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Instrumentation and Measurement, IEEE Transactions on

Issue 4 • Date Dec. 1974

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Displaying Results 1 - 25 of 74
  • Table of contents

    Page(s): c1 - 9c
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    Freely Available from IEEE
  • IEEE Instrumentation and Measurement Group

    Page(s): c2
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    Freely Available from IEEE
  • Preface

    Page(s): 253 - 254
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  • Editorially Spealing

    Page(s): 255
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  • A Low-Temperature Direct-Current Comparator Bridge

    Page(s): 256 - 260
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    The application of superconducting direct-current comparators to the measurement of resistance ratios is described. One comparator consists of a binary set of ratios between 1:1 and 160:1 providing for self-calibration by a buildup procedure. A second comparator exhibiting discrete ratios of 1:1, 10:1, and 100:1 is also described. Ratio uncertainty of less than 1 part in 109 is achieved by enclosing the ratio windings in overlapping toroidal superconducting shields. Superconducting quantum interference devices (SQUID's) serve as flux sensors for the comparators. One of these current comparators is used to calibrate a 100-¿:1-¿ resistive divider, which at a current of 10 mA exhibits a self-heating error of 0.0023 ppm. View full abstract»

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  • Ironless Cryogenic Current Comparators for AC and DC Applications

    Page(s): 261 - 263
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    The ac and dc errors of cryogenic current comparators with toroidal-shield configurations are reported. Based on these experiments and on theoretical considerations, geometric parameters of the superconducting shields could be determined, which govern the errors. These results may be used for the construction of cryogenic current comparators with predictably low errors. It seems to be possible to decrease the dc error far below our present resolution limit of 3 X 10-11. View full abstract»

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  • Cryogenic Voltage Comparator System for 2e/h Measurements

    Page(s): 264 - 267
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    The design and operation of a cryogenic voltage comparator system for precision 2e/h measurements is described. Major improvements embodied in the new 2e/h system include the use of 1) a single microstripline-coupled Josephson tunnel junction to obtain usable step voltages up to 10 mV at 10.0 GHz, 2) a cryogenic voltage divider comprised of two resistors whose ratio is calibrated with a low-temperature dc current comparator, 3) a superconducting quantum interference device (SQUID) null detector, and 4) superconducting switching. The accuracy of the present 196:1 divider system is estimated to be about 2 parts in 108 on the basis of preliminary tests and is limited by resistor self-heating during calibration. View full abstract»

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  • Operational Experience with a Cryogenic Volt Monitoring System

    Page(s): 267 - 271
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    An experimental cryogenic measuring system, employing the dc and ac Josephson effects, which has been used to monitor the National Physical Laboratory maintained voltage standard is described in detail. Results obtained with this system over a period of 1 years are presented and compared with those from a system using room temperature potentiometry, which has already been described. Emphasis is laid on experience gained with cryogenic components of the system. The final section outlines a design for a portable Josephson apparatus based on experience with the present system, which would be capable of calibrating standard cells with maximum possible precision. View full abstract»

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  • Maintaining the Unit of Voltage at PTB via the Josephson Effect

    Page(s): 271 - 275
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    In Section I a report on high precision voltage comparisons between the mean EMF of the former PTB voltage standard (consisting of a group of 39 saturated Weston cells) and the Josephson reference voltage is presented. The experiments were carried out with a total uncertainty (1 ¿) of 4 parts in 108. The measured rate of change of the mean EMF during a 1¿year period was - 1.3 X 10-7 V per year. This voltage stability is sufficient to maintain the unit of voltage by this group of standard cells for several months until a new comparison with the Josephson reference voltage becomes necessary. Due to the effects of thermal EMF's in the millivolt circuit of the measuring system used at present, the Josephson reference voltage (¿3 mV) is only stable during a short time. In Section II a prototype cryogenic voltage standard developed at PTB is described. By immersing the main measurement components into the superfluid liquid helium bath, a long term voltage stability can be achieved. These components include the cryogenic resistive divider, consisting of a new copper alloy, and the SQUID null detector. The resistance ratio of the cryogenic resistive divider of 320:1 is determined by a ten-decade inductive voltage comparator operating at 84 Hz. The effects of power dissipation introduce only errors of second order because the currents in the calibration mode and the measurement mode are the same. View full abstract»

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  • The AC Josephson Effect Monitoring of the Unit of EMF in Canada

    Page(s): 275 - 278
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    The experimental program outlined is directed toward the utilization of the ac Josephson effect to maintain surveillance of the unit of EMF in Canada. Preliminary results indicate a weighted mean value of 2e/h = 483 593.0 ± 0.2 (0.4 ppm) GHz/VNRc(73) which is, at present, not precise enough to detect the small drifts normally encountered in the mean value of the standard cell group upon which VNRC is based. View full abstract»

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  • Automatic Intercomparison of Standard Cells

