RU2590940C1 - Through-type eddy current converter - Google Patents

Abstract

FIELD: control equipment.

SUBSTANCE: invention relates to nondestructive control and can be used for quality control of double-layer wire with diameter less than 1 mm with top layer, having high electric conductivity, for example, stabilised Nb₃Sn superconductors with copper shell and core from alloy of niobium-tin. Eddy current converter of through type for quality control of wire comprises hollow cylindrical frame 1 with an solenoid and bifilar wound exciting coil 2 and measuring coil 3, hollow cylindrical frame 4 with identical measuring coils 5 and 6, arranged with axial gap and connected in series-anti-parallel. Frame 1 is arranged inside frame 4 symmetrically to it. Eddy current converter also includes potentiometer 7, frame 8, identical to frame 1, arranged on it and wound bifilar inductance coils 9 and 10 similar to exciting coil 2 and measuring inductance coil 3, respectively, but with a large number of turns W₄=W₅=(1.1…1.3)W_v, where W₄, W₅ and W_v - number of turns of fourth coil 9, fifth coil 10 and exciting inductance coil 2, respectively. Inductance coil 9 is connected in series with excitation inductance coil 2, inductance coil 10 is connected in parallel with potentiometer 7, connected by its middle lead to output of third measuring inductance coil. Converter allows a controlled ratio "copper/non-copper" in stabilised Nb₃Sn superconductors and detection of defects of type of pores and inclusions from different metals.

EFFECT: technical result is improved information value and threshold sensitivity control of stabilised superconductors, with diameter of less than 1 mm.

4 cl, 4 dwg

Description

The invention relates to non-destructive testing and can be used for flaw detection of electrically conductive objects, for example, quality control of a two-layer wire with an upper layer having high electrical conductivity.

Such wires, in particular, include stabilized Nb ₃ Sn superconductors, with a copper cladding and a niobium-tin alloy core. A copper sheath is necessary to maintain the required minimum level of electrical conductivity of the wire when the superconductor loses its superconductivity properties. The quality of stabilized superconductors is determined by the copper / non-copper ratio and the absence of defects in the form of inclusions of magnetic and non-magnetic metals, pores and other discontinuities in the copper shell. Stabilized superconductors have the form of a wire with a diameter of less than 1 mm and are used, in particular, in the current windings of powerful magnetic systems of the nuclear collider.

Known pass-through eddy current transducer [1. Non-destructive testing: Ref .: B 7 t / t 2. Book. 2: Eddy current control / Yu.K. Fedosenko, V.G. Gerasimov, A.D. Pokrovsky, Yu.Ya. Ostanin / Under the general. ed. V.V. Klyueva. M .: Engineering, 2004 p. 375, fig. 2.7-a)], containing coaxial exciting and measuring inductors placed on a frame with an axial hole for placement of a controlled object in it. The exciting coil to create a uniform magnetic field is performed with the ratio ℓ _in / D _in ≥4, where ℓ _in is the length and D _in is the diameter of the exciting coil, respectively. The measuring inductance coil is located inside the exciting coil, and its length and diameter are chosen much less than the length and diameter of the exciting coil.

A disadvantage of the known eddy current transducer is the lack of stability for measuring stabilized superconductors based on a niobium-tin compound with an external diameter less than 1 mm at a nominal ratio copper / non-copper = 0.5 ± 0 in the production flow of the copper / non-copper ratio , 01. This is due to the fact that the effect of changes in the process of monitoring the magnetic coupling between the exciting and measuring coils due to the micro displacements of the turns during temperature variation turns out to be comparable with the signals from the changes in the copper / non-copper ratio to be recorded.

