A Safe Communication Scheme for an Intelligent Wireless Networked Control System Coordination Agent

Abstract

Wireless networked control systems have begun to gain acceptance during the last decade, largely due to the increased flexibility and lower costs they promise to provide. The pace of application has been held back, however, by the reluctance of industry to make the accommodations necessary to allow wireless paths to be incorporated in process control loops, thus limiting the potential applications and benefits of wireless systems. The problem is that there are conflicts between maintaining the performance of control loops, which can be degraded by slow data rates and delays in wireless paths, and the usual objectives in managing a wireless sensor network, namely freedom to configure the network and to adjust data rates at will, to maximize efficiency and to conserve energy consumption in the network nodes, which are very often battery powered. We address this conflict by developing a new! component for use in industrial control systems, called a Wireless Networked Control System Coordination Agent. This agent is designed to be part of an intelligent supervisory control system, and to grant the wireless sensor network gateway as much latitude in meeting its objectives as possible while maintaining the performance of control loops that incorporate wireless paths, thus adding to the safety and reliability of future wireless networked control systems. In this discussion we deal with data rates and control-loop path delays as the two primary concerns; in the future we plan to extend the scope of this agent to handle more issues, such as jitter and wireless sensor network loading effects (e.g., variation of path delays with changes in loading).