SU1532864A2 - Electromagnetic/acoustic flaw detector - Google Patents

Abstract

This invention relates to instrumentation technology. The aim of the invention is to improve the detection accuracy of defects due to the operative correction of the gain in the amplification circuit in accordance with the change in the gaps. The goal is achieved by the fact that the electromagnetic-acoustic transducer 3, which includes an inductance coil made in the form of a bundle of insulated conductors, contains an additional insulated conductor, one end of which is free and the other connected to the output of the generator 5 continuous oscillations to which high-frequency resonant amplifier 8 is connected. , amplitude detector 9, low-pass filter 10, functional converter 11, multiplication unit 12, the second input of which is connected to the output of the amplifier 2. Transducer 3 is a sensor for measuring the working gap between the coil plane and the surface of the test item. The sensor works as a circuit element with reactive conductivity, one of the electrodes of which is the surface of a grounded monitored product, and the other is a conductor with a free end. 2 Il.

Description

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connected to the output of the oscillator 5 of continuous oscillations, to which a high-frequency resonant amplifier 8, an amplitude detector 9, a low-pass filter 10, a functional converter 11, an multiplication unit 12, the second input of which is connected to the output of the amplifier 2, are connected in series. instrumentation technology and can be used for non-contact ultrasonic inspection of metallic materials and products

The aim of the invention is to improve the accuracy due to the operative correction of the gain in the gain circuit in accordance with the change in the gap.

Figure 1 presents the block diagram of the electromagnetic-acoustic flaw detector; in fig. 2 shows a constructive embodiment of a converter coil with an additional insulated conductor.

Electromagnetic-acoustic flaw detector contains generator 1, amplifier 2, electromagnetic-acoustic transducer 3, which includes an inductance coil, which is made in the form of a bundle of insulated conductors, additional insulated conductor 4, intertwined in a coil of an electromagnetic-acoustic transducer, 5 non-damping harmonic oscillator with a frequency several times higher than the frequency of filling the probe pulse of generator 1 and located beyond the passband limit of amplifier 2, a capacitor 6, an additional coil 7 inductance, a high-frequency resonant amplifier 8 tuned to the operating frequency of the generator 5, an amplitude detector 9, a low-pass filter 10, a functional converter 11 and an multiplication unit 12. The first input of multiplication unit 1 is connected to the output of amplifier 2, the input of which is connected to the output of the electromagnetic-acoustic converter 3, the input of which is connected to the output of generator 1. The generator 5 is non-damping harmonic

sensor of the magnitude of the working gap between the plane of the coil and the surface of the test product. The sensor works as a circuit element with reactive conductivity, one of the electrodes of which is the surface of a grounded monitored product, and the other is a conductor with a free end. 2 Il.

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oscillations through a capacitor 6 is connected to an additional insulated conductor 4, one of the ends of the additional inductor 7 and the input of the resonant high-frequency amplifier 8, the second end of the additional inductor 7 is connected to ground 13. The output of the high-frequency resonant amplifier 8 is connected to the input of the amplitude detector 9, the output of which is connected to the input of the low-pass filter 10. The output of the low-pass filter 10 is connected to the input of the functional converter 11, the output of which is connected to the second input of the multiplication unit 12. The controlled article 14 is connected to the ground through a roller table 15. The sensor for the working gap is an electrostatic transducer operating as a circuit element with reactive conductivity, one of whose electrodes is the surface of a grounded monitored product, and the second is an additional insulated conductor 4 woven into the coil of an electromagnetic-acoustic transducer.

The capacitance of the electrostatic converter consists of two components

OS,

(ABOUT

   k

where Sep is the electrostatic capacity

converter;

C is the capacitance component of the electrostatic converter, depending on the size of the gap, Φ;

C k is the structural component of the capacitance of the electrostatic converter, independent of the size of the gap, Φ,.

L- -t, (2)

WITH,

(L}

where mF is the cyclic frequency of the continuous harmonic oscillations produced by the generator 5, rad / Co

In addition, an additional coil 7, shunting the input of the resonant high-frequency amplifier 8, protects its input stage from the effects of the voltage of the probe pulse. If the condition (2) is observed in the electric circuit consisting of capacitance Sk and inductance L connected in parallel, current resonance occurs, and component Sk from expression (1) can be eliminated, and the output signal of the device will not depend the working gap of the Mecda by the plane of the coil of the electromagnetic-acoustic transducer and the surface of the controlled product.

The device works as follows.

The high-frequency voltage from the output of the high-frequency resonant amplifier 8 is fed to the input of an amplitude detector 9, which serves as a rectifier. From the output of the amplitude detector 9, the signal is fed to the input of the low-pass filter 10, which attenuates possible high-frequency noise and generates a signal for estimating the size of the working gap and. This signal is fed to the input of the functional converter 11 The voltage at the output of the latter varies exponentially

. .

U

Fp

(3)

ft. where iff is the voltage at the output of the functional converter, V;

The signal for estimating the size of the working gap, B} ot, ft are the coefficients. The amplitude of the received signal at the output of the electromagnetic-acoustic transducer, and hence at the output of the amplifier 2, depends on the height of the working gap according to an exponential law. In general, this dependence can be described by the expression

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.e, (4)

where a y - the amplitude of the output signal

amplifier 2, V;

w is a function depending on the amplitude of the current of the probe pulse, the magnitude of the constant magnetic field strength, the design features of the electromagnetic acoustic transducer, the transmission coefficient of amplifier 2, the physical properties of the material from which the test article is made, the presence of defects in the controlled area;

h - the size of the gap between the coil of the electromagnetic-acoustic transducer and the surface of the test product, mm;

 - the average diameter of the transducer coil, mm; dimensionless factor The signal from the output of amplifier 2 is applied to one of the inputs of multiplication unit 12, to the second input of which voltage is supplied from the output of function converter 1.

Thus, the output of the multiplication unit 12 will receive a signal with amplitude A b „

wed to

35A6p A IFP

or taking into account (3) and (4)

Bp

If you meet the condition

kh / Dcp Un, we get the expression

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(6)

(7)

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JQ "- 45 Coefficient appropriate to choose from

-), (9) where

A () - signal amplitude per

output of the amplifier 2 when the working gap is equal to the nominal h H.

From condition (9) taking into account (8) and (4) g-bn / Oc (10)

Then the final result is L / B

00

As can be seen from expression (11), the amplitude of the signal at the output of multiplication unit 12 does not depend on the size of the gap between the coil of the electromagnetic-acoustic transducer and the surface of the tested product with

Claims (1)

Invention Formula Electromagnetic-acoustic flaw detector according to ed. St. No. 794491, which is characterized by the fact that; for the purpose of raising accuracy, it is equipped with an additional insulated conductor, interlaced into the converter coil, with one end of which is free from connection, a generator FIG. 2 undamped harmonic oscillations, a capacitor, an additional inductance coil connected in series by a high-frequency resonant amplifier, an amplitude detector, a low-pass filter, a functional converter and a multiplication unit whose second input is connected to the amplifier output, the output of a continuous-harmonic oscillator through a capacitor is connected to the second end of an additional insulated conductor, high frequency resonant amplifier input and one complement Flax inductor, the other end of which is grounded.