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This paper describes the most important factors influencing the aluminum electrolyte capacitor showing, in particular, the effect of temperature on the lifetime of this device. The automation of the measurement system, with the oven interfaced with a PC, was also completed to control all the involved parameters.

Optical machines with a vision system containing a video camera are designed to perform contact-less three-dimensional measurements. They are becoming more widely used in the industrial sector because of the many possibilities for automation they permit and because of the speed and economies in measurement tasks that can consequently be obtained. Within dimensional control these machines introduce significant characteristics of flexibility, savings and reliability. Therefore the purpose is to identify the principal metrological characteristics of such machines and so characterise the metrological traceability of the measurements obtained from them. The aim is to qualify each part of the optical machine as well as on the whole. Previously, no metrological traceability of this equipment has been provided in primary metrology, either at national (SIT—Sistema di Taratura in Italia—Calibration System in Italy) or at international level (EA–European co-operation for Accreditation). For this reason we develop a mathematical model that permits the evaluation of the measurement uncertainties in the use of such a device. The purpose is to obtain the certification of the measurement results furnished by the optical machine in as broad a context as possible. The experimental results of the tests are introduced for validating the proposed method. This paper provides the basis of the expression of the uncertainty of a measurement result obtained using the optical measurement machines and it shows the necessary requirements for the numerical evaluation of such uncertainty.

This paper describes a novel approach to the evaluation of the errors associated with the sampling strategy and the windowing process in digital spectral analysis. The proposed procedure, which is based on the introduction of a general expression for the estimation of input signal spectral components capable of separately pointing out the different sources of error, has been applied to the cascade of any number of rectangular windows in presence of periodic sampling. In addition, the approach has been further developed by assuming that the initial sampling time instant could be randomized, so that each spectral component estimated can be considered as a random variable, described through the classic statistical parameters. These parameters quantify the uncertainty associated with the windowing process considered and the sampling scheme adopted. In this paper, they have been theoretically deduced in a closed form in the case of a cascade of two and three rectangular windows respectively, along with a generalisation to the cascade of any number of elements, and compared with those of the single window in terms of the specific errors due to the sampling and windowing (i.e. resolution, leakage and aliasing). In particular, it has been shown that the cascaded technique can carry out a substantial reduction of the uncertainty associated with the input signal harmonic estimates. The comparison between theoretical findings and simulations is provided, showing a very good agreement.

A nonlinear dynamic "black box" model for sample-hold and analogue to digital conversion devices (S/H-ADCs) is proposed in this paper. It derives from the expansion of a Volterra-like series (previously introduced by authors for the general-purpose modelling of nonlinear dynamic systems) and it is based on a discrete convolution in the time domain, which describes the nonlinear dynamics of the system. The model carries out a functional description of the S/H-ADC nonlinear behaviour as the sum of two blocks which take separately into account the static and the purely dynamic contributions. Model characterization can be performed by means of a simple and reliable measurement procedure and the model analytical representation allows an easy implementation in the framework of commercial available CAD tools for circuit analysis and design. Preliminary experimental results, which validate the proposed approach, are presented in the paper together with some examples which show model capabilities in characterizing the device nonidealities under both DC and large-signal operating conditions.

The empirical “black-box” characterization of non-linear systems with memory is a complex problem which cannot be dealt with by means of a unique, general-purpose mathematical approach such as the Volterra series. In fact, from a metrological point of view, the feasibility and reliability of the measurement procedure must be the criterion on the basis of which any mathematical approach for modelling purposes must be evaluated. This paper describes different solutions for the behavioural identification of non-linear dynamic systems, all based on a modified Volterra series, which are characterized by a reduced number of operators with respect to the classical Volterra approach. The operator reduction, which does not affect the accuracy of the obtained models if a mild assumption on the system memory time duration is satisfied, allows a reliable extraction of the model parameters by means of conventional instrumentation, without the need for the generation of complicated input probing signals or additional approximations. A detailed discussion is provided in order to estimate when each of the proposed approaches can be practically used, by pointing out the hypotheses that must be taken into account in order to minimise the modified series truncation errors. Experimental examples, showing the validity of the proposed approaches, are given in the last section of the paper, as well as a comparison between the performances of the different solutions when applied to the important field of electron device characterization.

A new technique for power spectrum analysis is introduced, theoretically evaluated, and experimentally verified with a prototype. This technique is based on the estimate of the autocorrelation function for different delays. The proposed sampling strategy is random in the time domain and equally spaced, synchronous with the signal, in the delay domain, It is shown that the estimate of the power spectral components is asymptotically unbiased, and the experimental results are also given.

