Renata T. de Barros e Vasconcellos

A digital quadrature bridge for impedance measurements

This paper describes a digital alternating current (ac) quadrature bridge for impedance measurements under development at INMETRO. This bridge is primarily intended to allow the comparison of ac resistors with standard capacitors but it could be applied to a myriad of impedance-measurement tasks as the precise determination of dissipation factor of capacitors, of resistor time-constants, as well as an aid in investigations on the nonlinear behavior of passive electronic components. Aimed at attaining measurement uncertainties of around 10 μΩ/Ω at 1 kHz under sinusoidal conditions, it has prospects for further improvements.

A digital four terminal-pair impedance bridge

This paper describes a four terminal-pair digital impedance bridge aided by digital adaptive phase regulation. It allows the comparison of ac resistances and capacitances with outstanding accuracy and with measurement uncertainties bearing only some 10-06 Ω/Ω.

A new critically sampled non-uniform subband adaptive structure

A non-uniform subband adaptive structure with critical sampling of the subband signals is derived. With the assumption of non-overlapping between non-adjacent analysis filters, the resulting structure yields exact modeling of an arbitrary FIR system. An LMS-type adaptation algorithm, which minimizes the sum of the subband squared-errors, is obtained for updating the coefficients of the proposed structure, resulting in significant convergence rate improvement for colored input signals when compared to the fullband LMS algorithm. Computer simulations illustrate the convergence behavior of the proposed non-uniform subband adaptive filter in the applications of system identification and acoustic echo cancellation.

Capacitance measurements with a four terminal-pair coaxial bridge

This paper describes the modification of a four terminal-pair coaxial bridge, part of the traceability chain of the capacitance unit to QHE, originally constructed to measure AC resistances, with the objective to measure capacitances at the nano-farad range. We also present preliminary results and the uncertainty analysis.

A Digital Five-Terminal Impedance Bridge

This paper describes a five-terminal (four terminal with shield) digital impedance bridge aided by digital adaptive phase regulation. It allows the comparison of ac resistances and capacitances with outstanding accuracy and with measurement uncertainties bearing only some

Development of an AC current comparator based resistance measurement system aided by digital synchronization of AC signals

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Sampling systems with fractional-delay applied to high-accuracy measurements

, as corroborated by extensive experimental investigations.

Inmetro's coaxial calculable resistance project

This paper describes the development of an automated ac current comparator based resistance measurement system that uses precise and accurate phase synchronization of frequency locked ac signals aided by adaptive digital regulators. The aimed frequency range lies between 1 Hz to 20 Hz.

Prototype calculable coaxial resistor

For high-accuracy AC voltage measurements, sampling errors can contribute significantly to increase the incertitude. Fractional delay is a simple technique to reduce sampling errors, improving the accuracy of electrical digital measurements. In this paper we combine the fractional delay sampling technique with Principal Component Analysis, applying this technique to high-accuracy measurements.

SIM comparison of AC-DC current transfer difference, SIM.EM-K12

This work describes experiments on the feasibility of a mechanical support for the resistive element of a calculable resistor. Construction issues involved in the project of the resistor are discussed.