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Overview
Product Details
| ISBN-13: | 9780124157903 |
|---|---|
| Publisher: | Elsevier Science |
| Publication date: | 08/19/2011 |
| Sold by: | Barnes & Noble |
| Format: | eBook |
| Pages: | 320 |
| File size: | 15 MB |
| Note: | This product may take a few minutes to download. |
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Overview of Industrial Process Automation
By KLS Sharma
Elsevier
Copyright © 2011 Elsevier Inc.All right reserved.
ISBN: 978-0-12-415790-3
Chapter One
Why Automation?
1.1 Introduction
Over the past few decades, the industry emphasis world-wide has been to produce quality, consistent, and cost-effective goods/services to stay in the market. Quality, consistency, and competitiveness cannot be achieved without automating the process of manufacturing the goods and of providing the service. In line with this trend, the application of automation today is omnipresent in almost all the applications, starting from deep water to the space and has gained the confidence of the world for achieving the desired results.
Over the years, automation technology has advanced along with various other technologies, such as information, communication, networking, electronics. The list below shows advances in automation technology over the past decades:
• 1940–1960: Pneumatic
• 1960–2000: Analog
• 1980–1990: Digital—proprietary
• 2000 onward: Digital—open
The current trend is to move toward an open network of embedded systems. This chapter gives a brief introduction to automation and explains why it is necessary to automate the production of goods and providing of services to achieve the required quality, consistency, and cost for today's marketplace. In addition, there are many more complex requirements which cannot be achieved without automation.
In the subsequent discussions in the book, the term process refers to industrial processes/plants and system refers to automation systems/subsystems.
1.2 Physical Process
Physical process is a series of actions, operations, changes, or functions that takes place within bringing about changes or producing an output or a result. Also, the physical process as a sequence of interdependent operations or actions which, at every stage, consume one or more inputs or resources to convert same into outputs or results to reach a known goal or the desired end result.
Whatever we see and work within reality are all physical processes. The physical processes can be broadly divided into three categories as follows:
• Natural processes
• Self-regulated processes
• Man-made or industrial processes
1.2.1 Natural Processes
Natural processes are presented by or produced by nature. The best example is a human body that, generally, does not need any external assistance to regulate its body parameters (e.g., the body temperature) irrespective of the effects of the surrounding environmental conditions. The human body maintains or regulates all its parameters. Typically, in natural processes, no abnormal behavior is present in most of the conditions.
1.2.2 Self-Regulated Processes
Self-regulated processes are not natural but do not need any external assistance for their regulation. The best example is a domestic geyser in which the water level in the geyser is always maintained irrespective of its water temperature. All natural processes are self-regulated, but the reverse is not true.
1.2.3 Man-made or Industrial Processes
Man-made or industrial processes are systematic series of physical, mechanical, chemical, or other kinds of operations that produce a result. They manufacture goods or provide services. These processes are not always self-regulating and may need external regulation on a continuous basis.
Typical examples of goods are any products manufactured by an industrial process, such as food, chemical, engineering. Examples of typical services include the supply of electricity, water, gas, etc., to consumers in a municipal locality.
Some simple examples of the man-made processes are discussed in the following sections.
1.2.3.1 Water Tap
The function of the simple water tap in the house is to provide water when the tap is opened. The actions involved are to open the tap and wait for the water to flow. Here, the process is the water tap, the action is turning on the tap, and the output is the water. The intention is to get the water with the desired flow. This may not always happen for several reasons, such as low or no pressure (external factors) or a clog in the pipe or tap (internal factors) resulting in either inadequate or no flow of water.
1.2.3.2 Electric Bulb
Similarly, the function of a simple electric bulb in the house is to provide the light when it is switched on. The actions involved are to switch the bulb on and wait for the bulb to glow. Here, the process is the electric bulb, the action is turning on the switch, and the output is the light. Once again, the intention is to get the light with the desired illumination. This may not always happen for several reasons, such as low or no voltage (external factors) or a faulty or broken filament (internal factors) resulting in either improper or no illumination.
1.2.4 Undesired Behavior
As seen in the above two examples, undesired behavior is expected under unusual conditions due to external and/or internal factors which cannot be eliminated in manmade or industrial processes. Special efforts are required to overcome or minimize the effects of these factors to ensure that the process behaves or produces the results the way we want.
As our discussion will focus on the man-made or industrial processes and how to manage them to get the desired results, the term process will refer only to the manmade or industrial processes from now on. These processes may also be called plants or process plants.
1.3 Types of Industrial Processes
To facilitate their proper management, industrial processes are broadly divided into two categories. They are considered either localized or distributed processes, based on their nature, structure, or physical organization.
1.3.1 Localized Processes
The localized process is present in a relatively small physical area with all its subprocesses or components closely interconnected. Some simple examples of localized processes are the following:
• Water tap
• Electric bulb
• Electric motor
• Water heater
• Passenger lift
• Air-conditioner
• Traffic signal
1.3.2 Distributed Processes
Conversely, the distributed process is present in a relatively large physical area with its subprocesses or components loosely interconnected. Such a process is a network of many localized processes distributed over a large physical area. Some simple examples are as follows:
Several water taps (localized processes) connected to a common water supply line (water supply system) in a building. Here, the coupling or networking of the water taps is through the water pipeline supplying the water to all the taps. Each water tap is a localized process, while the group of water taps, networked through the common water supply pipe, is a distributed process.
