Direct comparison of two independent Josephson voltage standards at1 V and precision measurements up to 10 V

Two Josephson voltage standards have been compared using a room-temperature electronic nanovoltmeter with a peak-to-peak noise of about 2 nV at the 1-V level corresponding to a RMS uncertainty of 4×10^-10. The excellent stability in maintaining the desired voltage steps makes it possible to obtain recorder traces comparing Nb/Al₂O₃/Nb Josephson standards with Weston cells and Zener reference standards at 1 V and 10 V. At 10 V the best result shows a peak-to-peak noise of 250 nV corresponding to a RMS uncertainty of 5×10^-9 for a Zener reference and 50 nV corresponding to 1×10^-9 for a series connection of nine Weston cells. As an example for the application of the Josephson standard as a potentiometer the deviation in the linearity of a digital voltmeter is confirmed to be on the order of 0.1 p.p.m. in the range from -10 V to +10 V     

Dielectric properties of anodized Al-Ta alloy films with high Al content

At 1 mA cm^-2 the anodization voltage of sputtered Al-Ta alloy films with about 7 at.% Ta content rises linearly with time at a rate of 0.45 V s^-1. The Al-Ta thickness-anodization voltage ratio and the oxide growth constant have been determined, for 7–14 at.% Ta in the films with 1% citric acid electrolyte, to be 1.03-0.94 nm V^-1 and 1.42–1.5 nm V^-1, respectively. The permittivity was found to range from 10.0–11.4, corresponding to a capacitance density of about 330 pF mm^-2 for an anodization voltage of 200 V. The temperature coefficient of capacitance (t.c.c.) was 500 ppm K^-1. The capacitance between 400 Hz and 1 MHz remained constant within ±1%. At 1 kHz the disspation factor tan δ was 0.6%.Nearly all leakage currents were between 0.1 and 0.5 nA using 5.6 nF test capacitors and 50 V as the test voltage. This corresponds to an insulation resistance R of 10¹¹ Ω or more, or a time constant τ ( = RC) of approximately 1000 s. For the 50 V test the yield was about 90% and at least 80% of the capacitors had no short circuits after step stress tests up to 90 V.The current-voltage characteristics of capacitors made from Al-Ta (7 at.% Ta) films showed non-destructive breakdown voltages greater than 100 V. Only a slight deviation from symmetry was noticed whether the Al-Ta electrode was positive or negative, indicating that the capacitors were virtually non-polar. In some cases non-shorting breakdown was observed.     

CCE 92-05 intercomparison of ac-dc voltage transfer standards athigh frequencies (1-50 MHz)

From August 1995 to May 1998, the CCE 92-05 intercomparison of ac-dc voltage transfer standards at high frequencies was carried out. Two travel standards were measured by 15 national standards institutes. The results in the frequency range from 1 to 50 MHz show a good agreement between the majority of participants. The span of the majority of the reported ac-dc differences at 50 MHz is less than 1000 μV/V, which is similar to a previous intercomparison but with a greater number of participants     

Investigation of the error in transferring the dimensions of the volt using a transportable stabilitron voltage standard

The results of an investigation of the characteristics of transportable voltage standards based on stabilitrons for the purpose of using them as standards of comparison when transferring the dimension of the unit of constant voltage in accordance with the State Standard GOST 8.027-2001 are presented. It is shown that, using the standard investigated, one can transfer the dimensions of the unit of voltage with an overall relative error of 5·10⁻⁸ for a voltage of both 1.018 V and 10 V. __________ Translated from Izmeritel'naya Tekhnika, No. 1, pp. 34–38, January, 2006.     

