RU2476871C1 - Multi-element eddy current converter - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: multi-element eddy current converter has a group of 1-3 converters lying in a row along a drive line which is common for groups on a printed-circuit board 4 which is made on a substrate 5. Converters in each of the groups 1-3 are arranged across the drive line 15 and contain a differential eddy current converter 6 (7, 8), lying at the centre relative the drive line 15, and two induction transducers 9, 10 (11, 12; 13, 14) at opposite sides. The drive line 15 has a forward current section 16 on the printed-circuit board, and a back current section 17 inside the shield 18 covering the substrate 5. On the printed-circuit board, all elements of the device are made in a single process, which enables accurate reproduction of the shape of windings of all converters. Use of only one line 15 (single- or multi-winding) for exciting a field enables to reduce sensitivity of converters to skewing of the system relative the controlled surface.

EFFECT: technological effectiveness of manufacture, enabling complete diagnosis of the entire controlled area and high sensitivity to detected defects.

4 cl, 2 dwg

Description

The invention relates to non-destructive testing and can be used in the diagnosis of pipelines made of ferromagnetic materials.

Known multi-element eddy current transducer containing n single-element transducers located on a dielectric substrate, and including a ferrite core made in the form of a rod on which an inductor is mounted, while the number of single-element transducers is selected from the condition:

,

,

where: n≥2;

w is the width of the control strip, mm;

R _{with the} radius of the ferrite rod, mm -

RF patent for utility model No. 51748, G01N 27/90, 2006

The disadvantages of the known multi-element Converter are as follows:

- made according to traditional technology, the device provides for winding multi-turn coils on a rigid frame using ferrite cores. The designs of converters made using winding are low-tech and time-consuming in the case of multichannel systems consisting of a large number of elements of the same type;

- the round shape of the transducer does not allow for complete overlap of the diagnostic zone, i.e. there is a dead zone;

- the accepted distance between the coils equal to 3 R _s also increases the deadband.

Known multilayer eddy current transducer containing parallel rows of single-element transducers placed in a flexible structure consisting of many layers, each of which has a two-dimensional subarray, while parallel rows of single-element transducers located in one subarray are staggered in relation to parallel rows of transducers in other subarrays - US patent No. 5659248, G01N 27/90, 1997

In contrast to the previous analogue, this device during diagnostics completely covers the monitoring object (OK) due to the large number of converters.

The disadvantage of the device is precisely due to the excessive number of converters, the consequence of which is the complexity of manufacturing and increased cost.

Another disadvantage of the converter is the reduced accuracy of control due to the multilayer structure due to errors that are inevitable when combining layers of the entire structure.

A prototype of the invention is a multi-element eddy current transducer on a flexible basis, containing two rows of single-element transducers, while the transducers of one row are staggered relative to the transducers of the other row, the flexible longitudinal base has a central longitudinal cutout - application US No.2017003434, G01N 27/90, 2010 .

The prototype has the following disadvantages:

- low-tech device due to the complexity of manufacturing winding products;

- the round shape and placement of the transducers of one row in a checkerboard pattern relative to the transducers of another row does not allow for a complete overlap of the diagnostic zone, i.e. there is a dead zone;

- the presence in a flexible base of a central longitudinal cutout, which provides the flexibility of the board, introduces ambiguity in the data processing algorithm due to changes in the distance between the rows of converters.

In this regard, the technical problem solved by the invention is to increase the manufacturability of manufacturing, to ensure complete diagnostics of the entire controlled area and to increase the sensitivity to detectable defects.

This problem is solved by a multi-element eddy current transducer containing N> 1 groups of single-element transducers arranged in a row along a field bus common to all groups on a printed circuit board made on a substrate. The transducers in each group are placed across the excitation bus and contain a differential eddy current transducer - in the center relative to the excitation bus and two induction transducers - on opposite sides or one induction transducer - on the one hand, the excitation bus is made with sections of forward and reverse current, while the section of direct current is placed on the printed circuit board, and the reverse current portion is inside the screen covering the substrate.

In special cases, the execution of the Converter may have the following symptoms:

- a single-element eddy current differential transducer includes a rectangular measuring coil with an output;

- the common excitation bus is single- or multi-turn;

- the screen is partitioned in length.

Figure 1 shows the design of the device with three groups of converters; figure 2 is a view of the device with a screen.

The multi-element eddy current transducer of FIGS. 1, 2 contains groups 1, 2, 3 of single-element transducers arranged in a row along a field bus common to all groups on a printed circuit board 4 made on a substrate 5. Each of groups 1-3 includes differential eddy current converters 6, 7, 8 and induction converters 9, 10, 11, 12, 13, 14.

The transducers in each of groups 1-3 are placed across the excitation bus 15 and contain a differential eddy current transducer 6 (7, 8) - in the center relative to the excitation bus 15 and two induction transducers 9, 10 (11, 12; 13, 14) - from the opposite parties.

