Showing papers in "IEEE Transactions on Instrumentation and Measurement in 2000"

Identification of time-variant directional mobile radio channels

Abstract: For the identification of the time-variant, directional structure of the mobile radio channel impulse response (CIR), a broadband vector channel sounder is described. The measurement procedure relies on periodic multifrequency excitation signals, correlation processing, and joint delay-azimuth super-resolution based on the two-dimensional (2-D) unitary ESPRIT algorithm. Problems of imperfect receiver and antenna performance as well as antenna array calibration methods are discussed. Correlation analysis of the directional impulse response records is performed in the time-frequency-spatial domain and the corresponding Doppler-delay-angular domain. Results from measurements in the 5.2 GHz frequency range in an industrial environment are presented.

Infrared image registration and high-resolution reconstruction using multiple translationally shifted aliased video frames

Abstract: Forward looking infrared (FLIR) detector arrays generally produce spatially undersampled images because the FLIR arrays cannot be made dense enough to yield a sufficiently high spatial sampling frequency. Multi-frame techniques, such as microscanning, are an effective means of reducing aliasing and increasing resolution in images produced by staring imaging systems. These techniques involve interlacing a set of image frames that have been shifted with respect to each other during acquisition. The FLIR system is mounted on a moving platform, such as an aircraft, and the vibrations associated with the platform are used to generate the shifts. Since a fixed number of image frames is required, and the shifts are random, the acquired frames will not fall on a uniformly spaced grid. Furthermore, some of the acquired frames may have almost similar shifts thus making them unusable for high-resolution image reconstruction. In this paper, we utilize a gradient-based registration algorithm to estimate the shifts between the acquired frames and then use a weighted nearest-neighbor approach for placing the frames onto a uniform grid to form a final high-resolution image. Blurring by the detector and optics of the imaging system limits the increase in image resolution when microscanning is attempted at sub-pixel movements of less than half the detector width. We resolve this difficulty by the application of the Wiener filter, designed using the modulation transfer function (MTF) of the imaging system, to the high-resolution image. Simulation and experimental results are presented to verify the effectiveness of the proposed technique. The techniques proposed herein are significantly faster than alternate techniques, and are found to be especially suitable for real-time applications.

Properties of the IEEE-STD-1057 four-parameter sine wave fit algorithm

Abstract: The IEEE Standard 1057 (IEEE-STD-1057) provides algorithms for fitting the parameters of a sine wave to noisy discrete time observations. The fit is obtained as an approximate minimizer of the sum of squared errors, i.e., the difference between observations and model output. The contributions of this paper include a comparison of the performance of the four-parameter algorithm in the standard with the Cramer-Rao lower bound on accuracy, and with the performance of a nonlinear least squares approach. It is shown that the algorithm of IEEE-STD-1057 provides accurate estimates for Gaussian and quantization noise. In the Gaussian scenario it provides estimates with performance close to the derived lower bound. In severe conditions with noisy data covering only a fraction of a period, however, it is shown to have inferior performance compared with a one-dimensional search of a concentrated cost function.

A Web-based distributed virtual educational laboratory

Abstract: Evolution and cost of measurement equipment, continuous training, and distance learning make it difficult to provide a complete set of updated workbenches to every student. For a preliminary familiarization and experimentation with instrumentation and measurement procedures, the use of virtual equipment is often considered more than sufficient from the didactic point of view, while the hands-on approach with real instrumentation and measurement systems still remains necessary to complete and refine the student's practical expertise. Creation and distribution of workbenches in networked computer laboratories therefore becomes attractive and convenient. This paper describes specification and design of a geographically distributed system based on commercially standard components.

An extended complex Kalman filter for frequency measurement of distorted signals

Abstract: The design of an extended complex Kalman filter for the measurement of power system frequency has been presented in this paper. The design principles and the validity of the model have been outlined. A complex model has been developed to track a distorted signal that belongs to a power system. The model inherently takes care of the frequency measurement along with the amplitude and phase of the signals. The theory has been applied to standard test signals representing the worst-case measurement and network conditions in a typical power system. The proposed algorithm is suitable for real-time applications where the measurement noise and other disturbances are high. The complex quantities can be conveniently handled using a floating point processor. Comparison of the results of the proposed method with those obtained from a real extended Kalman filter reveals the superior performance of the former method.

