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Instrumentation and Measurement, IEEE Transactions on

Issue 4 • Date Nov. 1970

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Displaying Results 1 - 25 of 48
  • [Front cover]

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

    Page(s): c2
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    Freely Available from IEEE
  • Table of contents

    Page(s): 195
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  • Foreword

    Page(s): 196 - 197
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  • Scanning the issue

    Page(s): 198 - 199
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  • Measurement of the Unperturbed Hydrogen Hyperfine Transition Frequency

    Page(s): 200 - 209
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    The results of a joint experiment aimed primarily at the determination of the frequency of the H1 hyperfine transition (F = 1, mF = 0) ¿ (F = 0, mF = 0) is reported. In terms of the frequency of the Cs133 hyperfine transition (F = 4, mF = 0) ¿(F = 3, mF = 0), defined as 9192 631 770 Hz, for the unperturbed hydrogen transition frequency the value ¿H = 1420 405 751.768 Hz is obtained. This result is the mean of two independent evaluations against the same cesium reference, which differ by 2 × 10-3 Hz. We estimate the one-sigma uncertainty of the value ¿H also to be 2 × 10-3 Hz. One evaluation is based on wall-shift experiments at Harvard University; the other is a result of a new wall-shift measurement using many storage bulbs of different sizes at the National Bureau of Standards. The experimental procedures and the applied corrections are described. Results for the wall shift and for the frequency of hydrogen are compared with previously published values, and error limits of the experiments are discussed. View full abstract»

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  • Analysis of Modulation Method for Measuring Atomic Resonant Frequency

    Page(s): 209 - 215
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    In microwave spectroscopy and in atomic frequency standards, the atomic resonant frequency is often determied by the use of harmonic frequency modulation of a microwave signal. The effects of line asymmetry and modulating-signal nonlinear distortions are investigated by the use of an analytic approximation of the resonance line by means of an algebraic polynomial. The coefficients of the polynomial are determined experimentally and also derived theoretically. Detailed numerical results for a Ramsey resonance line in a cesium clock are given. View full abstract»

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  • A Test Set for the Accurate Measurement of Phase Noise on High-Quality Signal Sources

    Page(s): 215 - 227
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    The test set described here is capable of measuring the spectral density of phase noise on carrier frequencies from 1 to 500 MHz, for offset frequencies from 20 Hz to 50 kHz. Measurements to 50 MHz are described. The test set has a residual single-sideband phase-noise-power-to-signal-power ratio of -142 dB/Hz at 20 Hz offset from the carrier, which decreases to a floor of -172 dB/Hz at offset frequencies greater than 5 kHz. The estimated calibration accuracy achievable is ±0.8 dB, exclusive of random reading errors due to the Gaussian distribution of the phase fluctuations being observed. The estimated 1 ¿ repeatability of a measurement is 0.7 dB (70 percent of the observations on a given test will fall within ±0.7 dB of the average value). This test set is capable of characterizing the phase-noise performance of existing atomic frequency standards, crystal oscillators, frequency synthesizers, and other high-quality sources more accurately than has previously been possible. The increased accuracy has been achieved by a system design that minimizes readout fluctuations, allows for the accurate measurement of correction factors used to reduce systematic errors, and minimizes the possibility of operator error and bias. View full abstract»

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  • Comparison of National Time Standards by Simple Overflight

    Page(s): 227 - 232
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    The Office National d'Études et de Recherches Aérospatiales has devised a method of time synchronization by what is described as "simple overflight," relying on a high-precision airborne timepiece, without the need to go close to the clocks under comparison. The method has repeatedly been tested, and the results show the accuracy of synchronization to be better than 50 ns. A comparative experiment between the observatories of Paris, France, Hailsham, England, Ottawa, Canada, and Washington, D. C. will be carried out in September 1970. View full abstract»

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  • Time Synchronization by Television

    Page(s): 233 - 238
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    A simple technique for clock synchronization uses signals included in normal television transmissions as time markers. By use of automatic equipment built in the laboratory, it has been possible to make regular comparisons of time scales. Remote time laboratories can also be intercompared by this process. Accuracy of a fraction of a microsecond can be obtained easily. Numerical results of different experiments and comparisons with other methods are presented. View full abstract»

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  • Automated Characterization of Bolometric and Electrothermic Mounts

