Electricity: measuring and testing – Magnetic – Displacement
Patent
1990-12-03
1993-05-11
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Displacement
32420712, 324661, G01B 714, G01R 2726
Patent
active
052104915
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention relates to a measuring device comprising two bodies movable relative each other, and two coils arranged on one of the bodies and connected in at least one electrical bridge circuit. The other body has areas of electrically conductive and/or ferromagnetic material assigned to the coils. Respective alternating current resistance of the coils varies in accordance with relative change in magnitude of these areas. In known measuring devices, two identical coils are arranged on a body in a mirror symmetry. A disk is arranged parallel to this body and is connected with a structural component part whose rotational movement is to be measured. In the initial position, the electrically conducting surface of the disk overlaps the two coils by half, the same amounts of coil voltage can be formed in both coils. The measurement area with the greatest accuracy and smallest drift is located in the region of small angles in the proximity of the initial position. However, the measurement area itself is relatively greatly restricted. Only a relatively small symmetrical measurement area to the zero point is possible.
SUMMARY OF THE INVENTION
The object of the invention is a measuring device, in which the measuring point with the highest measuring accuracy and the smallest drift can be fixed as desired within a relatively large area. The object of the invention is achieved by providing coils having different electrical measurement sensitivities which permit to fix the place with the highest measurement accuracy and the smallest drift errors within the measurement area of the measurement device.
In particular, in a large linear measurement area, the measurement area with the highest measurement accuracy is located at small angles and the measurement area with relatively tolerance range is located at large measurement angles. Further, measurement errors caused by environmental influences or axial and radial play can be virtually completely eliminated at the desired point in the measurement area. The measuring device is constructed a particularly simple manner and can be adapted relatively easily to the desired instances of application. It is possible to eliminate virtually all errors at the desired place in the measurement area, such as fluctuations of the carrier voltage and/or the carrier frequency, carrier change in the coil quality due to increase in the surrounding temperature, etc.
The present invention both as to its construction so to its method of operation, together with additional objects and advantages thereof, will be best understood from the following detailed description of the preferred embodiments when read with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a perspective view of a measuring device according to the prior art;
FIG. 2 shows a measurement diagram;
FIGS. 3 and 5 each show a longitudinal cross-sectional view of a measuring device, according to the invention,;
FIG. 4 shows a perspective view of a modification of the embodiment according to FIG. 3;
FIG. 6 shows a cross-sectional view a modification of the measuring device for a capacitive measurement; and
FIG. 7 shows a cross-sectional view of a modification for linear travel measurement.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A sensor for measuring angles, which is known according to the prior art, is designated by 10 in FIG. 1. Two identical coils 12, 13 are fastened in mirror symmetry on a carrier 11 and are connected in a Wheatstone half-bridge. A semicircular disk 14 is arranged at a distance "a" from the carrier 11 and is connected with a structural component part, not shown, whose rotational movement is to be determined. The surface of the disk 14 facing the coils comprises an electrically conducting and/or ferromagnetic layer. The sensor 10 works according to the inductive or eddy current measuring principle. In the basic position of the disk 14, the two coils 12, 13 are equally overlapped in each instance by the disc, i.e., and, in the eddy current measuring method, edd
REFERENCES:
patent: 4833919 (1989-05-01), Saito et al.
Dobler Klaus
Hachtel Hansjorg
Robert & Bosch GmbH
Snow Walter E.
Striker Michael J.
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