JPH01277717A - Capacity displacement meter - Google Patents

Abstract

PURPOSE: To determine the position of a central electrode along the axis accurately by applying an AC input voltage to a tubular intermediate electrode and determining the difference between signals appearing on two tubular end electrodes. CONSTITUTION: A good AC input voltage produces a signal appearing at a central electrode even if it is a normal sine wave voltage. That signal causes to produce signals on one and the other tubular electrodes 1, 3 sequentially. These signals are determined by signals C1 , C2 at terminal 7 and the signal at terminal 8 is determined by signals C1 , C2 . Assuming the central electrode is confined within the region of an intermediate tubular electrode 2, capacitance of a capacitor formed by the central electrode and intermediate tubular electrode is invariant and thereby the C1 is kept constant. When the central electrode moves along an axis 5, physical properties of a capacitor formed by two outer electrodes 1, 3 and the central electrode are varied to cause variation of C2 , C3 . Consequently, the signals appearing at the terminals 7, 8 provide a positional reference of central electrode already.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to capacitive displacement meters, and more particularly, at least one outer cylindrical hollow electrode element and at least one inner cylindrical hollow electrode element disposed coaxially within the at least one hollow element. The invention relates to a capacitive displacement meter with a coaxial configuration, consisting of electrode elements, in which the inner and outer electrode elements are relatively coaxially movable.

A similar meter is disclosed in Dutch Patent Application No. 6902182 and can be used, for example, to replace known mechanical micrometers. The known meter consists of two spaced apart hollow tubes that support different voltages in operation. At the level of the gap between opposing insulations of the hollow tube, a cylindrical electrode is arranged for coaxial movement within the hollow tube. The voltage across the electrode is a reference to its position relative to the two hollow tubes. This voltage can be measured through electrical wires connected to the movable electrode.

One drawback of conventional meters is that, due to the use of different voltages on the hollow tube, the instrument is electrically asymmetric, and as a result the effect of spurious signals is relatively difficult to eliminate. It is. Another drawback is that conventional meters have movable connecting lines for movable electrodes. Due to the generation of friction and/or mechanical tension, this line can somewhat impede and/or retard the movement of the movable electrode, as a result of which the precision of the instrument is adversely affected.

Moreover, there is a danger of deterioration of the electrical contact between the clamp and the movable electrode after a given cycle of operation, or a risk of line breakage due to fatigue, which also affects the accuracy of the instrument.

The object of the invention is to overcome the above-mentioned disadvantages and generally to provide a robust, reliable and accurate displacement meter. Therefore, the present invention provides that one electrode element consists of three spaced arrays of cylindrical electrodes, the end electrodes of which are of equal length and the middle electrode of relatively short length, and the other electrode element at least one electrode extending coaxially with respect to the electrodes of one electrode element and in the inactive position being at the level of the intermediate electrode, and the intermediate electrode and the two end electrodes each comprising a plurality of terminals. A meter of the above-mentioned type is provided.

Hereinafter, the present invention will be explained in detail based on the accompanying drawings.

FIG. 1 schematically shows, in axial section, an example of a coaxial capacitive displacement meter according to the invention. The illustrated device has three hollow tubular electrodes 1.2.3 aligned in line with each other and having the same diameter.
Consisting of The two tubular end electrodes 1 and 3 are preferably of the same length and the intermediate electrode 2 placed between the tubular end electrodes is relatively short.

Coaxially arranged within the set of tubular electrodes is a central cylindrical electrode 4. The central electrode is movable according to a common axis 5, while in the inactive position the intermediate electrode 2
is at the level of However, the central electrode is considerably longer than the intermediate electrode and thus extends at a different distance from the two tubular end electrodes. The central electrode thus forms a coaxial capacitor with each of the tubular end electrodes and with the intermediate electrode. Due to the coaxial displacement of the central electrode, the capacitance value C of each capacitor formed by the tubular end electrode and the central electrode
2 and C3 are changed when the size of the opposing surface changes. However, the capacitance value C, of the capacitor formed by the central electrode and the intermediate electrode 2 is not changed in any case as long as the central electrode is in the area of the intermediate tubular electrode, which is the case in normal use.

According to the invention, the position of the central electrode along the axis 5 is precisely determined by applying an alternating input voltage to the intermediate tubular electrode and determining the signal difference between the signals appearing at the two tubular end electrodes. I can do it. To this end, the intermediate tubular electrode is provided with a terminal 6 for an alternating voltage source, and the end electrodes 1 and 3 are each provided with a terminal 7.8 for a line connected to the differential amplifier 90 input.
It is equipped with In the illustrated embodiment, electrode 1 is connected to the positive input of the differential amplifier and electrode 3 is connected to the negative input of the differential amplifier.

