Precise Current Measurements Research Articles

Single-crystal magneto-optic sensor with electrically adjustable sensitivity

A novel magneto-optic sensor with electrically adjustable sensitivity is proposed that is based on the approximate multiplication correlation between the linear electro-optic phase retardation and the Faraday magneto-optic rotation angle in a single bismuth germanate crystal. The measurement sensitivity and its temperature stability, linear and monotonic measurement ranges of the proposed sensor can be controlled in real time by adjusting the modulating voltage applied to the sensing crystal. In particular, the proposed sensor can be used for the precise measurement of dc magnetic field or dc current. The basic sensing performance is theoretically analyzed and experimentally demonstrated by dc current measurement.

Design of a New Faraday Cup to Measure the Beam Current of an Ion Source with Residual Gas

Different parameters affecting the faraday cup (FC) performance are investigated. It is shown that the FC design depends on the incident particle beam parameters. If FC is used to measure the beam current of a dense plasma focus device or if FC is used to measure the beam current of an ion source where there is residual gas, it should allow the secondary electrons to escape from the cup. Then the effect of the escaped electrons must be estimated somehow. Otherwise, to ease the calculations, FC should be designed to recapture the secondary electrons. Here, we propose a novel FC to measure the particle beam current of an ion source where residual gas or electromagnetic noise exists. To obtain precise beam current measurement, FC performance is simulated by CST Studio soft ware. In addition, a method is proposed for the analysis of the FC signals.

Development of an extremely precise buffer amplifier for AC shunt standards at audio frequencies

AbstractThe National Metrology Institute of Japan (AIST, NMIJ) launched a project for the development of AC shunt standards. AC shunts allow the most precise measurement of current. A high‐precision AC shunt is an important component of nonsinusoidal power standards. The AC shunt calibration system helps improve the uncertainty assessments of the national primary power standards. The calibration system design with uncertainties of up to 10 ppm requires a precise buffer amplifier which has uncertainties of up to 1 ppm in the frequency range from 10 Hz to 10 kHz, with other uncertainty components taken care of. The two buffer amplifiers dealt with in this paper were verified to have errors within 2 ppm and uncertainties within 1 ppm in in‐phase and quadrature error in the frequency range from 10 Hz to 10 kHz. This also implies a possibility of reducing both in‐phase and quadrature error at 10 kHz within 1 ppm, by taking advantage of both features. This paper describes the circuit design and evaluation results of two different buffer amplifiers. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(4): 24–31, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21218

用束流位置监测器精确测量储存环流强

用束流位置监测器精确测量储存环流强

Motor Fault Detection Using a Rogowski Sensor Without an Integrator

This paper presents a new approach for the current acquisition system in motor fault detection applications. This paper includes the study, design, and implementation of a Rogowski-coil current sensor without the integrator circuit that is typically used. The circuit includes an autotuning block able to adjust to different motor speeds. Equalizing the amplitudes of the fundamental and fault harmonics leads to higher precision current measurements. The resulting compact sensor is used as a current probe for fault detection in induction motors through motor current signal analysis. The use of a Rogowski coil without an integrator allows a better discrimination of the fault harmonics around the third and fifth main harmonics. Finally, the adaptive conditioning circuit is tested over an induction machine drive. Results are presented, and quantitative comparisons are carried out.

Diffuse mode and diffuse-to-filamentary transition in a high pressure nanosecond scale corona discharge under high voltage

The dynamics of a point-to-plane corona discharge induced in high pressure air under nanosecond scale high overvoltage is investigated. The electrical and optical properties of the discharge can be described in space and time with fast and precise current measurements coupled to gated and intensified imaging. Under atmospheric pressure, the discharge exhibits a diffuse pattern like a multielectron avalanche propagating through a direct field ionization mechanism. The diffuse regime can exist since the voltage rise time is much shorter than the characteristic time of the field screening effects, and as long as the local field is higher than the critical ionization field in air. As one of these conditions is not fulfilled, the discharge turns into a multi-channel regime and the diffuse-to-filamentary transition strongly depends on the overvoltage, the point-to-plane gap length and the pressure. When pressure is increased above atmospheric pressure, the diffuse stage and its transition to streamers seem to satisfy similarity rules as the key parameter is the reduced critical ionization field only. However, above 3 bar, neither diffuse avalanche nor streamer filaments are observed but a kind of streamer–leader regime, due to the fact that mechanisms such as photoionization and heat diffusion are not similar to pressure.

