UEE07 Electrotechnology Training Package UEENEED026B Design a computer based control system Learner Workbook Version 1 TRAINING AND EDUCATION SUPPORT INDUSTRY SKILLS UNIT, MEADOWBANK Product 5495
Acknowledgments The TAFE NSW Training and Education Support Industry Skills Unit, Meadowbank would like to acknowledge the support and assistance of the following people in the production of this learner workbook: Writers: Jeffrey Stokes TAFE NSW Reviewers: TAFE NSW Project Manager: Steve Parkinson TAFE NSW Enquiries Enquiries about this and other publications can be made to: Training and Education Support Industry Skills Unit, Meadowbank Meadowbank TAFE Level 3, Building J, See Street, MEADOWBANK NSW 2114 Tel: 02-9942 3200 Fax: 02-9942 3257 The State of New South Wales, Department of Education and Training, TAFE NSW, Training and Education Support Industry Skills Unit, Meadowbank, 2011. Copyright of this material is reserved to TAFE NSW Training and Education Support Industry Skills Unit, Meadowbank. Reproduction or transmittal in whole or in part, other than for the purposes of private study or research, and subject to the provisions of the Copyright Act, is prohibited without the written authority of, TAFE NSW. Training and Education Support Industry Skills Unit, Meadowbank. ISBN 978-1-74236-256-4 Developed by Training & Education Support Industry Skills Unit, Meadowbank @ TAFE NSW 2011
Table of contents Introduction... 9 1. General introduction... 9 2. Using this learner workbook... 9 3. Prior knowledge and experience... 11 4. Unit of competency overview... 11 5. Assessment... 16 Section 1:... 17 Control System Architecture... 17 1.1 Microprocessor Based Controllers... 17 1.2 PC Based Control Systems... 21 1.3 Distributive and Hybrid Systems... 30 1.4 Safety Considerations in Control System Design... 34 Section 2:... 39 Measurement, Signals and Connections... 39 2.1 Industrial Sensors... 39 2.2 Controller I/O Electrical Specifications... 42 2.3 Signal Conditioning and Calibration... 46 2.4 Input Protection Methods... 48 2.5 Data Signals and Connections... 51 Section 3:... 53 Control Programming... 53 3.1 PLC Programming... 53 3.2 SCADA Programming... 55 3.2 Data Acquisition Systems... 57 Section 4:... 61 Developed by Training & Education Support Industry Skills Unit, Meadowbank @ TAFE NSW 2011
Introduction to Labview... 61 4.1 Labview Installation and Setup... 61 4.2 Creating a Virtual Instrument (VI)... 66 4.4 Introduction to HMI Design... 72 Section 5:... 75 Analogue to Digital Conversion... 75 5.1 ADC Methods... 75 5.2 Resolution and Sample Rate... 77 5.3 Noise Reduction... 78 5.4 Data Logging... 82 Section 6:... 83 Introduction to Visual Basic.net... 83 6.1 VB.net Installation and Setup... 83 6.2 Navigating the IDE... 84 The Default Form... 86 6.3 Components and Properties... 87 6.4 Events, Methods and Functions... 97 6.5 Data Types and Variable Declarations... 98 6.6 Testing and Debugging a Program... 111 Section 7:... 115 Programming Structures... 115 7.1 If... Then... Else... 115 7.2 Select... Case... 117 7.3 For... Next... 118 7.4 Do... While and Do... Until... 119 7.5 Writing Function, Moving Objects... 120 Developed by Training & Education Support Industry Skills Unit, Meadowbank @ TAFE NSW 2011
Section 8:... 131 Advanced Maths Techniques... 131 8.1 Order of Operations... 131 8.2 Trigonometric Functions... 132 Section 9:... 133 Graphical Methods and Techniques... 133 9.1 Drawing in a Picture Box... 133 9.4 Form and Component Opacity... 136 Section 10:... 139 Control Programming Techniques... 139 10.1 Accessing I/O Devices... 139 10.2 The Basic Control Loop... 139 10.3 Timing Functions... 140 10.4 Counting External Events... 141 Reading and Scaling Analogue Values... 144 Section 11:... 147 Software Design Planning... 147 11.1 Top-Down Methodology... 147 11.2 Project Planning... 148 11.3 Modular Programming... 150 11.4 Documenting Software Design Projects... 151 Section 12:... 153 Software Design Implementation Project... 153 12.1 Control Algorithms... 153 12.2 Data Logging Features... 155 12.3 Programming Alarms... 156 Developed by Training & Education Support Industry Skills Unit, Meadowbank @ TAFE NSW 2011
12.4 Programming Access Control... 158 12.5 Managing Project Changes... 159 Section 13:... 161 Beta Testing and System Commissioning... 161 13.1 Testing Modules of Code... 161 13.2 Safety Testing and System Commissioning... 161 13.3 Commissioning Documentation... 161 13.4 Operating Manuals and Training... 161 Section 14:... 163 Data Communications Features... 163 14.1 Networks... 163 14.2 Network Topologies... 173 14.3 Network Standards and Protocols... 174 Section 15:... 177 Computer Based Control System Project... 177 15.1 System Planning... 177 15.2 System Implementation... 178 15.3 System Problem Solving... 179 15.4 System Completion... 180 Reference list... 183 Resource Evaluation Form... 185 Developed by Training & Education Support Industry Skills Unit, Meadowbank @ TAFE NSW 2011
