GB2159628A

GB2159628A - Capacitive inclination and levelness-measuring instrument

Info

Publication number: GB2159628A
Application number: GB08513163A
Authority: GB
Inventors: Jurgen Stotzer; Wolfgang Eberhard; Wolfgang Brandt
Original assignee: SUHL FEINMESSZEUGFAB VEB
Current assignee: SUHL FEINMESSZEUGFAB VEB
Priority date: 1984-05-28
Filing date: 1985-05-24
Publication date: 1985-12-04
Also published as: DD226068A1; GB8513163D0; GB2159628B; DE3512983A1

Abstract

The instrument enables differences in slope and levelness to be measured rapidly and with accuracy. In order to make the instrument universally useable, insensitive to electrical, mechanical and thermal environmental influences, and to make it sufficiently accurate over a large time domain, a special non- conductive liquid 1, which has a higher dielectric value than the ambient surrounding medium, is disposed in the space between at least two plate-shaped, circular sectorial pairs of electrodes 3 of a capacitor arrangement, such that, when in neutral position, the liquid fills about half of the space. Larger sector electrodes may be utilized in order to increase the measurement range (Fig. 3, not shown) and an arrangement with two different sized electrode arrangements may be provided (Figs. 4 and 5, not shown). In another arrangement each pair of electrodes is arranged in a respective container, the two containers being interconnected by a flexible line, (Fig. 6, not shown). <IMAGE>

Description

SPECIFICATION Capacitive inclination and levelness-measuring instrument The invention relates to an electronic inclination and levelness-measuring instrument by which inclination, levelness and angles may be measured relative to the gravitation vector of the earth over a large range of measurement. It may also be used for accurate measurements in the construction of apparatus and mechanical engineering, and for relatively large ranges of measurement in the building industry, crane construction, the construction of plant and similar cases of use.

Two different principles for incorporating the gravitation vector when measuring inclination by means of electronic levels are known.

Gravitation-sensitive elements are either sensitively suspended pendulums or liquids.

Mechanical pendulum arrangements are described in WP 123016, WP129488, German Auslegschrift 2038935 and German Offenlegungsschrift 3208811.

The inclinometers of the firms Taylor and Hobson (England), Tesa- und Wyler (Switzerland) and Federal (USA) also operate with mechanical pendulums. The disadvantages of these instruments are the relative small range of measurement, mechanical friction which leads to measurement errors, and the high cost of manufacture. These disadvantages are overcome by the solutions which operate with liquids.

The firm Sperry (USA) (German Offenlegungsschrift 2551798) utilizes the slope-dependent change in the level of an electrolyte relative to the housing. At least four electrodes are disposed symmetrically in an annular chamber made from non-conductive material. The chamber is partially filled with an electrolyte. As a result of the electrolyte, resistances, whose magnitude changes in dependence upon slope, are formed between the first two electrodes and a third common electrode. The changes in the resistance are processed and indicated.

The disadvantage of this solution is that the electrolyte has a high temperature-dependence which requires special compensating measures. Furthermore, both the electrolyte and the container require special damping measures. An electrolyte having current flowing therethrough involves problems of electrolysis and chemical changes which are disadvantageous to the system.

High sensitivity of slope with respect to time is associated with the geometrical arrangement of the electrodes. The solution disclosed in WP 205744, in which a magnetic fluid is used, has analogous disadvantages, and only a small range of measurement is realized.

An object of the present invention is to provide a capacitive inclinometer which can be manufactured at low expense and which enables rapid, adequately accurate measurement of differences in slope and levelness.

In accordance with the present invention, there is provided a capacitive inclination and levelness-measuring instrument wherein an electrically non-conductive liquid which has a higher temperature-constant dielectric value with respect to time than the ambient surrounding atmosphere medium, a good wetting capacity, only a slight tendency to foam-formation, and optimum viscosity, is disposed in the space between at least two symmetrical, plate-shaped pairs of electrodes of a capacitor arrangement, such that the liquid when in a neutral position fills about half said space, and the electrodes of the capacitor arrangement are connected to an electronic circuit whose output is arranged to produce a signal proportional to the difference in capacitance between said two pairs of electrodes.

Preferably, the capacitor arrangement is in the form of a differential capacitor, two individual electrodes in one plane being combined to form a common electrode. In the case of at least two capacitor arrangements provided, their electrodes are preferably in the form of circular sectors with different centring angles.

The capacitor arrangement can be disposed in at least two or more locally separable containers which are interconnected by a line.

When the capacitive inclinometer is in a horizontal position, the electrodes are all immersed in the dielectric liquid to the same depth, so that the two halves of the differential capacitor have the same capacitance.

