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Programmable Logic Controllers

Professor Charlton S. InaoDefence UniversityBishoftu ,Ethiopia

General Objectives To explain and understand the following PLC concept:

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Programmable logic controller; Structure of PLC and system components; Programming Languages;( LAD,STL,FBD)Logic Gates application for PLCCounterShift RegisterJumpProgramming Applications

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Programmable Logic Controllers

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• Defined by NEMA as a digital electronic apparatus with a programmable memory for storing instructions to implement specific functions (logic, sequencing, timing, counting, and arithmetic) to control machines and processes.

• Considered as the first industrial-based computer

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Advantages of Using PLC

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Shorter Project Implementation

Easier Modification Without Cost Penalty

Design Easily Change Using Software

Project Cost Can be Accurately Calculated

Shorter Training Time Required

A Wide Range of Control Operations

Easy Maintenance

Able to Withstand Harsh Plant Environment

High Reliability

Standardization of Controller Hardware

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Functions of PLC

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Sequence Control

Conventional Relay Logic Replacer

Timer and Counter Functions

Auto / Semi / Manual Control of Machines and Processes

Sophisticated Control

Arithmetic Operations

Analog Control (Temperature, Pressure, etc.)

PID (Proportional Integral Derivation)

Stepper / Servo Motor Control

Functions of PLC

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Supervisory Control

Process Monitoring and Alarm

Interfacing with Computers

Factory Automation network

Wide Area Network

Basic Control System

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Open Loop System

INPUT LOGIC OUTPUT

- Pushbuttons- Limit Switches- Level Switches- Flow Switches

- Relays- Timers- Counter

s

- Motors- Solenoid valves- Lamps- Alarm/

annunciator- Relays/contactorsPLC

Basic Control System

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Closed Loop System

Controller Final ControlElement

ProcessVariable

Transmitter

Set value

Error

Process Variable Primary

Element / Transducer

Temperature

Flow+

_

Hardware Components

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Central Processing Unit (CPU)

Micro PLC – less than 100 I/O’s

Small PLC – 0 to 128 I/O’s

Medium PLC – 0 to 256 I/O’s

Large PLC – 0 to 512 I/O’s

Power Supply

100 – 240 Volts AC

100 / 110 Volts AC

200 / 220 Volts AC

24 Volts DC

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Inputs

DC – 24 Volts

AC – 110 / 220 Volts

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Outputs

Transistor type (24 Vdc )

Relay / Contact type (24Vdc / 220 Vac)

TRIAC type (110 / 220 Vac)

PNP-type Transistor Input

• Source• Generates power

NPN-type Transistor Input

• Sink• Transmits power

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Relay

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Example: Omron Relay

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Peripheral Devices

Programming Console

CX-Programmer Software

Conversion Cables

Connecting Cables

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Software Components

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1. Ladder Diagram Language – a symbolic instruction type language

2. Boolean Language- Basic level language that composed of three (3) Boolean logic operation: AND, OR, NOT

Mnemonic Instruction – written in abbreviated form using 3 or 4 letters that generally imply the the operation of the instruction

3. Functional Blocks Language – high level instructions that permit the user to program more complex functions using the ladder diagram format

- Instruction set is composed of blocks that executes or performs specific function

4. English Statement Language – considered derivative of computer language such as BASIC.

-also known as Control Statements

Note:

OMRON PLC’s uses both Ladder Diagram Language and Boolean Language.

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Key Points to Know in Selecting or Using PLC

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I. Know the process to be controlled

II. Determine the type of control

Distributed control

Centralized control

Individual machine control

III. Determine I/O interface requirements

Estimate digital and analog I./Os

Check for I/O specifications

Determine if remote I/O is required

Allow for future expansion

IV. Define peripheral devices

Steps in PLC Programming

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Draw the Schematic Diagram

Draw Control Diagram

Develop PLC Ladder Diagram

I/O Assignment

Convert to Mnemonic (Boolean)

PLC Layout

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Basic Structure of PLC

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PLC

Spec

ficati

ons

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LOGIC GATES

AND, OR , NOT

NAND , NOR, EXOR

De Morgan’sTheorem

Boolean Algebra

• An algebraic system that describes the logic circuit, in which the variables are limited to two values, usually 0 and 1.

• George Boole developed an algebra for values for the systematic treatment of logic.

• Boolean algebra deals with variables that take on two discrete values, 0 and 1 , and with operations that assume logical meaning.

• Situations involving “yes-no, true –false,on-off” can be represented by Boolean Logical operations.

