SU1652894A1 - Method of controlling electric conductors by eddy current and device thereof - Google Patents

Abstract

The invention relates to non-destructive testing and can be used to control the quality of electrically conductive products. The purpose of the invention is to increase the sensitivity. This is achieved by registering a time-varying informative signal under conditions that provide greater sensitivity to the monitored parameter. The eddy current transducer 2 is moved along the normal to the monitored section; it is obtained with the aid of bgc 4 of differentiating the change in voltage U at the circuit output in time, fixed with the help of extremator 5 the maximum value of the voltage at the output of block 4 and fix the value U memory 2 sp.f-ly, 3 Il. "

Description

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The invention relates to non-destructive testing and can be used to control the quality of electrically conductive products.

The purpose of the invention is to increase the sensitivity by registering a time-varying informative signal under conditions that provide greater sensitivity to the monitored parameter.

FIG. 1 is a block diagram of a device for eddy current testing of electrically conductive products I in FIG. 2 shows the dependence of the input voltage U of the oscillating circuit on the gap h at the values of the specific electrical conductivity: 0.5; SG2 0.7; SG3 0,9MSm / controlled products; Fig. 3 shows the dependence of the output voltage Ug of the oscillating circuit on the electrical conductivity U of the product at the maximum sensitivity of the circuit with ECP over SG,

A device for eddy current monitoring of electrically conductive products is equipped with a harmonic voltage generator 1, an eddy current converter 2 connected to an oscillatory circuit, a signal processing unit 3 connected in series, a differentiation unit 4, an extremer 5, a memory block 6 connected by a second input to the output of the signal processing unit 3, the drive 7, mechanically connected to the eddy current transducer 2 and designed to move along the axis, and the output of the oscillating circuit with the eddy current transducer 2 n Connected to the input unit 3 signal processing.

The method is implemented as follows.

The eddy current transducer 2 is installed above the surface of the test product at a distance hpmax from the product surface. Using the drive 7, the eddy current transducer 2 is moved along the normal to the surface of the tested product from the maximum distance (gap) to h 0. Since the output voltage UK of the circuit varies as a function of the gap h as shown in Fig. 2, the output voltage The oscillation circuit changes as a function of time according to the same law.

Using the differentiation unit 4, the voltage variation UK is obtained over time. The extremmer 5 fixes the maximum value of the change in U c (time derivative). In this case, memory block 6 memorizes the value of U at the loop output, corresponding to the maximum change in Ufc with time.

The high sensitivity to the parameter being monitored is achieved as follows.

When powering the eddy current transducer 2 from the current source, the voltage on the circuit is determined by the resistance of the circuit. The relative change in the resistance AZ / Z of the circuit, expressed through the relative changes in the active resistance AR / R and inductance D L / L of the eddy current transducer, has the form

Lz

1-G + G /

Lh

Z (1-ЈZ) Z + p / Qi1 L

R

V

g (1- 2) g + f VQ 2 R;

where O is the quality factor of the contour

WITH

- - contour detuning;

Sor

O is the circular frequency of the current generator supplying the circuit;

SOR is the resonant frequency of the circuit;

L, R - inductance and resistance of the eddy current transducer, respectively; AR,

& L - increments R and L of the ECP from the monitored parameter G,

From expression (1), it can be seen that the sensitivity of the circuit to changes in L and R, and hence also (J of the product under test, depends on the detuning of the circuit. For Ј 1, i.e., at the resonance D Z / Z is determined by

AZ Z

UL L

(2)

five

By 1, the value expression indicates that the relative voltage variation on the circuit is determined only by the relative changes L and R

hfp

one

1652894

The magnitude of the detuning, corresponding to the maximum voltage on the circuit from the value of the monitored parameter, can be determined by examining the expression (1) for an extremum

- And expression (3) implies that par setting, in which the sensitivity of the circuit with & TP to the monitored parameter is maximum, depends on - t to the extent of Q of the circuit and the values of AL / L and LC / R. When O 1 and malmx changes j L / and D R / R of the con, ura, which have mag m changes of the congr – shg / –th parameter, vyragkeye e D E Z / Z takes the form:

SL 4L

 ъ

1 YES

2 R

at

G 1

(four)

z

 L

BUT

R

at

PG -1.

Consequently, the sensitivity of the oscillating circuit to a controlled parameter when y is many times greater than the sensitivity of the circuit at resonance. According to FIG. 2, the maximal smallness corresponds to the point of the curve with the greatest steepness. Moreover, for each monitored SG value, the maximum slope of the curve Uk (h) takes place at one h value, i.e. the change in the output voltage of the circuit in time (derivative) at the point of the greatest steepness of the curve UK (h) takes the maximum value. At other points in the curve, the derivative is smaller and at the point of resonance it is zero.

(3)

five

0

five

0

five

0

five

Claims (2)

1. A method of eddy current monitoring of electrically conductive products, which consists in including a eddy current converter into an oscillating circuit, feeding it with a harmonic voltage, sweeping the invertor converter normal to the surface of the tested product, fixing the output voltage of the oscillating circuit at an extreme the value of the informative signal, functionally related to the output voltage of the circuit, and the measured value of the output voltage is judged by the obtained value of the output voltage That, in order to increase the sensitivity of the control, the change in the output voltage of the circuit over time is used as an informative signal. 2. A device for eddy current monitoring of electrically conductive products, comprising a generator, a eddy current transducer included in an oscillating circuit, a signal processing unit connected by an input to the output of the oscillating circuit, and an extremer, characterized in that it is equipped with a unit for increasing sensitivity. the differentiation connected between the output of the signal processing unit and the extremer input, and the memory unit connected by the inputs to the outputs of the extremer and the signal processing unit. 0.2 Us