A different procedure for evaluating the errors introduced by the equally-spaced sampling technique in the asynchronous spectral analysis of a periodic signal was introduced. It is based on the assumption that the initial sampling instant can be randomized so that each estimated spectral component can be considered a random variable characterized by its statistical parameters. The theoretical expressions of these parameters were deduced and compared with the simulated ones denoting a very good agreement between them.

A new model has been proposed for the characterisation of the non-linear dynamic effects of a S/H-ADC device and a new mathematical approach has been introduced to describe its non-ideal dynamic behaviour. The measurement procedure to deduce the parameters of the proposed model is given together with the experimental results on a commercial device.

Heart rate is one of the main physiological variables to monitor the energetic behaviour of observed animals and also to study the influence of the environment around these animals. In 1996 at the University of Florence, the Departments of Animal Biology and Genetic and the Electronic Engineering, started a joint research project monitoring the cardiac activity of animals and building a hardware/software device in order to measure the instantaneous and average heart frequency of animals with a skeletal barrier.

A broadband digital harmonic vector voltmeter proposed previously and studied theoretically by the authors was implemented using a special-purpose, random sampling strategy, to avoid the bandwidth limitations due to the finite conversion time of the sample-and-hold and analog-to-digital-conversion (S/H-ADC) devices. The experimental results have shown that the bandwidth of the instrument is not limited by the finite conversion time of S/H-ADC devices, since good accuracy can be achieved even when the average sampling frequency is much lower than the signal bandwidth. The amplitude and phase uncertainty, with sinusoidal test signals up to 1 MHz and an average sampling rate of 10 kHz, was found to be lower than 3% and 0.03 rad, respectively. For more careful testing of the broadband performance of our instrument, we also carried out two-frequency, variable order harmonic measurements, which showed good accuracy (amplitude error less than 1.5% and phase error less than 0.03 rad) with harmonics up to 300 kHz. Reasonable accuracy (i.e., sufficient to correctly reconstruct the actual signal waveform) was also found with a highly distorted square-wave signal.

A new method for time-interval measurements is described and the results of measurements on a prototype are given. This method uses a virtually periodic exponential signal as the reference clock and consists of measuring both the phase deviation and the number of cycles of this clock signal between the beginning and the end of the unknown time-interval. The use of two auxiliary sinusoidal signals in order to measure the phase of the corresponding periodic exponential signal is discussed, also considering the main causes of error. The functional block diagram of the prototype is described in detail and the measurement results show that a resolution improvement of two orders of magnitude with respect to the period of the clock signal can easily be obtained.

Circulating levels of atrial natriuretic factor (ANF), the education of myocardial contractility (evaluated by ejection fraction, EF) and different pain intensity were assessed in patients with uncomplicated acute myocardial infarction (AMI). We investigated the relationships between ANF, or EF, and pain intensity by identifying appropriate statistical methods and introducing a procedure for pain intensity measurement. Pain in AMI is variable in intensity, often severe and in some instances intolerable, but in over 20% of AMI patients it may be absent. By using plasma ANF concentration and self-report of AMI pain as parameters, we described a statistical method verifying that AMI patients can be categorized into two significantly different groups: pain and no-pain. Pain is a purely personal experience that includes both the original pain sensation (OPS), depending on the intensity of the stimulus, and the individual emotional reaction component (ER). We developed a method to deduce the OPS from the patient's self-report of AMI pain and then devised an instrument which estimates the ER of each patient by applying electrical stimuli of different intensities. The procedure to disclose a significant correlation (not present by using the self-report of AMI pain) between OPS and ANF, or EF in pain patients is described. The inverse correlation found between EF and OPS suggests that the extent of myocardial damage may play a role in AMI pain onset and affect its intensity. However, when ANF concentration exceeds a threshold value, AMI patients reported only an unpleasant sensation; this result indicates that ANF may be involved in preventing AMI pain. The statistical method introduced for the comparison between the regression lines of ANF and EF in pain and no-pain patients showed that the interdependence between ANF and EF is not influenced by pain, confirming that EF is the major trigger for ANF release in AMI.

A basic optical time-domain reflectometry (OTDR) configuration is shown. An optical pulse typically 10-10000 ns long is launched into a test fiber via a directional coupler. The backscatter radiation from the fiber is detected and processed and the backscatter signature displayed. Since the backscatter power is directly related to the fiber loss and its arrival time back at the OTDR to the distance traveled, it is for these two parameters that the OTDR needs primarily to be calibrated. Several methods for carrying this out are described in the IEC 61746 document. In this paper, we present measurements made with the recirculating delay line, which is a passive method among the distance scale calibrating ones.