Calibration and performance evaluation of a 3-D imaging sensor based on the projection of structured light

Abstract: In this paper, the procedure developed to calibrate a whole-field optical profilometer and the evaluation of the measurement performance of the system are presented. The sensor is based on the projection of structured light and on active triangulation. The dependence of the measurements on the geometric parameters of the system is shown, as well as the criterion to calibrate the system. From the extensive set or experiments carried out to evaluate the measurement performance, good linearity has been observed, and an overall mean value of the measurement error equal to 40 /spl mu/m, with a variability of about /spl plusmn/35 /spl mu/m has been estimated.

Distributed measurement and control based on the IEEE 1451 smart transducer interface standards

Abstract: This paper details a framework developed at NIST that highlights the standardization efforts going on within the various levels of an Internet-based distributed measurement and control (DMC) system. The framework highlights state-of-the-art hardware and software techniques used at NIST to design, implement, and deploy next-generation Internet-based DMC applications and systems. The framework targets three important areas of standardization including transducer interfaces, open network communication, and distributed application development. An implementation of a DMC application on the Internet based on the NIST framework is also described. The paper concludes with a brief introduction to other research activities at NIST culminating from this core Internet-based DMC research.

Interpolating time counter with 100 ps resolution on a single FPGA device

Abstract: This paper describes the logic and performance of an interpolating time counter integrated on a single FPGA device. The resolution of 100 ps (LSB) was obtained because of the new design of the FPGA delay lines used for precise time-to-digital conversion, and the use of enhanced CMOS FPGA technology. The worst-case random error of 170 ps has been lowered to 70 ps by software correction of the nonlinearity of the delay lines. The counter can measure time intervals from 0-43 s and frequency up to 200 MHz. The maximum power consumption of the counter chip is 260 mW.

Reactive power measurement using the wavelet transform

Abstract: This paper provides the theoretical basis for the measurement of reactive and distortion powers from the wavelet transforms. The measurement of reactive power relies on the use of broad-band phase-shift networks to create concurrent in-phase currents and quadrature voltages. The wavelet real power computation resulting from these 90/spl deg/ phase-shift networks yields the reactive power associated with each wavelet frequency level or subband. The distortion power at each wavelet subband is then derived from the real, reactive and apparent powers of the subband, where the apparent power is the product of the v, i element pair's subband rms voltage and current. The advantage of viewing the real and reactive powers. In the wavelet domain is that the domain preserves both the frequency and time relationship of these powers. In addition, the reactive power associated with each wavelet subband is a signed quantity and thus has a direction associated with it. This permits tracking the reactive power flow in each subband through the power system.

Real-time 3-D spatial-temporal dual-polarized measurement of wideband radio channel at mobile station

Abstract: This paper describes a measurement system enabling the complete real-time characterization of the wideband radio channel. The system is based on a wideband radio channel sounder and a spherical antenna array, and it aims to describe the three-dimensional (3-D) spatial radio channel seen by the mobile terminal, including polarization. This information is highly valuable in designing antennas for mobile terminals. The spatial properties of the measurement system are analyzed through test measurements in an anechoic chamber. The system has a 40/spl deg/ spatial resolution and a 17 dB cross polarization discrimination. The values are well above those of a small mobile terminal antenna. The dynamic range in the spatial domain is 12 dB. The measurement is very fast, which makes real-time channel acquisition practical at normal mobile speeds.

Composite real-time image processing for railways track profile measurement

Abstract: Checking railway status is critical to guarantee high operating safety, proper maintenance schedule, and low maintenance and operating costs. This operation consists of the analysis of the rail profile and level as well as overall geometry and undulation. Traditional detection systems are based on mechanical devices in contact with the track. Innovative approaches are based on laser scanning and image analysis. This paper presents an efficient composite technique for track profile extraction with real-time image processing. High throughput is obtained by algorithmic prefiltering to restrict the image area containing the track profile, while high accuracy is achieved by neural reconstruction of the profile itself.