NBS Provides Voltage Calibration Service in 0.1-10-Hz Range Using AC Voltmeter/Calibrator

Prompted by the need to support vibration and pressure measurements at frequencies down to 0.5 Hz (with expected future needs to 0.1 Hz), NBS now offers a calibration service for voltage standards and rms voltmeters in the range of 0.1-10 Hz. The means for the service is an "ac Voltmeter/Calibrator," an NBS-developed instrument containing an rms digital voltmeter and ac and dc voltage calibrators. The methods used to calibrate the ac voltage calibrator are discussed; also, application of the ac Voltmeter/Calibrator to the calibration of customers' voltage and voltmeter standards is described. Finally, a multifrequency voltage reference source with frequency-independent amplitude is proposed as a more suitable transfer standard than thermal voltage converters (TVC's) for the 0.1-10-Hz range.     

Improved method of calibration of working standards of the amplitude modulation index

A new method of indirect calibration of working standards of amplitude modulation of the 1st class based on the K2-34 setup is described. Calibration is carried out with the aid of working standards of power, voltage, and nonlinear distorition factor adopted from other calibration schemes. Translated from Izmeritel'naya Tekhnika, No. 11, pp. 53–56, November, 1997.     

Precision RF Voltage Standard Using a Thermistor Bridge Covering the HF-UHF Range

This paper describes a thermistor mount designed so that residual inductances of leads in the thermistor are eliminated for use in the UHF range. The output voltage of the thermistor bridge is evaluated by the dc substitution method with an accuracy of 0.3 percent for 0.3-1 V over frequencies up to 1.5 GHz. The output voltage agrees with the voltage derived from power and impedance standards within the accuracy.     

An Elegant Method for Measuring MOST Drain-Source Conductance in the Saturated Current Region

An elegant method is presented for measuring the drain-source conductance of an MOST operating in the saturated current region. The measuring setup allows measurement of the drain-source conductance ranging from 10-3 to 1 mU with a sensitivity of less than 0.1 percent at a frequency of 1 kHz and also measurement of the variation rate in the drain-source conductance in excess of 0.2 percent. The lower limit to the measuring range of the drain-source conductance is widened from 10-3 to 10-5 mU when an FET preamplifier is used as a front end of a comparator in which signal voltage proportional to the drain-source conductance is compared with the reference voltage. This lower conductance range can be used in measuring the drainsource conductance of an MOST operating near the cutoff point.     

Key comparisons of the VNIIM and BIPM voltage standards

The results of key comparisons of the national primary standard of Russia for the unit of electrical voltage, the volt, at the Mendeleev Institute of Metrology (VNIIM) with the Josephson effect voltage standard at the BIPM are reported. For these measurements, VNIIM provided a voltage measure based on the Josephson effect with a nominal output voltage of 10 V. Measurements were made with apparatus from the BIPM voltage standard. The VNIIM voltage measure is planned for use as a transfer standard for comparison with national standards for the volt. The comparisons indicate a high degree of equivalence of the compared VNIIM and BIPM primary standards with a relative combined standard uncertainty of 2·10–10 at 10 V.     

A low-voltage and high-frequency ac-dc transfer system usinginductive dividers

A setup for the calibration of high-input-resistance ac-measuring instruments for low voltages (mV) and high frequencies (1 MHz) is presented. The low voltages generated down to one hundredth of an ac standard voltage (0.5 V to 2 V) are traced by means of a one-decade inductive voltage divider (IVD) cascaded by a sub-IVD with a fixed ratio of 10-to-1. Construction details of the main IVD which are necessary to meet the requirements are given. The error characteristics are mainly determined by capacitive currents acting on stray and mutual inductances. The internally built-in resistive dc voltage divider and a special switch allow calibrations to be performed via effective ac-dc transfer at the standard voltage level. The first results for the calibration of a transfer standard, Fluke 792A, at 100 mV and 200 mV were in good agreement with results obtained with very sensitive multijunction thermal converters. Using such converters as standards in the new system will enable ac calibrations down to voltages below 1 mV     

A device for audio-frequency power measurement

A device for the measurement of audio-frequency power, voltage and current is discussed. The full range of power factors are accommodated (cos φ=0 to 1). Voltage and current measuring ranges are 15-600 V and 0.1-10 A, respectively. When cos φ=1, the permissible error of the power measurement is from 50 to 150 p.p.m. over the frequency range of 40 Hz to 10 kHz (including the line power frequency)     

