Copyright © IF AC Programmable Devices and Systems, Ostrava, Czech Republic, 2003 ELSEVIER IFAC PUBLICATIONS www.elsevier.comllocalelifac SOFTWARE INDUSTRIAL CONTROLLER - "SOFT PLC" Miroslaw CHMIEL Edward HRYNKIEWICZ Adam MILIK Krzysztof ZAK Institute of Electronics Silesian Technical University. Akademicka 16; 44-100 Gliwice; Poland chmiel@boss.iele.polsl.gliwice.pl; eh@boss.iele.polsl.gliwice. pl Abstract: The paper presents state of work carried over Logic Controller assembled with standard PC computer and remote object units. Presented system is equipped with software package that allows programming of control algorithms with use of Ladder Diagram and execution of programmed algorithm. Some PC machine can be used for program development. system control and monitoring. Copyright © 2003 IFAC Keywords: PLC, Distributed I/O group, Software PLC, LAD 1. INTRODUCTION Since the 80's Programmable Logic Controllers were used with a grate success in the domain of industrial controllers. They have replaced relay control systems, analogue regulators and even minicomputers. New ideas and solutions made PLCs more versatile than ever. Quick modification and adaptation to applications demands was achieved by easier programming without need of hardware modification. Commonly it is thought that increasing number of PLC application was caused by: • Similarities in ladder diagram used in PLC programming to schematic diagrams of relay and switch based control systems • High and continuolJ.Sly rising reliability of industrial computers that can operate in severe industrial condition and environments • Programmatically supervised tests and diagnostic of controlled inputs and outputs and system diagnostics. • Design of specific set of instruction that takes into account industrial specific condition of control program execution • Human Machine Interface (HMI) that allows to communicate PLCs with operator panels, displays, personal computers and other devices in order to support external supervision of control and production process. 7 Since the 90's personal computers are used to programming PLC and to edit documentation of control programs. PLCs also become more complex and advanced offering work in large computer networks. Dynamically developing and growing software packages for Supervisory Control and Data Acquisition (SCADA) are the reason for trends in development of PLCs. SCADA systems are the top most layer of control system. Those systems complement and extend capabilities of PLCs. Following function can be carried out by SCADA systems: • Data acquisition, processing and archiving that are directly obtained from controllers system • Reporting current state of plant and equipment, use of supplies and other useful management reports • Visualisation of controlled industrial processes in graphical way • Alarm and warning generation caused by limit value exceeding • Collecting data useful for optimal production control and management. The paper presents an idea of PLC that uses PC computer as computing unit. Popularity, availability and versatility of PC computers made us to try it in control application. Software PLC is not quite new solution and some manufacturers offer similar constructions [Legierski et al 1998][Michel G. 1992]