Showing papers on "Fault detection and isolation published in 1996"

Design of unknown input observers and robust fault detection filters

Abstract: Fault detection filters are a special class of observers that can generate directional residuals for the purpose of fault isolation. This paper proposes a new approach to design robust (in the disturbance de-coupling sense) fault detection filters which ensure that the residual vector, generated by this filter, has both robust and directional properties. This is done by combining the unknown input observer and fault detection filter principles. The paper proposes a new full-order unknown input observer, and gives necessary and sufficient conditions for its existence. After the disturbance de-coupling conditions are satisfied, the remaining design freedom can be used to make the residual have the directional property, based on the fault detection filter principle. A nonlinear jet engine system is used to illustrate the robust fault isolation approach presented. It is shown that linearization errors can be approximately treated as unknown disturbances and be de-coupled in the design of a robust fault detect...

Actuator fault diagnosis: an adaptive observer-based technique

Abstract: This paper presents a novel approach for the fault diagnosis of actuators in known deterministic dynamic systems by using an adaptive observer technique. Systems without model uncertainty are initially considered, followed by a discussion of a general situation where the system is subjected to either model uncertainty or external disturbance. Under the assumption that the system state observer can be designed such that the observation error is strictly positive real (SPR), an adaptive diagnostic algorithm is developed to diagnose the fault, and a modified version is proposed for the general system to improve robustness. The method is demonstrated through its application to a simulated second-order system.

The combinatorial design approach to automatic test generation

Abstract: The combinatorial design method substantially reduces testing costs. The authors describe an application in which the method reduced test plan development from one month to less than a week. In several experiments, the method demonstrated good code coverage and fault detection ability.

HOPE: an efficient parallel fault simulator for synchronous sequential circuits

Abstract: HOPE is an efficient parallel fault simulator for synchronous sequential circuits that employs the parallel version of the single fault propagation technique. HOPE is based on an earlier fault simulator railed PROOFS, which employs several heuristics to efficiently drop faults and to avoid simulation of many inactive faults. In this paper, we propose three new techniques that substantially speed up parallel fault simulation: (1) reduction of faults simulated in parallel through mapping nonstem faults to stem faults, (2) a new fault injection method called functional fault injection, and (3) a combination of a static fault ordering method and a dynamic fault ordering method. Based on our experiments, our fault simulator, HOPE, which incorporates the proposed techniques, is about 1.6 times faster than PROOFS for 16 benchmark circuits.

A new approach to on-line turn fault detection in AC motors

Abstract: Turn fault detection is based on the principal that symmetrical (unfaulted) motors powered by symmetrical multiphase voltage sources will have no negative sequence currents flowing in the leads. A turn-to-turn fault will break that symmetry and give rise to a negative sequence current which may then be used as a measure of fault severity or to initiate protective action such as a circuit breaker trip. A new way of looking at the effects of turn faults has been developed that improves sensitivity and speed while reducing the probability of misdetection, taking into account voltage balance, load or voltage variation and instrument errors. The method has been implemented on a PC and tested, in real time, on a specially prepared small motor. Reliable detection of one shorted turn out of 648 turns per phase (in a Y connected motor) was demonstrated with the fault indicator becoming fully developed in two cycles of line frequency after initiation of the fault.

System and method for performing real time data acquisition, process modeling and fault detection of wafer fabrication processes

Abstract: A system and method for detecting faults in wafer fabrication process tools by acquiring real-time process parameter signal data samples used to model the process performed by the process tool. The system includes a computer system including a DAQ device, which acquires the data samples, and a fault detector program which employs a process model program to analyze the data samples for the purpose of detecting faults. The model uses data samples in a reference database acquired from previous known good runs of the process tool. The fault detector notifies a process tool operator of any faults which occur thus potentially avoiding wafer scrap and potentially improving mean time between failures. The fault detector also receives notification of the occurrence of process events from the process tool, such as the start or end of processing a wafer, which the fault detector uses to start and stop the data acquisition, respectively. The fault detector also receives notification of the occurrence of a new process recipe and uses the recipe information to select the appropriate model for modeling the data samples. The fault detector employs a standard data exchange interface, such as DDE, between the fault detector and the model, thus facilitating modular selection of models best suited to the particular fabrication process being modeled. Embodiments are contemplated which use a UPM model, a PCA model, or a neural network model.