    Page(s): 278 - 282
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    A system is described whereby precise intercomparisons of standard cells are accomplished under full computer control. The results obtained indicate accuracies (one standard deviation) of ±10 nV from which the individual values of the standard cells in a maintaining group of ten cells are estimated to be accurate to ±20 nV. The major source of indeterminacy continues to be the variation of standard cell EMF due to temperature, mechanical vibration, etc. View full abstract»

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  • A High-Resolution Prototype System for Automatic Measurement of Standard Cell Voltage

    Page(s): 282 - 286
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    The conceptual requirements, the design, and the initial performance of the prototype switching for connecting standard cells to an automatic measurement system are described. Features of the design include random selection of two cells at a time, inversion of connection polarity on command, modular construction for expansion, and less than 10-nV residual uncompensated error voltage. Also described briefly are controllers for manual operation of the switches and the rudimentary high-resolution digital potentiometer used to complete the measurement system. Results of tests of the switching and observations of the prototype system performance are presented. View full abstract»

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  • A Review of 12 Years of Performance of an Automatic Standard Cell Test Facility

    Page(s): 286 - 289
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    Operating experience and difficulties encountered in a 12-year use of the automatic standard cell test facility are reviewed. The facility was designed to acommodate 40 cells on test and to resolve the difference between the voltage of each test cell and that of a reference cell to 0.1 ¿V. The large amount of data obtained has led to a more complete characterization of cell performance and has identified an unexpected impulse-type response in unsaturated standard cells exposed to a varying thermal environment. Difficulties of various types have been expected over the operating period. An unexpected type of failure occurred, however, with snapaction switches used on low-voltage logic lines, and similar failures may be anticipated in new designs. View full abstract»

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  • Regional Maintenance of the Volt Using NBS Volt Transfer Techniques

    Page(s): 290 - 294
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    In cooperation with five industrial standards laboratories, the National Bureau of Standards (NBS) studied the feasibility of establishing a regional volt maintenance and surveillance program in the greater Los Angeles, Calif., area. The objectives were to improve surveillance, to reduce dependence on NBS, and to have each laboratory maintain its unit of voltage to within 1 ppm of the U. S. legal volt. A two-phase program was established, the first to characterize the five laboratories and the second to carry out the surveillance. After 3 years all laboratories were found to be maintaining their unit to within better than 1 ppm of the U. S. legal volt. View full abstract»

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  • Standard Cell Enclosure with 20-μK Stability

    Page(s): 295 - 298
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    Groups of standard cells are needed to maintain the National Bureau of Standards (NBS) volt between periodic reassignments via 2e/h. An enclosure to hold six standard cells has been designed and three enclosures have been assembled. The enclosures consist of four concentric aluminum cylinders separated by foamed polystyrene insulation. Two of the four cylinders are controlled, an outer one by a platinum resistance thermometer and dc amplifier and the inner one at 30°C by a second platinum resistance thermometer and an ac transformer-ratio bridge followed by a phase-sensitive detector, a dc amplifier, and a heater. The innermost of the four cylinders is a thermally lagged cell compartment. The temperature excursions over periods of at least several days were found to be less than 20 μK, thus having a negligible effect on the standard cell EMF's. View full abstract»

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  • Standard Cell Calibration via Current Transfer

    Page(s): 299 - 302
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    The EMF's of standard cells are now being transferred between laboratories over a 1¿-km cable with a precision of 4 parts in 108 to provide an instantaneous comparison of the 2e/h and ¿p¿ experiments being carried out at the two facilities. This is accomplished by transferring a constant current that produces a 1-V drop across standard resistors located at both ends of the cable. View full abstract»

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  • A more accurate determination of γ1p through improved dimensional measurement techniques

    Page(s): 302 - 305
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    An increase in the accuracy of the gyromagnetic ratio of the proton can be achieved by determining the magnitude of a calculable magnetic field to higher accuracy. Such an increase requires dimensional measurements of a physical object to an absolute accuracy of a few parts in ten million. A unique computer-controlled automated measurement system for carrying out such measurements has been developed at the U. S. National Bureau of Standards and is currently in operation at its nonmagnetic facility. This measurement system provides an order of magnitude improvement over all previous measurements. View full abstract»

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  • New NBS Measurements of the Absolute Farad and Ohm

    Page(s): 305 - 309
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    A recently completed calculable cross capacitor in conjunction with a previously described collection of ac and dc bridges has made possible a highly accurate measurement of the farad and the ohm. The cross capacitor and its auxiliary equipment, as well as those components of the measurement system which have not been covered in prior publications, are described in detail. The measurements indicate that the National Bureau of Standards (NBS) unit of capacitance is given by FNBS = 1 F + 1.787 ¿F, and that the NBS unit of resistance is given by ¿NBS = 1 ¿ - 0.819 ¿¿. View full abstract»

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  • Apparatus for Accurate DC Capacitance-Resistance Transfer

