117,948 research outputs found
Automatic compensation system for impedance measurement
No full textThis paper deals with the realization of the four-pair terminal definition of impedance standards. A simple, though reliable, system is described that allows an automatic compensation of the voltage at the low potential port of impedance standards to be obtained. Such a system employs a commercial data acquisition board and a signal generator with adjustable-phase capability, which acts as the phase reference for the generator that feeds the impedance standard. A standard PC controls the whole system and implements the demodulation and the control algorithms. Preliminary tests have been performed in the frequency range of 50 Hz to 20 kHz with different kinds of impedance standards (resistive, inductive and capacitive), obtaining a residual voltage at the low potential port of less than 5 μV
Short communication: improvements to INRIM Johnson noise thermometer
No full textThis paper presents a progress report for the Johnson noise thermometry experiment which is under development at the Istituto Nazionale di Ricerca Metrologica. In order to aim at an uncertainty level better than 10−5 and to reduce the measurement time, a new setup has been developed. In particular, several modifications have been applied to the experiment described by Callegaro et al. (Metrologia 46: 409,
2009) to improve the traceability to voltage, resistance and frequency standards, and new amplifiers have been designed in order to expand the working frequency range up to 20 kHz, with a sensing resistor of 1 kohm, while maintaining amplifier induced systematic errors to an acceptable level
Fundamentals of Measurement: Giovanni Giorgi and the International System of Units
No full textElectrical 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
On the cohomology of Artin groups in local systems and the associated Milnor fiber
No full textLet W be a finite irreducible Coxeter group and let X-W be the classifying space for G(W), the associated Artin group. If A is a commutative unitary ring, we consider the two local systems L-q and L'(q) over X-W, respectively over the modules A[q, q(-1)] and A[[q, q(-1)]] ,given by sending each standard generator of G(W) into the automorphism given by the multiplication by q. We show that H*(X-W, L'(q)) = H*(+1) (X-W, L-q) and we generalize this relation to a particular class of algebraic complexes. We remark that H*(X-W, L'(q)) is equal to the cohomology with trivial coefficients A of the Milnor fiber of the discriminant bundle of the associated reflection group
A simple algorithm to find the L-curve corner in the regularisation of ill-posed inverse problems
No full textWe propose a simple algorithm to locate the 'corner' of an L-curve, a function often used to select the regularisation parameter for the solution of ill-posed inverse problems. The algorithm involves the Menger curvature of a circumcircle and the golden section search method. It efficiently finds the regularisation parameter value corresponding to the maximum positive curvature region of the L-curve. The algorithm is applied to some commonly available test problems and compared to the typical way of locating the l-curve corner by means of its analytical curvature. The application of the algorithm to the data processing of an electrical resistance tomography experiment on thin conductive films is also reported
Study on the traceability of salinity measurements in seawater
No full textINRIM Measurement Report, EUROMET Electrochemical Analysis WG Project 91
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