Wideband digital phase comparator for high current shunts

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 0.05 mrad, 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.Comment: 20 pages, 9 figure

Ac-Dc Characterization of Coaxial Current Shunts and Application of the hunt in the Digital Sampling Wattmeter

The purpose of this paper is to give a review of ac-dc characterization of the current shunts and application of the current shunt (nominal current 1A) within the digital sampling wattmeter. It is described the ac-dc transfer difference measurement of six cage type ac shunts from 10 mA up to 10 A using step-up measurement procedure. Furthermore, the substantial part of the measurement setup is fast switching system which is also described in detail. For the purpose of measurement procedure, the application is developed in LabVIEW and whole process is fully automatized. Obtained results are analyzed and shown on graphs. This paper is extended version of two papers: [1] and [2] which are presented on 1st International Colloquium on Smart Grid Metrology. Thus, paper is extended with presented application of the shunt 1 A in the digital sampling wattmete

Asynchronous Phase Comparator for Characterization of Devices for PMUs Calibrator

This paper reports recent progress in developing a new asynchronous digital phase comparator for the precision measurement of phase difference of voltage ratio devices and calibration of functional elements of phasor measurement units (PMUs) calibrator. The phase error of the proposed digital comparator is below 300 nrad at 50 Hz and 100 μrad at 100 kHz with applied voltages ranging between 500 mV and 3 V, whereas the phase error of cables and connectors was estimated to be 4 μrad at 1 MHz. Besides resistive dividers, the phase comparator has been employed for the characterization of frequency behavior of phase difference between the output and input of voltage and transconductance amplifiers for a PMUs calibrator. The system can also be an important tool for phase-frequency characterization of devices employed for specific wideband power measurements

A CIRCULAR LOOP TIME CONSTANT STANDARD

A time constant standard, developed for the phase angle measurement of precision current shunts is developed and described, and its time constant has been determined. Based on a single circular loop placed in an air thermostat, its construction is very simple and it gives accurate results in the frequency band of interest, e.g. for frequencies between 50 Hz and 100 kHz. The influence of the shielding is calculated using numerical Finite Element Analysis (FEA). The thermostatic stability is analyzed, and the time-constant of the thermostat is determined using temperature measurement and Butterworth filtering. The power coefficient of the standard is determined, and limits of errors are discussed

Specifying and calibrating instrumentations for wideband electronic power measurements

The wideband electric power measurement related topics of electronic wattmeter calibration and specification are discussed. Tested calibration techniques are described in detail. Analytical methods used to determine the bandwidth requirements of instrumentation for switching circuit waveforms are presented and illustrated with examples from electric vehicle type applications. Analog multiplier wattmeters, digital wattmeters and calculating digital oscilloscopes are compared. The instrumentation characteristics which are critical to accurate wideband power measurement are described

Precision calculations of the characteristic impedance of complex coaxial waveguides used in wideband thermal converters of AC voltage and current

The article presents precision and numerically stable method of calculation of the characteristic impedance of cylindrical multilayer waveguides used in high-precision wideband measuring instruments and standards, especially calculable thermal converters of AC voltage and precision wideband current shunts. Most of currently existing algorithms of characteristic impedance calculation of such waveguides are based upon approximations. Unfortunately, application of such methods is limited to waveguides composed of a specific, usually low number of layers. The accuracy of approximation methods as well as the number of layers is sometimes not sufficient, especially when the coaxial waveguide is a part of precision measurement equipment. The article presents the numerically stable matrix analytical formula using exponentially scaled modified Bessel functions to compute characteristic impedance and its components of the cylindrical coaxial multilayer waveguides. Results obtained with the developed method were compared with results of simulations made using the Finite Element Method (FEM) software simulations. Very good agreement between results of those two methods were achieved

Precision calculations of the characteristic impedance of complex coaxial waveguides used in wideband thermal converters of AC voltage and current

The article presents precision and numerically stable method of calculation of the characteristic impedance of cylindrical multilayer waveguides used in high-precision wideband measuring instruments and standards, especially calculable thermal converters of AC voltage and precision wideband current shunts. Most of currently existing algorithms of characteristic impedance calculation of such waveguides are based upon approximations. Unfortunately, application of such methods is limited to waveguides composed of a specific, usually low number of layers. The accuracy of approximation methods as well as the number of layers is sometimes not sufficient, especially when the coaxial waveguide is a part of precision measurement equipment. The article presents the numerically stable matrix analytical formula using exponentially scaled modified Bessel functions to compute characteristic impedance and its components of the cylindrical coaxial multilayer waveguides. Results obtained with the developed method were compared with results of simulations made using the Finite Element Method (FEM) software simulations. Very good agreement between results of those two methods were achieved