In addition, the known Converter has a reduced relative sensitivity to the parameters of the wires of small diameter D, comparable with the minimum possible for mechanical protection of the coils with a thickness T of the frame wall of the measuring coil. The non-optimality of the relative sensitivity to the parameters of the controlled object is explained by the fact that the open circuit voltage U _{0 of the} eddy current transducer of this design is created by the magnetic flux of the exciting coil passing through the entire area S _and turns of the measuring coil, and the introduced voltage U _vn by the magnetic flux of eddy currents, which occupies part of the area coils S _ok filled with a controlled object. The ratio S _ok / S _and decreases with decreasing diameter of the controlled object. This is due to the fact that the difference between the internal diameter of the measuring coil and the diameters of the axial hole is determined by the requirements of mechanical strength and wear resistance. It cannot decrease in proportion to the decrease in the diameter of the axial hole and remains almost the same for transducers with different diameters of the axial hole. Another disadvantage of the known eddy current transducer is associated with an insufficient signal-to-noise ratio for reliable detection of unacceptable inclusions from magnetic and non-magnetic metals, pores and other discontinuities in the copper shell of stabilized superconductors with a diameter of less than 1 mm based on a niobium-tin compound.

Known pass-through parametric eddy current transducer containing an inductor placed on the frame with an axial hole for placement of a controlled object in it [2. Nondestructive testing of materials and products: reference book / P.I. The trouble, B.I. Vybornov, Yu.A. Glazkov et al. / Under the general. ed. G.S. Samoilovich. M.: Mechanical Engineering, 1976. - S. 206, Fig. 5 B].

However, this converter also does not have the required stability, which is associated with a strong influence of temperature changes on the output signal, leading to variations in the active resistance of the coil. In addition, this eddy current transducer also does not provide the identification of characteristic defects in the copper shell of stabilized superconductors with a diameter of less than 1 mm based on the niobium-tin compound due to the low signal-to-noise ratio.

Closest to the proposed technical essence, the eddy-current transducer for wire control adopted as a prototype is a prototype of a wire containing a hollow cylindrical quartz glass frame with a solenoidal exciting coil placed on it, a second hollow cylindrical frame with two identical measuring inductors located with an axial clearance and connected in series -conversely, the first frame is placed inside the second frame symmetrically with it [3. Fedosenko Yu.K., Shkatov P.N., Efimov A.G. Eddy current control / Under the general. ed. V.V. Klyueva. - M .: publishing house "Spectrum", 2011. - S. 130-131].

The thickness of the wall of the frame in the form of a tube made of quartz glass to obtain greater sensitivity of the eddy current transducer choose the minimum possible. The minimum wall thickness is limited by the requirements for mechanical strength and wear resistance of the frame under the influence of the wire moved during the control process.

Using this converter, in principle, it is possible to obtain information on the presence of defects in the copper sheath of the superconducting wire and on the copper / non-copper ratio in it. Information on the presence of defects is obtained by measuring the voltage between the external outputs of the measuring windings (differential signal), and on the ratio of copper / non-copper, the voltage between the terminals of one of the measuring windings (absolute signal).

However, this converter also does not have the required output voltage stability of the measuring coils for measuring the copper / non-copper ratio of stabilized superconductors based on a niobium-tin compound with a diameter of less than 1 mm. This is also due to the fact that the effect of changes in the process of monitoring the magnetic coupling between the exciting and measuring coils due to the micro displacements of the turns during temperature variation turns out to be comparable with the signals from changes in the copper / non-copper ratio to be recorded. In addition, the connection of an electric circuit to one of the counter-connected measuring coils leads to their unbalance, comparable with the signals from the defects of the copper shell of the superconducting wire to be detected.

The task is to increase the reliability of the quality control of stabilized superconductors.

EFFECT: increased information content and threshold sensitivity of control of stabilized superconductors with a diameter of less than 1 mm based on the Nb ₃ Sn compound.