Section 1: Control System Architecture 1.1 Microprocessor Based Controllers Control System History Figure 1 Manual Valve Early in the history of what we would call modern industrial development, control systems were manually operated. They relied on human measurement and decision making. This means that they were flawed. Over a period of time many manual systems, especially simple ON/OFF control systems, were replaced with relay control systems that were capable of a level of automation. These were more reliable and saved money because of the lower labour cost. Relay operation is still relatively slow to respond to process changes when compared with electronics and systems still broke down often, due to the electromechanical nature of the devices used. We still use relays today but only to isolate and control loads. They are not as part of the control. If a relay operation takes 15 milliseconds and there are 10 stages in the control circuit where one relay drives another, the propagation of the signal might be greater than 150 milliseconds. This is inadequate for many applications today. Figure 3 Early transistor circuits in computers With the invention and introduction of electronic devices, some relay control systems were replaced by dedicated digital systems. These systems were able to respond more quickly and required less maintenance as the devices were solid state, an old fashioned term meaning that they had no moving parts. They were essentially still hard-wired though, and process modifications and fixes meant that part of the system had to be re-designed and re-wired. It was not until the arrival of the microprocessor, that programmable control was made possible. Figure 2 3000 Type relays used for control Page 17 of 188
Eventually the PLC was invented. It came about because of the needs of the automotive manufacturers who needed to make changes to designs and build new models. PLCs became popular for control and are still currently the most common solution used by control engineers and electricians. They grew in size and power until their complexity made them too slow for some applications. It is now more common to use several small PLCs that communicate with each other than one very large PLC with a lot of processing power. Activity box A1.1 1. In what year was the very first PLC designed? 2. Why is it that PLC programs have a ladder like layout rather than being written in a normal programming language? Using the Internet links below, complete the following activities and respond in the space provided. http://en.wikipedia.org/wiki/programmable_logic_controller http://www.machine-informationsystems.com/plc_history.html http://www.plcs.net/chapters/links.htm Figure 4 A shoebox PLC 3. List four well known PLC manufacturers. Page 18 of 188
Microprocessor Control There are a number of choices in regard to a control system solution. The decision to utilise a specific type of controller and control system architecture is often based on the number of inputs and outputs required and the complexity of the control algorithms and therefore the processing power required to do the calculations. Other considerations might be the development time available, the lifecycle of the project, the likelihood of process changes and limits on the cost of system implementation. Some of the choices are; Figure 5 Embedded System An embedded system (a dedicated system) such as is used for TV remote controls, simple alarm systems and pool chlorination systems. In such systems, a microprocessor or microcontroller executes a program that is stored as firmware in EPROM memory. Costs for these systems are very low because of mass production. If large production numbers are not required, this sort of system is often not viable. A single PLC, or a number of PLCs, (a programmable system) where changes are easily made and the costs of both equipment and development time are relatively low. These systems are capable of some analogue measurement but only in a limited way. If a large number of analogue channels are required or very high sample rates, then other solutions might be more effective. A third option is to use what is popularly called a single board computer. This is something that has a PC operating system but is a limited configuration in terms of computing power, memory and communications capabilities. The benefits of a single board computer are that its power consumption is low and physically, it can be incorporated in pieces of equipment. Flash memory is used instead of a hard drive. Graphics processors are limited compared with a normal PC and the processor is a low power (slower) version of standard CPU. Even today, it is often a Pentium 4, not dual core PC architecture. Software can be developed easily as it is still essentially a PC platform. Figure 6 PLCs with SCADA control Figure 7 Single Board Computer with onboard graphics, Ethernet, expansion bus and USB ports Page 19 of 188
Ever since the advent of the personal computer, a PC based control system has been an option. The processing power available in such a system makes it perfect for complex measurement, analysis and advanced control systems. The use of a PC along with data acquisition hardware, is common in scientific circles. It is less commonly used in industry because of the relatively high cost. As industrial process control becomes more sophisticated and the price of PC technology continues to fall, this is becoming less of a constraint. This type of control is the focus of this unit of competency. Activity box A1.2 Figure 8 Two computers from different generations Try to guess what year each of the two computers above is from. The first is a relatively early PC. You will notice the two floppy drives. There was no hard drive. Each time you booted the PC you had to load the operating system from a floppy disk. The second PC is fairly recent. The flat LCD monitor places it within the last five years. Write your responses to the right. PC 1 PC 2 Technology Change 1. Why answer questions about historically irrelevant technology? Simply to bring into focus the fact that technology will not stop changing. The control solutions that are common today may not meet the needs of tomorrow s industry. Page 20 of 188