Wyniki wyszukiwania - Biblioteka Nauki

1

Uncertainty interval evaluation using the Chi-square and Fisher distributions in the measurement process

100%

Catelani M. , Zanobini A. , Ciani L.

|

2010

|

tom Vol. 17, nr 2

195-204

EN

Referring to the Guide to the Expression of Uncertainty in Measurement (GUM), the paper proposes a theoretical contribution to assess the uncertainty interval, with relative confidence level, in the case of n successive observations. The approach is based on the Chi-square and Fisher distributions and the validity is proved by a numerical example. For a more detailed study of the uncertainty evaluation, a model for the process variability has been also developed.

2

Measurement and Comparison of Reliability Performance of Photovoltaic Power Optimizers for Energy Production

100%

Catelani M. , Ciani L. , Graditi G. , Adinolfi G.

|

tom Vol. 22, nr 1

139--152

EN

Photovoltaic (PV) power optimizers are introduced in PV systems to improve their energetic productivity in presence of mismatching phenomena and not uniform operating conditions. Commercially available converters are characterized by different DC-DC topologies. A promising one is the boost topology with its different versions. It is characterized by its circuital simplicity, few devices and high efficiency values - necessary features for a Distributed Maximum Power Point Tracking (DMPPT) converter. PV power optimizer designs represent a challenging task since they operate in continuously changing operating conditions which strongly influence electronic component properties and thus the performance of complete converters. An aspect to carefully analyze in such applications is the thermal factor. In this paper, a necessity to have a suitable temperature monitoring system to avoid dangerous conditions is underlined In addition, another important requirement for a PV power optimizer is its reliability, since it can suggest a useful information on its diagnostic aspects, maintenance and investments. In fact, a reliable device requires less maintenance services, also improving the economic aspect. The evaluation of the electronic system reliability can be carried out using different reliability prediction models. In this paper, reliability indices, such as the Mean Time Between Failure (MTBF) or the Failure Rate of a Diode Rectification (DR) boost, are calculated using the evaluation of the Military Handbook 217F and Siemens SN29500 prediction models. With the reliability prediction results it has been possible to identify the most critical components of a DMPPT converter and a measurement setup has been developed in order to monitor the component stress level on the temperature, power, voltage, current, and energy in the DMPPT design phase avoiding the occurrence of a failure that might decrease the service life of the equipment.

3

New Galactic Multi-Mode Cepheids from the ASAS-SN Survey

100%

Jurcsik J. , Hajdu G. , Catelani M.

|

tom Vol. 68, No. 4

341--350

EN

A systematic search for multi-mode Cepheids using the database of the ASAS-SN survey has led to the detection of thirteen new double-mode and two triple-mode Cepheids in the Galactic disk. These discoveries have increased the number of Galactic disk multi-mode Cepheids by 33%. One of the new triple-mode variables pulsates simultaneously in the fundamental and in the first and the second radial overtone modes and the other in the first three radial overtone modes. Overtone triple-mode Cepheids were identified only in the Galactic bulge and in the Large and Small Magellanic Clouds previously.

4

Introduction to the t and chi-square distribution for a more accurate evaluation of measure of the Word Error Rate in Analog-to-Digital Converters

100%

Catelani M. , Zanobini A. , Ciani L.

|

2008

|

tom Vol. 15, nr 4

485-490

EN

The word error rate (WER) in an Analog to Digital Converter (ADC) is the probability of receiving an erroneous code for an input, after correction is made for gain, offset, and nonlinearity errors, and a specified allowance is made for noise. Typical causes of word errors are metastability and timing jitter of comparators within the ADC [1]. New statistical techniques which can better integrate what is sustained in the IEEE standard and in [2] have been proposed. In particular, Student and chi-square distributions have been introduced for a more accurate measurement of the word error rate in the case of n successive observations.

5

Environmental Testing: Behavior of a Radio receiver Chain Front-end

75%

Catelani M. , Scarano V. L. , Singuaroli R. , Montebugnoli S. , Bianchi G. , Perini F.

|

tom Vol. 16, nr 1

107-116

EN

The proposed approach has been conceived in order to test and characterize the new receivers developed for the Italian SKA (Square Kilometre Array) demonstrator, based on the re-instrumentation of part of the Northern Cross radio-telescope located in Medicina (Italy). SKA represents a new-generation radio-telescope that will have 1 km² of effective collecting area. It can be considered as the most sensitive radio-telescope ever built that allows a deeper knowledge of the universe. In order to guarantee the implementation of a reliable radio-receiver chain, we proposed to test the front-end that will be installed in the focal line of the antenna. The front-end has turned out as the most critical subsystem of the radio-receiver chain from a preliminary reliability analysis reported in [1]. For this reason, in the paper some results are obtained by vibration tests as well as shock and water tests are presented in order to prove the performance of the circuit under test (CUT) in particular environmental conditions.