RU2413180C1 - Apparatus for measuring thickness of dielectric coating - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: apparatus has a generator of electromagnetic oscillations 1, connected by the output to an emitter 2, a first receiver 3, a first detector 4, a second receiver 5 connected to the input of a second detector 6 and a computer 7. Operation of the apparatus is based on conversion of electric field strength of reflected electromagnetic waves from two boundary surfaces of media.

EFFECT: high accuracy of measuring thickness of dielectric coating deposited on a dielectric base.

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Description

The invention relates to the field of measuring equipment and can be used in process control systems.

A device is known that is implemented by a capacitive sensor of the coating thickness (see M. Chekhovsky. Control of the enamel thickness on the body. Radio, No. 7, 2004, p. 47), in which the enamel coating thickness on the car body is judged by measuring the capacitance of two series-connected capacitors connected to a capacitance meter.

The disadvantages of this known device are the contactivity of the sensor with a controlled coating surface and the measurement error due to temperature effects on the capacitance of the capacitors.

The closest technical solution to the proposed one is the device adopted by the author for the prototype, which implements a method for determining the thickness of the dielectric coating (see RF Patent No. 2262658, published October 20, 2005, Bull. No. 29). The operation of the method implemented by the specified device is based on sensing the dielectric coating with electromagnetic waves and measuring the electric field strength of the reflected wave from the controlled coating. Here, an emitter and a receiver are used for this, made in the form of mirror antennas, which respectively irradiate the coating and receive the signal reflected from it. With known values of the directivity and power of the emitter, by measuring the detected signal of the amplitude detector, the thickness of the dielectric coating deposited on the dielectric base is determined.

The disadvantage of this invention should be considered an inaccuracy associated with a change in the dielectric constant of the dielectric coating.

The objective of the claimed technical solution is to increase the accuracy of measuring thickness.

The problem is solved in that in the device for measuring the thickness of the dielectric coating deposited on a dielectric base, containing an electromagnetic oscillation generator connected to the output of the emitter, the first receiver connected to the input of the first detector, the emitter and the first receiver are made in the form of mirror antennas and are located in one plane at one distance from the controlled coating, introduced a second detector, calculator and a second receiver, made in the form of a mirror antenna and located in Este a transmitter and the first receiver in the same plane at the same distance from the controlled coating, wherein the second receiver is connected to the input of the second detector whose output is connected to the first input of the calculator, calculating a second input connected to the output of the first detector.

Salient features of the above population is the presence of a second receiver, a second detector and a computer.

In the claimed technical solution, due to the properties of the listed features, the conversion of the electric field strengths reflected from the first interface of the medium “air - dielectric coating” and the second interface of the medium “dielectric coating - dielectric base" of the waves makes it possible to solve the problem: to increase the accuracy of measuring the thickness of the dielectric coating .

The drawing shows a functional diagram of the proposed device.

The device comprises an electromagnetic oscillation generator 1, an emitter 2, a first receiver 3, a first detector 4, a second receiver 5, a second detector 6 and a calculator 7. In the drawing, pos. 8 and 9 denote the dielectric coating and the dielectric base, respectively.

The device operates as follows. The electromagnetic waves of the emitter 2 coming from the output of the electromagnetic oscillation generator 1 are directed towards the dielectric coating 8 deposited on the dielectric base 9. In this case, according to the theory of propagation of electromagnetic waves, reflection of waves from the first “air - dielectric coating” interface can take place , the passage of waves through a dielectric coating and the reflection of transmitted waves from the second interface of the media "dielectric coating - dielectric base".

For the reflection coefficient from the first media interface k _12, we can write:

where E _pad1 is the electric field strength of the wave incident on the first interface, E _otp1 is the electric field strength of the wave reflected from the first interface.

In the case under consideration, with the location of the dielectric base with a dielectric coating deposited on it in the wave zone (see page 3 of the above patent) for E _pad1, you can take:

,

,

where R is the distance from the emitter to the surface of the dielectric base, P is the power of the emitter, G is the directivity of the emitter and δ is the thickness of the dielectric coating.

By virtue of this, for _otpr1 we get:

Formula (2), taking into account that:

where ε ₂ is the dielectric constant of the dielectric coating, can be rewritten as:

It is assumed here that the dielectric constant ε of air _is equal to unity and the dielectric coating has no losses, i.e. g ₂ = 0, where g ₂ is the conductivity of the dielectric coating.

It can be seen from formula (3) that for constant values of P, G, and R, to determine δ from the value of E _CP1, it is necessary to have information on ε ₂ , since different materials used to coat the dielectric base can have different values of permittivity.

To do this, the proposed device uses reflection from the second interface of the media with a reflection coefficient K ₂₃ defined by the following expression:

where E _pad2 is the electric field strength of the wave incident on the second interface of media, E _otp2 is the electric field of the reflected wave from the second media interface.

According to the above conditions (the location of the dielectric base and coating in the wave zone) for this case, the electric field strength of the wave incident on the second interface (the surface of the dielectric base) of the wave can be represented as:

As follows from the last formula, in this case, the influence of the coating thickness δ on the formation of E _{pad2 is} not taken into account. This is explained by the fact that in the absence of a coating on a dielectric base, there is only one reflection from the surface of the dielectric base (the interface is “air - dielectric base”), which can exist in the presence of a coating, but from a different interface (“dielectric coating - dielectric base ") and with a different reflection coefficient. Therefore, when E _{pad2 is formed} at the second interface (the distance from the emitter to the surface of the dielectric base without taking into account δ), there is no need to take into account the coating thickness. By virtue of this assumption, formula (4), taking into account that:

where ε ₃ is the dielectric constant of the dielectric base, can be rewritten as:

It is assumed here that ε ₃ > ε ₂ and the dielectric base has no losses, etc. g ₃ = 0, where g ₃ is the conductivity of the dielectric base.

The last formula shows that in the case of constant values of P, G, R and ε ₃ = const, i.e. with the same material of the dielectric base, the value of E _OT2 becomes a function of ε ₂ .

Let the reflected wave from the first media interface be caught by the first receiver 3, and the reflected wave from the second media interface by the second receiver 5, which then goes to the inputs of the first 4 and second 6 detectors, respectively. In the case under consideration, due to the fact that the values of the strength E _Otr1 simultaneously change from changes in ε ₂ and δ, and the values of the strength E _Otr2 change only from changes in ε ₂ , they can be separated by reception by the first and second receivers experimentally.

According to the proposed technical solution, the signal received at the output of the first detector, which depends on changes in ε ₂ and δ, is then fed to the first input of the calculator 7. At the same time, the output of the second detector, depending on ε _{2, is} fed to the second input of the calculator. As a result of this, the transformation in the computer of the signals described by formulas (3) and (5) makes it possible to determine the coating thickness δ taking into account the change in ε ₂ , i.e. dielectric constant of dielectric coating.

Thus, in the claimed technical solution, it is shown that by converting the electric field strengths of the reflected waves from two media interfaces, it is possible to increase the accuracy of measuring the dielectric coating.

Claims (1)

A device for measuring the thickness of a dielectric coating deposited on a dielectric base containing an electromagnetic oscillation generator connected to the output of the emitter, a first receiver connected to the input of the first detector, the emitter and the first receiver are made in the form of mirror antennas and are located in the same plane at the same distance from the controlled coating, characterized in that it introduced a second detector, calculator and a second receiver, made in the form of a mirror antenna and located along with the radiation the sensor and the first receiver in the same plane at the same distance from the controlled coating, the second receiver connected to the input of the second detector, the output of which is connected to the first input of the computer, the second input of the computer is connected to the output of the first detector.