A Simplified Method to Calculate Failure Times in Fault-Tolerant Systems

A simplified method is presented to calculate moments of failure time and residual lifetime of a fault-tolerant system. The method is based on recent results in queueing theory. Its effectiveness is illustrated by considering a dual repairable system from the literature

A study of the selection of microcomputer architectures to automate planetary spacecraft power systems

Performance and reliability models of alternate microcomputer architectures as a methodology for optimizing system design were examined. A methodology for selecting an optimum microcomputer architecture for autonomous operation of planetary spacecraft power systems was developed. Various microcomputer system architectures are analyzed to determine their application to spacecraft power systems. It is suggested that no standardization formula or common set of guidelines exists which provides an optimum configuration for a given set of specifications

Performability of Integrated Networked Control Systems

A direct sensor to actuator communication model (S2A) for unmodified Ethernet-based Networked Control Systems (NCSs) is presented in this research. A comparison is made between the S2A model and a previously introduced model including an in-loop controller node. OMNET simulations showed the success of the S2A model in meeting system delay with strict zero packet loss (with no over-delayed packets) requirements. The S2A model also showed a reduction in the end-to-end delay of control packets from sensor nodes to actuator nodes in both Fast and Gigabit switched Ethernet-Based. Another major improvement for the S2A model is accommodating the increase in the amount of additional load compared to the in-loop model. Two different controller-level fault-tolerant models for Ethernet-based Networked Control Systems (NCSs) are also presented in this research. These models are studied using unmodified Fast and Gigabit Ethernet. The first is an in-loop fault-tolerant controller model while the second is a fault-tolerant direct Sensor to Actuator (S2A) model. Both models were shown via OMNeT++ simulations to succeed in meeting system end-to-end delay with strict zero packet loss (with no over-delayed packets) requirements. Although, it was shown that the S2A model has a lower end-to-end delay than the in-loop controller model, the fault-tolerant in-loop model performs better than the fault-tolerant S2A model in terms of less total end-to-end delay in the fault-free situation. While, on the other hand, in the scenario with the failed controller(s), the S2A model was shown to have less total end-to-end delay. Performability analysis between the two fault-tolerant models is studied and compared using fast Ethernet links relating controller failure with reward, depending on the system state. Meeting control system\u27s deadline is essential in Networked Control Systems and failing to meet this deadline represents a failure of the system. Therefore, the reward is considered to be how far is the total end-to-end delay in each state in each model from the system deadline. A case study is presented that simultaneously investigates the failure on the controller level with reward

Low cost computer subsystem for the Solar Electric Propulsion Stage (SEPS)

The Solar Electric Propulsion Stage (SEPS) subsystem which consists of the computer, custom input/output (I/O) unit, and tape recorder for mass storage of telemetry data was studied. Computer software and interface requirements were developed along with computer and I/O unit design parameters. Redundancy implementation was emphasized. Reliability analysis was performed for the complete command computer sybsystem. A SEPS fault tolerant memory breadboard was constructed and its operation demonstrated

Some extensions to reliability modeling and optimization of networked systems

Ph.DDOCTOR OF PHILOSOPH

The reliability of small digital controllers

Increasing use is being made of small digital controllers in Industry and Commerce. The failure of such controllers is important since it may cause either plant to become unsafe or the interruption of production. Fault tolerant techniques are discussed for improving the reliability of digital controllers with special reference to the development of a hybrid electromechanical gas governor, whose electronic controller is an example of a small digital controller. Three microprocessors are used in a two out of three majority voting configuration and the memory is Hamming code protected. Redundancy techniques are used to protect against faults in other parts of the controller and it will tolerate most classes of transient fault. When comparing designs or attempting to meet reliability criteria, it is necessary to predict the reliability of a system and its individual components. Several sources of failure rate prediction are compared and the wide variation in the failure rates of integrated circuits is highlighted. The comparison concludes by recommending which reliability data source is likely to be most accurate for each type of component. The gas governor is an example of a repairable system and analysis is developed for predicting the improvement in reliability for repairable redundant systems and for determining the optimum maintenance and repair times for equipment. The testing of redundant systems is difficult because of their complexity, and under certain circumstances the redundancy can mask design faults. Testing methods using complex test equipment are described, as well as the testing of the experimental controller. A review is included of other fault-tolerant systems. Although the work on large computers is not directly applicable to small controllers, many of the techniques can be used