    Page(s): 310 - 314
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    An apparatus, based on the analog intergrator principle, is designed to effect a 1-nF-108-¿ transfer with reversed dc, by permitting a digital interval timer to measure the product RC, repeatedly if necessary. Both systematic and random errors have been significantly reduced, and correction to data is not required. The apparatus is simple to construct and operate, and its transfer standard error is estimated to be ±0.23 ppm. View full abstract»

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  • 10-kV High-Accuracy DC Voltage Divider

    Page(s): 314 - 317
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    A high-accuracy voltage divider based on the Hamon/Rayleigh ratio principle has been made for the absolute measurement of the volt and also for building up the voltage scale to 10 kV. It is composed of 100 equal resistors of nominal value 100 k¿ and an adjustable 100-k¿ resistor with taps at 10 and 1 k¿. By using appropriate connections, a total 10-M¿ divider with 1-k¿ output is constituted in which various voltage ratios up to 104 can be obtained. A guard circuit is provided to minimize the leakage currents. The calibration of the divider is simplified by using parallel or series-parallel connection of resistance elements so that all comparisons are made at a ratio of 1:1. For 10 kV only, two comparisons are required. The measurement of performance of the divider and the analysis of errors have been made. The most important factor affecting the voltage ratio is self heating, for which a correction is necessary. The total error would be less than 0.58 ppm. View full abstract»

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  • A Technique for Calibrating Power Frequency Wattmeters at Very Low Power Factors

    Page(s): 318 - 322
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    The application of a current comparator capacitance bridge to the measurement of the error of power frequency wattmeters at zero and very low power factors is described. The desired voltage, current, and power factor, leading or lagging, are established with a capacitive-type artificial load. The power factor is adjusted with reference to a loss-free gas-dielectric capacitor to within 1 × 10-5 or to an accuracy of 1 percent, whichever is greater, and voltage and current to an accuracy of better than 1 percent. Results of the measurements on representative commercially available electrodynamic and electronic wattmeters are given. View full abstract»

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  • An Automatic RMS/DC Comparator

    Page(s): 322 - 325
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    The design of an instrument for the automatic comparison of an ac voltage with a stable dc source is described. A differential multijunction thermal converter is used as an rms/dc converter with an FET-switched input amplifier for ac/dc substitution. The output voltages of the rms/dc converter with ac and dc input voltages are sampled and stored, and the difference amplified and displayed on a panel meter or chart recorder. Accuracy is ±20 ppm of input ranges of 10-200 V at frequencies of 50 Hz-1 kHz, and maximum full scale deflection sensitivity is 0.01 percent of input range. The instrument may be used either as an rms comparator with a linear voltage scale or as a mean-square comparator with a linear power scale. View full abstract»

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  • AC/DC Thermal Converters of the ETL

    Page(s): 326 - 329
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    In order to establish alternating current and voltage standards, various types of thermal current and voltage converters have been constructed. From their detailed analysis, the specifications and characteristics have been determined. These converters have been used in a circular international comparison. A precise comparator of 0.1-ppm resolution has been also constructed. The estimated accuracy of current converters is better than 10 ppm up to 100 kHz and that of voltage converters is better than 25 ppm up to 50 kHz and 30 ppm at 100 kHz. View full abstract»

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  • A High-Resolution Electrodynamic AC-to-DC Power Transfer Instrument

    Page(s): 330 - 333
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    The design of an electrodynamic instrument for measurement of ac power at line frequency is described. The deflection of its moving coil is kept at zero by passing alternating and direct currents simultaneously through both coils. An automatic control circuit generates the balancing direct current related to the ac power to be measured. The high resolution of the instrument, 2 × 10-7 of rated power, makes a detailed investigation of its performance in the error range below 1 × 10-5 possible. View full abstract»

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  • A Current Comparator System to Establish the Unit of Electrical Energy at 60 Hz

    Page(s): 334 - 336
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    A compensated current comparator system to establish the United States legal unit of electrical energy at the National Bureau of Standards at energy levels of approximately 30 and 60 kJ is described. Analysis of the system uncertainties and experimental data indicates that the registrations of three standard type watthour meters were determined with total estimated uncertainties of about 30 ppm at unity power factor (PF) and 40 ppm at 0.5 PF. Of these uncertainties, 18 ppm represents the three standard deviation bound for the effects of random errors, and the remainder the root sum of squares of bounds to possible calibration and systematic effects. These results indicate that it should now be possible to disseminate the energy unit with uncertainties less than the presently quoted 500 ppm. View full abstract»

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Aims & Scope

Papers are sought that address innovative solutions to the development and use of electrical and electronic instruments and equipment to measure, monitor and/or record physical phenomena for the purpose of advancing measurement science, methods, functionality and applications.

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Meet Our Editors

Editor-in-Chief
Prof. Alessandro Ferrero
Dipartimento di Elettrotecnica
Piazza Leonardo da Vinci 32
Politecnico di Milano
Milano 20133 Italy
alessandro.ferrero@polimi.it
Phone: 39-02-2399-3751
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