Furthermore, the central electrode is equipped with a sensor 10 which determines the position of the central electrode during use of the instrument.

The operation of the instrument is as follows. An AC input voltage, which may be, for example, a conventional sinusoidal voltage, produces a signal that appears at the center electrode. This signal in turn produces a signal on one tubular electrode 1 and on the other tubular electrode 3. The signal at terminal 7 is determined by C1 and C2, and the signal at terminal 8
The signal at is determined by C1 and C8. Assuming that the central electrode does not cover the area of the intermediate tubular electrode 2,
The capacitor formed by the central electrode and the intermediate tubular electrode is not changed and C1 remains constant.

When the central electrode moves along the axis 5, the two outer electrodes 1
The physical shape of the capacitor formed by the central electrode with and 3 is changed so that C2 and C3 are also changed. The signal appearing at each terminal 7 or 8 is therefore already a reference for the position of the central electrode. Therefore, in principle it is sufficient to have a single tubular end electrode. However, the use of two outer electrodes on opposite sides of the middle electrode presents the advantage that different measurements can be used, so that spurious signals are valid as long as they appear to the same extent on both tubular end electrodes. can be removed.

The output signal from the differential amplifier 9 is therefore a precise reference for the position of the central electrode relative to the selected reference position, and therefore a reference for the spacing at which the sensor 10 has placed the central electrode relative to the reference position. It is.

The selected reference position can be, for example, the illustrated position where C2 and C3 are equal, so that the output signal from the differential amplifier is zero.

When the central electrode is moved upwards so that it simply cooperates with electrodes 1 and 2, the output signal from differential amplifier 9 is the same as the input signal. However, if the central electrode could simply cooperate with electrodes 2 and 3, the output signal from the differential amplifier would be equal to the inverse input signal.

FIG. 2 is a more detailed longitudinal sectional view of the device according to the invention. Corresponding parts are designated by the same reference numerals in FIGS. 1 and 2. In the embodiment of FIG.
The basic shape shown in the figure, with the exception of the differential amplifier, is mounted in a tubular casing 11, which is preferably made of metal and in that case also serves as electrical protection. The tubular electrodes 1 to 3 are positioned within the casing 11 by means of a plurality of positioning rings 12 made of insulating material and fixed in a known manner.

The tubular electrodes 1 to 3 leave a free space 13 between them and the casing, in which the connecting line for the tubular electrodes extends. If necessary, the locating ring 12 is provided with cutouts for the passage of these lines, as indicated schematically at 13.

In the embodiment shown in FIG. 2, the central electrode 4 is provided at each end with a cylindrical extension 14, 15 of insulating material. These extensions serve to guide the central electrode during the movements generated by the sensor 10 provided on at least one of them. In this example sensor 1
0 consists of a tungsten carbide pole 17 placed within a holder 16.

Three outer electrodes are arranged on the outer wall of a tubular carrier made of a suitable insulating material. This carrier therefore also at least partially forms the dielectric between the central electrode and each of the outer electrodes.

This configuration has the advantage that the connecting wire for the outer electrode can be placed in place in an hourly manner. However, in principle it can also be arranged on the outer electrode or on the inner wall of the tubular carrier. However, in that case the carrier must be provided with holes for the connecting lines and to fix them in place.

It should be noted that instead of a single central electrode, multiple central electrodes consisting of a plurality of spaced apart component electrodes can be used.

In this way, an electronic ruler can be created.

The principle is shown in Figure 3. The central electrode 41 corresponds to the central electrode 4 of FIGS. 1 and 2. However, in alignment with the central electrode there are several additional electrodes 42 and 4.
3 are provided, and these are connected to electrodes 1 to 3 in the illustrated state.
is outside the operating range of The spacing between consecutive central electrodes is (
As soon as the electrode 41 leaves the working area of the outer electrode (during the movement to the left in the drawing), the next central electrode 42 enters this working area. In this method, continuous signal cycles are created throughout the continuous coaxial movement of the central electrode in relation to the tubular electrodes 1-3. By counting the number of cycles and more accurately determining the initial and final positions of the next active center electrode, the total distance that the center electrode has moved can be determined. When it comes to relative movement here, it is of course possible to hold the central electrode constant and move the tubular electrode.

It should further be noted that the meter shown could in principle be set "inside out" as schematically illustrated in FIG.