Boolean Algebra Laws1) A + 1= 12) A + 0 = A3) A.0 = 04) A.1 = A5) A + A =A6) A.A = A7)A.A = 08) A + A = 19) A + B = B + A

10) AB + AC= A(B + C)11) A + BC =(A+B)(A+C)12) A + B = A.B13) A.B = A + B14) AΦ B= A.B + A.B(exor)

15) A + AB = A + Belec

elec

elec

elec

elec

elec

elec

elec

NAND

elec

elec

OR

OR

OR

OR

AND

AND

AND

EX OR

NOR

Boolean Algebra Laws1) Anything Ored to itself is equal to itself.2) Anything ANDed to itself is equal to itself. 3) It does not matter in which order we consider

inputs for OR and AND gates.

4) We can use truth table to show we can treat bracketed terms in the same way as the ordinary algebra.

A. (B +C)=A.B + A.C A +(B.C) =( A+B) . (A+C)

A + A =A

A . A =A

A + B = B + A A . B = B . A

Boolean Algebra Laws5) Anything ORed with its own inverse equals 1. A +A =16) Anything ANDed with its own inverse equals =0 A.A=07) Anything Ored with a zero is equal to itself. Anything

Ored with a 1 is equal to 1. A + 0 =A ; A + 1= 18) Anything ANDed with a 0 is equal to zeo; anything

ended with 1 is equal to itself. A.0 = 0 A.1 = A

Six Axioms on Properties of Boolean Algebra

Commutative Axiom:A.B=B.AA+B=B+ADistributive Axiom:A.(B+C)=(A.B) +(A.C)A+(B.C)=(A+B ).(A+C)Idempotency Axiom:A.A=AA+A=A

Absorption AxiomA.(A +B)=AA +(A.B)=AComplementation AxiomA.A=0A+A= 1A = ADe Morgan’s theorem

A.B= A + BA+B= A. B

Programming Format

1) Ladder diagram2)Mnemonic List3) Function Block Diagram

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NOR,NAND,EX-OR

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NOR

NAND

EX -OR

Timer: On delay and Off delay

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Cascaded timer/ On-OFF Cycle Timer

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COUNTERS

Counter UPCounter DownCounter Up/Down (Bi Directional Counter)

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Counter

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Week 15

• Internal Relays• Markers• Two Input Internal Relay Control• Latches Control of Internal Relays• Programming Application of Internal Relays

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Two Input control; Resetting a Latch

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Shift Register -Mitsubishi

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Shift Register

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i

M 0.0

Q 0.1

Q 0.2

Q 0.3

Q 0.4

Q 0.5

Q 0.6

Q 0.7

Q 0.0

I0.1

0UT

I0.0

I 0.2

M 0.0

M 0.2

M 0.3

M 0.4

M 0.6

M 0.5

M 0.7

SFT

RST

M 0.1

Shift Register Siemens Configuration

END

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Problem: Belt Sanding Machine

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Transfer Station

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Electric Relay Ladder Logic

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Liquid Level Sorter

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Wiring Diagram(Siemens LOGO)

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Liquid Level Sorter Electrical Ladder Diagram

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Liquid level Sorting Machine PLC Ladder Ladder Diagram

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M2.0

Artillery Cartridge Polishing Machine

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The designed and developed automated artillery cartridge polishing machine is intended for defence application to recondition the 122mm and 130mm diameter cartridges. The machine is intended to replace the traditional way of polishing the artillery cartridge with a modern and automated machine for HOMICHO Ammunition Factory. The Artillery cartridge polishing machine is a pneumatic type polishing machine which is basically used for polishing the external and internal surfaces of 122mm and 130mm artillery cartridges. The abrasive head can be moved to any point over the polishing area. The longitudinal and traverse movements of the polishing head are controlled using a programmable Language Control (PLC) integrated with pneumatically controlled cylinders. The PLC program is written using a ladder logic programming method using software for precise control of all the movements of the actuators in the two directions. Different directional control valves with pressure relieve valves are mounted to perform different functions. Standard design approaches and manufacturing sequences are followed to design and fabricate the polishing machine. The complete machine includes electric motor, pneumatic cylinders, polishing abrasives and a pneumatic line. The overall dimension of the machine is 2585x705x470mm and its spindle is designed to hold firmly different caliber cartridges and can be rotated at 800 RPM with a 5Kw spindle motor.

Since quality of the polishing machine is dependent on different polishing parameters like, polishing abrasives used, depth of polishing, RPM of the spindle and the feed rate of the polishing head, the surface quality of polished cartridges when it compared with previously polished parts it can expected to be in the range of 0.2 and 0

Cartridge polishing machine PLC Ladder diagram

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Hydraulic Missile Autoloader Mobile Machine

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The End

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