programmable logic controller “ fundamentals of logic…”

PROGRAMMABLE LOGIC CONTROLLER

“FUNDAMENTALS OF LOGIC…”

THE BINARY CONCEPT…• PLC operates on the binary principle like all digital

equipment.

• Term “binary principle” refer to the idea that many things can be thought of as existing in one of two states.

• states can be defined as “high” or “low”,“on” or “off”, “yes” or “no”, and “1” or “0”.

• This two-state binary concept, applied to gates, can be the basis for making decisions.

THE BINARY CONCEPT…

• Gate device that has one or more inputs with which it will perform a logical decision and produce a result at its one output.

• Logic ability to make decisions when one or more different factors must be taken into account before an action is taken.

“AND” GATE…

ANDLight Switch

High Beam Switch

High Beam Light

The automotive high beam lightcan only be turned on when thelight switch AND high beam switchare on.

FUNCTION OF “AND” GATE…

Binary 1 represents the presence of a signal or the occurrence of some event, while binary 0 representsthe absence of the signal or nonoccurrence of the event.

‘AND’ GATE APPLICATION…EXAMPLE 1

Basic Rules

The device has twoor more inputs andone output

If any input is 0,the output will be 0

If all inputs are 1,the output will be 1

‘AND’ GATE APPLICATION…EXAMPLE 2

The AND gate operates like a series circuit.The light will be “on”only when bothswitch A and switch Bare closed.

“OR” GATE…

Passenger Door Switch

Driver Door Switch

DomeLight

The automotive dome light willbe turned on when the passengerdoor switch OR the driver doorswitch is activated.

FUNCTION OF “OR” GATE…

An OR gate can have any number of inputs but only one output.

The OR gate output is 1 if one or more inputs are 1.

‘OR’ GATE APPLICATION…EXAMPLE 1

If one or more inputs are 1, the output will be 1

Basic Rules

If all inputs are 0,the output will be 0

‘OR’ GATE APPLICATION…Example 2

The OR gate operates like a parallel circuit.The light will be “on”if switch A or switch Bis closed.

FUNCTION OF ‘NOT’ GATE…

The NOT function has only one input and one output.

The NOT output is 1 if the input is 0.The NOT output is 0 if the input is 1.

Since the output is always the reverse of the inputit is called an inverter.

‘NOT’ GATE APPLICATION – Example 1

The light will be “on” if the pushbutton is not pressed.

Acts like a normallyclosed pushbuttonin series with the output.

The light will be “off” if the pushbutton is n pressed.

‘NOT’ GATE APPLICATION – Example 2

If the power is “on” (1) and the pressure switch is not closed (0), the warningindicator will be “on”

Low-pressureindicating circuit

When the pressurerises to close thepressure switch, thewarning indicatorwill be switched "off"

NAND FUNCTION

Functions - like an AND gate with aninverter connected to its output.

The only time the NAND gate output is 0 is when all inputs are binary 1.

NOR FUNCTION

Functions - like an OR gate with aninverter connected to its output.

The only time the NAND gate output is 1 is when all inputs are binary 0.

XOR (EXCLUSIVE-OR) FUNCTION

The output of this gate is HIGH only when one input or the other is HIGH, but not both.

Has two inputs and one output.

Commonly used for comparison of two binary numbers.

GATE BOOLEAN EQUATIONS

AB

YAND Y = A B

Gate Boolean Equation

ORA

BY Y = A + B

NOTA Y Y = A

BOOLEAN EQUATION – Example 1

Each logic function can be expressed in terms of aBoolean expression

BOOLEAN EQUATION – Example 2

Any combination of control can be expressed in terms of a Boolean equation

ABY = AB + C

A + B

Y = (A + B) C

BOOLEAN EQUATION – Example 2

AB

Y = AB + C

A + BY = (A + B) C

Producing A Boolean Expression From A GivenCircuit – Example 1

Producing A Boolean Expression From A GivenCircuit – Example 2

Final equation: Y= AB + AB

Hard Wired versus Programmed Logic

The term hardwired logic refers to logic control functions that are determined by the way devicesare interconnected.

Hardwired logic can beimplemented using relays and relay ladder schematics.

Hardwired logic is fixed:it is changeable only by alteringthe way devices are connected.

Hard Wired versus Programmed LogicExample 4-1

Hard Wired versus Programmed LogicExample 4-2

Hard Wired versus Programmed LogicExample 4-3

Hard Wired versus Programmed LogicExample 4-4

Hard Wired versus Programmed LogicExample 4-5

Hard Wired versus Programmed LogicExample 4-6

Hard Wired versus Programmed LogicExample 4-7

Hard Wired versus Programmed LogicExample 4-8

Hard Wired versus Programmed LogicExample 4-9