Electronic levelling cell

Details Electronic levelling cell Electronic levelling cell

1983-05-11

1985-06-11

Stearns, Richard R.

Geometrical instruments

Indicator of direction of force traversing natural media

Level or plumb, terrestrial gravitation responsive

33377, G01C 906, G01C 920

Patent

active

045219737

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a levelling device, namely a device for detecting deviation from level position of a surface using a gravity-levelled surface as reference.
Theodolites and other surveying instruments include devices serving to correct or compensate for inaccurate setting up of the instrument resulting from, for example uncontrolled movements of the tripod and the alidade, i.e. the rotatable base of the instrument. Known correcting or compensating devices suffer from various drawbacks, e.g. in that they occupy a substantial space both vertically and horizontally, so that they are not suitable for mounting on or near the vertical axis of rotation of the base, in that they have an unwanted hysteresis resulting in instability problems, or that they have insufficient sensitivity.
An object of the invention is to provide an improved electronic levelling device which is suited for incorporation in a theodolite or other surveying instrument having a vertical axis of rotation of the base and by means of which the rotatable base may be accurately adjusted to a level position so that the axis of rotation is accurately vertical and/or by means of which an indication of the vertical angular deviation of the base from level position may be obtained.
In accordance with the invention there is provided a device for detecting deviation of a plane from level position, including a conductive gravity-levelled reference element defining a horizontal reference surface, at least one pair of conductive, rigidly mounted sensing electrode members jointly defining said plane and disposed adjacent the reference surface in confronting relation therewith, a dielectric fluid separating the reference surface from the sensing electrode members, the reference element, the pair of sensing electrode members and the dielectric fluid forming a pair of capacitors the capacitances of which vary oppositely in response to deviation of said plane from parallelism between the reference surface and a line joining the pair of electrode members, and means for detecting variations of the capacitances of the pair of capacitors, characterised in that the detecting means includes an alternating current source connected to the pair of capacitors and adapted to apply oppositely phased first and second alternating voltages to respective ones of the capacitors, the product of the capacitance and the applied voltage being equal for both capacitors when the reference surface and said line are parallel, and an inverting amplifier including a feed-back capacitor and having its input connected to the gravity-levelled element.
If it is desired to use the device according to the invention for levelling e.g. the alidade or rotatable base of a theodolite, this may be accomplished automatically or manually. In the first-mentioned case the output of the device is used to control levelling motors adjusting the attitude of the base until the output of the device is zero. In the last-mentioned case, the operator adjusts the attitude of the base manually until the output is zero.
Other objects and features of the invention will become apparent from the following description taken in connection with the accompanying drawings, in which:
FIG. 1 shows a section along line I--I of FIG. 2 of a levelling cell forming part of the device according to the invention;
FIG. 2 is a plan view of the levelling cell shown in FIG. 1;
FIG. 3 is a circuit diagram of a device embodying the invention;
FIG. 4 is a simplified circuit diagram corresponding to a portion of FIG. 3;
FIG. 5 is an equivalent circuit diagram corresponding to FIG. 4;
FIG. 6 shows a modified electrode pattern for the levelling cell;
FIG. 7 is an equivalent circuit diagram of a device according to the invention incorporating the electrode pattern shown in FIG. 6;
FIG. 8 shows a further modified electrode pattern;
FIG. 9 is an equivalent circuit diagram of a further embodiment of the device according to the invention;
FIGS. 10 and 11 are respectively a perspective view and a sectional view of a further embodiment of

REFERENCES:
patent: 2592941 (1952-04-01), Moore
patent: 2711590 (1955-06-01), Wilcox
patent: 2825978 (1958-03-01), Davis
patent: 4028815 (1977-06-01), Buckley et al.
patent: 4377912 (1983-03-01), Hakhverdian

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