An LMI approach to H/sub -//H/sub /spl infin// fault detection observers

Abstract: A new approach, namely the mixed H-/H∞ estimation, to robust fault detection problem for dynamic systems is presented. The H-/H∞ fault detection observer is designed to minimise effects of disturbances on the residual of the observer whilst maximising the effects of faults on the residual signal. This takes into account the robustness of a fault detection observer against disturbances and sensitivity to faults simultaneously. The H-/H∞ fault detection observer problem is actually a mixed H-/H∞ estimation problem. The latter can be further reformulated as a constrained H∞ estimation problem and solved in a mixed linear matrix inequality (LMI) setting.

Altering a pseudo-random bit sequence for scan-based BIST

Abstract: This paper presents a low-overhead scheme for the built-in self-test (BIST) of circuits with scan. Complete (100%) fault coverage is obtained without modifying the function logic and without degrading system performance (beyond using scan). Deterministic test cubes that detect the random-pattern-resistant faults are embedded in a pseudo-random sequence of bits generated by a linear feedback shift register (LFSR). This is accomplished by altering the pseudo-random sequence by adding logic at the LFSR's serial output to "fix" certain bits. A procedure for synthesizing the bit-fixing logic for embedding the test cubes is described. Experimental results indicate that complete fault coverage can be obtained with low hardware overhead. Also, the proposed approach permits the use of small LFSRs for generating the pseudo-random bit sequence. The faults that are not detected because of linear dependencies in the LFSR can be detected by embedding deterministic cubes at the expense of additional bit-fixing logic. Data is presented showing how much additional logic is required for different size LFSRs.

Observer-based supervision and fault detection in robots using nonlinear and fuzzy logic residual evaluation

Abstract: A high degree of automation in flexible production units require powerful tools for supervision and fault detection to maintain quality and productivity. In this paper, an observer-based fault detection method is proposed which makes use of non-measurable process information instead of installing as many sensors as possible. The detection method is reviewed and applied to the fault detection problem in an industrial robot, using a dynamic robot model. The robot model is enhanced by the inclusion of nonlinear friction terms. A new residual evaluation approach of model-based fault detection methods is investigated for processes which exhibit unstructured disturbances, arising from model simplification. The present analytical approaches are applicable only to structured approaches. In this paper a fuzzy-logic approach is presented which is capable to address unstructured disturbances as well. Finally, some practical results for an industrial robot example are presented.

Optimal filtering and robust fault diagnosis of stochastic systems with unknown disturbances

Abstract: The paper studies the optimal filtering and robust fault diagnosis problems for stochastic systems with unknown disturbances. An optimal observer is proposed, which can produce disturbance decoupled state estimation with minimum variance for time varying systems with both noise and unknown disturbances. The existence conditions and the observer design procedure are presented. The output estimation error with disturbance decoupling and minimum variance properties is used as a residual signal. A statistical testing procedure is applied to examine the residual and is used to diagnose faults. The method developed is applied to an illustrative example, and simulation results show that the optimal observer can give good state estimation; the fault detection approach taken is able to detect faults reliably in the presence of both modelling errors and noise.

Evaluation and implementation of a system to eliminate arbitrary load effects in current-based monitoring of induction machines

Abstract: This paper presents a method for removing the load effects from the monitored quantity of the machine. Fault conditions in induction machines cause the magnetic field in the air gap of the machine to be nonuniform. This results in harmonics in the stator current of the motor which can be measured in order to determine the health of the motor. However, variations in the load torque which are not related to the health of the machine typically have exactly the same effect on the load current. Previously presented schemes for current-based condition monitoring ignore the load effect or assume it is known. Therefore, a scheme for determining machine health in the presence of a varying load torque requires some method for separating the two effects. This is accomplished by comparing the actual stator current to a model reference value which includes the load effects. The difference between these two signals provides a filtered quantity, independent of variations of the load, that allows continuous on-line condition monitoring to be conducted without concern for the load condition. Simulation and test results illustrate the effects on the spectrum of the monitored quantity for both constant and eccentric air gaps when in the presence of an oscillating load.