Several electric bulbs (localized processes) connected to a common electric supply line (electric supply system) in a building. Here, the coupling or networking of the electrical bulbs is through the electricity supply cable supplying the electricity to all the bulbs. Each electrical bulb is a localized process, while the group of electrical bulbs, networked through the common electricity supply cable, is a distributed process.
The distributed process treats the entire network of localized processes as a single entity (not as each individual localized subprocess). Here, each localized process has some effect on the operation and performance of other networked localized processes.
Figure 1.1 explains the concepts of localized and distributed processes using the water tap and electric bulb as examples.
The concept of the distributed process can even be extended to include geographically distributed processes, such as water distribution networks, electricity distribution networks, gas distribution networks, which are normally present in a town or city or even a region. In these cases, the area covered is physically large, and the interconnection among the subprocesses or components becomes loose.
1.4 Industry Classification
The industrial processes are further broadly classified, based on their application areas, into utility industries and process industries, as described below. This is being done to address the specific technical issues present in those sectors. Not all the manufacturers of automation systems follow this classification.
1.4.1 Utility Industry
The utility industry, including electricity, water, gas, transport, is with the public service sector (normally with municipal corporations) and has both localized and distributed processes, as shown in Tables 1.1–1.3.
A water distribution system is illustrated in Figure 1.2.
An electricity distribution system is illustrated in Figure 1.3.
1.4.2 Process Industry
The process industry is normally associated with the manufacturing or production sector, which includes chemical, metal, food, pharmaceutical. These industries have both localized and distributed processes, as laid out in Tables 1.3 and 1.4.
An oil transportation system is illustrated in Figure 1.4.
1.5 Process Automation System
A process automation system is an arrangement for automatic monitoring and control of the industrial process to get the desired results without any manual interventions.
Before we look into the automation, let us look at the behavior of the processes when they are unattended, manually attended, and automated. To understand the behavior of the unattended process, let us take the example of a simple water heating process, as illustrated in Figure 1.5.
1.5.1 Unattended Processes
The intention of a water heating process is to maintain the temperature of the water at a desired value. The actions involved are as follows:
• Turn on the power supply to the heating element of the water heater.
• Wait for the water to get heated.
Water continues to get heated even after crossing the desired level, if not checked. Also, no consideration is given for minimizing the effects of internal and/or external factors. This means that the heating process is totally uncontrolled and there is no guarantee that, at any point of time, we have the water with the desired temperature (see Figure 1.6).
There is no mechanism here to judge whether the temperature of the water is higher than, lower than, or equal to the expected level. Not only do the unattended processes not produce the desired result but they can also lead to serious consequences such as overheating of the water. Unattended processes do not produce the desired results.
1.5.2 Manually Attended Processes
To understand the behavior of the process when it is manually attended, let's take the same example of the water heater and apply the following steps to maintain the temperature of the water:
• Turn on the power supply to the water heater.
• Manually check the temperature of the water periodically.
• Manually turn off the power supply to the water heater when the temperature of the water reaches/crosses the desired level.
Following these steps, almost all the drawbacks seen in the unattended process are rectified, though with a lot of burden on the operator. The more frequently the operator checks, the better the result, but the increased work for the operator is very unproductive. The effects of both the internal and external factors are taken care of without any additional effort. Hence, in comparison to the unattended process, manually attended processes produce better, but average results. Figure 1.7 illustrates the steps involved.
1.5.3 Automated Processes
To understand the behavior of the process when it is automated (with a temperature controller installed), let's take the same example of the water heater and apply the following steps to maintain the temperature of the water:
• Set the desired or reference temperature on the temperature controller at which the temperature of the water is to be maintained.
• Start the process by turning on the power to the heater.
• The controller continuously measures the actual temperature and keeps the heater on automatically if the actual temperature is less than the reference temperature. It turns off the heater automatically if the actual temperature is equal to or more than the reference temperature.
• Repeat the cycle.
(Continues...)
Excerpted from Overview of Industrial Process Automation by KLS Sharma Copyright © 2011 by Elsevier Inc.. Excerpted by permission of Elsevier. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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Table of Contents
- Why automation? - Automation system structure - Instrumentation subsystem - Control subsystem - Human interface subsystem - Automation strategies - Programmable control subsystem - Hardware structure of controller - Software structure of controller - Programming of controller - Advanced human interface - Types of automation systems - Special purpose controllers - System availability - Common configurations - Advanced Input/Output system - Concluding remarks Appendixes - Appendix A - Hardwired control subsystem - Appendix B- Processor - Appendix C - Hardware-software interfacing - Appendix D - Instruction set of processor - Appendix E - Basics of programming - Appendix F - Advanced control strategies - Appendix G - Power supply system - Appendix H - Further readingWhat People are Saying About This
A comprehensive, systematic, completely illustrated detailed treatment of the basic concepts, methods, and techniques of industrial process automation systems