Measuring the Force of Interaction between a Metallic Probe and a Single Molecule

Precision current measurements are recorded at 5 K during the approach and contact between a Pt-inked probe and the carbon-carbon double-bond region of an isolated 1,3-cyclohexadiene molecule chemisorbed on a Si(100) surface. Scanning tunneling spectroscopic data reveal systematic features in the current at specific probe-molecule separations. Aided by density functional theory calculations, we show that these features arise from interaction forces between the probe and molecule, which can be interpreted as the relaxation of the probe-molecule system prior to and during contact.

공심코어를 사용한 교류전류 센서

본 연구는 미래의 가정에 설치되 전자식 전력량계의 정밀 전류측정용 센서 개발에 관한 내용이다. 전류센서는 공심코어 원리를 사용하기 때문에 일반 변류기(current transformer)의 자기포화와 비선형 오차의 한계 영향이 적다. 개발된 센서는 저전류 범위에서 선형도의 개선과 함께 공심코어를 사용하므로 제작이 간단한 장점을 가지고 있다. FEM solver 를 사용하여 자기장 해석을 하였으며 실제 측정된 값과 계산에 의한 값을 비교하였다. This paper describes a current sensor for precision current measurement of an electronic watt-hour meter that is going to install in houses in the future. As the current sensor is based on an cored principle (the Rogowski principle) it is not subject to usual limitations of saturation and non-linearity of general current transformers. An advantage of the developed current sensor is that non-linearity error in low current range is improved and the construction can be kept simple using an air core. We present a magnetic field analysis of the sensor using a finite-element solver. We compared the measured values versus the calculated values.

Transport Kinetics of Uncoupling Proteins: ANALYSIS OF UCP1 RECONSTITUTED IN PLANAR LIPID BILAYERS

According to alternative hypotheses, mitochondrial uncoupling protein 1 (UCP1) is either a proton channel ("buffering model") or a fatty acid anion carrier ("fatty acid cycling"). Transport across the proton channel along a chain of hydrogen bonds (Grotthus mechanism) may include fatty acid carboxyl groups or occur in the absence of fatty acids. In this work, we demonstrate that planar bilayers reconstituted with UCP1 exhibit an increase in membrane conductivity exclusively in the presence of fatty acids. Hence, we can exclude the hypothesis considering a preexisting H+ channel in UCP1, which does not require fatty acid for function. The augmented conductivity is nearly completely blocked by ATP. Direct application of transmembrane voltage and precise current measurements allowed determination of ATP-sensitive conductances at 0 and 150 mV as 11.5 and 54.3 pS, respectively, by reconstituting nearly 3 x 10(5) copies of UCP1. The proton conductivity measurements carried out in presence of a pH gradient (0.4 units) allowed estimation of proton turnover numbers per UCP1 molecule. The observed transport rate of 14 s-1 is compatible both with carrier and channel nature of UCP1.

Practical aspects for SQUID applications

Classical applications of superconducting quantum interference devices (SQUIDs), like biomagnetic measurements or precision voltage and current measurements have in almost all cases been carried out in a magnetically and electrically well shielded environment. Recently, the demonstration of highly sensitive HTS SQUIDs has increased the interest in SQUIDs for a broader range of applications like geophysical measurements or nondestructive materials evaluation. The operation of SQUIDs in an unshielded environment, however, leads in many cases to a significant reduction in their sensitivity due to numerous sources of interference and excess noise. The paper reviews recent work on aspects related to the operation of SQUIDs in unshielded environments.