The technical result is achieved in the inventive eddy current transducer type, containing the first hollow cylindrical frame with a solenoidal exciting coil placed on it, the second hollow cylindrical frame with the first and second identical measuring inductors located in axial clearance and connected in series - in the opposite direction, the first frame is placed inside the second frame symmetrically with it, and it is equipped with a third measuring coil placed on the first frame and wound bifilarly with an exciting inductor, while the eddy current transducer is equipped with a potentiometer that is third, identical to the first, cylindrical frame with bifilar fourth and fifth coils placed on it and similar to the exciting inductor and the third measuring inductor, with a large number of turns, respectively, but W ₄ = W ₅ = (1.1 ... 1.3) W _in , where W ₄ , W ₅ and W _in - the number of turns of the fourth, fifth and exciting inductors, respectively, the fourth inductor with connected in series with the exciting inductor, and the fifth inductor is connected in parallel with a potentiometer connected by its middle output to the output of the third measuring inductor.

In a particular embodiment, the diameter d _and wires of the third and fifth measuring coils are selected from the condition d _and <0.8d _in , where d _in is the diameter of the wire of the exciting inductor.

In a particular embodiment, the first and second frames are made with the possibility of mutual axial movement and rotation.

In a particular embodiment, the width b, the outer diameter D _n , the inner diameter D _{in the} first and second measuring coils and the axial clearance Ζ between their centers satisfy the ratios 0.3 <b / D _at <0.4; 1.3 <D _n / D _at <1.4; 0.75 <Z / D _at <0.85.

In FIG. 1 shows a diagram of the inventive eddy current transducer of a feed-through type, in FIG. 2 is an electrical diagram of the inventive eddy current transducer in FIG. 3 is a cross section of a controlled object, in FIG. 4 - distribution of the values of Cu / non Cu along the length of the superconductor obtained on the inventive experimental setup.

The eddy current transducer of a through type contains a hollow cylindrical frame 1 with a solenoidal induction coil 2 and a third measuring inductor 3 placed on it bifilarly wound on it, a hollow cylindrical frame 4 with identical measuring first and second inductors 5 and 6, respectively, located with an axial clearance and connected sequentially - counter. The frame 1 is placed inside the frame 4 symmetrically with it.

The eddy current transducer also contains a potentiometer 7, identical to the first frame 1 of the frame 8, with the fourth and fifth inductors 9 and 10 placed on it and wound bifilarly, respectively, similar to the exciting coil 2 and the third measuring inductor 3, respectively, but with a large number of turns W ₄ = W ₅ = (1.1 ... 1.3) W _in , where W ₄ , W ₅ and W _in are the number of turns of the fourth coil 9, the fifth coil 10 and the exciting inductor 2, respectively. The inductor 9 is connected in series with the exciting inductor 2, and the inductor 10 is connected in parallel with a potentiometer 7 connected by its middle terminal to the output of the third measuring inductor.

The controlled wire 11 consists of a copper sheath 12 and a superconducting core 13 based on a niobium-tin compound. Due to the particularity of the technology, the outer diameter of the wire is fixed, and the copper / non-copper ratio can only change due to variation in the size of the core 13. The outer diameter of the conductor remains unchanged and, depending on the modification, is of the order of 0.82 mm. In this regard, an increase in the volume fraction of stabilizing copper leads to a decrease in the size of the superconducting core. On the other hand, a decrease in the fraction of stabilizing copper leads to unacceptable overheating during the protective output of the current through the copper sheath. Therefore, there is an optimum ratio of the volume fractions of the copper and non-copper components of the superconducting wire. In accordance with existing requirements, the value of the ratio k _m = "copper / non-copper" should be within 1.0 ± 0.1.

Eddy current transducer operates as follows.

