RU1775037C - Differential capacitive angle displacement transducer - Google Patents

Abstract

The invention relates to measuring technique and aims to increase the accuracy of a differential capacitive angular displacement transducer by minimizing the influence of mutual distortion of the electrodes in the measurement range up to 90 °. The transducer contains two fixed water electrodes installed on the water plane, each of which is made in the form of several pairs of sections of ring segments of different diameters, placed diametrically opposite and electrically connected to each other. The number of pairs of these segments is even, and their radial sizes are selected based on predetermined mathematical relationships. The third electrode of this transducer is mounted for rotation in a parallel plane and is made of an even number of sections of the annular segments that have the same shape and dimensions that exceed the radial dimensions of the stationary electrodes. The number of ring segments of the third electrode is half the number of pairs of ring segments of one of the stationary electrodes. The ratio of the difference between the capacitances formed by the movable and fixed electrodes to their half-sum is practically independent of their non-parallelism due to the symmetric distribution of the segments of the ring segments around the circumference of the transducer. 2 ill. (L C

Description

The invention relates to measuring technique and can be used to convert the angular displacements of an object into an electrical signal.

A known angular displacement transducer made in the form of a capacitor of variable capacitance, comprising a dielectric housing, a rotor placed therein, made of an electrically conductive material in the form of a butterfly, a curved metal cover for sealing and creating uniform pressure, pressing the rotor against the base of the housing, and a fixed electrode in as a metallized layer on the outside

the surface of the base of the housing, made in the form of diametrically opposed annular segments 1.

A disadvantage of this converter is the effect of skew between the rotor and the fixed electrode on the type of output characteristic of the capacitor.

The closest in technical essence to the invention is a differential capacitive angular displacement transducer containing two stationary electrodes placed in the same plane, each of which is made in the form of one pair of electrically connected sections of the ring segments

h VI ate about sov VI

CA

of different diameters, diametrically opposed to the axis of symmetry of the transducer, separated by radial clearances and forming two concentrically spaced flat rings in which the ring segments of one pair alternate with the ring segments of the other pair in the circumferential and radial directions, and mounted coaxially with the concentric rings in a parallel plane rotatable relative to them, the third electrode, consisting of an even number of electrically connected sections of the annular egmentov 2. This converter is also sensitive to distortions of the movable electrode with respect to the fixed electrodes that has a significant effect on the accuracy of the transducer.

The purpose of the invention is to increase the accuracy of the transducer in the measuring range up to 90 ° by minimizing the influence of mutual distortion of the electrodes.

The goal is achieved. that a differential capacitive angular displacement transducer containing two stationary electrodes placed in one plane, each of which is made in the form of one pair of electrically connected sections of ring segments of different diameters, diametrically opposed to the axis of symmetry of the transducer, separated by radial gaps and forming two concentrically arranged flat rings in which the annular segments of one pair alternate with the annular segments of the other pair in an ok radial direction, and mounted coaxially with concentric rings in a parallel plane with the possibility of rotation relative to them, the third electrode, consisting of an even number of electrically connected sections of the ring segments, is provided with additional pairs of sections of the ring segments, which are identical to the segments of the first two pairs and placed in the plane of the same concentric rings, the total number N of pairs of segments of each fixed electrode is even, and their radial dimensions are related

R2 V (Ri + h) 4 + Ri4-Ro4 (1)

where Ro, RI and Ra are the inner radius of the first ring and the outer radii of the first and second rings, respectively; h is the insulating gap between the concentric rings. The segments of the ring segments of the third electrode have radial dimensions that exceed the radial dimensions of the concentric rings of the stationary electrodes, and their total number is 2N.

In FIG. 1 shows still and

movable electrodes of an angular displacement transducer having a measuring range from 0 to 90 °; in FIG. 2 shows the fixed and movable electrodes of an angular displacement transducer having a measuring range from 0 to 45 °.

