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Controllo automatico di un sistema di commutazione per misure di precisione di resistori campione basato su un microprocessore
No full textA system for controlling electrical and chemical parameters in the Faraday constant determination by dissolution of silver
No full textThe development of an electrochemical system for the Faraday constant determination has been undertaken at I.N.RI.M. In this system a new two-electrode cell for processing silver dissolution has been set up. The parts of this cell have been carefully designed to avoid sources of undue influence. New elements for monitoring the Ag+ ion concentration in the two half-cells have been introduced and the operations necessary to keep the electrochemical reactions under strict control have been identified and tested. The solution stability, the residue recovery, the O-2 prevention and the solution filtering process without its transfer to other containers are other merits. The electrical charge measurement equipment has been assembled and integrated with the one for monitoring the reaction parameters. A control apparatus displaying when some specific operations in the two half-cells are required has been added. The measurements showed that by employing the setup assembled with some proper precautions an uncertainty of about 1-2 parts in 10(5) can be reached, mainly limited by the silver purity, and the evolution toward a measurement system at a metrological level (parts in 10(6) or better) is attainable
Wideband digital phase comparator for high current shunts
No full textA 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 to the outputs of the shunts under comparison through
a pair of symmetric active guarded transformers. 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 2A up to
100 A, and frequencies ranging between 500 Hz and 100 kHz. Expanded uncertainty (k = 2)
less than 50 μrad, for frequency up to 100 kHz, is obtained in the measurement of the phase
difference of a group of 10A 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 the contribution to the uncertainty budget of the phase detector to be decreased by 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 a phase detector, depends on multiple factors derived from the analogue and digital imprint of each sampling system
Development of a flow-through cell for accurate measurements of low electrolytic conductivity
No full textThe present paper focuses on the development of a flow-through cell and a closed circuit that permit to carry out measurements of low electrolytic conductivity of aqueous solutions under flowing condition. The traceability path has been set as follows: samples with conductivity between 200 μS cm-1 and 50 μS cm-1 have been employed for the calibration of the geometric constant of the new cell, by comparison with the primary cell of Istituto Nazionale di Ricerca Metrologica (I.N.Ri.M.). Then the flow-through cell has been used to measure values with decreasing conductivities down to 1 μS cm-1. The measurement system capabilities have been evaluated to be limited by contamination effects
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