPONENTS OF PLC

• POWER SUPPLY MODULE: 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.

It consists of AI/AO cards & DI/DO cards.

• CPU or PROCESSOR: Provides intelligence to command and govern the activities of the entire PLC systems.

• IFM MODULE: IFM module helps a PLC to communicate with other PLCs. It also manages the communication between other modules and processor.

BASIC BLOCK DIAGRAM OF A PLC

I MN O P D U UT L E

POWERSUPPLY

O M U OT DP UU LT E

PROCESSOR

IFM MODULE

ToOUTPUT

Solenoids, contactors,

alarmsetc.

From SENSORSPushbuttons,

contacts,limit switches,

etc.

To Other PLC

PS

CPU

IFM

INPUT OUTPUT

Input & Output of PLCOutputsLED

s

Inputs

Programming Languages of PLC

• Ladder Logic• Functional Block Diagram• STL or Statement List

• Sequential Function Chart• Boolean mnemonics

Advantages of PLCsReliability.Flexibility in programming and reprogramming.Cost effective for controlling complex systems.Small physical size, shorter project time.High speed of operation.Ability to communicate with computer systems in the

plant.Ease of maintenance /troubleshooting. Reduced space. Energy saving.

Disadvantages of PLCs

PLC devices are proprietary it means that part or software of one manufacturer can’t be used in combination with parts of another manufacturer.

Limited design and cost optionFixed Circuit Operations.PLCs manufacturers offer only closed architectures.

Ladder Logic

• Ladder logic is the oldest programming language for PLC.• It is mostly used logic for controlling PLC. language for

PLC.• It is well suited to express Combinational logic.

Concept of NO, NC, EO & EC• Any Electrical Switch have 2 conditions: 1) Normal or OFF

state 2) Excited or ON state• Again on the basis of contact position any electrical switch

have 2 positions: 1) Open Position 2) Closed Position

• NO: Normally Open Position. When switch is pressed then its become closed. After releasing of switch its again go back to open position.

• NC: Normally Closed Position. When switch is pressed then its become open. After releasing of switch its again go back to close position.

• EC: Excited Closed Position.• EO: Excited Open Position.

EC(Excited Closed)

NO(Normally

Open)

EO(Excited Open)

NC(Normally Closed)

Addressing of Input & Output• Input: I:1/0, I:1/1, ……………., I:1/15• Output: O:2/0, O:2/1, …………, O:2/15• In Siemens Input is denoted by ‘I’ & Output is denoted by

‘Q’.

Problem Statement- 1• Develop a LAD programe such that the lamp L1 should

glow when the switch S1 is made ON and the lamp gets OFF when switch S1 is made OFF

Problem Statement- 2• Develop a LAD programe such that the Lamp L2 should not

glow when switch S2 is made ON Lamp should glow when switch S2 is made OFF.

Problem Statement-3• The lamp L3 should glow when both the switch S1 & S2 are

ON. If any one is OFF then L3 will not glow. Draw LAD logic.

Problem Statement-4 • The lamp L4 should glow when any one of the switch S1 or

S2 is ON. Draw the LAD logic.

Problem Statement-5• The lamp should glow when either the switch (S1 & S2) or

S3 is ON. Draw LAD logic.

Problem Statement-6• Develop Ladder Logic for a car door/seat belt safety

system. When the car door is open, or the seat belt is not done up, the ignition power must not be applied. If all is safe then the key will start the engine.

REALIZATION OF LOGIC GATES

AND GATE

OR GATE

NOT GATE

NAND GATE

NOR GATE

XOR GATE

XNOR GATE

Relay

• It was invented by Joseph Henry in 1835. • A relay is an electrical switch that opens and closes contacts

under control of another electrical circuit. • The switch is operated by an electromagnet (Solenoid) to open

or close one or many sets of contact points. • A relay is able to control an output circuit of higher power than

the input circuit which is at lower power.

http://en.wikipedia.org/wiki/Joseph_Henry

http://en.wikipedia.org/wiki/1835

http://en.wikipedia.org/wiki/Switch

http://en.wikipedia.org/wiki/Magnet

Lever(Magnetic Material)

Solenoid Coil

Spring

NC Contact

NO Contact

Common Contact

Operation of Relay• When a current flows through the coil, the resulting

magnetic field attracts an armature that is mechanically linked to a moving contact.