    Page(s): 239 - 245
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    The greatest inaccuracy in making a microwave power measurement is usually the uncertainty of the calibration factor or the effective efficiency. These terms account for the RF losses and substitution errors in the bolometric or electrothermic mount. A new method for transferring calibration from a standard mount to a mount to be calibrated has production line speed and simplicity; yet its accuracy rivals standards laboratory techniques. This method uses an automatic network analyzer to measure the quantities required and to solve the mismatch equation in transferring calibration from the standard mount to the one to be calibrated. A technique is also described to evaluate the errors of the transfer measurement. An accurate method of measuring the complex reflection coefficient of a stabilized source is another result of this work. The present implementation measures effective efficiency, calibration factor, and the magnitude and phase of the reflection coefficient of a mount at six calibration frequencies in 60 seconds. The uncertainty in transferring calibration factor and effective efficiency is about 0.5 percent. View full abstract»

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  • Automatic Self-Certification of a Computer-Controlled Calibration System

    Page(s): 245 - 252
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    The theory, techniques, and apparatus that are used to perform an automatic self-certification of a computer-controlled calibration system are described. This process determines the linearity and bias deviations of the instrumentation of the system. These deviations are stored in the digital computer for subsequent use as corrections to the nominal instrument values when the system is applied to external devices. Dc measurements and stimuli, the uncertainties of which are of the order of 0.001 percent, have been achieved using this technique, exceeding the specifications normally associated with the uncorrected instrumentation. A similar reduction in uncertainty results from the self-certification process in ac voltage and resistance measurements. Using a 1-volt dc source, 1000-ohm resistor, and ac-dc thermal transfer as references, the scales of measure are automatically reestablished over a wide dynamic range in less than five minutes. Laboratory applications of this computer-controlled system have been made to classical metrology problems that include measurements of standard resistors, saturated standard cells, and resistance thermometers. Semi-automatic calibrations of test and measuring instruments have been performed to demonstrate potential productivity and accuracy. View full abstract»

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  • Automated Precision Polarimeter for the HF-VHF Range

    Page(s): 252 - 259
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    An automated system for Stokes parameter-polarization analysis over the HF-VHF range is described. Axial ratio, orientation angle, polarization fraction, and polarization sense are determined by amplitude measurements using a conventional fieldintensity receiver. Six amplitude measurements from four crossed nonresonant dipoles, including quadrature sum and difference, eliminate the requirement for phase measurement. The antenna does not use active components and is adaptable for mobile or stationary operation. VSWR measurements on the antenna output cables show less than 1.2:1 (50 ohms) over the 2-70 MHz range. The antenna aperture increases from 1 × 10-5 square meters at 2.0 MHz to 0.019 square meters at 70 MHz. A solid-state sequencer processes each amplitude measurement separately through the receiver and digital conversion circuits (providing BCD output) to an incremental tape recorder. The Stokes parameter analysis is performed by an off-line digital computer using the magnetic tape data. This analysis permits computation of total received power from either set of orthogonal element measurements. When combined with the measured antenna aperture, power density (or field strength) also can be derived. Polarization fraction measurements for locally controlled signals show a mean of 1.02 as compared to a theoretical value of 1.00 (standard deviation of 0.1) over the 2-70 MHz range and polarization results consistent with propagation predictions. View full abstract»

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  • Redundant Measurements in Microwave Research and Development

    Page(s): 260 - 262
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    Capability and accuracy of microwave measuring methods and instruments can be substantially improved by the use of general-purpose digital computers. One of the fruitful applications is concerned with redundant measurements and their evaluation. In a redundant measurement more data are measured than would be necessary for a singular evaluation and the excess information is used to reduce measurement errors. Redundant measurements are advantageous for sophisticated microwave measurements where the final results can be determined only by tedious graphical or numerical transforms of measured data. Redundant measuring methods also can be used to verify network or device models and, to determine the parameters of these models. The evaluation of redundant measurements can be carried out in simple cases by averaging and generally by fitting the hypothetical parameters to the measured data (e.g., by least-square error method) or by using integral transform (e.g., Fourier transform) techniques. Digital computers enable one to make fast and accurate evaluations. View full abstract»

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  • Truly Transportable Standard-Cell Air Bath

    Page(s): 263 - 266
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    Dissemination of the volt is complicated by the complex temperature response of standard cells. Discribed are the design and performance characteristics of an experimental standard-cell airbath specifically optimized for transportable voltage-dissemination service. Salient features of this bath are 1) ±0.001°C control of the cell temperature in the laboratory, ±0.02°C maximum variation around 28°C in shipment; 2) exposure capacity from over 8 hours at 0°C or 45°C to over 72 hours in moderate temperatures; 3) shipping package weight 14.5 kg, size 20.3 × 22.9 × 30.5 cm; and 4) electrical power drain 0.8-0.2 watt. Cell temperature is determined primarily by an ambient-temperature-biased on-off heater system. Immunity to external environment is achieved by a unique secondary control, which employs the energy storage capacity of two heat-of-fusion alloys, which are reset simply by exposure to laboratory temperature. Experience with this bath has shown that the average value of cell voltage is reproducible to 0.1 ¿v within a few hours following shipment. This time delay is significantly shorter than the days-to-weeks for most air baths and the weeks-to-months for cells shipped without temperature control. View full abstract»

