Annalisa Liccardo

Remote Didactic Laboratory “G. Savastano,” The Italian Experience for E-Learning at the Technical Universities in the Field of Electrical and Electronic Measurements: Overview on Didactic Experiments

The Remote Didactic Laboratory Laboratorio Didattico Remoto - LA.DI.RE. ldquoG. Savastanordquo is the e-learning measurement laboratory supported by the Italian Ministry of Education and University. It involves about 20 Italian universities and provides students of electric and electronic measurement courses with access to remote measurement laboratories delivering different didactic activities related to measurement experiments. In order to demonstrate the versatility for didactic use, the overview of some experiments is given. The didactic experiments summarized in this paper concern measurement characterization of instruments and communication systems, measurement devices for remote laboratories, basic electrical measurements, magnetic measurements, electromagnetic-interference measurements, and signal processing for measurement applications.

Field Programmable Analog Arrays for Conditioning Ultrasonic Sensors

This paper proposes the use of field programmable analog arrays (FPAAs) as adaptive conditioning blocks for ultrasonic sensors. The uncertainty achievable through this technique, in fact, results very sensitive to the measurement conditions, due to the attenuation affecting the echo during its propagation. Indeed, FPAAs emulate analog circuits whose characteristics have to be dynamically tuned according to different operating conditions. Actually, the signal provided by the ultrasonic sensor is properly processed in order to improve the overall measurement accuracy. In this paper, the prototype of a distance meter based on time-of-flight (TOF) measurement is presented in order to evidence the advantages gained by FPAA features in processing the sensor output to compensate echo attenuation and distortion versus target distance. The prototype working is supervised by a digital signal controller (DSC) whose tasks are: 1) driving the ultrasonic transducer; 2) performing the echo acquisition; 3) tuning on the fly the FPAA features; 4) evaluating the TOF; 5) measuring the target distance; and 6) delivering the final result to the end user. This paper is completed by the results achieved in a number of experimental tests allowing interesting considerations to be drawn. In particular, the experiments confirm the prototype reliability and effectiveness also with ultrasonic echoes characterized by very low signal-to-noise ratios.

Remote Didactic Laboratory “G. Savastano,” The Italian Experience for E-Learning at the Technical Universities in the Field of Electrical and Electronic Measurement: Architecture and Optimization of the Communication Performance Based on Thin Client Technology

The Remote Didactic Laboratory Laboratorio Didattico Remoto -LA.DI.RE. “G. Savastano” is an e-learning measurement laboratory supported by the Italian Ministry of Education and University. It provides the students of electric and electronic measurement courses with access to remote measurement laboratories, delivering different didactic activities related to measurement experiments. The core of the software architecture is the integration of the Learning Management System (LMS) with the remotely accessible measurement laboratories through web services and thin client paradigm, providing a new approach to remote experiments on measurement instrumentation. The overview of this paper is on the different solutions concerning the thin client technology, and the solution implemented is described. This solution takes into account the delivered services to students and teachers and permits optimization of the communication performances. The results of the comparison among the performances of different implementations of the thin client paradigm highlight the advantages of the adopted solution. As a consequence, the description of the thin client protocol implemented, together with the presentation of the LMS and delivered services given in a previous paper, makes an exhaustive analysis of the software architecture of the LA.DI.RE. “G. Savastano.”

ANOVA-Based Approach for DAC Diagnostics

In order to assess the performance of digital-to-analog converters (DAC) the attention is generally focused on the integral nonlinearity INL. Useful diagnostic tools to detect the causes of poor linearity are the linearity and intermodulation errors, which can be evaluated from INL measurements. Linearity and intermodulation errors highlight and quantify erroneous calibration and unwanted interactions between current sources inside the DAC hardware. Unfortunately, their estimates, particularly those related to high-order intermodulation errors are characterized by high uncertainty. On the base of their very uncertain value, it is difficult to establish if interactions represent relevant factors or not. It is shown that by means of the analysis of variance (ANOVA) the relevance of intermodulation errors can be assessed from a limited set counting a minimum of two INL measurements. ANOVA is in fact capable of distinguishing if the variance in INL measurements has to be addressed to active factors or noise, even if the effect of each factor is widespread upon different elements of the INL array and in different combinations with the other factors.

Modeling DAC Output Waveforms

Digital-to-analog converters (DACs) are widely employed in control and automation, test and measurement, and communication systems. However, guidelines for the definition of static and dynamic features of DACs, as well as models capable of describing the different effects of the major nonidealities or drawbacks the DAC can suffer from, are still incomplete. This paper presents a new model capable of describing the functioning of a real DAC affected by horizontal quantization, clock modulation, vertical quantization and integral nonlinearity. The model permits evaluating the effects of the aforementioned nonidealities through straightforward formulas, which are characterized by a low computational burden. Results of experiments conducted on a real DAC to verify the reliability of the model are also shown.

