SU1226025A1 - Applied variable-capacitance transducer - Google Patents

Abstract

The invention relates to measurement technology and can be used to control the thickness of polymer films during their production. It makes it possible to increase the accuracy of thickness measurements using a capacitive patch sensor by reducing the effects of temperature changes in the dielectric properties of monitored films. Capacitive overhead sensor contains a measuring and reference capacitors located on opposite convex sides of the dielectric substrate. The low-potential electrodes of both capacitors are made in the form of pairs of coplanar rings, between which in the body of the substrate the annular grooves are hermetically closed from the surface side, along with the chamber filled with electrically conductive liquid, the temperature coefficient of expansion of which exceeds the temperature coefficient of expansion of the substrate. When the sensor operates under conditions of changing the ambient temperature, the electrically conductive fluid, such as mercury, expands and fills all or part of the annular grooves, changing the working area of the low-potential electrodes of the sensor accordingly. Dp of adjusting the initial capacitance value of the sensor are the means of adjustment, made in the form of a piston installed at the end of the chamber, and a micrometric unit connected with it. 1 hp f-ly. 2 Il. (L IND YO O5 O tc ate

Description

The invention relates to a measurement technique. It can be used to control the thickness of floor films in the course of their production.

The aim of the invention is to improve the measurement accuracy by reducing the influence of temperature changes in the dielectric properties of the film.

Fig. 1 shows a bill of lading sensor, a slit; in fig. 2 - the same, view from the side of the working surface.

The capacitive patch sensor contains a measuring capacitor 1 and a reference capacitor 2 located on opposite convex sides of a dielectric substrate 3, made of a material with high dielectric properties and a large thermal conductivity coefficient. Low and high potential ring electrodes 4 and 5, respectively, of the measuring capacitor 1, as well as low and high potential ring electrodes 6 and 7 of the reference capacitor 2 are arranged in an alternating sequence on the convex surfaces of the sub-floor 3 and are coated with abrasion resistant sections of the substrate separating them layer 8 di elektrshga.

Making the working surfaces of the capacitors convex ensures the adherence of the polymer film over the entire controlled surface without a gap, which leads to a high accuracy of measuring its thickness, and applying to the working surface a resistant abrasion of the dielectric layer on

an example of a layer of fused silica,

It bakes the absence of microparticles of the material of the controlled film and dust in the inter-electrode space, prevents the passage of through current. conduction between the electrodes, eliminates the possibility of closing the electrode of the sensor, and also prevents their corrosion, which also increases the accuracy of measuring the film thickness.

The low-potential electrodes 4 and 6 of both capacitors are made in the form of pairs of coplanar rings, between which in the body of the substrate 3 ring-shaped grooves 9 are hermetically sealed from the surface. These grooves communicate through channels 10 with a camera 1.1 made in the body of the substrate and filled with an electrical wire

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liquid 12, such as mercury, whose temperature expansion coefficient exceeds the temperature coefficient of expansion of the substrate. At the end of the chamber 11, the piston 13 can be disposedly movable along it and connected to its displacement micrometer assembly 14.

The sensor works as follows.

The polymer film, the thickness of which is controlled by the process of fabrication: production, is superimposed on the working surface of the measuring capacitor 1. Low and high potential electrodes 4-7 of the measuring and reference capacitors 1 and 2 are connected to a measuring circuit (not shown). The displacement of the monitored film changes the total capacitance of the measuring capacitor 1, which is proportional to the average contact area of the film thickness. Since the capacitance of the reference capacitor 2, which is identical to the measuring capacitor 1, does not change, the comparison of the capacitances of the capacitors 1 and 2 eliminates the influence on the measurement results of destabilizing factors, such as ambient temperature and humidity, which significantly affect the geometrical dimensions electrodes 4 and 7 and the dielectric properties of sasifiTHoro layer 8.

