NASA ground terminal communication equipment: Automated fault isolation expert systems

This paper describes the prototype expert systems that diagnose the Distribution and Switching System I and II (DSS1 and DSS2), Statistical Multiplexers (SM), and Multiplexer and Demultiplexer systems (MDM) at the NASA Ground Terminal (NGT) located at White Sands, New Mexico. A system-level fault isolation expert system monitors the activities of a selected data stream, verifies that the fault exists in the NGT and identifies the faulty equipment. Equipment-level fault isolation expert systems will be invoked to isolate the fault to a Line Replaceable Unit (LRU) level. Input and sometimes output data stream activities for the equipment are available. The system-level fault isolation expert system will compare the equipment input and output status for a data stream and perform loopback tests (if necessary) to isolate the faulty equipment. The equipment-level fault isolation system utilizes the process of elimination and/or the maintenance personnel's fault isolation experience stored in its knowledge base. The DSS1, DSS2, and SM fault isolation systems, using the knowledge of the current equipment configuration and the equipment circuitry, will issue a set of test connections according to the predefined rules. The faulty component or board can be identified by the expert system by analyzing the test results. The MDM fault isolation system correlates the failure symptoms with the faulty component based on maintenance personnel experience. The faulty component can be determined by knowing the failure symptoms.

The NGT fault isolation prototype is implemented in Prolog, C, and VP-Expert, on an IBM AT compatible workstation. The DSS1, DSS2, SM, and MDM equipment simulators are implemented in PASCAL. The equipment simulator receives connection commands and responds with status for the expert system according to the assigned faulty component in the equipment. The DSS1 fault isolation expert system was converted to C language from VP-Expert and integrated into the NGT automation software for offline switch diagnoses.

Potentially, the NGT fault isolation algorithms can be used for the DSS1, SM, and MDM located at Goddard Space Flight Center (GSFC). The prototype could be a training tool for the NGT and NASA Communications (Nascom) Network maintenance personnel.     

一款蓝牙车载免提故障的维修--免提喇叭无声的故障的维修

主要描述了一款蓝牙车载免提的故障维修。该蓝牙车载蓝牙部分电路主要使用了CSR蓝牙芯片,回音处理部分电路主要使用了Fortemedia公司的FM1073.主要描述了该免提的基本原理以及一种无声的故障的修理。     

Availability model for self test and repair in fault tolerant FPGA-based systems

Dynamically reconfigurable Field Programmable Gate Array （dr-FPGA） based electronic systems on board mission-critical systems are highly susceptible to radiation induced hazards that may lead to faults in the logic or in the configuration memory.The aim of our research is to characterize self-test and repair processes in Fault Tolerant （FT） dr-FPGA systems in the presence of environmental faults and explore their interrelationships.We develop a Continuous Time Markov Chain （CTMC）model that captures the high level fail-repair processes on a dr-FPGA with periodic online Built-In Self-Test （BIST） and scrubbing to detect and repair faults with minimum latency.Simulation results reveal that given an average fault interval of 36 s,an optimum self-test interval of 48.3 s drives the system to spend 13％ of its time in self-tests,remain in safe working states for 76％ of its time and face risky fault-prone states for only 7％ of its time.Further,we demonstrate that a well-tuned repair strategy boosts overall system availability,minimizes the occurrence of unsafe states,and accommodates a larger range of fault rates within which the system availability remains stable within 10％ of its maximum level.     

A general repair, proportional-hazards, framework to model complex repairable systems

