A new, practical approach to maintaining an efficient yet acceptably-performing wireless networked control system

Wireless networked control systems have begun to gain acceptance during the last decade, due to the increased flexibility and lower costs they promise to provide compared with wired installations. 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 safely in process control loops, thus limiting the potential applications and benefits of wireless systems. Wireless control signals face time delay that may degrade the performance of the control loop or even lead to instability. This time delay depends on the network configuration. The sampling rate also has a great impact on the stability and performance of the closed-loop control system over the communication networks, yet the data rate should be minimized to conserve node battery life. The main goal of this paper is to present and discuss a real-time nonlinear control system approach that (1) checks a proposed network configuration to determine the time delay which the control data packets will encounter, and reject any proposed configuration that would lead to poor closed-loop system performance; and (2) determines the minimum acceptable sampled data rate that does not degrade control loop performance excessively. The jacketed continuous stirred-tank reactor will be presented as a typical application, to illustrate and validate this development.