In FIG. 4, the three tubular electrodes of FIGS. 1 and 2 are designated by numerals 20-22 and are used as central electrodes located on the inner wall of the live tubular insulating carrier 23. A connecting wire extends into the tubular electrode. It is also possible for the tubular electrode to be arranged outside the tubular carrier, for example by first fixing the connecting wire and then filling the tubular electrode with a suitable material.

At the level of the intermediate tubular electrode 21, the wide tubular electrode 2
4 is provided around a combination of three tubular electrodes, the electrodes 24 of which can be attached to a carrier 25. The wide electrode 24 performs the same role from an electrical point of view as the central electrode 4 of FIGS. 1 and 2 does. The carrier 23 or the carrier 25 can be provided with sensors, which are not shown.

Further, similar to the arrangement of FIG.
FIG. 5, which falls within the operating range of .about.22, schematically shows a modification of the instrument shown in FIG. The apparatus shown in FIG. 5 is constructed in such a way that the input signal is applied to the two tubular end electrodes by terminals 50 and 51, respectively, while the signal to be measured is supplied through terminal 52 of the intermediate tubular electrode. This is different from the device shown in FIG. Conveniently, the input signals applied to terminals 50 and 51 are alternating voltages having the same amplitude, but 180° out of phase with each other. The output signal at terminal 52 is then equal to zero volts at the midpoint of the center electrode.

One advantage of this method of wiring is that the result of the measurement is less influenced by the amplifier connected to the output.

FIG. 6 schematically shows a practical embodiment of the meter according to the invention in a side view, and FIG. 7 shows a sectional view along the line Vll--VII of FIG. In Figures 6 and 7, the housing of the instrument is omitted and has the actual sensor there.

FIG. 6 again shows three aligned tubular electrodes 60, 61 and 62. Each electrode is secured to a longitudinally extending loft or bar 66, 67 and 68 of the instrument by a plurality of suitable ears 63, 64 and 65. The ends of the rods are secured to insulating end discs 69 and 70.

The end discs are provided with central holes 71 and 72, which serve as a guide for the rod-shaped carrier 73 of the central electrode 74, which is aligned with one another and is shown separately in FIG. 6 for the sake of clarity. The carrier 73 can be made of glass or ceramic material or of a suitable synthetic resin, to which the end discs 69 and 70 are also applied.

The ears 63-65 can consist of metal tubular sections that are fixed to the tubular electrodes. In the illustrated embodiment, each tubular electrode has two diametrically opposed tubular portions that fit onto a corresponding rod or bar. Therefore, there are a total of six rods, as shown in FIG.

Conveniently, the rods are made of metal and they also serve as wiring for the electrodes. To this end, at least one of the rods associated with each electrode is threaded one-sidedly through the end disc to form the appropriate electrical connection, as indicated at 75 in FIG.

The advantage of such a structure is that the wiring is completely symmetrical and extends along all electrodes. The possible parasitic capacitance effects are therefore equal for all electrodes. In addition, a separate carrier for the tubular electrodes is unnecessary, so that the only dielectric present between the electrodes is air. Advantageously, the ears are movable over the rod to allow precise setting and possible adjustments.

It should be noted that various modifications will readily occur to those skilled in the art after reading the above description. Thus, each electrode in FIG. 6 can have, for example, three ears. As a result, the total number of rods becomes nine. It is also possible to provide special means, such as a set screw, for fixing at least one ear of the electrode on the rod. Such modifications are considered to be within the scope of this invention.

[Brief explanation of the drawing]

FIG. 1 is an axial sectional view schematically showing an embodiment of the meter according to the invention, FIG. 2 is a detailed view of the embodiment of the meter according to the invention, and FIG. 3 is a schematic diagram showing a modification of the meter according to the invention. 4 is a schematic diagram showing a second modification of the meter according to the invention, FIG. 5 is a schematic diagram showing a modification of the instrument of FIG. 1, and FIGS. 6 and 7 are respectively shown in FIG. FIG. 3 is a side view and a sectional view showing a practical example of the shown meter. In the figure, 1, 2, 3, 60, 61, 62 are hollow tubular electrodes, 4 is a center electrode, 12 is a positioning ring, 25 is a carrier, 63, 64, 65 is an ear piece, and 69.70 is an insulated end. It is a disk. Lf) Procedural amendment 9-7 June 1986 θ; Right j゛

Claims (23)

