电气工程 自动化 外文翻译 外文文献 英文文献 PLC未来发展趋势.doc

4th International DAAAM Conference INDUSTRIAL ENGINEERING – INNOVATION AS COMPETITIVE EDGE FOR SME 29 - 30th April 2004, Tallinn, Estonia PROGRAMMABLE LOGIC CONTROLLERS IN PROCESS AUTOMATION Ahti Mikkor, Lembit Roosim?lder Department of Product Development, Institute of Machinery, Tallinn Technical University, Ehitajate tee 5, 19086 Tallinn, Estonia ahti.mikkor@ Abstract: Nowadays, control problems are solved using operating components from a wide variety of technologies: electronics, hydraulics, pneumatics and mechanics. Functio-nality, reliability and price of the controlled system are deter-mined by the quality of the solution made. The paper concentrates on practical use of programmable logic controllers (PLC) that is based on the five years project development experience in this area. Successful solutions and problems are under focus. Specific hardware, controller programming problems, data/signals exchange and human machine interfaces are considered. As a result the method for selecting programmable controllers according to specific needs is developed. Practical suggestions, possible hazards and warnings are proposed that could help to avoid mistakes. Key words: programmable controllers, PLC, automation, automation systems, process automation. 1. INTRODUCTION Modern machinery consists of both mechanical and electronic parts. Overall functionality is determined by “balance” between these components. Initial planning and solution selection plays critical role in final result. In control methods the selection has to be made between relay-based circuits, special devices, programmable logic controllers (PLC) and new development electronics. This article is concentrated on PLC-s and experience that has collected over 5-year practical work with PLC-s. Strong and weak sides, positive and negative practices are discussed. Suggestions weather to use programmable controllers or not have been formed to help decision making. The most important decision i