This paper evaluates the effect of time-jitter in the equally spaced sampling wattmeters on the hypothesis of equal effects in the two channels and a jitter uncorrelated with the input signals. It is shown that time-jitter, which is a random fluctuation with respect to the nominal sampling time, introduces a frequency limitation which is evaluated together with that due to the sampling strategy and filtering algorithm. The theoretical results are compared with the simulated ones. >

A recursive random-sampling strategy is proposed for the implementation of a digital broadband wattmeter. In this strategy each sampling instant is obtained by adding to the preceding one a predetermined constant lag plus a random increment. In order to correlate the measurement uncertainty to the bandwidth, the asymptotic mean-square error arising from the sampling strategy and the filtering algorithm is evaluated and analyzed; it has been shown that the proposed sampling strategy does not limit the bandwidth of the instrument if an appropriate statistical distribution of the random increments is selected. The theoretical results are compared with those obtained by simulating the measurement process. >

A symbolic formulation approach is applied to the problem of computing testability features of analog linear networks. The program, SAPTES, obtained by following this approach is presented. The program can be a very useful tool for designers and researchers in the field of linear analog circuits. SAPTES, which is written in LISP and runs on MS-DOS personal computers, is able to compute the testability of linear circuits of rather high complexity (composed of tens of components and nodes). Computational times range from a few tens of seconds to some tens of minutes on medium speed computers. The program is easily transportable to workstations or a mainframe, and, for the mainframe, program performance will considerably increase. >

Nowadays spectrum analyzers permit to achieve relatively simple real time data processing of the input signal. In the near future complex mathematical routines shall be more and more easily implemented using the numerical processing capabilities incorporated into the modern instrument architectures. In this work is demonstrated that the detection and measurement accuracy of the amplitude of a weak signal in the equivalent noise at the input of a spectrum analyzer can be dramatically enhanced employing signal processing techniques. The feasibility of the signal amplitude estimation method is experimentally demonstrated through an application to real world data.

In this paper techniques for the compensation of the overall non-idealities affecting the operation of digital data acquisition channels are proposed, which are based on the exploitation of a non-linear dynamic model of these measurement sub-systems. It is shown how the non-linear dynamic equations of the model, which inherently describe both the static and the dynamic non-linearities associated with the behaviour of the channel, can be numerically inverted, and more accurate information on the properties of the system input signal achieved, starting from the corrupted sample records available at channel output. The procedure is based on the identification of a non-linear problem on the basis of the Harmonic-Balance approach, which can be solved by means of different recursive algorithms according to the application-dependent best trade-off between numerical convergence robustness and computational cost.

A model of comparison loss in microwave power meter calibration is considered in the case when the standard power meter used for calibration and the signal generator to which this meter and the meter to be calibrated are connected are reflectionless. The uncertainty associated with an estimate of the model output quantity, viz., the ratio of the power absorbed by the meter being calibrated and that absorbed by the standard, is to be evaluated given estimates of the model input quantities, the standard uncertainties associated with those estimates, and a correlation coefficient relating to the estimates. This problem is addressed using three approaches, viz.: (1) the GUM uncertainty framework; (2) the propagation of distributions, implemented using a Monte Carlo method; and (3) analytical or semi-analytical. Circumstances in which approach: (1) can provide invalid solutions, whereas (2) provides sound numerical solutions, are identified

The maximum entropy approach is a flexible and powerful tool for assigning a probability distribution to a measurable quantity treated as a random variable subjected to known moment constraints. The aim of this paper is to describe how the principle of maximum entropy may be used to transform information about the value of a quantity into a probability density function (pdf) that reflects exactly that information and nothing else. This principle will be applied to common cases of metrological interest, where different kinds of information are available. The derivation of the pdf is given in each case, and two practical examples with numerical results are reported to demonstrate the efficiency of the maximum entropy method

This paper discusses the possibility of using Bayesian inference methods and entropy optimization principles for the evaluation of uncertainty in a measurement process. In particular, the proposed approach is applied to the recalibration of a measurement device which incorporates a calibrated reference quantity. An a priori estimate and an uncertainty for the reference quantity are supposed to be available from a previous calibration. The adopted method is shown to produce a posteriori estimates for the reference quantity, regarded as the recalibrated value and for the measurand which are correlated.

