Electrical Units, Fundamental Constants, and the 1983 Least Squares Adjustment

This review touches upon four topics: (1) The International System or SI electrical units, specifically, the volt (V), ohm (?), ampere (A), and the so-called laboratory or as-maintained units for the same quantities; (2) the relationships between these laboratory units, experiments to realize their SI definitions, and the fundamental constants of nature; (3) the 1983 least squares adjustment of the constants; and (4) future electrical measurements research which can improve our knowledge of the constants.     

Fundamental physical constants and systems of units for physical quantities

Fundamental questions of contemporary metrology connected with redefinition of the basic units of physical quantities are discussed. Some new definitions of the kilogram, ampere, Kelvin, and mole are suggested and their consequences are analysed. The possibility of fixing some fundamental physical constants at the level of accuracy contemporary for 2011 is considered. Alongside the practical system of units, use of a fundamental (theoretical) system is proposed. The importance is noted of considering possible variations of physical constants for a fundamental system of units, whereas in practical metrology these variations are not currently essential. __________ Translated from Izmeritel’naya Tekhnika, No. 1, pp. 3–7, January, 2007.     

The watt balance: determination of the Planck constant and redefinition of the kilogram

Since 1889, the international prototype of the kilogram has served as the definition of the unit of mass in the International System of Units (SI). It is the last material artefact to define a base unit of the SI, and it influences several other base units. This situation is no longer acceptable in a time of ever-increasing measurement precision. It is therefore planned to redefine the unit of mass by fixing the numerical value of the Planck constant. At the same time three other base units, the ampere, the kelvin and the mole, will be redefined. As a first step, the kilogram redefinition requires a highly accurate determination of the Planck constant in the present SI system, with a relative uncertainty of the order of 1 part in 10(8). The most promising experiment for this purpose, and for the future realization of the kilogram, is the watt balance. It compares mechanical and electrical power and makes use of two macroscopic quantum effects, thus creating a relationship between a macroscopic mass and the Planck constant. In this paper, the operating principle of watt balance experiments is explained and the existing experiments are reviewed. An overview is given of all available experimental determinations of the Planck constant, and it is shown that further investigation is needed before the redefinition of the kilogram can take place. Independent of this requirement, a consensus has been reached on the form that future definitions of the SI base units will take.     

The Absolute Measurement of the Ampere by Means of NMR

This paper describes the principle, apparatus, and uncertainties of the absolute measurement of the ampere by the nuclear magnetic resonance (NMR) method. A conversion factor between the as-maintained ampere of NIM and the absolute ampere is given by k = 1 -(5.81 ± 1.8) × 10-6 with a total uncertainty (1?) of 1.8 ppm. Since two methods have been used to determine the gyromagnetic ratio in proton at the same laboratory, systematic errors of the as-maintained unit can be eliminated.     

论新国际单位制(SI)的“秒制”特征及其未来发展

2019年5月20日起实行新的国际单位制,其主要变化在于7个基本单位用一个或多个定义的基本常数推导出,为基本单位确立了完美的标准定义。论述了新一轮国际单位制变革中基本单位千克、安培、开尔文和摩尔的新定义和特点;通过回溯国际单位制的发展历程,阐释了新国际单位制的“秒制”特征;最后分析了新国际单位制的问题和局限性,提出一种更加开放和包容多学科量值发展的新国际单位制体系的构想,并以此构建了新国际单位制未来发展的概念图。     

Improved estimation of residual capacity of batteries for electric vehicles

Abstract

This paper proposes an improved means of estimation for the residual capacity of lead‐acid batteries used in electric vehicles. The residual capacity of batteries in commercial products is usually indicated by the state of charge (SOC) of the battery set, in terms of the measurement of amp‐hours, or roughly an instant voltage. More practical and accurate SOC in the operation of electric vehicles must consider the original capacity when the battery is first installed, capacity deficiency due to high discharge rate, capacity dissipated in internal resistance, and correcting parameters for the battery aging process. The proposed estimation techniques include the amp‐hours measurement weighted by a correction function of various discharge rates, the transient open‐circuit voltage measurement to compensate for the energy dissipation from internal resistance, and the reset of parameters in the linear function of SOC and open‐circuit voltage for the aging effect. A monitoring circuit with a programmable logic chip is implemented, and the experimental results show that a more accurate indication of SOC is achieved using the modified estimation techniques, namely a weighted ampere‐hour measurement with transient open‐circuit voltage combined with the aging effect.     