Practical High Impedance Fault Detection for Distribution Feeders

Abstract: Distribution protection systems must balance dependability with security considerations to be practical. This is quite difficult for high-impedance faults. Only highly sensitive algorithms can achieve absolute dependability in detecting very low current faults. This high sensitivity results in a propensity for false tripping, creating a less secure, system and resulting in the potential for decreased service continuity and lower reliability. Researchers at Texas A&M University have balanced fault detection with fault discrimination, resulting in a practical combination of detection algorithms in a commercially viable system. This device has many "intelligent" features, including the ability to analyze and correlate numerous fault characteristics in real time, so that a correct determination of the status of the feeder can be made with a high probability of accuracy. This paper describes the use of multiple algorithms to detect various types of faults and the use of an expert decision maker to decipher incoming data, to determine the status and health of a distribution feeder. Requirements for a practical, secure high-impedance fault relay are also discussed. Finally, Texas A&M has licensed this technology to a commercial partner, which manufactures a device that detects high-impedance faults, in addition to performing numerous other monitoring and protection functions.

Generic fault tolerant platform

Abstract: A fault tolerant platform is provided that comprises two systems running pairs of processes in the active and standby state, one process from each pair running on each system. Each system comprises a fault-tolerance controlling process, first communication channels provided between the fault-tolerance controlling process and the processes in the active or standby state running on its system, and second communication channels provided between the fault-tolerance controlling processes. Management of fault tolerance (that is, promoting a process in a standby state to the active state, and making a process in an active state exit from the active state) is handled by the fault-tolerance controlling processes. A generic management of fault tolerant processes is thus provided in which fault detection and switchover is carried out independently of the applications. The invention thus ensures efficient and coherent switchover between active and standby processes.

Distribution System Reliability Assessment Using Hierarchical Markov Modeling

Abstract: Distribution system reliability assessment is concerned with power availability and power quality at each customer's service entrance. This paper presents a new method, termed hierarchical Markov modeling (HMM), which can perform predictive distribution system reliability assessment. HMM is unique in that it decomposes the reliability model based on power system topology, integrated protection systems and individual protection devices. This structure, which easily accommodates the effects of backup protection, fault isolation and load restoration, is compared to simpler reliability models. HMM is then used to assess the reliability of an existing utility distribution system and to explore the reliability impact of several design improvement options.

Virtual sensor based monitoring and fault detection/classification system and method for semiconductor processing equipment

Abstract: A virtual sensor based monitoring and fault detection/classification system (10) for semiconductor processing equipment (12) is provided. A plurality of equipment sensors (14) are each operable to measure a process condition and provide a signal representing the measured process condition. A plurality of filtering process units (16) are each operable to receive at least one signal from the plurality of equipment sensors (14) and to reduce data represented by the at least one signal and provide filtered data. A plurality of virtual sensors (24) are each operable to receive the filtered data. The plurality of virtual sensors (24) model states of the processing equipment (12) and a work piece in the processing equipment (12). Each virtual sensor is operable to provide an output signal representing an estimated value for the modeled state. A rule based logic system (26) is operable to receive and process the signals provided by the plurality of equipment sensors (14) and the output signals provided by the virtual sensors (24) to monitor processing equipment (12) or to detect and classify faults within the processing equipment (12).

Loop-back test system and method

Abstract: A loop back test system and method for providing local fault detection within the core or macrocell of an integrated I/O interface device on an integrated circuit is disclosed. The system and method of this invention is suitable for use in any I/O interface having both a transmitter and a receiver section. The loop back of input test data from the transmitters output directly to the receiver's input permits fault detection within the core of an integrated I/O interface. By illustration, in a serializer/deserializer I/O, the loop back of serialized, alignment pattern encoded parallel data from the output stage of the I/O transmitter to the receiver's input stage permits identifying faults occurring within the integrated I/O transceiver macrocell. The loop back test system and method of this invention permits fault isolation of within the boundaries of the I/O core and independent of external logic or testers.

FIRE: a fault-independent combinational redundancy identification algorithm

Abstract: FIRE is a novel Fault-Independent algorithm for combinational REdundancy identification. The algorithm is based on a simple concept that a fault which requires a conflict as a necessary condition for its detection is undetectable and hence redundant. FIRE does not use the backtracking-based exhaustive search performed by fault-oriented automatic test generation algorithms, and identifies redundant faults without any search. Our results on benchmark and real circuits indicate that we find a large number of redundancies (about 80% of the combinational redundancies in benchmark circuits), much faster than a test-generation-based approach for redundancy identification. However, FIRE is not guaranteed to identify all redundancies in a circuit.