Metrological comparisons test and quantify the agreement of the measurements performed in different laboratories to support equivalence statements. Central to the area of key comparison is the degree of equivalence of measurement standards and a "region" of compatibility including all the measurement results that are consistent with reference values may be individuated. The level of confidence of that region is a parameter qualifying the comparison. This paper considers an approach concerning the representation of a compatibility region in an interlaboratory comparison process based on the introduction of the probability intervals and evaluates the level of confidence of that region, giving an estimation of the uncertainty of the comparison process.

In this work, the law of propagation of uncertainty is studied for complex system with nonlinear properties. Sensitivity analysis is carried out using the Taylor's series expansion of higher-order terms than the usual one presented in the ISO (GUM). An experimental problem is considered to verify the obtained theoretical results and to asses the validity of the implemented formulation.

The offer provided by an electric utility combines many characteristics of a service together with the continuous delivery of electricity as a product. The quality of electricity as a processed material, resulting from a continuous process and having immediate delivery in continuous flow can he adversely affected by the end-use processes of other customers, as well as by the continuous-process reliability. Hence, the guidelines endorsed by ISO Standard 9004-3 for the quality management of processed materials must be suitably tailored in the case of electricity. Problems that must be dealt with to control the characteristics critical to quality of electricity are discussed. In this connection, measurement activities oriented to quality management are considered, mainly to outline unsolved problems.

A method for the performance evaluation of digital measurement instruments based on asynchronous sampling and nonlinear signal conversion is proposed. The authors propose a performance index for the comparison of different asynchronous strategies and develop the analytical form of that index for two sampling techniques, equally spaced and random. The idea is to interpret the instantaneous output of the instrument as a discrete random variable with a uniform distribution over the successive occasions of measurement. Thus, the asymptotic variance of the reading can be a sum of contributions, each of which is obtained by weighting the contributions relative to each spectral component of the signal according to a frequency-dependent coefficient which is assumed to the performance index. >

A new interesting technique for fault diagnosis in non-linear analog systems is presented. The approach is based on a neural network interpolator for the construction of a fault dictionary in the frequency domain. A multi-layered architecture with one hidden layer is chosen in order to locate and to identify the most likely faulty element of the System Under Test (SUT). >

This paper presents a digital harmonic vector voltmeter based on a random asynchronous sampling strategy. The measurement procedure is described and the problem of estimating both the error due to the time discretization and to the estimation of the periodic complex exponential associated with the input reference signal is discussed. >

The explicit recognition of uncertainty is central to any measurement process. In this work a computer-intensive approach is adopted to the estimation of uncertainty at a given coverage probability, that is, at a given region of confidence in a measurement process. The method is adaptable to a large range of situations and is based on the use of Monte Carlo approximation and bootstrap resampling iteration. An experimental model is examined to understand the applicability of the numerical technique and to check the potentiality of the proposed method.

This paper describes a power spectrum analyzer whose bandwidth is not limited by the mean sampling time. The procedure is based on the estimation of the spectral components of the autocorrelation function of the input signal through the simultaneous random sampling of the given input signal and its randomly "delayed copy". The samples are therefore randomly taken in a double-dimension space, time, and delay. By using a random process in the time domain with a recursive mean previously introduced by the authors in order to avoid any bandwidth limitation due to the sampling strategy, it is shown both theoretically and through simulation that the estimate of the power spectral components is asymptotically unbiased on the unique hypothesis of a synchronized random sampling in the delay domain, i.e., the sampling delays are uniformly distributed in an interval equal to the period of the input signal. The simulation results confirm the theoretical findings.

This paper evaluates the effect of time-jitters in the equally spaced sampling wattmeters on the hypothesis of jitters uncorrelated with the input signals. The general case of two distinct time-jitters is considered, one common to the two channels and the other different for each one of them. The performance of the wattmeter has been evaluated by considering the asymptotic statistic parameters of the output. It has been shown that the different time-jitters introduce a bias and that both time-jitters contribute to the variance of the output. In any case, time-jitters introduce further bandwidth limitations which must be taken into account in the wattmeter accuracy evaluation. The theoretical results have been compared with simulated and experimental findings. Experimental results were obtained with a prototype in which both common and different time-jitters were separately added to the equally spaced sampling instants of the two input channels. In both cases, all the results were in good agreement with theoretical expectations.

The paper presents a theoretical study on the convergence properties of the new modified Volterra-like modeling approach for non-linear dynamic systems in comparison with the classical Volterra series representation. In particular, the assumptions which enable a single-fold non-linear convolution integral to be adopted also in the presence of strong non-linearities are pointed out. Experimental and simulation results which confirm the theoretical considerations are also provided.