The differential capacitive angular displacement transducer contains two stationary electrodes 1 and 2,

placed in the same plane and made in the form of ring segments of different diameters, mounted in parallel and coaxially with it of the movable electrode 3, which is connected to the inputs of the measuring

circuits 4. All ring segments forming each of the electrodes are electrically connected to each other. The fixed electrode 1 forms a capacitor Ci with the movable electrode 3, and the fixed

the electrode 2 forms a capacitor C with a movable electrode 3. The differential capacitance of the Ci-Ci converter. The values of the radii R0 and RI can be arbitrarily selected. Radius R2

is found by expanding the differential capacitance C in the Taylor series in the angle of bias between the electrodes and equating to zero the linear and quadratic terms of the expansion.

8, when the dielectric constant of the transducer e is constant during its operation, the measuring circuit 4 is a device whose output voltage is directly proportional to the differential capacitance of the transducer C. If the dielectric constant varies significantly during operation, the transducer is provided with an additional constant a CNI capacitor physically designed in such a way that its dielectric constant depends on the parameters of the external medium in the same way as the differential bone transducer. The measuring circuit 4 in this case contains an additional division unit, the output voltage of the measuring circuit is directly proportional to the ratio

55

Ci - Ci

(2)

The measuring circuit 4 is based on well-known transducers

capacitance values into an ac or dc signal. It is advisable to use the total capacity of Ci + Cu as Cm. However, this capacitance largely depends on the skew angle between the electrodes, since its expansion in the Taylor series contains a non-zero quadratic term. To eliminate this drawback, the transducer is equipped with an additional annular fixed electrode 5 (see FIGS. 1 and 2) connected to the input of the measuring circuit 4, whose external radius is

Rz

.

cKa +

M4 + R24 - (Ri + h) 4 + Ri4 - Ro. (3)

where hi is the radial clearance between electrode 5 and electrodes 1 and 2. The radius Bz is determined by equal to zero the quadratic term of the expansion in the Taylor series by the angle of the difference

Cm Ci + Ci - Civ,

where Civ is the capacitance formed by the electrode 5 and the electrode 3. The outer radius of the movable electrode 3 is increased so that the movable electrode 3 has a total area of overlap with the electrode 5.

In the presence of electrode 5, measuring circuit 4 contains an additional subtraction unit, and its output voltage is directly proportional to (4).

The disadvantage of the total capacitance Ci + Cu can also be eliminated by 90 ° shift of the annular segments of the movable electrode located above the outer concentric ring relative to the annular segments of the movable electrode located above the inner concentric ring.

The device operates as follows.

With the angular movement of the movable electrode relative to the stationary ones, the overlap area between them varies linearly. If distortions occur between the movable and stationary electrodes of the capacitor transducer, the capacitors Ci and Cu change in the same way and, therefore, the differential capacitance of the transducer will not depend on the distortions between the electrodes and the output voltage of the measuring circuit

We 4 will be directly proportional to the magnitude of the angular displacement.

This converter allows to reduce the error introduced by the distortion of the electrodes themselves by 3-5 times. or with the same error, respectively, reduce its dimensions in comparison with the known Converter.

Claims (1)

The claims 10 A differential capacitive angular displacement transducer containing two stationary electrodes placed in the same plane, each of which is made in the form of one pair of electrically connected 15 segments of ring segments of different diameters, diametrically opposed to the axis of symmetry of the transducer, separated by radial gaps and forming two concentrically arranged flat rings of the same area in which the ring segments of one pair alternate with the ring segments another pair, and mounted coaxially with concentric rings in a parallel plane with the possibility of rotation relative to them, the third electrode, consisting of an even number of electrically connected sections of the ring segments, is distinguished by the fact that, in order to increase its accuracy in the measurement range up to 90 ° due to minimizing the influence of mutual bias of the electrodes, it is equipped with additional pairs of ring segments 35 segments, which are identical to the segments of the first two pairs and are located in the plane of the same concentric rings, the total number N of pairs of segments of each stationary electrode is even, and their radial dimensions are related by the ratio: R2 V (Ri + h) 4 + Ri4 - R047 where RO, Ri and R2 are the inner radius of the first ring and the outer radii of the first and second rings, respectively; h is the insulating gap between the concentric rings, the sections of the annular segments of the third electrode are identical in shape and have radial dimensions greater than the radial dimensions of the concentric rings of the stationary electrodes, and their number is N / 2, Qutj