DISTRIBUTED CONTROL NETWORK FOR AGRICULTURAL APPLICATIONS Loukas V. Hadellis, Vassilios D. Kapsalis Laboratory of Microcomputers, TEI of Patras, Patras, HELLAS Abstract: This paper presents the design and development of a distributed and integrated control network for irrigation and other agricultural applications employing the LonWorks technology standard. A single control network infrastructure integrates irrigation, pumping and optionally fertilizing, syringing and environmental control systems that interoperate and can be programmed, monitored and optionally controlled over the same PC. Emphasis was given to the communication capabilities to external PSTN and TCP/IP networks; a LonWorks to PSTN gateway was developed. Keywords: Control applications, Networks, Integration, Agriculture, Distributed control. 1. INTRODUCTION Control Technology is moving to the 4 th generation of distributed I/O interconnected via control networks, where no central PLC is required any more (Kapsalis, et al., 1996; Pinto, 1996; Pinto, 1997). These systems consist of programmable and intelligent I/O control network nodes, with sensors and actuators directly connected to them, implementing all measurement and control algorithms locally and independently without requiring a central controller (Madan, 1996; Madan, 1997; Raji, 1994). A PC can be used for programming (application download, node/network configuration), monitoring and optionally control. LonWorks, developed by Echelon, is a de facto standard for control networks employing distributed architecture (Lockareff, 1996). Its concept is based on a democratic structure where individual network nodes run independently their own object-oriented control algorithms (Schneider, et al., 1997). These nodes are connected to the communication network infrastructure and exchange messages by means of a highly reliable protocol called LonTalk that employs event-driven and request-response techniques (LonTalk Protocol Specification, 1994). LonTalk protocol supports a bi-directional network communication based on the 7-layer ISO/OSI standard optimized for control, incorporating error detection/correction that increases reliability and provides real-time feedback about the actual control implementation (Kapsalis, et al., 1997). LonWorks technology is a complete platform for interoperable control systems. Its fully distributed and open architecture along with interoperability offers certain major advantages compared to the older PLC / centralized control systems such as: • No single point of failure due to highly decentralized structure. • The system computing power is exponentially increasing as the number of nodes increases. • Heterogeneous control system integration within the same control network and programming or monitoring through the same PC. • Highly robust communications network with true free topology physical layer which allows bus, star, ring, tree and mixed configurations. • Reliable communication over wired (TP, PL, fiber) or wireless (RF) media. • Multiple connectivity devices (routers, repeaters, gateways, bridges, net-interfaces).