Phase-shift ambiguity in microwave dielectric properties measurements

Abstract: Phase measurements of the transmission coefficient are important when used for the dielectric characterization of materials. They are required for industrial material monitoring applications, where the phase is correlated with parameters such as moisture content and density, which need to be continuously determined, However, when the thickness of the material under test is greater than the wavelength in the material, a phase problem is encountered. Two methods are proposed to solve this problem. The first is based on the selection of the appropriate material thickness; the second requires the use of measurements at two frequencies. Advantages and limitations of both methods are discussed, and numerical validations are given for particulate materials.

A microwave inverse scattering technique for image reconstruction based on a genetic algorithm

Abstract: The problem of reconstructing locations, shapes, and dielectric permittivity distributions of two-dimensional dielectric objects from measurements of the scattered electric field is addressed. A numerical approach is proposed which is based on a multi-illumination multiview processing. In particular, the inverse problem is recast as a global nonlinear optimization problem, which is solved by a genetic algorithm. The final objective of the approach is the image reconstruction of highly contrasted bodies.

An intelligent pressure sensor using neural networks

Abstract: In this paper, we propose a scheme of an intelligent capacitive pressure sensor (CPS) using an artificial neural network (ANN). A switched-capacitor circuit (SCC) converts the change in capacitance of the pressure-sensor into an equivalent voltage. The effect of change in environmental conditions on the CPS and subsequently upon the output of the SCC is nonlinear in nature. Especially, change in ambient temperature causes response characteristics of the CPS to become highly nonlinear, and complex signal processing may be required to obtain correct readout. The proposed ANN-based scheme incorporates intelligence into the sensor. It is revealed from the simulation studies that this CPS model can provide correct pressure readout within /spl plusmn/1% error (full scale) over a range of temperature variations from -20/spl deg/C to 70/spl deg/C. Two ANN schemes, direct modeling and inverse modeling of a CPS, are reported. The former modeling technique enables an estimate of the nonlinear sensor characteristics, whereas the latter technique estimates the applied pressure which is used for direct digital readout. When there is a change in ambient temperature, the ANN automatically compensates for this change based on the distributive information stored in its weights.

A measurement procedure for viscous and coulomb friction

Abstract: This paper presents a viscous and coulomb friction measurement procedure for mechanical systems equipped with high-precision velocity sensors. The proposed method exploits the structure of the velocity response predicted by several standard friction models when a force or torque is applied in a ramp fashion. Experimental results show the high accuracy of the proposed measurement procedure.

Microwave near-field reflection property analysis of concrete for material content determination

Abstract: One of the most important parameters associated with concrete is its compressive strength. Currently, there is no reliable nondestructive testing technique that is capable of robust determination of this parameter. Concrete is a heterogeneous mixture composed of water, cement powder, sand (fine aggregate), rocks of various size or grade (coarse aggregate), and air (porosity). Water and cement powder chemically combine into a cement paste binder which, in due curing time, produces concrete with its specified compressive strength. Compressive strength of concrete is strongly influenced by its water-to-cement (w/c) ratio as well as its coarse aggregate-to-cement (ca/c) ratio. Therefore, if these two parameters are determined using a nondestructive testing technique, then they may be correlated to the compressive strength. Near-field microwave nondestructive testing techniques, employing open-ended rectangular waveguide probes, have shown tremendous potential for evaluating concrete constituent make-up. In this paper, the results of an extensive set of measurements, using these probes, are presented. The results demonstrate that the statistical distribution of the multiple measurements of the magnitude of reflection coefficient of concrete specimens with various constituent make-ups follows two well-known distributions as a function of frequency. It is shown that for the specimens investigated this distribution is Gaussian at 10 GHz and uniform at 3 GHz. Furthermore, the standard deviation of the measured magnitude of reflection coefficient at 10 GHz is shown to correlate well with ca/c ratio, whereas, the mean of this parameter at 3 GHz is correlated well with w/c ratio. Subsequently, these parameters may be used in conjunction with well established formulae or a look-up table to determine the compressive strength of a given concrete specimen.

