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This paper describes a technique for digitally calibrating an ac signal against another one taken as reference, which is not obligatorily of the same frequency as the first. The requirements of this technique are: knowledge of the spectrum of the ac reference signal, coherent generation of the signals with respect to a single time-base, a well-known bandwidth characteristic of a digitizer over frequency,...
This paper describes a method to extend the frequency range of Programmable Josephson Voltage Standard based ac voltage calibrations. It requires coherent (synchronous) signal generation and sampling to a common reference time-base of a digitizer and accurate phase alignment of ac signals. Practical and physical limitations of the underlying principle are covered in the text. Experimental investigations...
This paper describes the development of a primary single-phase sampling ac power standard, which uses a programmable Josephson voltage standard (PJVS) in its core. Magnetic transducers are used to scale down to low levels the ac signals to be compared with the PJVS by digital sampling. Independent digital adaptive regulators in form of algorithms in a control software guarantee stable and accurate...
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.
This paper describes a system for generating and measuring extremely accurate phase angles that combines the digital synchronous signal generation with the synchronous subsampling technique, aided by digital phase regulators. The system can be set up with commercially available instrumentation with a minimum of hardware development. Experimental evidences suggest that the phase between two generated...
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.
This paper describes capacitance comparisons among three impedance bridges in operation at Inmetro in the nF range: the two- and four-terminal-pair coaxial bridges and a digital quadrature bridge. This comparison has the objective to verify the performance and reliability of the coaxial bridges between themselves and to infer on the capabilities of a digital one, recently put in operation. The results...
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...
This paper describes a new calibration system developed at INMETRO to guarantee traceability of low-frequency alternating (ac) voltage calibrations (up to around 1 kHz) to a programmable Josephson ac waveform synthesizer. The automated full synchronous system allows the synchronization of a calibrator or signal synthesizer with a programmable Josephson voltage synthesizer system to be made by employing...
This paper describes a measurement setup employed to investigate differential voltage measurements to be done with a spectrally pure sine wave and a dc reference. The system enables adjustment, to a very high accuracy, the start phase of ac sampling. Repeatabilities of some 0.1 µV/V were obtained with the help of adaptive digital control.
This paper presents the setup for investigating INMETRO's programmable ac voltage standard with thermal converters. Of primary interest is the validation of differential ac voltage calibrations of the Josephson system with thermal converters and their calibration against the quantum system. Proposals for attaining these goals are presented.
This paper covers some aspects of voltage dependence of solid dielectric capacitors and resistors to be used for metrology purposes. The investigations are motivated by the need of a quantitative rather than qualitative information on components' voltage dependency when one faces challenges on precision low noise analog electronic circuit design. Current measurement methods under development to determine...
This paper describes the design, construction and evaluation of a precise resistive voltage divider for the measurement of harmonics of power line frequencies employing digital sampling techniques.
The present PTB primary standard allows power measurements with a measurement uncertainty of about 2.5 μW / VA (k = 2). It operates at voltages up to 240 V and currents up to 10 A in the frequency range from 16 Hz up to some kHz. This paper gives a short overview of the working principle of the standard and recent improvements.
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