SHEKHAR MAURYA09106068

INSTRUMENTATION & CONTROL

SOFCON INDIA PVT. LTD.SOFCON INDIA PVT. LTD.

PROGRAMMABLE LOGIC CONTROLLER

MENTOR:PROF. S.K.PAHUJA

PLCPLC

The PLC is an assembly of solid state The PLC is an assembly of solid state digital logic elements design to make digital logic elements design to make logical decisions and provide outputs.logical decisions and provide outputs.

PLC is programmed interface between PLC is programmed interface between input sensor &output device.input sensor &output device.

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Programmable Logic Controllers

Advantages of PLC : They are fast and designed for the rugged

industrial environment. They are attractive on Cost-Per-Point Basis. These Devices are less Proprietary ( E.g.. Using

Open Bus Interface.) These Systems are upgraded more Capabilities

with dedicated PID and Ethernet Modules.Disadvantages of PLC : PLC one time cost is high To maximize PLC performance a number of IO

Modules to be added. PLC hold only one copy of program.DEK 3113DEK 3113 33

P L C Components(Hardware)P L C Components(Hardware)

Central Processing Unit (CPU) Input ModulesOutput ModulesPower Supply Bus system

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Advantage of PLC Over RelayAdvantage of PLC Over Relay RELAY RELAY PLCPLC 1-More wiring 1-Less wiring1-More wiring 1-Less wiring

2-Changes difficult 2-Changes easy 2-Changes difficult 2-Changes easy

3-More power 3-Low power3-More power 3-Low power

4-More maintenance 4-Solid state 4-More maintenance 4-Solid state reliabilityreliability

5-Difficult to expand 5 -Easy to expand 5-Difficult to expand 5 -Easy to expand DEK 3113DEK 3113 55

PLC CyclePLC Cycle

Sense the Input Sense the Input Process the LogicProcess the Logic Give Output Give Output

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Inputs CPU Outputs

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Ladder Diagram

Ladder diagrams are specialized schematics commonly used to document industrial control logic systems.

It is a language or a method to create a program. The first PLCs were programmed with a technique that was based on relay logic wiring schematics.

Basic concept of this diagram is similar to the electrical wiring. However in ladder logic, the symbol has changed and been standardized.

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Ladder Diagram cont..

Type of graphic language automatic control systems.

A drawing program of a switching circuit.

Called "ladder" diagrams because they resemble a ladder, with two vertical lines representing the power trails (supply power) and circuits are connected in horizontal lines called rungs. Connection between the element in the rung called link.

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Ladder Diagram Operational Principle

Referring to figure below, between these two rails, a horizontal straight line was drawn with two symbols. These two symbols refer to the input and output devices, which are used in the actual process/system.

On the left, we put all kinds of input. While on the right, we place all types of the outputs.

Once we complete one line of the program it seems like a ladder. This horizontal line which places the input and output make one rung.

Input

Interface Output

+24V -0V

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Ladder Diagram Symbols Ladder diagram uses standard symbols to

represent the circuit components and functions found in a control system.

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Normally Open Schematics (NO)-Input Schematics

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Normally Closed Schematics (NC)-Input Schematics

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Output Schematics

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Logic Function

There are 5 logic functions can be developed by combination of switches

1. AND2. OR3. NOR4. NAND5. EX-OR (XOR)

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Logic Function…cont

1. AND logiccoils is not energized unless both switch A and B closed. Fig. (b) represent for PLC input.

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Logic Function…cont - AND

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Logic Function…cont

2. OR logicCoils is not energized until either A or B closed

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Logic Function…cont – OR

DeMorgan's Theorem would predict:

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Logic Function…cont

3. NOR logicSince there has to be an output when neither A nor B have an input, and when there is an input either A or B.

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Logic Function…cont - NOR

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Logic Function…cont

4. NAND logicThere is no output when both A and B have an input

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Logic Function…cont - NAND

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Logic Function…cont - NOT

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Logic Function…cont

5. XOR logicThere is no output when both input 1 and 2 given.

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Combination of AND, OR, and inverter (NOT) gates

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Control CircuitStart stop circuit

-PB is pressed, output IR is activated-IR contact will closed-When PB is depressed, the output IR is still activated since current can go through contact IR unless is disturbed by stop button.

-PB is pressed, output IR is activated-IR contact will closed-When PB is depressed, the output IR is still activated since current can go through contact IR unless is disturbed by stop button.

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Vibrating/Jog circuit

-When, PB is pressed, output IR is activated.

-But after several microsecond, the normally closed IR is open then will stop the output IR.

-This applicable to move an object which need to locate at precise location.

-When, PB is pressed, output IR is activated.

-But after several microsecond, the normally closed IR is open then will stop the output IR.

-This applicable to move an object which need to locate at precise location.

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