This thesis is an effort to develop closed-loop control strategies on computer networks and study their stability in the presence of network delays and packet losses. An algorithm using predictors was designed to ensure the system stability in presence of network delays and packet losses. A single actuator magnetic ball levitation system was used as a test bed to validate the proposed algorithm. A brief study of real-time requirements of the networked control system is presented and a client-server architecture is developed using real-time operating environment to implement the proposed algorithm. Real-time performance of the communication on Ethernet based on user datagram protocol (UDP) was explored and UDP is presented as a suitable protocol for networked control systems. Predictors were designed based on parametric estimation models. Autoregressive (AR) and autoregressive moving average (ARMA) models of various orders were designed using MATLAB and an eighth order AR model was adopted based on the best-fit criterion. The system output was predicted several steps ahead using these predictors and control output was calculated using the predictions. This control output output was used in the events of excessive network delays to maintain system stability. Experiments employing simulations of consecutive packet losses and network delays were performed to validate the satisfactory performance of the predictor based algorithm. The current system compensates for up to 20 percent data losses in the network without loosing stability.

This thesis is an effort to develop closed-loop control strategies on computer networks and study their stability in the presence of network delays and packet losses. An algorithm using predictors was designed to ensure the system stability in presence of network delays and packet losses. A single actuator magnetic ball levitation system was used as a test bed to validate the proposed algorithm. A brief study of real-time requirements of the networked control system is presented and a client-server architecture is developed using real-time operating environment to implement the proposed algorithm. Real-time performance of the communication on Ethernet based on user datagram protocol (UDP) was explored and UDP is presented as a suitable protocol for networked control systems. Predictors were designed based on parametric estimation models. Autoregressive (AR) and autoregressive moving average (ARMA) models of various orders were designed using MATLAB and an eighth order AR model was adopted based on the best-fit criterion. The system output was predicted several steps ahead using these predictors and control output was calculated using the predictions. This control output output was used in the events of excessive network delays to maintain system stability. Experiments employing simulations of consecutive packet losses and network delays were performed to validate the satisfactory performance of the predictor based algorithm. The current system compensates for up to 20 percent data losses in the network without loosing stability.

International Telemetering Conference Proceedings / October 28-31, 1996 / Town and Country Hotel and Convention Center, San Diego, California / The White Sands Missile Range (WSMR) Water Supply Control System (WSCS) controls and monitors the water wells, tanks and booster pumps located at the southern end of the missile range. Figure 1 is an overview of the WSMR water supply system. The WSCS provides water for approximately 90 square miles of the 3,700 square mile missile range. The WSCS was designed and installed in 1990 and in need of upgrading and repair. The system was evaluated and found to be only moderately functional. The WSCS consists of an IBM compatible personal computer (PC) based user interface, located at the WSMR Water Plant and Fire Dept. and industrial-type computers called Programmable Logic Controller (PLC) based stations at the Water Plant, water wells and tanks. The stations communicate over a 400 MHz radio half-duplex link. The serial message utilizes the Cyclic Redundancy Check (CRC) and Block Check Character (BBC) type of error checking. The Master station controls pumping by downloading pump settings to the slave stations. The slave stations upload data to the master such as tank level, pump status, energy usage, gallons of water pumped and various alarms. The system was analyzed and the design was found to be sound. The system did require improvements. These improvements include adding surge suppressors, software upgrades, absolute reading flow rate sensors, and providing adequate environmental cooling for the control system. Procedures for periodic maintenance and calibration of the sensors and schedules for radio equipment maintenance were also developed. Software modifications to reduce WSMR energy usage by reducing pumping during peak energy demand times are being integrated into the WSCS. The peak energy demand times are determined by historical energy usage data.

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This work reports the development of an approach to computer-aided control system design (CACSD). Of primary concern is the quality of co-operation between the designer and his computer. In order to achieve an effective co-operation, we propose a conceptual view of the CACSD problem to the designer, and develop a framework for the computer. The conceptual view is named Generalized Cooperative Search (GCS), which suggests the designer to treat a CACSD problem as a search problem, in which he and the computer co-operate to locate satisfactory designs among sets of candidates. The framework is Interactive Multi-Objective Programming (IMOP), which defines the level of abstraction as well as the organization of the design facilities in the computer. While IMOP methods and control system design methods provide readily usable tools organized by the framework, a design strategy is developed to guide the designer in their effective use. The strategy is a two-level plan of the design process which helps the designer to conduct his search problems as ones of IMOP. He constructs parametrized sets of candidate designs using the design methods (innovates in level I) and matches his design wishes with the design possibilities amongst these candidates using the IMOP methods (trade-offs in level II). The advantages of this approach are (1) a proper emphasis is put on an effective designer-computer co-operation, the designer is supported rather than forced to follow any planned course of actions; (2) a uniform trade-off among design objectives receive their long due attention and (3) it is pluralistic and different design methods may be combined for their respective strengths. The work conducted is likely to be the first integrated approach to designing control systems by search, and may even be the first which supports the principal design stages (formulation, generation and evaluation) in a co-ordinated as well as most general manner. The proposed approach has a promising prospect of being one for the general areas of computer-aided design in engineering and decision support systems in scientific management.

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