Application of black-box models to HVAC systems for fault detection

Abstract: This paper describes the application of black-box models for fault detection and diagnosis (FDD) in heating, ventilat-ing, and air-conditioning (HVAC) systems. In this study, mul-tiple-input/single-output (MISO) ARX models and artificial neural network (ANN) models are used. The ARX models are examined for different processes and subprocesses and compared with each other. Two types of models are established--system models and component mod-els. In the case of system models, the HVAC system as a whole is regarded as a black box insteati of as a collection of compo-nent models. With the component model type, the components of the HVAC system are regarded as separate black boxes

High impedance fault detection implementation issues

Abstract: Faults on distribution circuits are normally detected by simple overcurrent relays. Faults through a high impedance such as dry earth or asphalt do not have sufficient current to operate overcurrent relays and must be cleared manually. Such high impedance faults may pose a hazard to the public. Equipment is now commercially available to detect a high percentage of high impedance faults, but use of this equipment introduces operational issues which affect applications. This paper discusses technical as well as nontechnical issues associated with applying high impedance fault detectors. Recognizing all the issues is important to the effective implementation of these new fault detecting techniques.

Error detection and fault isolation for lockstep processor systems

Abstract: A lockstep processor system adds error detection, isolation, and recovery logic to one or more lockstep processor system functions; namely, control outputs, processor inputs, I/O busses, memory address busses, and memory data busses.

Arc burst pattern analysis fault detection system

Abstract: A method and apparatus are provided for detecting an arcing fault on a power line carrying a load current. Parameters indicative of power flow and possible fault events on the line, such as voltage and load current, are monitored and analyzed for an arc burst pattern exhibited by arcing faults in a power system. These arcing faults are detected by identifying bursts of each half-cycle of the fundamental current. Bursts occurring at or near a voltage peak indicate arcing on that phase. Once a faulted phase line is identified, a comparison of the current and voltage reveals whether the fault is located in a downstream direction of power flow toward customers, or upstream toward a generation station. If the fault is located downstream, the line is de-energized, and if located upstream, the line may remain energized to prevent unnecessary power outages.

Integrated gps/inertial fault detection availability

Abstract: Different techniques have been proposed for combining GPS and inertial sensor information, and recent published findings seem to indicate that primary-means integrity availability is achievable with standard 2 nmi/h (95 percent) inertial sensor performance. This paper investigates and quantifies the different inertial effects that contribute to enhanced integrity of the integrated GPS/inertial system, such as coasting or Schuler feedback. A Kalman filter-based integration scheme that preserves the integrity information in an optimal fashion is presented and used to quantify integrity performance. This paper also proposes an approximate model, incorporating the main inertial effects contributing to integrity, that can be used to calculate the achievable horizontal protection level (HPL) at any geographical location and time. This model is used to estimate the availability of fault detection for an integrated GPS/inertial system. In addition, the paper compares the availability of fault detection for the GPS/inertial system with that for other augmentations to provide trade-off information.

Fault detection in an air-handling unit using residual and recursive parameter identification methods

Abstract: A scheme for detecting faults in an air-handling unit using residual and parameter identification methods is presented. Faults can be detected by comparing the normal or expected operating condition data with the abnormal, measured data using residuals. Faults can also be detected by examining unmeasurable parameter changes in a model of a controlled system using a system parameter identification technique. In this study, autoregressive moving average with exogenous input (ARMAX) and autoregressive with exogenous input (ARX) models with both single-input/single-output (SISO) and multi-input/single-output (MISO) structures are examined. Model parameters are determined using the Kalman filter recursive identification method. This approach is tested using experimental data from a laboratory`s variable-air-volume (VAV) air-handling unit operated with and without faults.

Typical faults of air conditioning systems and fault detection by ARX model and extended Kalman filter

Abstract: Since faulty operation of heating, ventilating, and air-conditioning (HVAC) systems is detrimental to energy conservation, and maintenance experts are no longer able to detect faults due to the sophistication of current air-handling units (AHUs), automated fault detection and diagnosis (FDD) is increasingly important In the present study, the results of a survey about typical faults that are commonly encountered in air-handling systems are summarized, and two methods of finding abrupt faults are described To investigate the development of automated fault detection schemes, two methods to detect an abrupt fault are tested, and the effectiveness of the methods is analyzed Both are based on a mathematical model of system dynamics The first one is an autoregressive exogenous (ARX) model and the second is based on an extended Kalman filter It is shown that faults that are difficult to detect by a simple limit checker method can be detected in both cases on the basis of computer simulation by HVACSIM+