On the Web Service-Based Remote Didactical Laboratory: Further Developments and Improvements

In the paper, the authors report the improvements brought to the remote didactical laboratory, a project to which they have been working for the last two years as presented in P. Daponte et al. (2004). The project has risen from the need to reduce laboratory load, due to the increasing number of undergraduates in Italian University; successively, jointly with the realization of an e-Learning portal for Electric and Electronic Measurement courses, it has represented a way to provide the laboratory experiences to students attending on-line courses. Through the remote laboratory, students are able to execute measurements controlling real instruments, only by means of a common browser. In order to make the laboratory flexible and to grant freedom from software to users, a solution based on Web services, realized in Visual Basic .NET, has been chosen. The recent work has been focuses on the management of connections and queues, for whose aim SQL databases have been involved

Test Equipment for DAC's Performance Assessment: Design and Characterization

In this paper, the authors present a new practicable method and the related measurement station for digital-to-analog converters (DAC) characterization. The method relies on the accurate reconstruction of a sine-wave test signal generated by the DAC under test based on the simultaneous acquisitions of the signal attained by filtering the DAC output and the difference between the DAC output and the filter output. Thus, due to straightforward data processing, the signal generated by the DAC is gained with a resolution much better than the resolution (usually poor) of the analog-to-digital converter (ADC) exploited for the acquisition. The main feature of the method is the ease of implementation that requires only traditional electronics and actual measurement instrumentation. In this paper, the authors also suggest simple rules aimed at evaluating the resolution achievable by each guessed measurement station. To confirm the expected encouraging outcomes, experimental results obtained through a measurement station implemented by using a two-channel 8-bit digital scope and based on the presented method are discussed. In particular, signals generated by 12- and 14-bit DACs have been acquired and processed with the measurement station and reconstructed, with a resolution greater than 17 equivalent bits, due to the proposed method.

On the suitability of compressive sampling for the measurement of electrical power quality

The deeper interconnection and the increasing presence of active devices on the electrical networks is raising many issues concerning with the monitoring of Power Quality phenomena. Voltage parameters related to the supply of electricity and current parameters related to the working of electrical apparatuses have to be monitored as accurately as possible. To this aim specific international standards impose strict measurement methods and complex measurement instrument architectures, usually based on the computation of real time Fast Fourier Transforms, to be adopted for the purpose. In particular, considering poly-phase systems, four currents and four voltages have to be detected, synchronized, measured and analyzed with good accuracy and spectral resolution. This imposes to the measurement the calculation of eight FFTs in a very short time. These requirements conflicts with the need of cost-effective measurement instruments required by spread and distributed monitoring systems in many points of the electrical plant. To face this issues this paper proposes the study and the tuning of compressive sampling (CS) techniques capable of assuring reliable reconstruction of the signal of interest from very low acquired samples. In particular, to make the CS use more feasible, the authors have also exploited some peculiarities of the CS approach in order to reduce the computational burden usually associated with the mere application of its acquisition and reconstruction protocol. Preliminary results confirm the applicability of the proposed solution.

A virtual instrument for estimation of optimal calibration intervals by a decision reliability approach

This paper leads to provide a methodological procedure, in order to establish optimal calibration intervals according to the reference standards. At this aim a virtual instrument has been developed to perform the proposed procedure. Generally speaking, the goal of a calibration process is to reduce out-of-tolerance occurrences to an acceptable level with respect to the desired quality target. The inevitable calibration uncertainty contributions can affect the measurement capability, and an inappropriate estimation of these aspects could lead to incorrect calibration intervals. So, the proposed methods base themselves on a statistical procedure for the evaluation of the impact of calibration process uncertainty on the decision risks. The adopted statistical approach is suitable for estimating the maintenance time needed to meet desired reliability goals. By evaluating the erroneous decision probabilities regarding the in-tolerance state within fixed limits, the statistical and metrological features of the calibration process take part in computing the most reliable interval according to an acceptable decision reliability target. The proposed methodology presents full compliance with the standards of the sector and the guidelines of ISO-9000 for quality assurance.

Design and assessment of a low-cost, electromyographically controlled, prosthetic hand

The study reported here explored the design and realization of a low-cost, electromyographically controlled hand prosthesis for amputees living in developing countries. The developed prosthesis is composed of a light aluminum structure with opposing fingers connected to a DC motor that imparts only the movement of grasp. Problems associated with surface electromyographic signal acquisition and processing, motor control, and evaluation of grasp force were addressed, with the goal of minimizing cost and ensuring easy assembly. Simple analog front ends amplify and condition the electromyographic signals registered from two antagonist muscles by surface electrodes. Analog signals are sampled at 1 kHz and processed by a microcontroller that drives the motor with a supply voltage proportional to the muscular contraction, performing the opening and closing of the opposing fingers. Reliable measurements of the level of muscle contractions were obtained by specific digital processing: real-time operators implementing the root mean square value, mean absolute value, standard deviation, and mean absolute differential value were compared in terms of efficiency to estimate the EMG envelope, computational load, and time delay. The mean absolute value operator was adopted at a time window of 64 milliseconds. A suitable calibration procedure was proposed to overcome problems associated with the wide variation of electromyograph amplitude and background noise depending on the specific patient’s muscles selected. A pulse-width modulated signal drives the DC motor, allowing closing and opening of the prosthesis. The relationship between the motor-driver signal and the actual hand-grasp force developed by the prosthesis was measured using a hand-held grip dynamometer. The resulting force was proportional to current for moderate values of current and then saturated. The motor torque, and, in turn, the force elicited, can be measured by sensing the current absorbed by the motor. Therefore, the grasp force can be opportunely limited or controlled. The cost of the only electronic and mechanical components of the electromyographically controlled hand was about US