能量天平水平安培力与电磁转矩引起对准能量误差的评估

在能量天平法原理的基础上,研究悬挂线圈特征矢量非对准状态的产生机理,分析非对准状态下水平安培力和电磁转矩之间相互耦合的作用特性,揭示两者对能量天平对准误差的影响机制;设计水平安培力和电磁转矩的双柔性铰链解耦结构,实现了两者在作用范围上的解耦,同时基于转矩平衡原理分别建立了水平安培力和电磁转矩的求解模型,并基于该模型评估了由水平安培力和电磁转矩做功引起的能量天平对准相对误差值为1×10^-6。      

SI基本单位量子化重新定义及其意义

第26届国际计量大会(CGPM 2018)表决通过了国际单位制(SI)中7个基本单位的重新定义,其中千克、安培、开尔文和摩尔的定义基于新的物理概念,米、秒和坎德拉的定义表述进行了重新修订;运用自然法则创建测量规则,自此,新修订后的SI基本单位的定义来自一组定义常数,实现了量子化定义。新SI更具有稳定性和普适性,新SI的实现为各国计量领域将带来机遇与挑战。     

电脉冲对2024 铝合金力学性能的影响

目的研究电脉冲辅助作用下铝合金板材的力学性能。方法通过直流电脉冲辅助单向拉伸实验,研究25 Hz频率下,不同电流密度脉冲电流对2024-T4态铝合金的力学性能的影响规律。结果在所通频率及电流密度脉冲电流作用下,随着脉冲电流密度的增加,2024-T4铝合金板延伸率和流变应力均减小,说明所采用参数脉冲电流辅助可以起到降低成形载荷的目的,但不利于提高材料成形极限。结论 25 Hz频率下脉冲电流辅助不利于2024铝合金的塑性提高,却可降低材料的成形载荷,且塑性、成形载荷随电流密度的增加而降低。     

The Characteristic of a Probe in Moving Collisional Plasma for the Flow Stagnation Point

The volt–ampere characteristics of a wall probe located at the critical point of a sphere or cylinder subjected to the flow of a collisional weakly ionized plasma in the boundary layer mode are obtained for the case of a thin layer of volume charge.     

Programmable Current Regulator for High-Voltage Operation

A current regulator for the operation of gas discharges is described, capable of delivering peak currents up to 1 ampere and average currents of up to 0.5 ampere with voltage excursions to 9 kV. Completely floating two-terminal operation accomodates different load configurations. By means of externally supplied timing pulses the output current can be programmed to generate rectangular or trapezoidal current waveforms. For rectangular output pulses, switching speeds of 5 ?s into low-impedance loads and slewing rates of 500 V/?s for high-impedance loads can be obtained. The output resistance is in excess of 107 ohms, shunted by 50-250 pF, depending on regulator configuration.     

非晶Co-W-B/碳布复合电极材料的制备及其电解水催化性能

通过湿化学还原在碳布(CC)表面沉积非晶Co-W-B催化活性物质,制备一种自支撑Co-W-B/碳布(Co-W-B/CC)复合电极材料。电化学研究结果表明,Co-W-B/CC材料在NaOH溶液(1 mol/L)中表现出良好的电解水催化性能。制备过程中[WO₄^2-]/([WO₄^2-]+[Co²⁺])比值为50%的Co-50W-B/CC样品其催化活性最高：10 mA/cm²时的OER过电位为0.394V,OER过程的Tafel斜率为96.8 mV/dec;-10 mA/cm²时的HER过电位为0.098 V,HER过程的Tafel斜率为117.4 mV/dec。对电化学阻抗的分析结果表明,本征催化活性和电化学活性面积两者的提高,使Co-50W-B/CC样品在较低的电流密度下具有与贵金属基材料相近的催化活性。     

Adapting the International System of Units to the twenty-first century

We review the proposal of the International Committee for Weights and Measures (Comité International des Poids et Mesures, CIPM), currently being considered by the General Conference on Weights and Measures (Conférences Générales des Poids et Mesures, CGPM), to revise the International System of Units (Le Système International d'Unitès, SI). The proposal includes new definitions for four of the seven base units of the SI, and a new form of words to present the definitions of all the units. The objective of the proposed changes is to adopt definitions referenced to constants of nature, taken in the widest sense, so that the definitions may be based on what are believed to be true invariants. In particular, whereas in the current SI the kilogram, ampere, kelvin and mole are linked to exact numerical values of the mass of the international prototype of the kilogram, the magnetic constant (permeability of vacuum), the triple-point temperature of water and the molar mass of carbon-12, respectively, in the new SI these units are linked to exact numerical values of the Planck constant, the elementary charge, the Boltzmann constant and the Avogadro constant, respectively. The new wording used expresses the definitions in a simple and unambiguous manner without the need for the distinction between base and derived units. The importance of relations among the fundamental constants to the definitions, and the importance of establishing a mise en pratique for the realization of each definition, are also discussed.     

