Wideband digital phase comparator for high current shunts

Abstract

Abstract.A 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 through a pair of symmetric active guarded transformers to the outputs of the shunts under comparison. 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 several hundred of milliampere 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 10 A 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 to decrease the contribution to the uncertainty budget of the phase detector of 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 phase detector, depends on multiple factors derived from both analog and digital imprint of each sampling system.

Four-Terminal Pair Digital Sampling Impedance Bridge up to 1MHz

“…Validation of the linearization method and its implementation was performed by numerical simulation and also by measuring the voltage dependencies for various ratios of the resistors and applying the correction according to (7). The example of the achieved suppression of the nonlinear voltage dependence is shown in Fig.…”

“…Several special setups capable of shunt calibration exist for a frequency range above 100 kHz. For example, a phase comparator developed at INRIM [7] based on the isolation transformers should be extendable to 1 MHz. However, usage of this topology was not yet demonstrated for ac-dc difference measurement.…”

A system for the accurate characterization of wideband wattmeters, power quality analyzers and PMUs

“…Some of these shunts have been built at INRIM [1] and have been characterized in ac/dc difference and in phase by methods previously developed [2]. -The voltages (up to 600 V) are converted by means of resistive dividers, built specifically for the purpose [3], using equal resistors put in series and in parallel on proper supports, which are surrounded by a coaxial screen.…”

Asynchronous Phase Comparator for Characterization of Devices for PMUs Calibrator

“…Its use is intended for precision measurement of phase error at various frequencies of passive and active devices employed in PMUs calibrator, as reported in [3]. A similar phase comparator system operating from 500 Hz up to 100 kHz [4] was realized for phase error measurements of high current shunts [5] and its intrinsic phase error was determined by means of a FPGA-DAC based dual synthesizer [6] having 96 dB of spurious free dynamic range (SFDR).…”