• The moving contact is supported by a spring, which keeps the common contact normally connected to the NC and when the coil get activated and a magnetic field is produced, the moving contact get attracted.

• Resulting a closed path between NO contact and Common contact.

• The movement either makes or breaks a connection with a fixed contact.

http://en.wikipedia.org/wiki/Current_(electricity)

http://en.wikipedia.org/wiki/Coil

http://en.wikipedia.org/wiki/Magnetic_field

Inside a Relay Magnetic force deflectsthe lever downwardwhen the coil is energizedSpring force restores

the lever when the coil is not energized

Connections to coilNormally opencontact

Normally closedcontact

NO

NCCommon contact

Magnetic force deflectsthe lever downwardwhen the coil is energizedSpring force restores

the lever when the coil is not energized

Connections to coilNormally opencontact

Normally closedcontact

NO

NCCommon contact

Inside a Relay

Wiring diagram of a Relay

Problem Statement• When a switch S1 is pressed, then it activated a relay.

After activating the relay a bulb B1 gets on, which was previously off. Another bulb B2 gets off which was previously on.

INTERLOCKING

MEMORY• It is a internal device of PLC and can be used as output.• Memories are generally used for providing internal

switching in program.• Memory is denoted by ‘B3’.• Range of memory is 0/0 to 31/7.

PROBLEM STATEMENT• In a one way tunnel there are three proximity sensors S1,

S2 & S3. When the car passes sensor S1 the bulb B1 glows. When the car passes sensor S2 the bulb B1 gets OFF & the bulb B2 glows. When the car finally passes the sensor S3 the bulb B2 gets OFF.

TIMER• Basically Timer is a device which counts time and provides a

delay in a circuit.• Timer is addressed with ‘T4’.• Timer range is 0 to 255.• There are 3 types of timer in PLC- 1) On Delay Timer 2) Off Delay Timer 3) Retentive On Delay Timer

ON DELAY TIMER• Initially Contact Part of this timer remains in NO position.• After getting power supply its started achieving its preset

value.• After achieving its preset value the Contact of the Timer

becomes EC.

PROBLEM STATEMENT• A lamp will be on 10 sec after pressing a switch. If switch

will be off then timer will reset automatically.

OFF DELAY TIMER• When We provide power supply Off Delay Timer

remains in on position.• When we off the power supply its start achieving

preset value.• After achieving the preset value timer becomes off.

PROBLEM STATEMENT• A lamp should be get off 5 sec after pressing a switch.

Retentive ON DELAY TIMER• Same as ON DELAY TIMER.• The only difference is when power is interrupted its retain its

accumulated value, when power is again on then its starts counting from its accumulated value.

• To reset this timer we use ‘Reset’.

COUNTER• Basically Counter is a device which counts no of events.• Counter is denoted by ‘C5’.• Counter range is 0 to 255.• To reset the counter we use ‘RESET’.• There are Two types of counter in PLC- 1) UP COUNTER 2) DOWN COUNTER

UP COUNTER• UP COUNTER counts up.• Initially up counter remains in off position.• When count reaches counter becomes on.

PROBLEM STATEMENT• There is a conveyor belt. After passing 5 elements a

indicating lamp will glow. A switch is used to reset the counter.

DOWN COUNTER• DOWN COUNTER counts down.• Initially down counter remains in on position.• After count reaches counter becomes off.

PROBLEM STATEMENT• A lamp L1 is on. After 5 men enter a room the lamp should

go off. A switch is used to reset the counter. Use Down Counter.

PROBLEM STATEMENT• A lamp L1 will glow after pressing a switch S1 10 times.

Another lamp L2 is already lit. It will be off when switch S2 is pressed 5 times after L1 glows. A reset switch S3 is used to reset both the counters.

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