Selection of test nodes for analog fault diagnosis in dictionary approach

Abstract: In this paper, the selection of test nodes has been studied extensively and efficient techniques are proposed. Two broad categories of methods called inclusion methods and exclusion methods are suggested. Strategies are presented to select or delete a test node without affecting the diagnosis capabilities. Examples show that these strategies give a lesser number of test nodes some times. Starting from the fault-wise integer coded table of the test circuit, sorting is employed to generate valid sets and minimal sets. The order of computation of these methods is shown to depend linearly on number of test nodes. It is also proportional to (f log f) where "f" is the number of faults. This is much faster than well-known methods. The concept of minimal set of test nodes is new in analog circuit fault diagnosis. Polynomial time algorithms are proposed in this paper for the first time to generate such sets.

Automatic calibration of analog and digital measuring instruments using computer vision

Abstract: This paper presents an automatic calibration system capable of calibrating measuring instruments that do not have a digital interface. Image analysis algorithms are used to automatically determine the instrument reading. It can be used with analog and with digital displays. The maximum uncertainty in the detection of the pointer's position in analog instruments is less than the human eye can discriminate.

Wavelet-transform-based method of analysis for Lamb-wave ultrasonic NDE signals

Abstract: A new acoustic nondestructive method using Lamb waves as a probe is presented. These waves are generated and received by an ElectroMagnetic Acoustic Transducer (EMAT). The position of flaws in the structure under test is computed from the time of arrival of the main peak of the reflected signal. Due to the noisy nature of the received signal, we use a wavelet transform algorithm to extract the required time information. The main advantage of such a multi-scale method of signal analysis is to be suitable for peak detection problems especially in highly noisy environments. We explain how we proceed to do the feature extraction, and we propose two methods for reconstructing the image of the inspected structure. Results of real-world ultrasonic Lamb waves signal analysis are presented. In addition, to test the noise robustness of the method, the case of synthetic noisy signals is also treated.

Using cereal grain permittivity for sensing moisture content

Abstract: A brief history of cereal grain moisture measurement by sensing the electrical properties of grain is presented. The basic principles are also described for using radio-frequency (RF) and microwave dielectric properties, or permittivity, of grain for sensing moisture through their correlation with moisture content. The development of density-independent functions of the permittivity is explained. The findings of recent research are summarized, which indicate that reliable density-independent moisture content determinations can be realized by measurements on grain at RF and microwave frequencies. Development of these techniques will provide useful instruments for on-line monitoring of moisture content in flowing grain to manage moisture in grain, prevent spoilage in storage and transport, improve processing, and provide information important for yield determinations in precision agriculture applications.

An integrated active-quenching circuit for single-photon avalanche diodes

Abstract: We introduce the first integrated active quenching circuit (I-AQC) that drives an avalanche photodiode (APD) above its breakdown voltage, in order to detect single photons. Based on the I-AQC, we developed a compact and versatile photon-counting module suitable for applications in which very weak optical signals have to be detected, as for instance, photon correlation spectroscopy, luminescence measurements, and laser ranging. The prototype photon-counting module features quenching pulses up to 60 V amplitude, minimum dead time of less than 36 ns, corresponding to a saturated counting rate exceeding 25 Mcounts/s, user-controllable hold-off time, for reducing the afterpulsing effect, and nanosecond gating capability. The power dissipation is 60 mW in stand-by conditions, and the module size is less than 1 cm/spl times/2 cm.

A comprehensive model for power line interference in biopotential measurements

Abstract: Power line interference is a major problem in high-resolution biopotential measurements. Because interference coupling is mostly capacitive, shielding electrode leads and a high common-mode rejection ratio (CMRR) are quite effective in reducing power-line interference but do not completely eliminate it. We propose a model that includes both interference external to the measuring system and interference coming from its internal power supply. Moreover, the model considers interference directly coupled to the measuring electrodes, because, as opposed to connecting leads, electrodes are not usually shielded. Experimental results confirm that reducing interference coupled through electrodes yields a negligible interference. The proposed model can be applied to other differential measurement systems, particularly those involving electrodes or sensors placed far apart.

