RU2016377C1 - Method of measuring dielectric articles thickness - Google Patents

Abstract

FIELD: non-destructive inspection of articles. SUBSTANCE: method involves placing an article to be tested in an electric field of a measuring capacitor, a potential of free surface of an article portion being tested being a linear function of a thickness at small thickness compared to an interelectrode distance. EFFECT: enhanced measurement accuracy. 1 dwg

Description

 The invention relates to instrumentation, in particular to methods of non-destructive testing of materials, and can be used in the engineering industry.

 As a prototype, a method for measuring the thickness of dielectric products is selected, which consists in placing the product between the plates of the measuring capacitor and judging the thickness by changing its capacitance.

 The disadvantage of this method is the low accuracy of the measurements.

 The aim of the invention is to improve the accuracy of measurements.

 The goal is achieved in that the measuring capacitor is previously informed of a charge of a known magnitude, and the measured thickness is judged by the magnitude of the voltage across the measuring capacitor.

 The essence of the proposed method is as follows.

 A compensating capacitor with a capacity much smaller than the capacitance of the measuring capacitor is selected. Measuring and compensating capacitors are connected in series. A voltage is applied to the two-terminal network formed and the voltage drop across one of the capacitors is measured. It is proportional to the measured thickness.

, (1) где U - величина приложенного напряжения; ω - его частота;
С_х и С_о - емкости соответственно измерительного и компенсирующего конденсаторов.We will show this and evaluate the required degree of smallness of the compensating capacitor, since an unlimited decrease in its capacitance reduces the energy value of the formed system and reduces the possibility of an informative signal, which increases the requirements for measuring instruments. For the current I flowing through the studied two-terminal network, we can write the expression
I =

, (1) where U is the value of the applied voltage; ω is its frequency;
C _x and C _o are capacitances of the measuring and compensating capacitors, respectively.

, (2) где, пренебрегая по условию С_х >> С_о емкостью С_о в знаменателе, имеют
U_x≈

(3) или
^Ux⁼

, (4) где С_п - получаемое в результате действия способа значение емкости измерительного конденсатора.Using expression (1), the voltage drop U _x on the measuring capacitor C _x can be expressed as
U _x =

, (2) where, neglecting the condition С _х >> С _{about the} capacity С _о in the denominator,
U _x ≈

(3) or
^U x ⁼

, (4) where C _p is the value of the capacitance of the measuring capacitor obtained as a result of the method.

, имеют
С_п = С_х + С_о или
С_х = С_п - С_о, т.е. истинное значение емкости С_х измерительного конденсатора всегда меньше получаемой при реализации способа на величину емкости компенсирующего конденсатора С_о, что и определяет величину ошибки при реализации способа.Expression (4) represents the desired linearized dependence. Since the left sides of expressions (3) and (4) are equal, equating their right sides

have
C _p = C _x + C _o or
C _x = C _p - C _o , i.e. the true value of the capacitance C _{x of the} measuring capacitor is always less than the value obtained during the implementation of the method by the value of the capacitance of the compensating capacitor C _о , which determines the amount of error in the implementation of the method.

 The method is implemented using a device, a diagram of which is presented in the drawing, as follows.

The measured element 1 of the product is located between the grounded electrode-substrate 2 and the electrode probe 3 connected to the input of the repeater 4 by means of a probe 5, which is a coaxially made linearizing capacitance С _о . From the generator 6 relative to the ground, a signal is supplied to the common output of the repeater 4, and the measured thickness is judged by the voltmeter 7, which measures the output voltage of the repeater relative to the ground. This inclusion of the repeater allows you to receive an informative signal in the most convenient form.

Claims (1)

 METHOD FOR MEASURING THICKNESS OF DIELECTRIC PRODUCTS, namely, that the controlled product is placed between the electrodes of the measuring capacitor and the thickness is judged by the thickness, characterized in that, in order to increase the accuracy of measurements, the measuring capacitor is preliminarily informed of the charge of a known value, and the thickness being measured judged by the magnitude of the voltage across the measuring capacitor.

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