Miniaturized coil arrangement made by planar technology, for the

Details Miniaturized coil arrangement made by planar technology, for the Miniaturized coil arrangement made by planar technology, for the

1996-07-30

1998-11-03

Strecker, Gerard R.

Electricity: measuring and testing

Magnetic

With means to create magnetic field to test material

32420714, 32420717, 3242072, 324235, 324243, 336199, 336221, G01R 3302, G01R 3312, G01B 700, G01V 310

Patent

active

058314318

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The invention relates to an arrangement for the detection of materials having a magnetic permeability differing from zero, in particular ferromagnetic materials.
Aside from detecting materials having a magnetic permeability other than zero, the arrangement in accordance with the invention may also be used for indirectly measuring various other values. For this purpose, the value to be measured must cause a change in the magnetic permeability in the direct vicinity of the arrangement in accordance with the invention.
This occurs, for instance, during relative movement between a ferromagnetic structure (e.g., a structure or scale with equidistant ferromagnetic indicia) and the arrangement in accordance with the invention. For instance, the translation of a toothed rack or the rotation of a pinion moving relative to an arrangement in accordance with the invention, may be detected in this manner. Position and/or angle may thus be defined in connection with an incremental process.
Another field of application is materials testing. Work pieces may be scanned with one or more arrangements in accordance with the invention. The generated signals are a measure of magnetic characteristics or of the local variation of magnetic characteristics (of predetermined sections in stainless steel, for instance) and may thus serve to evaluate and recognize a workpiece. For the recognition of forward or backward movement of a body, a structure comprising equidistant magnetic indicia applied to the body may, for instance, move by two arrangements in accordance with the invention which are displaced from each other by 90.degree., whereby the direction of movement of the structure and, hence, of the body may be defined on the basis of the signal position of the two signals.


STATE OF THE ART

A rotational angle measuring sensor provided with a permanent magnet as the flux generating component and a coil with a core as the flux detecting component is known from German patent specification DE 3,133,061. There is no conduction of flux by ferromagnetic materials, air being the medium of propagation. The magnetic flux emanating from the permanent magnet is altered as a function of the angular disposition of a rotatably journaled ferromagnetic component and causes a change in the pulse width of the electrical pulses fed through the measuring coil. It has been possible by this special kind of detection to improve the linearity and to achieve reliable detection of the rotational angle with great accuracy. Furthermore, no special geometric configuration of the permanent magnet is required any longer; it may instead be configured conventionally. The unguided magnetic flux path which in connection with the use of a permanent magnet renders miniaturizing of the rotational angle measuring sensor to the sub-millimeter range impossible, constitutes a disadvantage. Moreover, the uncontrollability of the magnetic flux of a permanent magnet is disadvantageous, for it prevents the application of highly sensitive electrical measuring processes, so that any reduction in the size of the rotational angle measuring sensor is subject to very narrow limits, and optimum signal quality cannot be obtained.
In German patent specification DE 4,238,861 there is described a device for defining the position of an axially movable body. One or more coils serve simultaneously as flux generating and flux detecting components. The body to be detected is provided with a ferromagnetic layer which alters the flux in the measuring coil. Because of this, the inductance of this coil also changes which is evaluated as an impedance change by a (half-) bridge circuit. The objects of the disclosure are a higher response sensitivity and maximum independence from ambient conditions. This is accomplished solely by optimizing the ferromagnetic layer applied to the body to be detected, in that any problem of occurring eddy currents is counteracted especially by increasing the electrical resistance of the ferromagnetic layer. The disadvantages mentioned supra in conne

REFERENCES:
patent: 3002384 (1961-10-01), MacDonald et al.
patent: 3614618 (1971-10-01), Schrader et al.
patent: 3747085 (1973-07-01), Bala et al.
patent: 4021728 (1977-05-01), Makino et al.
patent: 4649755 (1987-03-01), Volz
patent: 4864238 (1989-09-01), Seitz
patent: 5111138 (1992-05-01), Kramer

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