Wide-Range Low Current Measurements of Diode Reverse Currents with Automatic Ranging Features

This paper describes a method used successfully by the author in measuring silicon diode reverse leakage currents. The technique used is straightforward and provides wide-range, low current measurements with improved accuracies and automatic ranging features. The full-scale indications extend from 10-3 through 10-10 amperes in eight decade ranges. The full-scale accuracies achieved are better than ±0.5 per cent on ranges 10-3 through 10-8 amperes, ±1 per cent on the 10-9 ampere range, and ±10 per cent on the 10-10 ampere range. The automatic ranging feature exhibits a response of 10 msec per range. The method used is based on sensing the voltage drop (ES) across a sensing resistor (RS). This sensing resistor is in series with the reverse biased diode, as shown in Fig. 1. The sensing voltage is then amplified to an appropriate level (Eo) which can be more easily and accurately measured and/or digitized, depending upon the type of output display and storage method used.     

The NBS Absolute Ampere Experiment

We have constructed a current balance with superconducting field coils for the realization of the SI ampere by comparing mechanical to electrical work. The estimated ultimate accuracy of the realization is 0.1 ppm. We describe and present preliminary results obtained with a room temperature version of the apparatus.     

The Realization of the Ampere at NBS

We present a method for the realization of the ampere based on Faraday's induction law and using a modification of the classic Pellat balance. A preliminary apparatus has been constructed and initial measurements have been obtained. This balance is also compared with a balance similar to one proposed earlier.     

Enhanced Portable LUT Multiplier with Gated Power Optimization for Biomedical Therapeutic Devices

Digital design of a digital signal processor involves accurate and high-speed mathematical computation units. DSP units are one of the most power consuming and memory occupying devices. Multipliers are the common building blocks in most of the DSP units which demands low power and area constraints in the field of portable biomedical devices. This research works attempts multiple power reduction technique to limit the power dissipation of the proposed LUT multiplier unit. A lookup table-based multiplier has the advantage of almost constant area requirement’s irrespective to the increase in bit size of multiplier. Clock gating is usually used to reduce the unnecessary switching activities in idle circlet components. A clock tree structure is employed to enhance the SRAM based lookup table memory architecture. The LUT memory access operation is sequential in nature and instead of address decoder a ring counter is used to scan the memory contents and gated driver tree structure is implemented to control the clock and data switching activities. The proposed algorithm yields 20% of power reduction than existing.     

Fine-structure constant obtained from an improved calculation ofthe electron g-2

A preliminary result is presented for an accurate determination of the fine-structure constant α based on an improved evaluation of the sixth- and eighth-order radiative corrections to the electron anomalous magnetic moment α_e. In combination with a very precise measurement of α_e, this leads to the most accurate value of α obtained thus far, with a relative standard uncertainty of less than 4×10^-9     

Design Concepts of Optimized MRI Magnet

This paper describes a simple technique to design compact air core magnets for magnetic resonance imaging (MRI). The optimum geometry is obtained by a combination of analytical and numerical methods. The technique emphasizes achieving the required field homogeneity with a shorter magnet having a minimum amount of ampere turns. The code calculates the total inductance of the set of coils, total conductor length, force, and maximum field on each coil. The code also calculates the allowable geometrical tolerance to achieve the field uniformity. The code is flexible and can be used for various geometries. Here, we present three different cases to demonstrate the efficiency of the code. First, we present the design details of a 1.5 m long 1.5 T actively shielded magnet, where the stray field is reduced to less than 4 gauss outside the sphere of radius 3.65 m using a pair of shielded coils. A total of four pairs of coils provide a field uniform to within 5.2 parts per million (ppm) within a sphere of 50 cm diameter. Calculated values of all the higher order moments lie within a few ppm. Second, we describe optimized geometry of unshielded 1.5 T symmetric magnets having three pairs of coils. Third, we optimize the geometry of a 1.2 m long 1 T asymmetric magnet having five coils. Here, the good field region starts at 20 cm from one of the edges of the magnet, providing the attending physician better accessibility to the patient. But the ampere turns and computation time required are quite large compared to a symmetric magnet.      

Thermal Calculation of the Furnace Chamber of a Fire‐Tube Boiler With a Dead‐End Furnace

An engineering procedure for calculating the thermal regime of the furnace chambers of firetube boilers with a deadend furnace is given. The procedure proposed is devoid of many drawbacks that are inherent in the standard method for calculating boiler units and permits more accurate allowance for the special features of combined energy exchange in furnace chambers of boilers that differ significantly in type and size from traditional ones.