Search

The eddy-current type proximity sensor is a noncontact type sensing device to detect the approach of a conductor by increase of coil resistance due to eddy-current loss. This paper proposes to add the cap-shaped magnetic flux shield at the top of the ferrite core for the actual sensor. In conventional proximity sensors, main magnetic flux path passes through the air between the target conductor and ferrite core. The proposed sensor, in contrast, has dosed magnetic circuit geometry. This means that main magnetic flux path is almost completed by the core and the shield. Therefore, it is predicted that flux does not reach the target conductor and it causes debasement of sensing property. However, it is shown that the calculated results by finite element method and measured results of the sensing property of the proposed sensor is enhanced compared with the actual sensor. This paper quantitatively accounts the electromagnetisms of the proposed sensor from sensing property, flux distributions, and eddy-current loss in each part of the sensor body. Index Terms--Coil quality factor, eddy current loss, magnetic circuit, proximity sensor.

Eddy-current-type proximity sensor is a noncontact-type sensing device to detect the approach of a conductor by an increase of coil resistance due to eddy current loss. This paper investigates electromagnetic (EM) characteristics of the actual proximity sensor by the finite-element method and provides knowledge to enhance sensing property. In particular, the influence of eddy current loss to sensing property is shown and quantitatively estimated. Furthermore, modified models of the actual sensor are proposed and calculated as numerical experiments. As a result, enhanced sensing properties of the proposed models are shown. Index Terms--Coil quality factor, eddy current loss, proximity sensor.

Three-dimensional Finite Element Method (FEM) has been widely applied for practical analysis use of electromagnetic field. However, numerical error estimation methods which focuses on the governing equations of electromagnetic field, not FEM formulations, have been reported in few papers. This paper proposes a new posteriori error estimation concept based on Ampere's circuital law which is one of the basic equations of electromagnetic field. Numerical error is quantitatively estimated as the current value which should be equivalent to the exciting current of the field. Index Terms - Ampere's circuital law, posteriori error estimation, three-dimensional FEM

The material transfer due to arcing in relays and switches was investigated based on the physical behavior of the arc. The system used to test the arc erosion on electrical contacts includes an electromagnetic energizing part that is similar to the real magnetic relay. Results showed that taking the arc voltage waveform is one of the best procedures to compare material transfer for different contact materials.

This paper describes investigations for the optimal design of Switched Reluctance Motor(SRM). They are given by theoretical calculation of inductance of SRM and numerical analysis by two-dimensional finite element method(FEM). As the results of investigation, the ideal waveform of stator current under the voltage-constant condition and improved shape of rotor are proposed.

The wear of a copper-graphite brush in gasoline and in air was investigated. Specifically, the arcing, nonarcing and switching arc tests were carried out in conjunction with scanning electron microscopy and electron problem microanalysis to assess the brush wear caused by sliding against the copper commutator of a dc motor for an automotive fuel pump. The results indicated that the brush wear in air was less severe than that in gasoline.

A study of the impact of dc electric current, varying from 0 amperes to 4 amperes, and passing through wiping palladium contacts, shows that the current level can significantly reduce the resistance degradation in the electrical contact through a self-cleaning action via thermal expansion. The critical wiping number is highly dependent on the wipe amplitude at zero amperes, but is only slightly affected at higher current levels. Static and dynamic contact resistance depend considerably on the generation and migration of insulating material.

The contact resistance degradation of silver is due to oxide films formed on contacts operating in normal air conditions and in mixed oxygen-nitrogen gas. Contact resistance degradation is dependent on oxygen density and also on the difference of arc duration in both the metallic and gaseous phases. The longer the arc duration in gaseous phase, the thicker the oxide films on the center of anode contact spot and the more severe is the contact resistance degradation.

An experiment on unsymmetrical material combination of palladium and silver shows that polarity affects arc erosion and electrical contact resistance behavior. Arc erosion is dominated by the cathode material and contact resistance is dominated by the anode material, especially Ag, due to the surface oxidation in the late gaseous phase. Contact resistance is also affected by metal transfer between the electrodes due to changes in surface composition of the anode.

The degradation of electrical resistance and material transfer of Pd and Ag contacts during breaking of arcs occurs by a deposition and particle sputtering process. The process causes the arced contact morphology to undergo a transition state in its metallic and gaseous phase, the state of transition increasing with increase in load current. The degradation and material transfer during breaking of arcs in nitrogen gas at different concentrations of oxygen also occurs by the some process. The contact failures between the arcs, which cause this degradation and material transfer, are caused by the oxide films formed on the surface of contact.

Experimental studies of silver contacts in low dc current arcs reveal a dependence of the contact resistance on contact morphology, arc duration and occurrence possibility and surface compositions. Arc erosions and mechanical wear cause contact morphologies, which correspond to three contact resistance characteristics. Beyond a critical value of transition current, the resistance increases and becomes unstable.

Scanning electron microscopic analysis of pure Pd contacts in DC breaking arcs reveals three patterns for arc erosion. These patterns indicate the occurrence of pips and craters on the electrode surfaces at different ranges of load current. An electronic balance measures the material transfer. At critical current value of 2.5 A, the direction of material transfer changes.

Gold contacts used in electric switches operated in mechanical break-make actions under no load conditions atmosphere showed a substantial increase in the contact resistance. Three-fourths of the samples used in the test, which was conducted in laboratory atmosphere, revealed a significant increase in their contact resistance. Mechanical actions were found to have a great bearing on this phenomena.

Direct current (DC) motors are commonly used in automotive fuel pumps to supply gasoline to the car's engine due to their high efficiency and controllability. Long life and reliable materials are required for the motor's commutator in this particular type of application since gasoline has great effects on the duration of the commutation arc. An investigation of the commutation phenomena in gasoline is presented.