[Claims] (1) comprising at least one outer cylindrical hollow electrode element and at least one inner cylindrical electrode element coaxially disposed within the at least one hollow element, the inner and outer electrode elements being relatively coaxial; In a capacitive displacement meter with a coaxial configuration, which is movable in the an electrode element comprising at least one electrode extending coaxially with respect to the electrode of said one electrode element and in the inactive position is at the level of said intermediate electrode, and said intermediate electrode and said two end electrodes are A capacitive displacement meter characterized in that each terminal has a plurality of terminals. 2. The capacitive displacement meter of claim 1, wherein the three aligned electrodes are hollow tubular electrodes and at least one central cylindrical electrode is disposed coaxially within the tubular electrode. 3. The capacitive displacement meter of claim 2 further comprising an insulated tubular carrier directing said three tubular electrodes to its wall. 4. The capacitive displacement meter of claim 3, wherein the three tubular electrodes are arranged on the outer surface of the tubular carrier. (5) A capacitive displacement meter according to any one of claims 1 to 4, characterized in that the outer electrode element is mounted within a cylindrical casing by an insulating positioning ring. 6. Capacitive displacement meter according to claim 5, characterized in that the casing is made of electrically conductive material and serves as electrical protection. (7) Capacitive displacement meter according to claim 5 or 6, characterized in that at least one of the positioning rings has at least one cutout for passage of a connector for the three tubular electrodes. (8) The capacitive displacement meter according to any one of claims 2 to 7, wherein the central cylindrical electrode is provided with a projection extending beyond the tubular electrode and supporting a sensor at at least one end. . (9) at least one further cylindrical electrode is disposed in alignment with and spaced from said central cylindrical electrode and in an effective working area of said three tubular electrodes, said central cylindrical electrode in said central cylindrical electrode; 9. A capacitive displacement meter according to any one of claims 2 to 8, characterized in that the capacitive displacement meter is arranged throughout the movement of the central electrode in relation to the three tubular electrodes so as to enter immediately upon exiting the central electrode. 10. The capacitor of claim 1, wherein the three aligned electrodes are coaxially disposed within at least one tubular electrode, which tubular electrode is at the level of the central electrode in the inactive position. displacement meter. (11) at least one further tubular electrode is arranged in alignment with and spaced from said tubular electrode and in the effective working area of said three electrodes, said first-mentioned tubular electrode exiting this area; 11. A capacitive displacement meter according to claim 10, characterized in that the capacitive displacement meter is arranged throughout the movement of the tubular electrode in relation to the three electrodes so as to enter immediately. (12) Claim 1 further comprising an insulated tubular carrier supporting the three tubular electrodes on its wall.
0 or 11. 13. The capacitive displacement meter of claim 12, wherein the at least one tubular electrode is located on an inner surface of the tubular carrier. (14) the three aligned electrodes are tubular and the three aligned electrodes are tubular;
14. Capacitive displacement meter according to any one of claims 10 to 13, characterized in that the connecting wires of the two electrodes are passed through the electrodes. (15) The capacitive displacement meter according to claim 14, wherein the three tubular electrodes are filled with an insulating material. 16. The capacitive displacement meter of claim 14, wherein the three aligned electrodes are disposed on an inner wall of an insulated tubular carrier. 17. Capacitive displacement meter according to claim 1, characterized in that the intermediate electrode is provided with a terminal for an input signal and the two end electrodes are each provided with a terminal for one of the inputs of the differential amplifier. (18) The intermediate electrode is provided with a terminal for an output signal, and the two end electrodes are each provided with a terminal for an alternating current voltage, one alternating voltage being in opposite phase with respect to the other alternating voltage, and two alternating current Capacitive displacement meter according to claim 1, characterized in that the voltages are of equal amplitude. (19) two spaced apart insulating discs have a central hole for guiding the cylindrical carrier of the central electrode, and a plurality of rods extend between said insulating discs, each rod being one of the cylindrical electrodes; 2. The capacitive displacement meter according to claim 1, wherein the capacitive displacement meter passes through one of the ear pieces. 20. The capacitive displacement meter of claim 19, wherein each cylindrical electrode is attached to the associated rod by at least two ears. (21) The capacitive displacement meter according to claim 20, wherein the rod is a conductor and the ear piece forms an electrical connection with a corresponding cylindrical electrode. 22. The capacitive displacement meter of claim 21, wherein one of the rods associated with each cylindrical electrode is threaded externally through the insulating disc to form an electrical terminal. (23) At least one of the ears of the cylindrical electrode is provided with means for fixing the ear to a rod cooperating with the ear. Capacitive displacement meter as described.