A change in the temperature of the material of the controlled film leads to a change in its dielectric constant, which causes non-in-. a formative increment of the capacitance of the measuring capacitor 1, and therefore the occurrence of a significant measurement error. To eliminate this error, it is necessary to change the capacitance of the measuring capacitor 1 by an amount equal to the increment of the capacitance caused by the temperature change of the dielectric constant of the film material.

Since the capacitance in a patch measuring capacitor brought in by the film being monitored depends on the area of the low and high potential electrodes, their number and distance between them, the dielectric constant of the film material and its thickness, therefore, compensate for the capacitance of the capacitance in the mother - a film, you can, for example, by

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changing the area of the low and high potential electrodes of the sensor or changing the distance between them. In this case, this compensation is made by changing the area of the low potential electrodes 4 and 6 of the capacitors 1 and 2. The compensation for this error occurs as follows.

Due to the fact that the polymer film fits tightly to the measuring capacitor 1, and the dielectric substrate 3 is made of a material with a high thermal conductivity, the temperature at each point of the substrate 3 is always equal to the temperature of the controlled film. As the temperature of the monitored film changes, for example, as it increases, the temperature of the sensor also increases and reaches the temperature of the film. Since it is temperaturns. The expansion coefficient of the substrate material 3 is less than that of the electrically conductive liquid 12, then, as their temperature increases, this liquid expands from chamber 11 through channels 10 into the annular grooves 9. As a result, the working area of low potential electrodes 4 and 6 increases.

Since the electrically conductive liquid 12, the filling of the grooves 9, is in contact on both sides across the entire width with the rings of the low-potential electrodes, the electrical contact between them improves, and therefore the stability of the sensor.

Thus, an increase in temperature leads to a decrease in the dielectric constant of the film and, consequently, to a decrease in the capacitance introduced by the film to the measuring capacitor 1. At the same time, this increase in temperature leads to an increase in the working area of the low-potential capacitor electrodes, which provides an increase in the capacitance introduced by the film to the measuring capacitor. capacitor 1. Due to this, compensation of the temperature non-informative effect on the output signal of the sensor occurs. To more fully compensate for the temperature non-informative effect, the depth of the grooves 9 along the length of the low-grade ones is necessary. electrodes to choose such that more fully compensate for the temperature variation of the dielectric

permeability of the film material in a wide temperature range.

Initial compensation of the temperature non-informative change in the dielectric properties of a film made of a different material or at a different temperature can be carried out by means of adjustment implemented, for example, as

to the piston 13 and the micrometric unit 14 of its movement. When the piston 13 moves from the periphery of the chamber 11 to the center of the sensor, an additional displacement of the electrically conductive liquid occurs.

15, bones 12 in the annular grooves 9, whereby the initial capacitance value of the sensor is adjusted by changing the area of the low-grade electrodes.

20 Improving the accuracy of measuring the bulk of polymer films due to the weakening effect of temperature changes in the dielectric constant of the film material makes it possible to increase

25 quality (reduce thickness variation) of the film during its production.

Claims (2)

1. Surface-mounted capacitive sensor for controlling the thickness of polymer films containing measuring and reference capacitors separated by a dielectric substrate, high and low potential electrodes of which are deposited on opposite convex surfaces of the substrate and are coated with an abrasion-resistant dielectric layer separating them from the substrate, which, in order to improve the measurement accuracy by reducing the effect of temperature changes on the dielectric properties of the film, the low-potential electrodes of both capacitors are made as pairs of complanar rings, between which annular grooves tightly closed on the surface of the substrate body are connected to a chamber made in the substrate body and filled with an electrically conductive liquid, the temperature expansion coefficient of which exceeds the temperature coefficient of expansion of the substrate. 2. The sensor pop. 1, which differs from the fact that it is equipped with means of regulating the initial value of the capacitance, made in the form a piston mounted at the end of the chamber with the ability to move along it and the associated micrometric piston displacement unit. 9. / 0. S. 5, ten. 9 Editor O. Yurkovetska Compiled by S. Skrypnik. Tehred V. Kadar Proofreader S. Shekmar Order 2109/27 Circulation 670Subscription VNIIPI. USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4 f1Ag.2