SU1397821A1 - Eddy-current flaw detector - Google Patents

Abstract

The invention relates to eddy current detection and can be used to detect defects in rods and tubes. The purpose of the invention is to increase the reliability of the control by equalizing the sensitivity at the radial displacements of the test article. The signals in the four superimposed transducers are converted by the corresponding amplitude-phase signal processing circuits and fed to the inputs of the decision block. Two additional channels, each of which consists of a measuring bridge, powered by a second generator, a selective amplifier, and an amplitude-phase detector, generate signals about the presence of displacement of the tested product relative to the axis of the excitation winding. The received signals are also fed to the additional inputs of the decision block implementing the function + KV / and + Uj C + + IC D / Un Е, where A, B, C, D are the output signals of the amplitude-phase signal processing circuits; Е - output signal of the decision block; U and U. are the output voltages of the amplitude-phase detectors; K is a constant coefficient. 2 Il. C (L

Description

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The invention relates to eddy current flaw detection of metals and can be used to detect local defects in rods and tubes.

The purpose of the invention is to increase the reliability of control by reducing the non-uniformity of sensitivity at the radial displacements of the test item.

Figure 1 shows the structural diagram of the instrument; Fig. 2 is a diagram of the mutual arrangement of the windings of the ECP.

The flaw detector contains a generator 1, a transducer block 2 consisting of an excitation winding 3 connected to a generator 1, and a number of overhead transducers 4-7, made in the form of elongated rectangular loops, the short sides of which are aligned, and the long sides lie on circles, axially symmetrical relative to the excitation winding 3, four 8-11 amplitude-phase signal processing (SAFOS) circuits, the first inputs of which are connected to the corresponding converters 4-7, and the second to the generator 1, the decisive unit 12, the input and which are connected to the corresponding outputs of the circuits 8-11, and the shaper 13 of the radial displacement signal of the monitored product 14. The shaper 13 consists of a second generator 15, four resistors 16-19, each of which is connected between the output of the generator 15 and the potential input of the corresponding converter 4- 7, with the formation of two measuring bridges, two selective amplifiers 20 and 21, included in the bridge diagonal, and two amplitude-phase detectors 22 and 23, the first inputs of which are connected to the outputs of amplifiers 20 and 21, sec They are connected to the generator 15, and the outputs are connected to the fifth and sixth inputs of the decision block 12.

Eddy current flaw detector works as follows.

The generator 1 powers the excitation winding 3 of the block 2 of eddy current transducers (VTP) 4-7. The signal from each converter 4-7 is fed to the input of the corresponding SAFOS 8-11, the signals A, B, C and D, respectively, are generated at the outputs (Fig. 1). The phases of the reference voltages of the circuits 8-11 are selected from the condition of the detuning from the radial displacements of the test article 14.

5 0 Q,

P

five

The signal from a point defect appears only in the converter in which it is located. The shape of the pulses from the defect at the output of each SAFOS 8-11 is similar to the signal from a differential ECP through passage with conventional measuring windings. The total signal of the SAFOS 8-11 chautie is identical to the signal of a differential ETP throughput with its amplitude-phase processing.

The generator 15, whose frequency is higher than the frequency of generator 1, powers the two measuring bridges, consisting of elements 4, 6, 16, 17 and 5, 7, 18, 19. Signals about the radial displacements of the test article are separated by switching on the opposite ones. converters 4 and 6 into one bridge, and converters 5 and 7 into the other. The unbalance voltage of the bridges caused by the displacement of the product 14 is fed to the input of selective amplifiers 20 and 21 tuned to the generator frequency 15, and further to the input of the amplitude-phase detectors 22 and 23, in which the phase of the reference voltage coincides with the phase of the signal caused by radial offsets. In the absence of product 14 and at its central position (the axis of product 14 coincides with the axis of excitation winding 3), if the bridges are balanced, the voltage at the output of amplifiers 20 and 21 is close to zero. When product 14 is biased towards converter 4, a positive polarity appears at the output of detector 22, and when shifted to converter 6, it is negative.

The amplitude of the signals from point defects at the output of SAFOS 8-11 depends on the distance between the transducers 4-7 and the defective section of the monitored product 14. The output voltages of the amplitude-phase detectors 22 and 23, and Uf, are shifted to positive values by introducing into the circuits 22 and 23 of the bias voltage or by detuning bridges, by changing the resistors 16, 17 and 18, 19. The magnitude of the bias is determined from the condition of equality of the ratios of the maximum and minimum amplitudes of the signals A or C and the signals from defects at the displacements of the controlled product and 14, i.e.

A jajic y jJlPiE.

AMIMUu miiS, y | AI

Jij / and

3

In this transformation of the stresses and, and Uu, the products of A-U and C LL are less dependent on radial displacements. The magnitude of signals B and D from defects varies inversely with the magnitudes of signals A and C, respectively.

In decision block 12, the output signals L, B, C, D of SAFOS5-11 are multiplied by the corresponding coefficients characterizing the position of the test article 14 relative to each converter 4-7, and then summed up. The output signal E of block 12 is equal to

13

E Ai,

AT

i; -

where K is a constant coefficient serving to equalize the values of the terms.

Block 12 may be implemented, for example, from four analog multiplication-division circuits and a sumator.

Claims (1)

Invention Formula Eddy current flaw detector containing the first generator, circular excitation winding connected to it, series-connected amplitude-phase signal processing, the reference input of which is connected to the output of the first generator, and the decisive block, four overhead converters uniformly distributed around the circumference, perpendicular to p 1397821 the axis of the excitation winding, and the radial displacement signal generator, to the inputs of which is connected. corresponding transform overhead that, in order to increase the reliability of the control panel, it is equipped with identical first three schemes of amplitude-phase signal processing, the reference inputs of which are connected to the output of the first generator, and the outputs to the corresponding inputs of the decisive unit, the converters are made in the form of elongations The carbon loops, the short sides of which are aligned, and the longer ones lie on the circles, are located 1 axially symmetrically with respect to the excitation winding, and connected to the signal inputs of the corresponding circuits of amplitude-phase processing The radial displacement driver was designed as a second generator, four resistors, forming two measuring bridges connected to the generator with two oppositely located overhead converters, and two identical channels, each of which includes series-connected selective amplifiers connected to the measuring the diagonal of the corresponding bridge, and the amplitude-phase detector, the second input of which is connected to the output of the second generator, and the output to the corresponding th input input block. 1 VNIIPI Order 2600/43 Circulation 847 Random polygons pr-tie, Uzhgorod, st. Project, 4 FIG. 2 Subscription