Improvement of the Voltage Dependence of High-Voltage AC–DC Transfer Differences at the NMIJ

A new ac–dc comparator system of 20–1000 V has been developed at the National Metrology Institute of Japan (NMIJ) for the calibration of ac–dc thermal voltage converters (TVCs), which are used as national ac–dc transfer standards. The ac–dc transfer differences of high-voltage transfer standards were evaluated by a traditional step-up procedure. The voltage dependence of the ac–dc transfer difference was observed in the earlier step-up procedures over 300 V, as reported by the latest international intercomparison. The experimental results for high-voltage TVCs with several different range resistors at the NMIJ suggest that the voltage dependence may primarily be caused by input connectors of range resistors and the change in the resistance value of the resistor and TVC modules due to heating from resistors. This paper describes the voltage dependence improvement of ac–dc transfer differences over 300 V at the NMIJ.      

Automation and Evaluation of Two Different Techniques to Calibrate Precision Calibrators for Low Frequency Voltage Using Thermal Devices

Low frequency (LF) voltage and current are important parameters in electrical metrology. The standards for LF voltage and current are established by assigning AC–DC transfer difference to thermal devices, i.e. thermal converters or thermal transfer standard along with current shunts. Automated calibration systems have been developed based on Null method and measurement technique developed by Budovsky for calibration of precision calibrator in LF voltage and current against thermal devices. The technique based on the Algorithm developed by Dr. Ilya Budovsky (National Metrology Institute (NMI), Australia) has been compared with the conventional null technique. Indigenously developed software has been used to calibrate the precision calibrator in the entire LF voltage and current range using Holt thermal converters and current shunts. Calibration results at 1 V, 10 V in the frequency range from 10 Hz to 1 MHz as well as calibration results of 1 A in the frequency range from 40 Hz to 10 kHz are presented in this paper. These result shows that the measurement technique developed by Budovsky has reduced the complexity of AC–DC transfer measurements, measurement time and the uncertainty in measurement.     

A reevaluation of the NIST low-frequency standards for AC-DCdifference in the voltage range 0.6-100 V

A reevaluation of the NIST standards of ac-dc difference was undertaken in an effort to reduce the calibration uncertainty offered by NIST for thermal voltage converters (TVC's) at frequencies below 100 Hz. This paper describes the measurements taken in support of this effort, as well as the devices used for the reevaluation process and the analysis of the uncertainty of the measurements. This reevaluation of the NIST low-frequency standards will permit a significant reduction in uncertainty for ac-dc difference calibrations at 10 Hz in the voltage range from 0.6-100 V     

Effect of assist ion beam voltage on intrinsic stress and optical properties of Ta2O5 thin films deposited by dual ion beam sputtering

The optical properties and intrinsic stress of Ta₂O₅ thin films deposited by dual ion beam sputtering (DIBS) were studied as a function of the assist ion beam voltage (250-650 V). When the assist ion beam voltage was in the range of 350-450 V, the transmittance at the quarter-wave point reached its highest value (lowest absorption). The refractive index increased to 2.185 as the assist ion beam voltage increased from 250 to 350 V, but decreased as the assist ion beam voltage was further increased from 350 to 650 V.     

Experimental studies of the RF-DC differences of voltage standards

The RF-DC differences (d) of primary voltage standards have been determined by experimental and theoretical processes. Comparisons of five different types of voltage standards have been made. The RF-DC differences of some standards at frequencies from 10 Hz to 300 MHz, or even up to 1 GHz, are quite small, but the d value at frequencies from 0.1 to 50 MHz are not as small as they could be. The recommended method for determining d values is to derive an empirical formula and then to correct it from measured data. The uncertainties of primary voltage standards established by this method are ±0.007% at 1 MHz, ±0.01% at 3 MHz, ±0.02% at 10 MHz, ±0.07% at 30 MHz, ±0.15% at 50 MHz, and ±0.3% at 100 MHz     

