SU1670573A1 - Process of checking products using eddy currents - Google Patents

Abstract

The invention relates to non-destructive testing methods and can be used in the metallurgical and machine-building industry for flaw detection of products made of non-magnetic materials with a low conductivity value (σ * 982MCM / M). THE PURPOSE OF THE INVENTION IS THE ENVIRONMENTAL IMPROVEMENT OF CONTROL OF PRODUCTS WITH LOW ELECTRICAL CONDITION. For this eddy current converters included B oscillating circuit, feeds harmonic voltage high frequency drive T B vibrational motion along the normal K tested article surface, determined Derivative voltage output circuit according to time, measured maximum value of derivatives and on it is judged O CONTROLLED PARAMETER. 3 il.

Description

The invention relates to non-destructive testing methods and can be used in the metallurgical and machine-building industry for flaw detection of products made of non-magnetic materials with a low conductivity value (a 2 MS / m)

The purpose of the invention is to increase the sensitivity in the control of products with low electrical conductivity due to the detuning from interfering parameters.

FIG. 1 shows a block diagram of a device implementing the proposed method; in fig. 2 shows the dependence of the output voltage of the UK oscillatory circuit on the power reserve at values of electrical conductivity ai 0.5 MS / m. 72 0.7 MS / m, od -0.9 MS / m of controlled products; in fig. 3 shows the dependence of the maximum values of the time derivative of the output voltage of the oscillating circuit on the electrical conductivity of the controlled products.

The device implementing the method consists of a high-frequency harmonic voltage generator 1, eddy current transducer 2, vibromechanism 3 for mechanical vibrations of eddy current transducer 2 normal to the surface of the tested product, oscillatory circuit 4. signal processing unit 5, differentiating unit 6, rectifier 7 amplitude value, dial gauge 8.

The generator 1 is connected to the oscillatory circuit 4. The element of which is the eddy current transducer 2, mechanically attached to the vibromechanism 3. The output of the oscillating circuit 4 is connected to the input of the signal processing unit 5. The output of the signal processing unit 5 is connected to the input of the differentiating unit 6. The output of the differentiating unit b is connected to the input of the rectifier 7 of the amplitude value. A dial indicator 8 is connected to the output of the rectifier 7 of amplitude value.

The method is implemented as follows.

The current transducer included in the oscillatory congur is installed above the surface of the monitored product and, by means of the vibro-mechanism 3, is vibrated with a constant frequency and amplitude along the normal v of the monitored surface. Then, the time-dependent input of the loop input circuit is determined and the maximum value of the derivative is found, go to 1,., Rsy is judged to control the parameter

When powering V1P from generator 1 to the voltage on the circuit is determined by the resistance of the circuit. The relative change in the resistance of the circuit AZ / Z, expressed in terms of the relative changes in the active resistance of the DN / R and the induction. -T- -. L / 1 S: P :: geyutvid

AZ 1-Ј + ЈlQL x

z (1; 2 + с2 / о2

AL

- (i + Ј / &

where O is the goodness of the circuit: j. but)

s ojb

O) - circular feed circuit,

 resonant frequency of the circuit;

L, R - inductability and active resistance of the eddy-current converter;

L1, L R increments of L and R VTP from contractors; - my parameter is 0.

Hj of expression (1) shows that the sensitivity of the circuit to changes in L and R, and, consequently, to the controlled product, depends on the detuning ks; At Ј 1, i.e., at the resonance AZ / Z is determined by the expression

AZ AL & RT

L -. ,

The resulting interference indicates that the relative change in voltage on the circuit is determined only by the relative changes in L and R of the ECP.

The detuning value Јi corresponding to the maximum voltage increment on the circuit from the value

LR

B. (1)

contour detuning.

part of the current gsneratopa,

controlled parameter can be determined by examining the expression (1) at the extremum:

t about (-IL L °

AR

R

(3)

Og 1)

AL, AR

eleven

From the expression (3) it follows that the detuning at which the sensitivity of the circuit with

VTP to the controlled parameter is maximum, depends on the quality of the circuit Q and the values of Al./Ln AR / R. With Q 1 and small changes in the AL / L and AR / R contours, which is the case for small changes in the monitored parameter (control of products with low (t), the expression for L Z / Z takes the form

-. iALiAtt, .Л

at & - - - “t -t- - - - - -, (4)

0

five

0

five

0

at 1 2

Consequently, the sensitivity of an oscillating circuit with an ESP to a monitored parameter c / at много is many times greater than the sensitivity of the contour to a about at resonance

Pa figs. 2 it is shown that the maximum sensitivity corresponds to a point of the curve with the greatest steepness, with each value of a corresponding to its own maximum steepness of the curve UK (h), and it takes place at its own value of h. Consequently, the derivative of the output voltage of the circuit with respect to time at the point of maximum steepness of the curve 1) k (n) takes the greatest value. In addition, its value depends on the value of the monitored parameter of art.

Due to the VTP oscillations above the surface of the tested product, the output voltage of the differentiating unit 6 is variable. The amplitude value of this voltage is proportional to the product of the maximum of the derivative and the oscillation frequency of the ECP. If the input voltage of the differentiating unit ivvh varies according to the harmonic law

Ubx Sin Wnt, (5)

ine Wn - circular frequency of oscillations of ECP. then the output voltage of the differentiating unit U of y

aivh.d

U in

their d5

dt

(From, UmCOSWnt. (6)

The output voltage of the amplitude rectifier is equal to the value of WnUm. Therefore, the dial indicator 8 -. Tests the voltage of the oscillating circuit at maximum sensitivity to a.

As can be seen from FIG. 3, there is a one-to-one connection between Us and the measured parameter a of the product under test. This shows that the control results are not affected by such a strongly interfering parameter as the gap.

Claims (1)

Claims of the eddy current testing method for products, which consists in the fact that a eddy current transducer included in an oscillating circuit fed by a high-frequency harmonic voltage oscillates along the normal to the surface of the product being tested and uses the output voltage of the oscillating circuit to obtain control results, characterized in that, in order to increase the sensitivity when testing products with low conductivity, The maximum value of the time derivative is used as a parameter of the output voltage of the circuit. 2 four 0.1 0.2 0.3 0.4 MP L / rl 7