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Precise contactless DC and AC magnetic sensors are required by car industry, chemical industry, for measurement of power and many other applications. The emphasis is given on current sensors based on magnetic materials, but other ...
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Precise contactless DC and AC magnetic sensors are required by car industry, chemical industry, for measurement of power and many other applications. The emphasis is given on current sensors based on magnetic materials, but other methods are also mentioned for comparison. Discussed are the factors influencing precision and geometrical selectivity.
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The basic structure and dynamics of the primary electric current systems in the Earth's magnetosphere are presented and discussed. In geophysics, the word current is used to describe the flow of mass from o
The basic structure and dynamics of the primary electric current systems in the Earth's magnetosphere are presented and discussed. In geophysics, the word current is used to describe the flow of mass from one location to another, and its analog of electric current is a flow of charge from one place to another. An electric current is associated with a magnetic field, and they combine with the Earth's internally generated dipolar magnetic field to form the topology of the magnetosphere. The concept of an electric current is reviewed and compared with other approaches to investigate the physics of the magnetosphere. The implications of understanding magnetospheric current systems are discussed, including paths forward for new investigations with the robust set of observations being produced by the numerous scientific and commercial satellites orbiting Earth.
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Mixed-signal or analog chips often require a wide range of biasing currents that are independent of process and supply voltage and that are proportional to absolute temperature. This paper describes CMOS circuits that we use to ge...
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Mixed-signal or analog chips often require a wide range of biasing currents that are independent of process and supply voltage and that are proportional to absolute temperature. This paper describes CMOS circuits that we use to generate a set of fixed bias currents typically spanning six decades at room temperature down to a few times the transistor off-current. A bootstrapped current reference with a new startup and power-control mechanism generates a master current, which is successively divided by a current splitter to generate the desired reference currents. These references are nondestructively copied to form the chip's biases. Measurements of behavior, including temperature effects from 1.6 and 0.35μ implementations, are presented and nonidealities are investigated. Temperature dependence of the transistor off-current is investigated because it determines the lower limit for generated currents. Readers are directed to a design kit that allows easy generation of the complete layout for a bias generator with a set of desired currents for scalable MOSIS CMOS processes.
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The magnetic configuration of the Wendelstein 7-X (W7-X) stellarator is optimized following a set of criteria including a rotational transform profile with low shear and minimized bootstrap current that must be controlled for prop...
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The magnetic configuration of the Wendelstein 7-X (W7-X) stellarator is optimized following a set of criteria including a rotational transform profile with low shear and minimized bootstrap current that must be controlled for proper functioning of the island divertor. This paper studies the compensation of residual bootstrap current by using electron cyclotron current drive (ECCD). The modeling shows that the loop voltage induced by ECCD leads to a redistribution of the current density with a diffusion time of ～2 s. The relaxation time of the total current is much longer, however—for W7-X plasma parameters the total toroidal current reaches steady state after several L/R times requiring hundreds of seconds. In order to keep the toroidal current and its profile in the acceptable range, a feed-forward or predictive control method using ECCD as actuator is proposed. The main steps are as follows: (a) calculate the bootstrap current distribution using plasma parameters measured in the online transport analysis and (b) determine and apply ECCD as needed. For the current control to work properly and to avoid long relaxation times, the reaction time of the control loop must be less than the current skin time.
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Effect of various forms of currents on regular nonlinear waves in shallow water is investigated by use of a computational fluid dynamics approach. A range of wave conditions with different wave heights and wave periods are conside...
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Effect of various forms of currents on regular nonlinear waves in shallow water is investigated by use of a computational fluid dynamics approach. A range of wave conditions with different wave heights and wave periods are considered. Effect of three types of currents on these waves is investigated, namely (i) uniform current over the water depth, (ii) shear current from the seafloor to the still-water level, and (iii) a custom current profile that changes over the water depth. The current profiles are considered in both following and opposing directions of the incoming wave, forming in total 18 wave-current configurations. The Navier-Stokes equations for a laminar flow are solved computationally in two dimensions. A numerical wave-current maker is created to generate combined nonlinear waves and currents in shallow water. The effect of the currents on the change of the wave field, including quantitative change of the surface elevation, wave height, wavelength, horizontal particle velocity, and the velocity and pressure fields is presented and discussed. It is found that presence of the current can alter the wave field significantly, and the current profile and direction play a significant role in the change of the wave field. A following current in shallow water increases the peak of surface elevation, horizontal particle velocity and pressure, along with an increase in wavelength and wave height, while an opposing current reduces these. The change of wave height with current direction appears to be opposite to that observed in deep water in the literature. It is also concluded that a linear superposition of the undisturbed wave and current velocities can describe the horizontal particle velocity of the wave-current field for following currents (particularly under the wave trough) reasonably well, but larger differences are observed for opposing currents.
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The review makes a brief overview of traditional methods of measurement of electric current and shows in more detail relatively new types of current sensors. These include Hall sensors with field concentrators, AMR current sensors...
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The review makes a brief overview of traditional methods of measurement of electric current and shows in more detail relatively new types of current sensors. These include Hall sensors with field concentrators, AMR current sensors, magneto-optical and superconducting current sensors. The influence of the magnetic core properties on the error of the current transformer shows why nanocrystalline materials are so advantageous for this application. Built-in CMOS current sensors are important tools for monitoring the health of integrated circuits. Of special industrial value are current clamps which can be installed without breaking the measured conductor. Parameters of current sensors are also discussed, including geometrical selectivity. This parameter specific for current sensors means the ability to suppress the influence of currents external to the sensor (including the position of the return conductor) and also suppress the influence on the position of the measured conductor with respect to the current.
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This paper discusses the fundamentals of different methods for current decomposition and non-active power compensation in polyphase power systems. The basic concepts and the results of the instantaneous active and reactive power t...
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This paper discusses the fundamentals of different methods for current decomposition and non-active power compensation in polyphase power systems. The basic concepts and the results of the instantaneous active and reactive power theory on the one side, and of the active/reactive average power theory on the other side, are critically compared.
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This paper proposes a sensor for leakage-current detection based on the magnetic modulation technology. The sensor can measure both nonlinear current with an arbitrary waveform and linear current from dc to several kilohertz. The ...
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This paper proposes a sensor for leakage-current detection based on the magnetic modulation technology. The sensor can measure both nonlinear current with an arbitrary waveform and linear current from dc to several kilohertz. The current sensor consists of only one magnetic core and one winding, which significantly reduces the sensor size. The structure and operating principle of the current sensor are introduced, and the dynamic process of the current sensor is analyzed. In addition, the mathematical model of dynamic process with hysteresis considered for the current sensor is presented. Both the simulation and the experimental results are presented to verify the effectiveness of proposed current sensor.
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Direct measurements of current density perturbations associated with nonlinear phenomena in magnetized plasmas can be carried out using in situ magnetic measurements. In this paper we report such measurements for three different k...
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Direct measurements of current density perturbations associated with nonlinear phenomena in magnetized plasmas can be carried out using in situ magnetic measurements. In this paper we report such measurements for three different kinds of phenomena. Current density fluctuations in the edge density gradient region of a fusion plasma confined in reversed field pinch configuration and in a density gradient region in the Earth magnetosphere are measured and compared, showing that in both environments they can be attributed to drift-Alfv′en vortices. Current structures associated with reconnection events measured in a reversed field pinch plasma and in the magnetosheath are detected and compared. Evidence of current filaments occurring during ELMs in an H-mode tokamak plasma is displayed.
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