The excitation coil 2 connected to a sinusoidal voltage generator (not shown) creates an alternating magnetic field that induces eddy currents in the wire 11. The wire 11 moves through the inner cavity of the frame 1. The electrical conductivity σ _{but the} superconductor tends to infinity at a temperature below 4 ° K. However, at ordinary temperatures specific electric conductivity σ _m copper sheath material 12 at least 10 times the electrical conductivity σ of the superconductor _but niobium-tin. Due to this, the secondary electromagnetic field generated by the eddy currents in the superconducting core 13 is very small compared to the secondary electromagnetic field of the eddy currents in the copper shell 12. To obtain information about the ratio of copper / non-copper, associated with the thickness of the copper shell 12, register a secondary the voltage introduced into the measuring coil 3. To obtain the maximum possible electromagnetic interaction between the controlled shell and the eddy current transducer, the measuring coil 3 and the excitation ayuschuyu coil 2 perform identical, and their bifilar winding wound on the frame 1. As is known [1, p. 413, fig. 4.3], the greatest degree of electromagnetic interaction is achieved in the parametric converter, when the information on the introduced parameters is determined by the change in the complex resistance of the exciting coil itself. However, this solution is unacceptable in this case due to the low stability of measurements using a parametric transducer. In the proposed eddy current transducer, the magnetic coupling coefficient with the controlled object is close to the magnetic coupling coefficient with the controlled object of the parametric converter. Moreover, the proposed converter, being transformer, does not have the inherent disadvantages of the parametric converter associated with low temperature stability. At the same time, due to the bifilar winding of coils 2 and 3, a high stability of the magnetic coupling between them is achieved. To increase this stability, the diameter d _{and the} wires of the measuring coil 3 is recommended to be selected from the conditions d _and <0.8d _in , where d _in is the diameter of the wire of the exciting coil 2. At the same time, a greater bifilar winding density coefficient of coils 2 and 3 is achieved, resulting in a cross-section of coils after impregnation with the compound, it becomes less susceptible to micro changes during thermal and mechanical stresses, primarily due to the inevitable friction against the surface of the frame 1 of the movable wire.

The importance of the stability of the magnetic coupling between inductors 2 and 3 is determined by two factors. Firstly, the impossibility of changing the settings of the device during the monitoring process, the duration of which, when continuously moving through the cavity of the eddy current transducer of a wire coil up to 30 km long, is tens of hours. Secondly, the low level of signals associated with the variation of the copper / non-copper ratio in a given tolerance field. So, for example, for a wire with an external diameter of 0.82 mm and with a nominal ratio of copper / non-copper = 0.5 (thickness of the copper sheath -t = 0.12 mm), the ratio decreases by 0.01 (change t from 0 , 1126 mm to 0.127 mm) leads to a change in the voltage introduced into the coil 3 by an amount of the order of 10 ^-5 × U ₀ , where U ₀ is the open-circuit voltage induced in the coil 3 by the magnetic flux of the exciting coil 2. Changes were obtained with the ratio optimal for measuring copper / non-copper for the given operating frequency parameters.

, наводимого в катушке 3, необходимо на соответствующем уровне провести его компенсацию (установить 0 перед контролем). Для этого используют часть напряжения, наводимого в катушке 10 магнитным потоком катушки 9. Напряжение $${\underset{\_}{U}}_{10}$$

на внешних зажимах катушки 10 поддерживается на уровне, соответствующем уровню стабильности напряжения $${\underset{\_}{U}}_2$$

, так как ее магнитная связь с катушкой 9 поддерживается на том же уровне, а по катушкам 2 и 9 протекает один и тот же ток. При подключении катушки 2 к среднему выводу потенциометра 7 происходит векторное суммирование двух синусоидальных напряжений. Меняя местами подключаемые концы катушки 2, выбирают соединение, при котором суммируемые напряжения оказываются в противофазе. Минимального отклонения от нуля напряжения U_A между соответствующими внешними выводами катушек 2 и 10 добиваются при отсутствии контролируемой проволоки путем регулировки потенциометра 7. За счет большего числа витков у четвертой и пятой катушек индуктивности 9 и 10 соответственно, чем у возбуждающей катушки 2 и третьей катушки индуктивности 3 напряжение $${\underset{\_}{U}}_{10}$$

превышает по амплитуде $${\underset{\_}{U}}_2$$

, что необходимо для выполнения регулировки.From the above example, it can be seen that in order to ensure reliable registration of signals carrying information about the quality of the superconducting wire, it is necessary to ensure stability of measurements at the level of 10 ^-6 × U ₀ . To exclude uninformative component from sinusoidal voltage $${\underset{\_}{U}}_2$$

induced in coil 3, it is necessary to carry out its compensation at the appropriate level (set 0 before monitoring). To do this, use part of the voltage induced in the coil 10 by the magnetic flux of the coil 9. Voltage $${\underset{\_}{U}}_{10}$$

at the external terminals of the coil 10 is maintained at a level corresponding to the level of voltage stability $${\underset{\_}{U}}_2$$