A system (machine) is observed to operate in 1 of 2 modes. The most common mode is loaded (or regular) operation. Occasionally the system is placed in an unloaded state, wherein while the system is mechanically still operating, it is assumed that the failure intensity is lower due to this reduction in operating intensity. A proportional hazards framework is used to capture this potential reduction in failure intensity due to switching of operating modes. In either operating condition, analyzed maintenance-records indicate that the system was occasionally shut down, and either a minor or a major repair was undertaken. Furthermore, despite such repairs, it is observed that both modes of operation (loaded or unloaded) resulted in random failures. On failure, 1 of 3 actions are taken: (1) failures were minimally repaired, (2) given a minor repair, or (3) given a major repair. Both minor and major repairs are assumed to impact the intensity following a virtual age process of the general form proposed by Kijima. This research develops a statistical model of such an operating/maintenance environment. Its purpose is to quantify the impacts of performing these repair actions on the failure intensities. Field data from an industrial-setting demonstrate that appropriate parameter estimates for such multiple phenomena can be obtained. Providing a richer, more detailed, modeling of the failure intensity of a system incorporating both operating conditions and repair effects has important ramifications for maintenance planning. This paper refers to related research, in which optimal timing of maintenance repairs depends fundamentally on the failure rate of the system.     

Implicit deductive fault simulation for complex delay fault models

This paper introduces an implicit version of the well-known deductive fault simulation technique suitable to delay fault models with an exponential number of faults. The proposed method calculates the fault coverage by generating lists of entities for each line during a single topological circuit traversal. Each stored entity only contains a number and a subset of the test vectors. No delay faults are stored, and no special data structures are required. There are significant differences between the presented implicit method and fault coverage using deductive fault simulation. The method is shown to be effective for delay the path and segment delay fault models.     

Instantaneous power compensation in three-phase systems by using p-q-r theory

This paper proposes a novel power compensation algorithm in three-phase four-wire systems by using p-q-r theory. The p-q-r theory is compared with two previous instantaneous power theories, p-q theory and cross vector theory. The p-q-r theory provides two-degrees of freedom to control the system currents by only compensating the instantaneous imaginary power without using any energy storage element. The definition of powers maintains power conservation, and agrees well with the general understanding of power. Simulation results show the superiority of p-q-r theory both in definition and compensation.     

色散补偿光纤传输系统的最佳补偿方案

研究了采用色散补偿光纤传输系统的最佳补偿方案,经研究发现,混合补偿方案可以大大减小光纤非线性效应的影响,提高系统传输距离.此外,还对非归零码(NRZ)和归零码(RZ)的传输性能进行了比较.     

CT故障的系统化功能化维修分析

设备是医院进行诊断的最主要基础,不过CT设备由于使用的特殊性和设备使用环境的特殊性,其维修管理一向是一个制约CT大规模诊断的关键环节。对于CT医疗设备的操作与运行中常见的设备故障,不但要根据故障进行科学的处理,而且要保障CT医疗设备的最佳工作状态,提高医疗临床的服务质量。CT设备的故障应该还是有规律可循的,因为许多故障是可以进行系统化与功能化预防的。本文为此具体探讨了CT故障诊断中系统化功能化维修思路的建立。     

场扫描电路的检测与故障维修

场扫描电路是电视形成图像信号的一个重要组成部分,通过对黑白电视场扫描电路原理的分析、电路功能的测试,以及对可能出现的故障进行详细的分析,在分析的基础上对电路故障进行检修,从而实现场扫描电路能够很好的实现它的功能,达到正确扫描的目的.     

ARCHGEN: Automated synthesis of analog systems

High-level design of analog systems is an open area that needs to be addressed with the emerging trend of integrating mixed analog-digital systems. Design methods compatible across the analog-digital boundaries would expedite the design process, and in this paper we address analog high-level design issues. An approach for systems-level synthesis of a class of analog systems is presented. A behavioral level for the analog domain is characterized in terms of state equations and transfer functions in the continuous and discrete domains. State-space representations are generated from transfer function specifications that exhibit system level characteristics such as controllability and observability as, well as decoupled and parallel architectures. These state-space representations are synthesized into behavioral-level, technology-independent architectures composed of analog functional components. An intermediate architecture in a circuit implementation technology is synthesized from the behavioral architecture. The various algorithmic procedures for synthesis are implemented in the program ARCHGEN. Behavioral simulation is used for architecture verification and design space exploration     

Analysis of fault tolerant computer systems

In many critical applications of digital systems, fault tolerance has been an essential architectural attribute for achieving high reliability. In recent years, the concept of the performability of such systems has drawn the attention of many researchers. In this paper we develop a general Markov model for fault tolerant computer systems. Various important performance measures, including the performability measures as well as some new performance measures, are treated in a unified manner. Furthermore, general and efficient computational procedures are developed for calculating these performance measures based on the uniformization technique of Keilson. A numerical example is given to illustrate the computational procedures developed.     

