Plc Introduction Essay

3478 words - 14 pages

5

2. PROGRAMMABLE LOGIC CONTROLLERS

Topics: • PLC History • Ladder Logic and Relays • PLC Programming • PLC Operation • An Example Objectives: • Know general PLC issues • To be able to write simple ladder logic programs • Understand the operation of a PLC

2.1 INTRODUCTION
Control engineering has evolved over time. In the past humans were the main method for controlling a system. More recently electricity has been used for control and early electrical control was based on relays. These relays allow power to be switched on and off without a mechanical switch. It is common to use relays to make simple logical control decisions. The development of low cost computer has brought the most ...view middle of the document...

When a voltage is

6

applied to the input coil, the resulting current creates a magnetic field. The magnetic field pulls a metal switch (or reed) towards it and the contacts touch, closing the switch. The contact that closes when the coil is energized is called normally open. The normally closed contacts touch when the input coil is not energized. Relays are normally drawn in schematic form using a circle to represent the input coil. The output contacts are shown with two parallel lines. Normally open contacts are shown as two lines, and will be open (non-conducting) when the input is not energized. Normally closed contacts are shown with two lines with a diagonal line through them. When the input coil is not energized the normally closed contacts will be closed (conducting).

input coil

OR

normally closed

normally open

OR

Figure 2

Simple Relay Layouts and Schematics

Relays are used to let one power source close a switch for another (often high current) power source, while keeping them isolated. An example of a relay in a simple control application is shown in Figure 3. In this system the first relay on the left is used as normally closed, and will allow current to flow until a voltage is applied to the input A. The second relay is normally open and will not allow current to flow until a voltage is applied to the input B. If current is flowing through the first two relays

7

then current will flow through the coil in the third relay, and close the switch for output C. This circuit would normally be drawn in the ladder logic form. This can be read logically as C will be on if A is off and B is on.

115VAC wall plug

relay logic

input A (normally closed)

input B (normally open)

output C (normally open)

A

B

C ladder logic

Figure 3

A Simple Relay Controller

The example in Figure 3 does not show the entire control system, but only the logic. When we consider a PLC there are inputs, outputs, and the logic. Figure 4 shows a more complete representation of the PLC. Here there are two inputs from push buttons. We can imagine the inputs as activating 24V DC relay coils in the PLC. This in turn drives an output relay that switches 115V AC, that will turn on a light. Note, in actual PLCs inputs are never relays, but outputs are often relays. The ladder logic in the PLC is actually a computer program that the user can enter and change. Notice that both of the input push buttons are normally open, but the ladder logic inside the PLC has one normally open contact, and one normally closed contact. Do not think that the ladder logic in the PLC needs to match the inputs or outputs. Many beginners will get caught trying to make the ladder logic match the input types.

8

push buttons

power supply +24V com.

PLC
inputs

ladder logic

A

B

C

outputs

115Vac AC power neut. Figure 4 A PLC Illustrated With Relays

light

Many relays also have multiple outputs (throws) and...

Other assignments on Plc Introduction

New Product Launch Marketing Plan Essay

922 words - 4 pages this product is marketed to a targeted buyer PLC Strategy Plan PLC (Product Life Cycle) is defined as the life span of a particular product. It entails of four stages which are labeled as introduction, growth, maturity and decline. The introduction stage is when the product is first introduced on the market. This stage of the cycle could be the most expensive for a company launching a new product ("Product Life Cycle", 2014). The growth stage

Financial Management Analysis

4171 words - 17 pages | | | Bibliography____________________________________________ | 23 | Introduction The aim of this report is to analyze and critically evaluate the financial and non financial abilities and efficiencies of PZ Cussons Plc for the fiscal years 2011 and 2012 through Financial Ratios which are tools to measure the overall efficiency of an organization. This report also aims to analyze the competitive advantage PZ Cussons Plc may or may not have

Sainsbuyr

2443 words - 10 pages Introduction: A UK based company J Sainsbury plc a firm which is into grocery, retailing and financial services business. The research is mainly to do the financial assessment of Sainsbury and the performance in compared to its industry competitors. Looking at the last 2 years report the company is now recovering from its passed performances. In recent years there has been many changes in the management and the board which has adopted many

Business Environment

4002 words - 17 pages bnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnmqwertyuiopasdfghjklzxcvbnm Business Environment Assessor: The Business and Environment Date Submitted: 12/01/2015Student Name: Student ID: | Contents Introduction 2 Task 1 Identify the purposes of different type of organisation 3 Private

Abcde

3685 words - 15 pages customer. December 2013 QUESTION 3 a)With the aid of a diagram,describe the stages of a product life cycle (PLC). First is introduction stage, this stage of the cycle could be the most expensive for a company launching a new product. The size of the market for the product is small, which means sales are low, although they will be increasing. On the other hand, the cost of things like research and development, consumer testing, and the

