Carlo Offelli

Digital time-of-flight measurement for ultrasonic sensors

Ultrasonic sensor measurements are mostly based on the determination of the time of flight (TOF). The authors present the development of a digital algorithm for pulse-echo measurement applications, based on the use of a cross-correlation function to determine the TOF. Some experimental results are presented, and the possibility of realizing a low-cost real-time measurement system is considered. >

Interpolation techniques for real-time multifrequency waveform analysis

It is well-known that in discrete-Fourier-transform- (DFT-) based waveform analysis of multifrequency signals, spectral parameter accuracy can be increased by windowing the time samples and interpolating the DFT coefficients. It is shown that some relationships used in interpolation are affected very little by the number of processed samples, so that only the characteristics of the analyzed signal and the required accuracy affect the choice of this parameter. In particular, this makes the approach well suited for real-time analysis of signals with slowly time-varying spectra. Polynomial approximations of some relationships reduce the processing effort and, allow a greater freedom in the choice of the window functions, improving both accuracy and frequency resolution. >

A Web-based distributed virtual educational laboratory

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 students 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.

The influence of windowing on the accuracy of multifrequency signal parameter estimation

The author investigates the influence of windowing on the accuracy of a frequency-domain procedure suitable for real-time estimations of multifrequency signal parameters. Imposing very weak assumptions about the statistical description of the noise, simple and accurate expressions for the estimator variances are established. They allow both the evaluation of the result accuracy and the design of the measurement procedure. Simulation results confirm the validity of the presented analysis. >

A client-server architecture for distributed measurement systems

This paper describes a client-server architecture for the remote control of instrumentation over the Internet network. The proposed solution allows multi-user, multi-instruments sessions to be obtained by means of a queueing process and provides instrument locking capability. Client applications can be easily developed by using conventional high-level programming languages or well-assessed virtual instrumentation frameworks. Performance tests are reported, which show the low overhead due to network operations with respect to the direct control of the instruments.

A frequency-domain procedure for accurate real-time signal parameter measurement

A method for real-time measurement of multifrequency waveforms based on the evaluation of certain energy parameters is discussed. Very low processing effort is achieved by means of a frequency-domain approach, whereas amplitude, frequency, and phase of each spectral component are obtained with high accuracy. Unlike other frequency-domain methods, the proposed procedure provides accurate results even with a small number of analyzed samples and with measurements taken over a short time interval; therefore, real-time tracking of time-varying signals can be achieved. >

A/D converter performance analysis by a frequency-domain approach

An analysis of the frequency domain approach in the test of analog-to-digital convertors (ADCs) is presented. Following the introduction of a spectral analysis algorithm based on the use of windows with minimum sidelobe energy, expressions are given to determine ADC performance parameters. Corrections are introduced to improve accuracy in practical cases, and simulation results are presented to support the discussion. The approach presented is sufficiently precise in the characterization of a device, even with data records of comparatively small size. Provided the appropriate correction factors are taken into account in some determinations, the accuracy is not dissimilar to that of other test methods, with the advantage that both data acquisition and data processing procedures are fairly simple.<<ETX>>

Weighting effect on the discrete time Fourier transform of noisy signals

The effect of weighting on the uncertainty of the discrete time Fourier transform (DTFT) samples of a signal corrupted by additive noise is investigated. Making very weak assumptions, it is shown how the adopted window sequence and the autocovariance function of the noise affect the second-order stochastic moments of the frequency-domain data. The relationship obtained extends the results reported in the literature and is useful in many frequency-domain estimation problems. It is shown how the knowledge of the second-order moments of the transform has allowed the application of the least squares technique for the estimation of the parameters of a multifrequency signal in the frequency-domain. The estimator obtained is very useful when high-accuracy results are required under real-time constraints. The procedure exhibits a better accuracy than similar frequency-domain methods proposed in the literature. >

Analysis of dampled sinusoidal signals via a frequency domain interpolation algorithm

An algorithm for the estimation of the parameters that characterize a linear combination of damped sinusoids is presented. The procedure is based on an interpolation scheme applied to the discrete Fourier transform samples. At first, a single damped exponential signal is analyzed; then the results are extended to multiple damped sinewaves. Numerical simulations show the good accuracy obtained under various measurement conditions; both the effects of spectral interference and wideband noise are considered, proving the reliability of the proposed method in a number of engineering applications. >

Real-time high accuracy measurement of multifrequency waveforms

This paper discusses the operating principles and the main characteristics of a digital instrument for multifrequency signal analysis. The instrument provides real-time performance in a frequency range of 5–6 kHz with high measurement accuracy, obtained by combined windowing and interpolation of computed discrete Fourier transform (DFT) coefficients. Its hardware structure and measurement software for real-time operation are thoroughly illustrated and experimental results are given.