Caractéristiques Courant-Tension Des Structures Ti/TiO2/Électrolyte Et Ti/TiO2/Métal: Effet Schottky Et Claquage

Anodic layers of TiO₂ were made with a potentiostatic setting and voltages from 1 to 90 V in 1 N sulphuric acid. The current-applied voltage characteristics of the structures Ti/TiO₂/Au and Ti/TiO₂/electrolyte are compared and analysed with the Schottky mechanism. The barrier heights calculated for the rectifying interfaces TiO₂-Au and TiO₂-electrolyte are respectively 1.2±0.1 eV and 0.88±0.05 eV. Three domains of voltage were distinguished for the anodic oxidation of titanium in the potentiostatic mode as follows: from 1 to 10 V corresponding to a natural oxide thin layer and the beginning of anodic oxidation; from 10 to 90 V corresponding to oxidation with electronic breakdown; beyond 90 V relating to oxidation accompanied by thermal breakdown.     

Experimental Verifcation of the Five-Terminal Ten-Kilohm Resistor as a Device for Dissemination of the Ohm

An experimental evaluation of five-terminal 10-kilohm hermetically sealed standard resistors as interlaboratory (transport) standards indicates that the typical drift is +0.4 ppm per year; the effects of mechanical shock to 100 G and of vibration up to 10 G at 80 Hz, less than 0.1 ppm; the effect of hot shock to 65° C, less than 0.1 ppm after five days recovery; the effect of cold shock to -20° C, less than 0.1 ppm; the effect of temperature, applying corrections, 0.06 ppm over the range 18 to 280°C, and ignoring corrections, 0.92 ppm over the range 20 to 260°C. Greater precision of comparison can be achieved at the 10-kilohm than at the 1-ohm level. Incidental to the test, agreement among the values of the ohm as derived from the computable capacitor at NSL, Australia, and from the national standards at NBS (USA) and NRC (Canada) were found to be within 0.3 ppm of the expected values from data published by the International Bureau of Weights and Measures.     

An Automatic Data Acquisition System for Semiconductor Device Testing

An automatic data acquisition system was designed and fabricated from both commercially available and proprietary special-purpose equipment to obtain the large quantities of accurate voltage versus current data needed to define and study the voltage-current characteristics of semiconductor devices exposed to neutron bombardment. The operation of the system in tracing out the entire current-voltage characteristic, per preprogrammed instructions, requires only a start command from the operator. The system is capable of measuring currents in the range of 10-10 to 2×10-1 amperes with an absolute accuracy of ±1 percent of reading and a precision (repeatability) of ±0.3 percent of reading, with a maximum voltage drop across the current sampling element of only 5 mV. This low value of voltage drop across the sampling element is made possible by the use of an autoranging technique, which selects discrete values of resistance for sampling the current being measured. The system is capable of programming input voltages from 0 to 50 V in 0.1-mV increments, or input currents from 0 to 2 amperes in increments of 0.01 to 10 ?A, depending on current range. The currents are sampled by the current sampler, whose output voltage is amplified by low-noise amplifiers, and measured by a Dymec 2401C-M31 digital voltmeter. The voltmeter readings, along with resistor identification information in digital form from the current sampler, are serialized by a Dymec 2540B coupler and recorded on a Friden Model SFD Flexowriter in both typewritten form and on punched paper tape.     

S-Co复合掺杂LiMn2O4的合成与性能

为了扩大锂离子电池正极材料LixMn2O4的工作电压范围，在保证良好循环性能的基础上提高材料的容量，本文对S-Co复合掺杂LiMn2O4的合成工艺和电化学性能进行了研究．溶胶-凝胶法合成的各试样均为纯的立方尖晶石相，且结晶状态良好．S—Co复合掺杂综合了S掺杂效应和Co掺杂效应，改善了LiMn2O4的电化学性能，在2．4—4．3V充放电压范围内，初始容量较高，达到170mAh／g，30次循环后容量不但没有衰减而且有一定增加．