Heblon

2190 words - 9 pages ACCT5919 Business Risk Management Syndicate Report HEBLON PLC CASE STUDY Semester 2, 2013 Wenjia Wu 3489021 Wing Kin Lam 5011203 Xuan Zhang 5024642 Xin Su 3468927 1. Introduction This report will examine the key risk management issues in Heblon PLC (Heblon), with emphasis on the risk identification process. Established in 1950s in the UK, Heblon provides high quality wooden furniture in traditional

Three Firms: Changes In Their Enviroment

2506 words - 11 pages Sainsburys- The Guardian Dec 16th 2014. 5 3. Conclusion 6 4. References 8 1. Introduction This report aims to recognize key economic factors that are affecting three different firms and provides a clear link between the discipline of economy and real life examples. The first story focuses on the merge between BT Group plc and EE that could result in economies of scale and scope as finalisation of the purchase would create the UK's biggest

Test

2451 words - 10 pages Spot The Weakness Heinz Ketchup Joe Maalouf Rita Nazarian Jennifer Khoury Notre Dame University Table Of Contents: I. Introduction………………………………………………………3 A. Product category B. Retail outlets visited C. Target market D. Positioning statement II. Product strategies…………………………………………………4 E. Product classification F. Product attributes G. Brand name H. Product support services

History Of Beer

1065 words - 5 pages , Bacardi, and Grolsch. Miller Brewing produces more than 130 million barrels of beer annually and has operations in 40 countries with hundreds of brands. In July 2002, South African Breweries purchased Miller Brewing Company, forming one of the largest brewers in the world, called SABMiller plc. Brands range from Miller, Milwaukee's Best, Leinenkugel's, Peroni, Sparks, and Fosters. Adolph Coors produced 42.1 million barrels in 2006 through 12

Hnd Business Level 5

1321 words - 6 pages LO1: Be able to compile marketing audits Task 1: The internal and external marketing environment for Hiscox Ltd (LO 1.2, 1.3, 1.4, 2.1, 2.2) Introduction: The case study I have chosen for this assignment would be Hiscox Ltd. is a Bermuda-incorporated insurance provider, listed on the London Stock Exchange. An underwriter at Lloyd's of London, the company largely specializes in niche areas of the market, offering property and casualty

Cadbury Beverages Inc Crush Brand

2906 words - 12 pages SUMMARY Introduction p.2 I- The carbonated soft drink industry in the US - Industry structure p.4 - Industry economics p.5 - Brands & Products p.6 - Consumption behavior p.7 II- Changes in the orange category during the period 1985-1989 - Orange category p.8 - Relation between market share & market coverage p.11 - Relation between market share

Similar Documents

Just Info To Join This Site

297 words - 2 pages than epidemics.[2][1]:55, 354 Epidemics of infectious disease are generally caused by a change in the ecology of the host population (e.g. increased stress or increase in the density of a vector species), a genetic change in the parasite population or the introduction of a new parasite to a host population (by movement of parasites or hosts). Generally, an epidemic occurs when host immunity to a parasite population is suddenly reduced below that

Measurement Of Ip3 In Cultured Cells

1157 words - 5 pages INTRODUCTION Histamine which is an agonist induced an accumulation of inositol phosphate (IP3) in cultured cells both in the presence of calcium and in the absence of calcium. This mechanism of cellular response to the histamine receptor s a G-protein mediated activated (GTP) (Hill,1990). This mechanism occurs when a response to a photon of light called rhodopsin causes a change in the G-protein which is associated. Transduction then occurs

Business Environment Essay

9246 words - 37 pages Lankan business organizations. * Being a member state, UK has a lot of benefits from EU such as Educational, Social, Environmental, Economical and Technological etc. TABLE OF CONTENTS 1.0 INTRODUCTION 6 2.0 BODY 7 2.1 Task 1 7 2.1.1 LO1.1 7 2.1.1.1The Mission Statement of Bogawanthalawa PLC 7 2.1.1.2 The Mission Statement of Vallible Power Erathna PLC 7 2.1.1.3 The Mission Statement of Swarnamahal Financial services PLC 8

What Are The Main Types Of Agency That Organisations Use In Recruitment? What Are Their Major Costs And Benefits?

3590 words - 15 pages What are the main types of agency that organisations use in recruitment? What are their major costs and benefits? I. Introduction This essay examines the major cost and benefits of the main types of agencies, that organisations use in recruitment. In first part I will explain background of the market. Then I will move on to explain each of the types of agency used in recruitment. After that I will carefully examine their major costs and