John V. James

Microprocessor Based Data Acquisition for Analysis of Engine Performance

A computer system for data acquisition and analysis has been assembled and tested as an engineering development tool for advanced diagnostic techniques. This system includes custom hardware and software to facilitate high-speed acquisition of data, both digital and analog. The digital data is acquired via a time-stamping procedure, whereas the analog signals are sampled with a multiplexed A/D converter. By simultaneously monitoring both types of signals available to the engine control module, the performance parameters of an engine can be analyzed as functions of either time or engine position. Examples of misfire detection are given which illustrate the need for accurate digital data. Other examples include high-resolution velocity profiles of a defective engine, and samples of signals obtained from a normal engine.

Absorption technique for OH measurements and calibration

An absorption technique is described which utilizes a stabilized frequency-doubled tunable dye laser and a long-path White cell with high mirror reflectivities both in the red and UV. In laboratory conditions we have been able to obtain routinely a detection sensitivity of 3 parts in 10(6) over absorption paths <1 m in length and a detection sensitivity of ~6 parts in 10(5) over an absorption path of the order of 1 km. The latter number corresponds to 3 x 10(6) OH molecules/cm(3), and therefore the technique should be particularly useful for calibration of our fluorescence instrument for OH measurements. However, the presence of atmospheric fluctuations coupled with intensity variation accompanying frequency scanning appears to degrade the detection sensitivity in outdoor ambient conditions, thus making it unlikely that this technique can be employed for direct OH monitoring.

Shot noise limited detection of OH using the technique of laser induced fluorescence

This paper reports nearly shot noise limited detection of OH using the technique of laser-induced fluorescence. A lidar configuration is used to excite fluorescence in a large volume, and a narrow-bandwidth interference filter provides spectral discrimination. This arrangement alleviates the effect of ozone interference and facilitates image processing at relatively close distances. The detection limit is determined mainly by the shot noise of the solar background. Ground-based measurements in Dearborn indicate a detection limit of ~2 × 106 OH/cm3 over a 40-min acquisition period. In favorable conditions, a comparable detection limit is also expected for airborne measurements.

Performance Evaluation of Dynamic Monitoring Systems: The Waterfall Chart

Abstract Computers are increasingly employed to monitor the performance of complex systems. An important issue is how to evaluate the performance of such monitors. In this article we introduce a three‐dimensional representation that we call a “waterfall chart” of the probability of an alarm as a function of time and the condition of the system. It combines and shows the conceptual relationship between the cumulative distribution function of the run length and the power function. The value of this tool is illustrated with an application to Pages one‐sided Cusum algorithm. However, it can be applied in general for any monitoring system.

Signal Processing by Neural Networks to Create ``Virtual'' Sensors and Model-Based Diagnostics

This paper discusses the application of advanced neural network methods to the development of diagnostics for complex, nonlinear dynamical systems, for which accurate, first-principles models either do no exist or are difficult to derive. We consider two approaches to detect and identify failures in these systems. First, neural networks are trained to act as virtual sensors that emulate the performance of laboratory-quality sensors; this approach provides higher quality diagnostic information than is available directly from production sensors. Second, neural networks are trained to emulate nominal (fault-free) system behavior; model-based fault diagnosis is subsequently achieved by detecting significant deviations between actual and predicted system performance. We present experimental evidence of the viability of both approaches for a difficult automotive diagnostic task.

Characterization of ion implanted silicon: correlation of optical measurements with microstructural observations

Abstract Laser, electron and ion beam techniques were used to probe the near surface crystallography of silicon implanted with various ion species. Optical third harmonic radiation (THR) generated in reflection with short laser pulses was found to be a sensitive monitor of lattice damage. The isotropic part, or the part of the third harmonic signal which does not vary with crystalline orientation, reaches a minimum value at a critical ion dose and increases slightly at higher doses. The anisotropic part, or the part which exhibits the symmetry of the lattice, becomes negligible at the critical dose and remains so at higher doses. The critical dose depends on the mass and energy of the implanted ion. The consquences of making the measurements in air as opposed to making them in vacuum are discussed. Transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS) and ion channeling were used to correlate the nonlinear optical response (the intensity and polarization of the generated THR) with the near surface microstructure. Samples with the critical ion dose exhibited an amorphous layer containing residual crystalline particles near the surface. As the dose increases above the critical level the residual crystallites disappear and the surface layer becomes completely amorphous. Further implantation has no effect on the nonlinear response.

Accelerated testing of on-board diagnostics

Modern products frequently feature monitors designed to detect actual or impending malfunctions. False alarms (Type I errors) or excessive delays in detecting real malfunctions (Type II errors) can seriously reduce monitor utility. Sound engineering practice includes physical evaluation of error rates. Type II error rates are relatively easy to evaluate empirically. However, adequate evaluation of a low Type I error rate is difficult without using accelerated testing concepts, inducing false alarms using artificially low thresholds and then selecting production thresholds by appropriate extrapolation, as outlined here. This acceleration methodology allows for informed determination of detection thresholds and confidence in monitor performance with substantial reductions over current alternatives in time and cost required for monitor development. Copyright