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  • Resistive Voltage-Ratio Standard and Measuring Circuit

    Page(s): 266 - 277
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    This paper describes a highly stable, guarded dc voltage-ratio standard and the measuring network and techniques used to establish the values of its ratios to an accuracy of 0.2 ppm. The entire system is housed within a dry-air enclosure whose temperature is maintained at 23 ± 0.05°C. Discrete ratios from 1:1 to 1000:1 are provided, with maximum rated voltage set at 1000 volts. The design of the standard was chosen so that a redundancy of measurement could be incorporated in the system. Thus each successive ratio is measured by a substitution or "bootstrap" method and by satisfying the conditions of the series-parallel principle, the 10:1, 100:1, and 1000:1 ratios are measured by a second independent method. The design also admits additional checks on the validity of the measurements. An analysis of measurement errors and a discussion of their possible origin are included. Since the intent also was to design the ratio standard for low-frequency operation some preliminary data are included on its ac performance. View full abstract»

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  • 10-kY 10-mA DC Supply with 0.1-ppm Stability

    Page(s): 278 - 281
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    A 10-kV stabilized supply with a dc capacity of 10 mA has been constructed. Its drift rate measured over time intervals greater than about 1 minute and extending to times of more than 10 hours is about 1 part in 107 per hour. For shorter times from 1 second to 1 minute the peak-to-peak deviation from the mean is about 2 mV at 9.2 kV or ±1 part in 107. This performance has been achieved by the use of an initially well regulated commercial 10-kV supply in a closed-loop control system. High dc loop gain has been achieved by the use of a chopper-stabilized amplifier, and a guarded resistive divider of special design. The reference voltage is made up of a bank of unsaturated standard cells enclosed in a temperature-controlled air bath whose short term temperature stability is ±0.001°C. The control resistive divider, together with a measuring divider and a guard divider, are enclosed in an oil bath whose temperature is controlled near ambient to within ±0.01°C. View full abstract»

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  • Dual Highly Stable 150-kV Divider

    Page(s): 281 - 285
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    A highly stable (± 1-ppm) 500-kV power supply is being developed for use in a high-resolution (~1-Å) electron microscope. One of the critical components in such a power supply is, of course, the feedback element, which, in this case, is a resistive voltage divider. A dual 150-kV divider has been constructed to determine the stability of such devices. The dividers are compared in a guarded Wheatstone bridge circuit and appear to be stable to within a few parts in 108 when operating at 150 kV. The high-voltage section of each divider consists of 150 1-M¿ resistors. View full abstract»

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  • Pulsewidth Modulation DC Potentiometer

    Page(s): 286 - 290
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    This instrument uses pulsewidth modulation techniques in which a crystal oscillator, frequency divider, and preset counter replace the resistive divider to form a precision potentiometer. The smoothing of the time-division intervals to a steady-state direct current without introducing prohibitive time constants is solved by a "sectional average" integrating circuit. This utilizes a short time-constant integrator combined with a switched unity-gain buffer amplifier in the feedback to integrator input. This switch, integrate, and sample-and-hold circuit provides output within ±0.1 percent of the eventual steady-state value in less than 400 ms after a step change and within ±0.001 percent in 600 ms. The system provides digital compatibility with tape, cards, digital voltmeters, etc. An engineering prototype has 7 decade dials covering a 0-100.0000-volt range with ±(0.1 ppm + 5¿V) voltage-ratio accuracy and, ±0.05 ppm/50°C temperature coefficient and ±0.05 ppm/ 10-week long-term stability, and it is expected that this may be improved. View full abstract»

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  • Direct-Current Comparator Bridge for Resistance Thermometry

    Page(s): 291 - 297
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    The design, construction, and performance of a dc bridge that covers the complete range of both platinum-and germanium-resistance thermometry in four ranges, 0-11 up to 0-11 000 ohms, is described. The bridge uses a potentiometric method based on the current comparator. In the design, emphasis has been placed on reducing the noise level, on obtaining a single-balance operation, and on providing a recorder output. Detector sensitivity and noise level (with a three-second time constant) permit full eight-decade bridge resolution to be achieved at a thermometer current of I mA on all ranges except the lowest, which requires 5 mA. Bridge errors are believed to be less than 10-7 of a reading or one step on the last dial, whichever is larger. A facility is provided for measuring the self-heating effect of the thermometer, even if the measured temperature is not constant. The bridge is also suitable for the measurement of four-terminal standard resistors over the same ranges. View full abstract»

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  • Improved Horizontal Cross Capacitor