Microdischarges in air-fed ozonizers

The behaviour of microdischarges in air-fed ozonizers is investigated experimentally and theoretically. High-speed streak and single-picture photographs as well as precise current measurements reveal details in the discharge development, which are modelled by a quasi two-dimensional numerical simulation. The modelling is based on the solution of a system of continuity equations in connection with the Poisson equation. Space charge effects have been taken into account. The results of the modelling are compared with those of experiments. Fundamental features of microdischarges, which influence the properties of air-fed ozonizers are described.

Electrical transport analysis of ultra-pure silicon

Silicon with ever increasing purity and perfection is demanded for devices with smaller feature sizes and for specialized applications such as infrared detectors. Achievement of high purity Si has necessitated development of measurement procedures and data analysis techniques that are quantitatively sensitive to very low concentrations (<10 ppta) of electrically active impurities. Described are results from a research program that has improved all aspects of the temperature dependent Hall effect experiment while emphasizing p-type Si with very low concentrations of residual impurities. The improvements cover sample preparation and contacting, precise voltage and current measurements over a broad temperature range (4.2–400 K), sensitive temperature control, and calculations of the effective mass, m *( T), and the Hall scattering factor, r( T), that incorporate the valence bands' non-parabolicities and anisotropies. This is a quantitative technique that can be used as a standard for other analytical methods such as photoluminescence and photoabsorption. Two classes of high purity Si have been studied, namely undoped intrinsic material with boron as the dominant residual impurity at concentrations below 10 12 cm -3 (20 ppta) and material doped (generally with Group III elements) to concentrations in excess of 10 16 cm -3 in the presence of residual impurity concentrations near or below 10 12 cm -3. Results from the measurement of samples with a variety of doping and impurity concentrations are shown. Comparisons between the mobility calculations and the measured mobilities are discussed as well as direct measurements of r( T) made on intrinsic Si at low temperatures. Significant improvements in the ability to measure high purity samples have been realized and in some cases the accuracy has been increased by over 50% in the measured dopant and impurity concentration values.

Observation of a current-limited double layer in a linear turbulent-heating device

Time- and space-resolved measurements of strong double layers (DLs) have been carried out for the first time on a linear turbulent-heating device, together with those of fluctuation spectra and precise current measurements. A stable stong DL is formed even when the electric current through the DL is less than the so-called Bohm value. Discussion of the formation and decay processes is given, indicating a transition from an ion-acoustic DL to a monotonic DL.

An accelerator voltage regulating system using a position sensitive Faraday cup

A Faraday cup has been developed for precise current measurements in accelerator mass spectrometry, which provides in addition information on the beam position. These data are used to monitor the energy of the beam and, if necessary, the terminal voltage of the accelerator is automatically adjusted.

Picoammeter for Ion Chamber Spans Six Decades without Range Switching

Precise current measurements in the range 10-13A to 10-7A can be done without range switching using an active integrator built around a varactor-bridge Op-Amp. The information is supplied by the time required to cross the voltage gap between two thresholds and is carried out by a pulse-width analog signal. Conversion into current or gamma dose rate is done by a simple digital encoder. Suitable contrivances have been adopted in the circuit to minimize leakage and drift effects and to prevent the need of any recalibration of the electrometer.

Precision double-phase infrasonic generator

A new method for reproducing electrical quantities in the range of low and infrasonic frequencies has been suggested and developed. The equipment produced on the basis of this method can be widely used for precision current and voltage measurements. The facility of controlling smoothly the phase shifts of output voltages in the range of 0–360‡ with an error not exceeding 0.1‡ serves to measure the majority of phase meters in the infrasonic and voice-frequency ranges. The utilization of a current and voltage power amplifier at the output of the equipment makes it also suitable for measuring power and certain other electrical quantities.

Instrument for Measurement of Hydrogen Atom Population

A transistorized Wheatstone bridge suitable for precise current or resistance measurements is described. The bridge is inexpensive, compact, and versatile, and was used for measuring hydrogen atom populations by the recombination wire probe method.