An Overview Of Programmable Logic Controller System Types And Application

 ABSTRACT

Early Programming Logic Control (PLC) were designed to replace relay logic systems. These PLCs were programmed in “Ladder Logic”, which strongly resembles a schematic diagram of relay logic. Programming logic control has several features like protection from the open area conditions such dust, heat and cold. PLC also has the ability to arrangement the inputs/outputs. It has low cost compared with microcontroller systems because using PLC in different applications only required to change the software for each application but in case of using microcontroller the hardware components itself must be changed with different applications.

Two important applications for programming logic control and also an engineering solution to save the human life are explained in this paper, one application is a robot used as a toxic chemical substances spraying, and the other application is a robot used for washing the faces glasses of skyscrapers. These mobile robots used PLC as a controlled tool for its motion and liquid flow rate also.

TABLE OF CONTENTS

COVER PAGE

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

CHAPTER ONE

1.0      INTRODUCTION

1.1      BACKGROUND OF THE PROJECT

• OBJECTIVE OF THE PROJECT
• SCOPE OF THE PROJECT
• ADVANTAGES OF PLC
• DISADVANTAGES OF PLC

CHAPTER TWO

LITERATURE REVIEW

• OVERVIEW OF THE STUDY
• HISTORICAL BACKGROUND OF THE STUDY
• BASIC FUNCTIONS OF PROGRAMMABLE CONTROLLER
• FEATURES OF PLC

 CHAPTER THREE

METHODOLOGY

• PROGRAMMING LOGIC CONTROL STRUCTURE
• TYPES OF PROGRAMMABLE LOGIC CONTROLLERS
• WORKING PRINCIPLE
• PROGRAMMING PLCs
• PLC SOFTWARE PREPARATION
• AREA OF PLC’s APPLICATIONS

 CHAPTER FOUR

• PROGRAMMABLE LOGIC CONTROLLER FAILURE

CHAPTER FIVE

• CONCLUSION
• REFERENCES

CHAPTER ONE

1.0                                                              INTRODUCTION

A programmable logic controller (PLC) or programmable controller is an industrial digital computer which has been ruggedized and adapted for the control of manufacturing processes, such as assembly lines, or robotic devices, or any activity that requires high reliability control and ease of programming and process fault diagnosis.

PLC is a special form of microprocessor- based controller. It includes a programmable memory to store instructions and to implement functions such as logic, sequencing, timing, counting and arithmetic as shown in figure1. In order to control machines and processes, PLC is designed to be operated by engineers even by a limited knowledge of computers and computing languages [1]. It has a great advantage of changing the PLC Ladder Diagram after it had been built or worked, which gives the facility of using the same PLC unit for controlling different systems after erasing it each time.

Fig.1: Programmable Logic Controller

PLCs could be considered as special computers for industrial use. It does not affected by vibrations, temperature, humidity and noise which mean that it is an open area controller. It could be easily programmed by using a simple programming language which is primarily concerned with logic and switching operations. PLCs contain a hardware and software systems which used for single Input/Output or multi Inputs/Outputs modular systems. PLCs are also used for analog or digital controller systems.

They were first developed in the automobile manufacturing industry to provide flexible, ruggedized and easily programmable controllers to replace hard-wired relays, timers and sequencers. Since then they have been widely adopted as high-reliability automation controllers suitable for harsh environments. A PLC is an example of a “hard” real-time system since output results must be produced in response to input conditions within a limited time, otherwise unintended operation will result.

1.2                            BACKGROUND OF THE STUDY

Programmable logic controllers [PLC] are computer-based, solid-state, single processor devices that emulate the behavior of an electric ladder diagram [1] capable of controlling many types of industrial equipment and entire automated systems [2]. PLCs are usually a main part of automatic systems in industry [3]. They are very efficient and reliable in applications involving sequential control and the synchronization of processes and auxiliary elements in the manufacturing, chemical and process industries [4,5].