Dispersion compensation for optical fiber systems

Much of the currently embedded optical fiber was originally designed for light with a wavelength of 1.3 microns. If this fiber is to be used with tomorrow's optically amplified, high-speed, long span-length lightwave system operating at 1.5 microns, the chromatic dispersion in the fiber must be compensated. Dispersion compensation will be required in long-haul l0 Gb/s systems using conventional fiber. Many compensation techniques have been demonstrated and they exhibit a variety of different and often complimentary properties. Transmitter compensation techniques are the most easily implemented but provide a limited amount of compensation. The most commercially advanced technique is negative dispersion fiber. Chirped Bragg gratings are advancing rapidly, but will always be hampered by their narrow bandwidth. The adoption of any particular technique for use in a high-speed network will depend on the constraints imposed by the, as yet, undefined network architecture     

On fault tolerance in manufacturing systems

The physical and control structure of manufacturing systems is described, and a hierarchical model for supporting fault tolerance is proposed. The main advantage of the model is that it allows different fault tolerance and recovery techniques to be used in different segments of the network. To help in the choice of specific techniques in particular network segments, a set of metrics to evaluate fault tolerance techniques is presented along with preliminary ideas about integrating the different techniques. Design issues in applying the model to a given manufacturing system are discussed     

Adaptive nonlinear compensation for CDMA communication systems

This paper deals with nonlinear compensation in code-division multiple-access communications systems. We analyze the performance of the generalized cerebellar model articulation controller neural network in two problems: predistortion in nonlinear transmitters and adaptive interference cancellation in multiuser and multipath scenarios. Our examples demonstrate the performance of the compensators in typical mobile channels     

高速光通信系统中的色散补偿技术

高速光纤通信系统中，色散补偿和极化模色散补偿是提高信噪比、改善系统性能的必要手段。本文介绍了几种常用商用传输光纤及其色散特性，分析了相应的色散补偿技术，重点分析了其中普遍采用的色散补偿光纤技术。     

Linearization and feedforward compensation for switching systems

The linearization of a switching system including a feedforward compensation for power supply perturbations is obtained by the addition of a high-frequency signal. A general expression for the required shape and amplitude of this high-frequency signal is derived. The method is analyzed for its application to AC phase control systems. The method is outlined for the case of a DC electric motor phase control. It is then generalized to any nonlinear switching system     

Neuro-fuzzy networks saturation compensation of DC motor systems

A neuro-fuzzy networks (NFN) saturation compensation scheme for DC motor systems is presented. The scheme that leads to stability, command following, and disturbance rejection is rigorously proved. The on-line weights tuning law, the overall closed loop performance, and the boundedness of the NFN weights are derived and guaranteed based on the Lyapunov approach. The actuator saturation is assumed to be unknown and the saturation compensator is inserted into a feedforward path. The simulation and experimental results show that the proposed scheme can effectively compensate for the saturation nonlinearity in the presence of system uncertainty.     

Transmission distance of in-line amplifier systems withgroup-velocity-dispersion compensation

Group-velocity dispersion (GVD) compensation in in-line amplifier systems is evaluated from the viewpoint of improving the transmission distance. The nonlinear Schrodinger equation, which simulates signal propagation in optical fibers, is numerically evaluated to clarify the optimum configuration for GVD compensation. It is shown that the optimum amount of GVD compensation is about 100% of the GVD experienced by the transmitted signal. The optimum compensation interval is found to be a function of the bit rate, signal power, and dispersion parameter. For dispersion parameter values ranging from about -0.1 ps/nm/km to -10 ps/nm/km, and an amplifier noise figure of about 6 dB, the optimum compensation configuration can eliminate the GVD from in-line amplifier systems, thus improving transmission distances to those limited by self-phase modulation and higher-order GVD