    Page(s): 297 - 302
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    A new horizontal cross capacitor was constructed to achieve higher accuracy in the determination of absolute capacitance values. To eliminate some major causes of the uncertainty that had been found in the earlier capacitor, the bars were finished more precisely and new mechanisms were adopted. These are a fine adjusting mechanism for alignment of the bars and a supporting mechanism of the bars that prevents them from bending because of gravity. A nonrotating guard-tube driving mechanism was used. The bars could be aligned within 0.1 pm or less. The alignment was inspected with capacitance-type electronic micrometers. The bending dip of the bars was estimated to be negligibly small. The uncertainty in the absolute determination of 0.2 pF with this capacitor is estimated to be of the order of 10-7. View full abstract»

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  • New Fused-Silica-Dielectric 10-and 100-pF Capacitors and a System for Their Measurement

    Page(s): 302 - 307
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    New instruments have been designed to bring to standards laboratories the improved accuracy of capacitor calibrations developed by the National Bureau of Standards. The new 10-and 100-pF reference standard capacitors, based upon an NBS design, use a fused-silica dielectric with gold electrodes to provide the time and voltage stability required for calibrations to parts in 107. To maintain the capacitor temperature constant to within 0.01 °C, one model of the capacitors is designed for use in an oil bath, the other model is fitted with a new, stable, thermostatically controlled air bath. The system to measure these capacitors with a precision of parts in 108 consists of a bridge, detector, and oscillator. For these special measurements and for the general calibration of a wide range of capacitors, the new transformer-ratio-arm bridge has 12 capacitance decades and a range of 10 MAF-10-7 pF, and five conductance decades and a range of 103110-10 tmho. The new phasesensitive detector and power oscillator provide high sensitivity to bridge imbalance over the frequency range 10 Hz-100 kHz. View full abstract»

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  • Four-Terminal Equal-Power Transformer-Ratio-Arm Bridge

    Page(s): 308 - 311
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    A transfonner-ratio-arm bridge is described that combines the high sensitivity of equal-power bridges with the immunity from lead errors of ac bridges analogous to the Kelvin double bridge. The latter apply either equal current or voltage to both impedances being compared and suffer a reduction in sensitivity when the impedance ratio is high, while the sensitivity of bridges that apply equal power (or voltamperes) to both impedances is independent of this ratio. The new bridge has two transformers in addition to the two of the usual equal-power bridge to reduce lead-impedance errors. Two current loops are formed around each of the two impedances being compared making four-terminal connections to both. The auxiliary transformers couple between loops on the two sides of the bridge and act to maintain accurate current and voltage ratios in spite of series impedance. The expression for the error due to lead impedance is given and is compared with those for other four-terminal bridges and with measured results. A lead-impedance-balance procedure is given that reduces lead errors still further. View full abstract»

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  • Isolated-Section Inductive Divider and Its Self-Calibration

    Page(s): 312 - 317
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    A high-precision isolated-section inductive divider, designed for self-calibration, has been developed. In this new design principle, the two major sources of ratio error, excitation current and current through stray capacitance between sections of divider windings, have been greatly reduced by the use of a separate excitation winding and a guard for the divider winding. In a self-calibration divider ten divider winding sections are electrostatically isolated from each other by their guards. The divider can be calibrated by internal exchange of the winding sections and comparison with an auxiliary divider having a fixed nominal ratio of 0.1, similar to the calibration of a resistive divider. The design principle is also applied to another divider in which a second winding is added. This divider can be used for a high-precision multidecade divider and for the calibration of other ininductive dividers using a "boot-strapping" method. Construction details of the dividers, sources of errors, results of self-calibration, and evaluation of uncertainties are presented. The uncertainties of the self-calibration are estimated to be ±3 X 10-9 of the input at 100 Hz to 1 kHZ, and ±30 X 10-9 at 10 kHz. View full abstract»

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  • New Coaxial RF-DC Ammeter

    Page(s): 318 - 323
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    A unique new type of RF ammeter is described. The ammeter combines broad frequency coverage with broad current range and is designed for use in a 50-ohm coaxial transmission line. The ammeter consists of an elliptic-cylinder silver reflector of infrared energy with a cylindrical thick-film heater along one focus and a heat-sensing thermopile along the other focus. Advantages over older ammeter designs include a shielded construction with inherent electrical isolation between the RF and dc circuits, a large dc output (approximately 1-100 mV) corresponding to a decade dynamic range (0.25-2.5 amperes), and a frequency range from dc to about 1 GHz. This coaxial ammeter is believed to be the first to have very low standing-wave ratio (SWR) (1.03) in a 50-ohm transmission line. Ammeters of lower current range can be built, but at a penalty of increased SWR due to the larger heater resistance required. 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
Fax: 39-02-2399-3703