Besides having technological advantages of using PLC, it also decreases the prices in the advanced level and complex control system [5–7]. Nowadays, most of the control elements used to execute the logic of the system was substituted by the PLCs [8].

The term logic is used because the programming is primarily concerned with implementing logic and switching operations. Input devices such as switches, and output devices such as motors, being controlled are connected to the PLC and then the controller monitors the inputs and outputs according to the machine or process [9]. Originally PLCs were designed as a replacement for hard-wired relay and timer logic control systems. (Hard-wiring means that all of the components were manually connected by wires). PLC consists of two parts i.e. the PLC hardware and programming.

PLCs were first used by the automotive industry in the late 1960s [2,10–13], its automated equipment was primarily controlled by discrete inflexible circuits consisting of electromagnetically relays and coils hardwired on panels. General Motors developed the specifications for a programmable controller that could replace the hard-wired relay circuits [2,11,12]. The most radical idea, was the implementation of a programming language based on a relay schematic diagram, with inputs (from limit switches, push buttons, etc.) represented by relay contact, and outputs (to solenoids, motor starters, lamps, etc.) represented by relay coils [12].Fig. 1(a) shows a simple hydraulic cylinder which can be extended or retracted by push buttons. Its stroke is set by limit switches which open at the end of travel, and the solenoids can only be operated if the hydraulic pump is running. This would be controlled by the computer program of Fig. 1(b) which is identical to the relay circuit needed to control the cylinder. These programs look like the rungs on a ladder, and were consequently called ‘Ladder Diagrams.’

In the mid-1960s, Hydramatic, a division of General Motors Corporation, envisioned that a computer could be used to perform the logic functions then performed by relays [2]. The engineering team wrote a list of features of the proposed computing device. GM initiated the development of the computing device by specifying certain design criteria, including:

• The device must be durable so that it can operate in the harsh environments (dirty air, humidity, vibration, electrical noise, etc.) encountered in a factory
• It must provide flexibility by implementing circuit modifications quickly and easily through software changes.
• It must be designed to use a programming language in ladder diagram form already familiar to technicians and electricians.
• It must allow field wiring to be terminated on input/output terminals of the controller.

1.3                              OBJECTIVES OF THE STUDY

The aim of this work is to write on A programmable logic controller, PLC, or programmable controller  which is a digital computer used for automation of typically industrial electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many machines, in many industries.

1.4                                    SCOPE OF THE STUDY

PLCs are continuously growing and evolving to be the best option for a variety of industrial automation applications. Scope of plc programming is increasing rapidly because of greater programming flexibility and ease, scalability, more memory, smaller sizes, very high-speed (gigabit) Ethernet, and built-in wireless features. PLCs are getting benefits from USB technology and thus make it easier than ever before to get online, program, and monitor your control systems. PLC programming will evolve, and with the availability of smaller micro and mini USB connectors, you can expect to see this option on more of the smaller PLCs. In the future, PLCs will continuously evolve while adapting technology enhancements in communications, hardware, and software.

1.5                                    ADVANTAGES OF PLC

Advantages of PLC are:

Flexibility: It can an easily run many machines

Corrects Errors: With PLC control any change in circuit design or sequence is as simple as retyping the logic. Correcting errors in PLC is extremely short and cost effective.

Space Efficient: We can generate more & more contacts, coils, timers, counters, sequences etc and we can have thousands of contact timers and counters in a single PLC.

Low Cost: Prices of Programmable Logic Controllers vary from few hundreds to few thousands.

Testing: A Programmable Logic Control program can be tested and evaluated in a lab. The program can be tested, validated and corrected saving very valuable time.

Easier Troubleshooting: Troubleshooting a circuit is really quick, easy and simple.

1.6                                 DISADVANTAGES OF PLC

Disadvantages of PLC are:

• It is difficult to find errors and require skillful work-force to operate.
  • When a problem occurs, hold-up time is indefinite, usually long.
  • There will be too much work required in connecting wires
  • There will be difficulty with changes or replacements