The level of the liquid in the inclinometer varies in dependence upon slope, whereby less liquid with a high dielectric constant is located between the first pairs of capacitor plates, although more medium (for example air) arrives between these two plates, so that the capacitance of the first pair of capacitor plates decreases to the same extent as the capacitance of the second capacitor increases.

In the chosen form of the electrodes, a linear relationship exists between the change in the slope of the level of the liquid and the change in capacitance when the level of the liquid extends through the imaginary centre point of the circular sector-shaped electrodes.

The invention enables the provision of an inclinometer which can be used universally by virtue of small mass and volume, is insensitive to electrical, mechanical and thermal environmental influences, is sufficiently accurate over a large time domain, and which supplies an electrical signal which may be further processed and which, for example, enables connection to a microcomputer.

In addition to its simple construction, further advantages of the invention reside in its high independence of environmental influences, its insensitivity to lateral slope, and the inherent damping of the change in level as a result of the small distance between the electrodes.

The invention will be further described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a section through an arrangement having a small range of measurement; Figure 2 is a section taken along the line A-A in Fig. 1; Figure 3 is a section through an arrangement having a large range of measurement; Figure 4 is a section through an arrangement having a switchable range of measurement; Figure 5 is an elevation viewed in the direction B in Fig. 4; and Figure 6 shows an arrangement having locally separable capacitor arrangements.

Fig. 1 shows a hermetically sealed prismatic housing 10 which is half filled with a dielectric liquid 1 in which are immersed the symmetrically disposed pairs of electrodes of a capacitor arrangement 3 which comprises four circular-sector-shaped electrodes. The medium 2 adjacent to the liquid is air.

Fig. 2 shows the arrangement sectioned along the line A-A. The four electrodes of the capacitor arrangement 3 are wired as a differential capacitor and are connected to a suitable electronic circuit 4 whose output 5 supplies an electrical signal which is proportional to the difference in capacitance and which can be indicated in a digital or analog manner.

Fig. 3 shows an arrangement for a larger range of measurement for example to j 45 .

Fig. 4 shows an inclination and levelnessmeasuring instrument having two differential capacitor arrangements 6, 7 with different centring angles. Equal measuring signals are thereby obtained for two switchable measurement ranges, and hence higher resolutions are obtained than when working with the arrangement having a smaller centring angle.

Fig. 6 shows an arrangement in which the two capacitor arrangements 3 are located in containers 9 which are inconnected by a flexible line 8. Hence, the basic distance between the two capacitor arrangements 3 is variable, and test objects, whose difference in slope or level is to be ascertained may be at different distances from one another.

Fig. 5 shows an end elevation of the arrangement of Fig. 4.

Claims

1. A capacitive inclination and levelnessmeasuring instrument wherein an electrically non-conductive liquid which has a higher temperature-constant dielectric value with respect to time than the ambient surrounding atmosphere medium, a good wetting capacity, only a slight tendency to foam-formation, and optimum viscosity, is disposed in the space between at least two symmetrical, plate-shaped pairs of electrodes of a capacitor arrangement, such that the liquid when in a neutral position fills about half said space, and the electrodes of the capacitor arrangement are connected to an electronic circuit whose output is arranged to produce a signal proportional to the difference in capacitance between said two pairs of electrodes.

2. A capacitive inclination and levelnessmeasuring instrument as claimed in claim 1 wherein the plate-shaped electrodes are each in the form of a circular sector.

3. A capacitive inclination and levelnessmeasuring instrument as claimed in claim 1, wherein the capacitor arrangement is in the form of a differential capacitor, two individual electrodes in one plane being combined to form a common electrode.

4. A capacitive inclination and levelnessmeasuring instrument as claimed in claim 1, wherein, in the case of at least two capacitor arrangements provided, their electrodes are in the form of circular sectors with different centring angles.

5. A capacitive inclination and levelnessmeasuring instrument as claimed in claim 1, wherein the capacitor arrangement is disposed in at least two or more locally separable containers which are interconnected by a flexible conduit.

6. A capacitive inclination and levelnessmeasuring instrument wherein an electrically non-condutive liquid is disposed in the space between at least two symmetrically disposed pairs of plate-shaped electrodes which are each in the form of a circular sector and which together form a capacitor arrangement, the liquid level being such that in a neutral position of the instrument the liquid fills at least half said space, and the electrodes of the capacitor arrangement being connected to an electonic circuit whose output is arranged to produce a signal proportional to the difference in capacitance between said two pairs of electrodes.

7. A capacitive inclination and levelnessmeasuring instrument substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.