Noise removal from image data using recursive neurofuzzy filters

Abstract: Neurofuzzy approaches are very promising for nonlinear filtering of noisy images. An original network topology is presented in this work to cope with different noise distributions and mixed noise as well. The multiple-output structure is based on recursive processing. It is able to adapt the filtering action to different kinds of corrupting noise. Fuzzy reasoning embedded into the network structure aims at reducing errors when fine details are processed. Genetic learning yields the appropriate set of network parameters from a collection of training data. Experimental results show that the proposed neurofuzzy technique is very effective and performs significantly better than well-known conventional methods in the literature.

A low-cost laser range finder based on an FMCW-like method

Abstract: The purpose of this paper is to present the prototype of a low-cost laser range finder. It belongs to the flight time measurement category. In this case, the time of flight is converted into a beat frequency proportional to the distance to be measured. This physical conversion is realized with an optical power modulation of the laser beam by a chirped wave. The experimental set-up is detailed with the main functional blocks. Experimental results are provided and the main possible improvements are discussed.

Self-mixing laser speckle velocimeter for blood flow measurement

Abstract: A velocimeter using speckle phenomena in self-mixing laser diodes (SM-LDs) is used to evaluate the blood flow noninvasively. The mean frequency of the speckle signal obtained from the self-mixing laser diode reflects the activity of the blood flow in a certain probing area. The experimental results show that this new type of speckle velocimeter can be useful for the relative evaluation of blood flow in human tissues.

A comparison of wavelength dependent polarization dependent loss measurements in fiber gratings

Abstract: We have measured wavelength dependent Polarization Dependent Loss (PDL) in chirped fiber Bragg gratings for dispersion compensation, grating filters for wavelength add/drop multiplexing and long period gratings for EDFA gain flattening. The PDL is measured in devices used in reflection and in transmission by applying the Jones matrix method, the Mueller matrix method and the polarization scanning method. A comparison of the experimental results and an analysis of the sources of errors are presented.

Correlation of accelerometer and microphone data in the "coin tap test"

Abstract: In the "coin tap test," an operator taps with a coin-like light tool on the structure to be inspected, feeling the subtle difference of impact force and hearing the resulting sound to discriminate defective regions from normal ones. The test remains largely subjective, and there has been considerable uncertainty about the physical principles behind it. Analyzing and comparing the force measured by an accelerometer in the hammer and the resulting sound recorded with a microphone, this paper seeks an understanding of the fundamental principles underlying the individual measurement techniques. It gives a paradigm for sensor fusion via using the data from one modality to select the optimal time window for signal analysis of another modality.

Nonlinear distortions and multisine signals. I. Measuring the best linear approximation

Abstract: This paper examines the effects of nonlinearities on frequency response function measurements using periodic multifrequency signals. A class of broadband pilot test signals is proposed, termed sparse odd multisines, which can be used to establish the system bandwidth and detect nonlinearities. Signals are then defined within this class which allow the measurement of the best linear approximation of a nonlinear system. A comparison is made with related work in this area.

Fuzzy modeling of measurement data acquired from physical sensors

Abstract: The measurement uncertainty in physical sensors is often represented by a probabilistic approach, but such a representation is not always adapted to new intelligent systems. Therefore, a fuzzy representation, based on the possibility theory, can sometimes be preferred. We previously proposed a truncated triangular probability-possibility transformation to be applied to any unimodal and symmetric probability distribution which can be assimilated to one of the four most encountered probability laws (Gaussian, double-exponential, triangular, uniform). In this paper, we propose to build a fuzzy model of data acquired from physical sensors by applying this transformation. For this purpose, a minimum of knowledge about the probabilistic modeling of sensors is required. Three main situations are considered and for each situation, an adapted fuzzy modeling is proposed. Examples of these three situations are based on FM-chirped ultrasonic sensors.

A linear resistance-to-time converter with high resolution

Abstract: A resistance-to-time converter employing a bridge amplifier, an integrator and a comparator is described. While possessing a resolution and linearity of the same order as that of a recently reported resistance-to-frequency converter, the present circuit has the advantage of grounded detecting resistance. Further, no compensation arrangement need be incorporated for maintaining wide-range linearity.