SU1567967A1 - Eddy current method of nondestructive check of physicomechanical parameters - Google Patents

Abstract

The invention relates to non-destructive testing and can be used in thickness gauging, inspection and measurement of other physicomechanical parameters of materials and products. The aim of the invention is to improve the accuracy of control due to the detuning from the effect of a change in the oscillation frequency of the circuit due to the temperature instability of the inductance and the capacitance of the circuit. This is achieved by the fact that in the eddy-current method of non-destructive testing, which consists in the fact that the eddy-current transducer included in the oscillating circuit is placed above the object being monitored, the circuit is impressed and the transition parameter is measured as the absolute minimum of the difference - or an RL circuit with a constant time, a smaller transient time constant, and the voltage of the damped transition oscillations, and the parameters of the RC or RL circuit before measurement The absolute minimum is changed to match the absolute minimum of the difference and minimum of the differential voltage envelope. 3 il.

Description

The invention relates to non-destructive testing and can be used in thickness gauging, flaw detection and in the measurement of other physicomechanical parameters of materials and products.

The purpose of the invention is to improve the accuracy of control due to the detuning from the effect of a change in the oscillation frequency of the circuit due to temperature instability of the inductance and capacitance of the circuit.

In FIG., The device by which the method is implemented; Figures 2, 3 are curves that explain the eddy current method of nondestructive testing of physical and mechanical parameters 4

The device consists of a source 1 of a constant voltage E, to the output of which, via a switch 2 assembled, for example, on a transistor, i are connected via a resistor 3 with resistance R. an oscillating circuit of shock excitation containing an eddy current converter 4 with inductance and a capacitor 5c , and an RC circuit containing a resistor 6 with a resistance Rft, a resistor 7 with a resistance RJ, and a con-, sensor 8 with a capacitance Ca. The circuits are connected to the inputs of the differential amplifier 9, the output of which is connected to the input of the peak detector 10.

In Fig. 2, curve 11 describes the voltage of damped oscillations, cree.

cl

0E J

12 are their envelopes at maxima and minima, curve 13 is the discharge voltage of an RC or RL circuit.

In Fig. 3, curve 14 characterizes the difference voltage between the discharge voltage of the RC-NPP RL-circuit and the voltage of the damped oscillations; curve 15 - its envelope at the minimum; point A is the minimum differential edge coinciding with the minimum envelope; measured voltage. A change in the frequency of damped oscillations within small limits almost does not reflect on the measurement results, since point L then moves along the envelope with respect to its minimum.

The method is carried out as follows.

The eddy current transducer 4 is placed above the surface of the test object (not shown). In the initial state, the key is open. The current through converter 4 and the voltage on capacitor 5 are zero. After the key 2 is closed, the LC and RC circuits are charged. At the end of the charge, a current E / R flows through converter 4, and capacitor 5 is charged to voltage E. When key 2 is opened, oscillating and RC circuits are discharged: the magnetic energy stored in converter 4 is converted into energy of damped oscillations ( The oscillatory circuit (LC (), and the capacitor 8 (C) is discharged through resistors 6 (R) and 7 (Rj). Voltages from the circuits are fed to the inputs of the differential amplifier 9, from which the difference voltage is applied to the peak detector 10.

Vibration decay process, descriptions

equation

and,

U.e .cos 2, ft,

(one)

and, is the instantaneous value of the voltage on the circuit; initial voltage; - time; - constant time transitive

and,

t

go process; f is the oscillation frequency.

Expression (1) shows that the envelopes of the damped oscillations are exponential. The exponent is also the voltage curve on the RC or RL circuit at x discharge

 ua U city (2)

7967 where

and „U

instantaneous voltage on the circuit; initial voltage; - constant transition time,

If the voltage u4 is subtracted from the voltage U 2 (for example, using a differential amplifier), then at -g. Ј c the envelope to the minima of the differential voltage will have a minimum with the abscissa t determined by

five

by equality

/ v. A

b, y t

t In

oh c

U-g

s

(3)

Expression language

varies. given

/ jj

 .- l. )

IJ, -2

(3) it follows that, (with

U., and

and

lt

6,

),

can be combined

0

five

five

0

0

45

five

0

tQ with a minimum of any half-wave differential voltage. The minimum difference voltage is then measured with a peak detector, and the object is monitored.

Example, Let the damped oscillations of the circuit, when installed on the product, have parameters f 10 Hz, C, 5 μs. By combining the minimum of the differential voltage envelope with the minimum of the fourth half-wave of the differential voltage, i.e. t 4 μs, taking in / Ј, 0.9, and solving equation (3) with respect to U2 / U1, we get U2 / U, 0.98.

Suppose that it is required to measure the thickness of the dielectric coating on an nsmaglitic base of 0.5 µm. When using an eddy current transducer with a core core, this VTP displacement will correspond to a useful change in the voltage of the oscillating circuit by approximately 3-E. Accepting voltage instability due to instability of the oscillation frequency of the circuit is not more than 0.3% of its useful change, i.e. no more than I0 voltage and analyzing the differential voltage envelope, we see that such a change in voltage at the point of its minimum corresponds to the frequency instability of the contour of 0.5%, which is easy to implement.

Claims (1)

The use of the method allows to increase the sensitivity and accuracy of measurements, to expand the boundaries of the application of the eddy current control method. Invention Formula Eddy current method of nondestructive testing of physicomechanical parameters of electrically conducting objects, 51 the eddy current transducer included in the oscillating circuit is placed above the object being monitored, the circuit is shock-driven and the transient parameter is measured, characterized in that, in order to improve the control accuracy, the absolute minimum difference is used as the transient process parameter 679676 between the discharge voltage of an RC or RL circuit with a constant time, less constant transient time, and a voltage of damped  oscillations of the transient process, and the parameters of the RC or RL circuit before changing the absolute minimum are changed until the absolute minimum of the difference and minimum of the envelope at the minima of the differential voltage coincides. ten Thebes. / Vrep Phage. g / Phage.Z