Wideband digital phase comparator for high current shunts

A wideband phase comparator for precise measurements of phase difference of high current shunts has been developed at INRIM. The two-input digital phase detector is realized with a precision wideband digitizer connected through a pair of symmetric active guarded transformers to the outputs of the shunts under comparison. Data are first acquired asynchronously, and then transferred from on-board memory to host memory. Because of the large amount of data collected the filtering process and the analysis algorithms are performed outside the acquisition routine. Most of the systematic errors can be compensated by a proper inversion procedure. The system is suitable for comparing shunts in a wide range of currents, from several hundred of milliampere up to 100 A, and frequencies ranging between 500 Hz and 100 kHz. Expanded uncertainty (k=2) less than 0.05 mrad, for frequency up to 100 kHz, is obtained in the measurement of the phase difference of a group of 10 A shunts, provided by some European NMIs, using a digitizer with sampling frequency up to 1 MHz. An enhanced version of the phase comparator employs a new digital phase detector with higher sampling frequency and vertical resolution. This permits to decrease the contribution to the uncertainty budget of the phase detector of a factor two from 20 kHz to 100 kHz. Theories and experiments show that the phase difference between two high precision wideband digitizers, coupled as phase detector, depends on multiple factors derived from both analog and digital imprint of each sampling system.Comment: 20 pages, 9 figure

A Measurement System for the Characterization of Wireless Charging Stations for Electric Vehicles

This paper describes a new traceable measurement system, designed for the characterization of inductive charging stations for electric vehicles. The measuring system is able to measure on-site the performance and efficiency of the charging station and converters. The basic relative uncertainty is 10-3, but actual measurement conditions could worsen this figure. The measurement system aims at accurately measure the power at the batteries and the power transferred from the ground to the on board resonant circuit and makes possible a benchmarking between station measuring systems. Finally, it allows the characterization of the magnetic emissions by correlating them with the electric current in the coils

Assessment of the Overall Efficiency in WPT Stations for Electric Vehicles

The on-site assessment of the efficiency of a charging station is not a trivial process and is a topic of discussion for professionals. The efficiency of electric Vehicle Supply Equipment (EVSE), is an important parameter for both the user and the EVSE operator. This paper deals with a particular type of EVSE, using static wireless power transfer (WPT). This paper proposes a clear method to account for the parameters which can affect the correct determination of efficiency, such as in particular the accuracy of the meters and the effect of temperature. This work proposes a method to define the accuracy of the power and efficiency on-site assessment, and is aimed at clarifying that despite distorted waveforms at the charging stations, it is possible to reach a good accuracy in a wide temperature span (expanded uncertainty <0.5% between 5∘C and 40∘C). Analysis initiated from the measurement conditions and the actual waveforms recorded at two WPT EVSEs with differently rated power. This paper paves the way for the possibility of verifying class 0.5 meters on-site, desirable for this type of application. The paper also clarifies that despite the evident presence of voltage and current ripple at the batteries, the weight of the ripple power on the total power is nevertheless lower than 0.1%. Finally, the paper highlights how, for the correct measurement of the ripple, it would be advisable to calibrate the instrumentation in DC and in AC, at a frequency double that of the working frequency of the EVSE coil

A measurement system for the characterization of wireless charging stations for electric vehicles

This paper describes a new traceable measurement system, designed for the characterization of inductive charging stations for electric vehicles. The measuring system is able to measure on-site the performance and efficiency of the charging station and converters. The basic relative uncertainty is 10-3, but actual measurement conditions could worsen this figure. The measurement system aims at accurately measure the power at the batteries and the power transferred from the ground to the on board resonant circuit and makes possible a benchmarking between station measuring systems. Finally, it allows the characterization of the magnetic emissions by correlating them with the electric current in the coils

Toward A New Visual Culture Of The News

This paper argues that the rise of new digital technologies and new amateur/citizen practices of photographic production have constituted a “short-circuit” that has critically destabilized but also productively challenged professional photojournalism. In this context, the paper focuses on the practice of digital post-production (i.e. digitally “retouching” and “enhancing” photographs), as an empirical prism through which to theoretically discuss wider technological, professional, and cultural shifts that have been affecting news photography over the last decade. In particular, drawing on in-depth interviews with international photojournalists, jury members of press photo contests, and directors of digital post-production labs, the paper analyzes a few paradigmatic case studies of post-produced news photographs that have recently won prestigious professional awards, yet have generated considerable controversies. Through the analysis of the case studies, the paper aims to shed light on the contested construction of aesthetic conventions and professional-ethical standards within digital photojournalism, in relation to (1) the shifting professional ideal of visual news “objectivity,” and (2) the shifting symbolic boundaries between professional and non-professional news photo producers. Finally, introducing the notion of “digital cultural capital,” the paper suggests the theoretical relevance of a (post-)Bourdieusian approach to photojournalism, which frames the conflictual implementation of new digital technologies and the diffusion of new social and material practices as a symbolic struggle for professional distinction within the wider visual culture