SU1250836A1 - Capacitance converter of linear movements - Google Patents

Abstract

The invention relates to a measurement technique and makes it possible to increase the accuracy of converting small linear displacements using a capacitive converter, which is a double geometrically symmetric cross-capacitor. The capacitive transducer contains two groups of electrodes mounted on relatively movable bases. Each group includes two high-potential electrodes separated by two parallel insulating gaps from a low-potential rectangular electrode placed between them and a pair of grounded guard electrodes coplanar with them, the low-potential electrode being separated from the guard electrodes by additional parallel insulating gaps perpendicular to the first two gaps. The remaining parts of the surface of the bases are made with shielding metal coatings. When one dielectric base with electrodes is displaced relative to another, a signal is generated at the output of the converter, which is proportional to the difference in capacitance between high-potential electrodes placed on one base and a low-potential electrode placed on another base. 3 il. (L o JV about 00 with O5 Fig. 1

Description

The invention relates to a measurement technique and can be used to change small linear movements with high accuracy, for example, to measure the relative position of segmented mirror portions of ground-based or space-based telescopes.

The aim of the invention is to improve the accuracy of linear transformations by improving the stability of the conversion characteristic by eliminating the influence of mechanical contacts between the design details of the capacitive transducer and ensuring its insensitivity to changes in the surface properties of the electrodes and to their temperature changes.

FIG. I depicts the design of a capacitive converter; in fig. 2 - location of the capacitive converter on the controlled object; in fig. 3 is a simplified diagram of the connection of the converter electrodes to the power and signal processing units.

The capacitive linear displacement transducer contains two relatively mobile dielectric bases 1 and 2, on which the groups of electrodes are mirrored by the metallization method. A group of electrodes on each base contains two high-potential electrodes, for example, 3 and 4 on base 2, which are separated by two narrow parallel insulating gaps from the low potential, which is placed between them, of the rectangular electrode 5. These same gaps separate the high-potential electrodes 3 to 4 from with them are coplanar of two pairs of 6 and 7 grounded guard electrodes, which are separated from the low potential. two additional insulating gaps, perpendicular to the first two gaps. The remaining surface areas of both bases 1 and 2 are made with shielding (grounded) metal coatings 8 and 9, respectively. Electrodes of the converter are supplied with electric conclusions: 10-I and 12-13 dl. high potential electrodes placed on bases I and 2, respectively, and pins 14–15 for low potential electrodes. The capacitance transducer fastens with a controlled object so that the surfaces of the measuring electrodes 3, 4 and 5 on its dielectric base 2 and the corresponding measuring electrodes 16-18 on its base 1 are mutually parallel and opposite to each other in the initial state. The insulating gaps were also mutually parallel. The AC power supply 19 is connected via a transformer 20 with a grounded average.

a tap from pi o w of the primary winding to the high-potential power e. yktrodam 1G) and 17 converter. Wherein. nor; 4cog potential electrode 18 and high potential

electrodes 2 and 4 are grounded, and lowcc electrode 5 is connected via an intermediate amplifier 21 with a phase-sensing amplifier 22, the output of which forms an informative signal as a function of the relative displacement of the edges 23 and 24 of the test object in the X direction.

Capacitive converter works as follows.

In the absence of relative displacement of the bases 1 and 2 of the capacitive transducer installed during the measurement on the test object, the capacitance C i and Cj between the electrodes 16-5 and 17-5 are determined by the following mathematical expressions, respectively.

C, Cr. , (I)

where L is the length of low-potential electrodes along the X axis; .. Sr, is the relative dielectric constant of the medium between the electrodes;

io is the dielectric constant of a vacuum.,

The width bj of low potential electrodes (along the Y axis), width bg of high potential electrodes, and the distance d along the Z axis between the surfaces of the electrodes must satisfy the following condition:

, (2)

and the width g of the insulating gaps must be chosen from the condition

g

ten

(3)

As a result, when one part of the monitored object (edge 23) is shifted along the X axis relative to the other (edge 24), one of the capacitances increases and the other decreases, due to which an output signal is generated at the output of the capacitive converter and is proportional to the difference Ci and Ct capacities

 s, f.S ..

(four)

Due to the fact that the capacitive transducer, being a double geometrically symmetric cross capacitor (in its differential version), has in accordance with the Thompson – Lampard theorem, the property of independence of each cross capacitance on the shape and size of the capacitor cross section is achieved move transforms one by one

coordinate axis when measurement results are independent of movement along other coordinate axes.

Claims (1)

Formula of invention A capacitive linear displacement transducer containing two relatively movable bases on which surfaces facing one another are placed mirror-symmetrically groups of electrodes, characterized in that, in order to increase the conversion accuracy, the groups The electrodes on each base contain two high-potential electrodes, separated by two parallel insulating gaps from the izopotential rectangular electrode and pairs of grounded guard electrodes aligned with them, and the potential electrode separated from the guard electrodes by additional parallel insulating gaps, and the surfaces of the bases are made with shielding metal coatings. ffij I QnL.J Fig.Z Compiled by S-Skripnik Editor T. ParfenovaTehred I. VereyeThe Corrector M. Maximishnnets Order 4398/34 Circulation 670 Under Pod VNIIPI USSR State Committee AO cases of 11 inventions and openings II303S, Moscow. , Raushsk "Ivb., D. 4/5 Branch PPP cPateet, Uzhgorod, st. Project, 4