Fundamentals of Measurement: Giovanni Giorgi and the International System of Units

Electrical engineers and technicians face today many professional challenges, but the problem of the choice of the measurement units and their conversion is not one of those. Our colleagues working in mechanics or thermal engineering have to deal with inches and metres, gallons and litres, calories, BTUs and joules. In electricity, everything is smoother: the voltage is always measured in volt, the resistance in ohm; one volt times one ohm gives one watt, and so on. No ambiguities occur, no calculations with weird conversion factors are needed

Two different ways in evaluating the uncertainty of S-parameter measurements

The expression of uncertainty of scattering parameter measurements in vector network analysis is an active research subject, since no full consensus about proper algorithms for such expression has been reached so far. Recently, two software packages have been acquired at INRIM, which allow to perform this task in a metrological framework. In this paper we compare the result of analysis performed by two packages, VNA Tools II and Multiport Measurement Software version 4 (MMS4). Both packages claim to perform uncertainty analyses fully compliant to the Guide of expression of uncertainty in measurement, but following completely different approaches. We organized a comparison by performing, with both packages, analyses of the very same datasets. These have been generated by real measurements on passive standards with a commercial vector network analyzer. Results of the comparison give consistency of the uncertainty analyses performed by the software packages, which can be therefore considered equivalent and mutually validated

Role of plasma-induced defects in the generation of 1/f noise in graphene

It has already been reported that 1/f noise in graphene can be dominated by fluctuations of charge carrier mobility. We show here that the increasing damage induced by oxygen plasma on graphene samples result in two trends: at low doses, the magnitude of the 1/f noise increases with the dose; and at high doses, it decreases with the dose. This behaviour is interpreted in the framework of 1/f noise generated by carrier mobility fluctuations where the concentration of mobility fluctuation centers and the mean free path of the carriers are competing factors. Published by AIP Publishing

Realization of the farad from the dc quantum Hall effect with digitally-assisted impedance bridges

A new traceability chain for the derivation of the farad from dc quantum Hall effect has been implemented at INRIM. Main components of the chain are two new coaxial transformer bridges: a resistance ratio bridge, and a quadrature bridge, both operating at 1541 Hz. The bridges are energized and controlled with a polyphase direct-digital-synthesizer, which permits to achieve both main and auxiliary equilibria in an automated way; the bridges and do not include any variable inductive divider or variable impedance box. The relative uncertainty in the realization of the farad, at the level of 1000 pF, is estimated to be 64E-9. A first verification of the realization is given by a comparison with the maintained national capacitance standard, where an agreement between measurements within their relative combined uncertainty of 420E-9 is obtained.Comment: 15 pages, 11 figures, 3 table

On the calibration of DC resistance ratio bridges

Current comparator bridges are employed for the realization of the resistance scale from the quantum Hall effect in several National Metrology Institutes and calibration centers. Quantum resistance standards under development, based on novel materials and tabletop dry cryostats, make the more achievable DC current comparator bridges (DCCs) a viable alternative to the more accurate but more expensive cryogenic current comparator bridges (CCCs). A DCC ratios' calibration against a reference CCC is a straightforward way to improve the DCC's performances and the resistance scale overall accuracy.The paper reports the calibration results of two DCCs on the ratios employed in a 1 omega to 10 k omega resistance scale traceable to a 12.906 k omega quantized Hall resistance, showing a good reproducibility and stability of the DCC readings over the measurement period and supporting the possibility of a DCC errors' correction and of a realization of the primary resistance scale at the 10-8 level

Inductive voltage divider modeling in Matlab

Inductive voltage dividers have the most appropriate metrological characteristics on alternative current and are widely used for converting physical signals. The model of a double-decade inductive voltage divider was designed with the help of Matlab/Simulink. The first decade is an inductive voltage divider with balanced winding, the second decade is a single-stage inductive voltage divider. In the paper, a new transfer function algorithm was given. The study shows errors and differences that appeared between the third degree reduced model and a twenty degree unreduced model. The obtained results of amplitude error differ no more than by 7 % between the reduced and unreduced model

Recommended implementation of electrical resistance tomography for conductivity mapping of metallic nanowire networks using voltage excitation

The knowledge of the spatial distribution of the electrical conductivity of metallic nanowire networks (NWN) is important for tailoring the performance in applications. This work focuses on Electrical Resistance Tomography (ERT), a technique that maps the electrical conductivity of a sample from several resistance measurements performed on its border. We show that ERT can be successfully employed for NWN characterisation if a dedicated measurement protocol is employed. When applied to other materials, ERT measurements are typically performed with a constant current excitation; we show that, because of the peculiar microscopic structure and behaviour of metallic NWN, a constant voltage excitation protocols is preferable. This protocol maximises the signal to noise ratio in the resistance measurements—and thus the accuracy of ERT maps—while preventing the onset of sample alterations

The S-matrix Method for High Frequency Capacitance Calibration

The S-matrix Method for High Frequency Capacitance Calibration ---- at NVNA Users' Forum (Fall 2013 - Columbus, Ohio