Figure 1, 2 shows a device with two induction converters in each of groups 1-3 and a multi-turn excitation bus 15, but it is possible to implement a device with one induction converter in each of groups 1-3; for example, a converter 9 (11, 13), placed on one side only, and a single-turn excitation bus 15. This implementation depends on the control object and the required sensitivity.

The excitation bus 15 has a forward current section 16 on the printed circuit board 4 and a reverse current section 17 inside the screen 18 covering the substrate 5.

The location of the differential eddy current transducers 6-8 in the center relative to the excitation bus 15 is achieved high sensitivity to defects.

On a printed circuit board, all the elements of the device are created in a single technological process, which ensures accurate reproduction of the geometry of the windings of all converters.

The printed circuit board 4 is glued to the screen 18 having a groove 19 to accommodate the reverse current portion 17 of the bus 15.

The design of the screen 18 may be detachable (as shown in figure 2) in order to simplify the manufacture of the groove.

To diagnose a curved surface, the screen 18 can be made sectioned along the length. In this case, the converter becomes flexible and is easily placed on a surface having bends and irregularities.

The symmetry of the arrangement of induction converters 9-14 in groups 1-3, provided that the excitation bus 15 with a forward current section 16 and a reverse current section 17, completely shielded from section 16, allows to increase the field level in the OK material while maintaining a high degree of balancing of the eddy current differential converters 6-8.

The use of only one bus 15 (single or multi-turn) to excite the field in the OK allows to reduce the sensitivity of the converters to distortions of the system relative to the controlled surface.

The operation of the device is as follows.

The current is excited in the surface layer OK by the forward current section 16 of the excitation bus 15, the reverse current section 17 is located inside the screen 18 and does not interact with the metal OK.

Differential eddy current transducers 6-8 are used to diagnose defects in OK by measuring the values of eddy currents at high frequencies. The purpose of induction converters 9-14 is to measure the gaps between the surface of the OK and the dielectric substrate 5 by measuring the values of the induction currents at low frequencies. Since the channels for measuring gaps operate at a very low frequency, the influence of eddy currents in them can be neglected, as a result of which the transducers 9-14 are induction.

All induction and eddy-current transducers 6-14 in groups 1-3 form a matrix of elements involved in the formation of the surface OK map when moving a multi-element eddy current transducer, which can be placed on the platform of any mobile device. The sequence of differential eddy-current transducers 6-8 in groups 1-3, having an optimal rectangular shape of the measuring coils and placed along a common excitation bus 15 without bias and without a gap between groups 1-3, allows you to scan the surface without gaps, simplifying the algorithm for converting the received information into surface map ok.

In the case of a parallel arrangement of the crack plane OK and the excitation bus 15, the tangential component of the magnetic flux intersects the OK defect in the transverse direction. Due to its scattering on the air gap in the metal formed by the cavity of a crack or other defect, the magnetic field in the defect zone changes, and the eddy currents accompanying the magnetic flux change, therefore, transducers 6-8 record the defect signal.

In another case, with the normal location of the crack plane relative to the excitation bus 15, the eddy current circuit crosses the crack plane and experiences a deviation from the rectilinear direction, which also causes a signal at the output of the differential transducers 6-8.

In all other cases of the mutual orientation of the cracks and the excitation bus, a joint effect of the interaction of the two described modes is observed.

Due to the fact that the measuring coils of the differential transducers 6-8 are rectangular and symmetrically located relative to the excitation bus 15, their total signal is nonzero only if there is a defect in the excitation zone of the bus 15.

The output voltage of the induction converters 9-14 is proportional to the total magnetic flux emerging from the edges of the screen 18 to the metal OK. The magnitude of this flow is related to the distance between the screen 18 and OK.

By measuring the signals of transducers 9-14, it is possible to unambiguously determine the distances between the corresponding group of transducers and the surface OK on the left and right relative to the axis of symmetry of the corresponding transducer, determine the distance to OK in the center of the group of transducers, and also the difference in the distances to OK along the edges of the group. Using these parameters, it is possible to evaluate the surface geometry of the OC, as well as adjust the gain level in the corresponding channel to compensate for the effect on its sensitivity of changes in the distances to the surface of the OC.

The invention is a technological device, all elements of which are placed on a printed circuit board, are created in a single technological process, providing complete diagnostics of the entire controlled area with increased sensitivity to detectable defects due to the relative positioning of the elements.

Claims (4)

1. A multi-element eddy-current transducer containing N> 1 groups of single-element transducers arranged in a row along a field bus common to all groups on a printed circuit board made on a substrate, the transducers in each group are placed across the field bus and contain a differential eddy-current converter in the center relative to the field bus and two induction converters on opposite sides or one induction converter on one side, the excitation bus is made with sections of direct and reverse current, while the forward current section is located on the printed circuit board, and the reverse current section is inside the screen covering the substrate. 2. The multi-element eddy current transducer according to claim 1, in which the single-element differential eddy current transducer includes a rectangular measuring coil with an output. 3. The multi-element eddy current transducer according to claim 1, wherein the common field bus is single or multi-turn. 4. The multi-element eddy current transducer according to claim 1, in which the screen is sectioned along the length.

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