, since its magnetic coupling with coil 9 is maintained at the same level, and the same current flows through coils 2 and 9. When connecting the coil 2 to the middle output of the potentiometer 7 is a vector summation of two sinusoidal voltages. By interchanging the connected ends of the coil 2, choose a connection in which the summed voltage are in antiphase. The minimum deviation from zero of the voltage U _A between the respective external terminals of the coils 2 and 10 is achieved in the absence of a controlled wire by adjusting the potentiometer 7. Due to the larger number of turns of the fourth and fifth inductors 9 and 10, respectively, than in the exciting coil 2 and the third inductor 3 voltage $${\underset{\_}{U}}_{10}$$

exceeds in amplitude $${\underset{\_}{U}}_2$$

that is necessary to perform the adjustment.

To detect characteristic defects in the copper shell 12 in the form of pores and inclusions from various metals (cracks do not occur due to the high ductility of copper in the shell), differentially-connected measuring coils 5 and 6 are used. The output voltage stability of differentially-connected identical coils 5 and 6 is quite high , since under various influences, changes in the parameters of the coils occur simultaneously and by the same amount. Signals generated under the influence of pores are significantly smaller than signals caused by cracks, which requires special technical solutions to provide the necessary sensitivity.

The threshold sensitivity to such defects is determined by the level of balancing of the coils 5, 6 by their geometric parameters and relative position.

To ensure the required level of balancing, the frames 1 and 4 are recommended to be executed with the possibility of their mutual axial movement and rotation. This allows you to minimize the imbalance of the coils by displacing the center of the frame 4 relative to the frame 1 and its rotation. In this case, the difference in magnetic bonds (M) between each of the coils 5, 6 and the exciting coil 2 changes very smoothly.

It was found that the optimal sensitivity to defects such as pores and inclusions in the copper shell 12 is achieved by fulfilling the following relations for the width b, the outer diameter D _n , the inner diameter D _{in the} measuring coils 5, 6 and the axial clearance центра between their centers

$$0.3<b/D_{\mathrm{at}}<0.4\left(\mathrm{one}\right)$$

$$1.3<D_n/D_{\mathrm{at}}<1.4\left(2\right)$$

$$0.75<Z/D_{\mathrm{at}}<0.85\left(3\right)$$

The more turns in the inductor, the larger its diameter, and as a result, the greater the absolute sensitivity to the defect, but less locality of control. At the same time, if there are few turns, the signals are weak and cannot be detected.

Inequalities (1) and (2) are a compromise between the locality of control and absolute sensitivity, and inequality (3) is between the degree of suppression of variation in the properties of a solid metal and absolute sensitivity to a defect.

между внешними выводами катушек 5 и 6 при наличии дефектов в проволоке, перемещаемой через полость каркаса 1 вихретокового преобразователя, несет информацию о наличии в нем дефектов. Взаимного влияния дефектоскопического канала, образованного катушками 5, 6 и абсолютного канала, образованного катушками 3, 10 не происходит при условии, что магнитная связь между катушками 2, 3, 5 и 6 с катушками 9 и 10 пренебрежимо мала. Это достигается соответствующим размещением и ориентацией каркасов 1 и 8.Voltage $${\underset{\_}{U}}_D$$

between the external terminals of the coils 5 and 6 in the presence of defects in the wire moved through the cavity of the frame 1 of the eddy current transducer, carries information about the presence of defects in it. The mutual influence of the defect channel formed by coils 5, 6 and the absolute channel formed by coils 3, 10 does not occur, provided that the magnetic coupling between coils 2, 3, 5, and 6 with coils 9 and 10 is negligible. This is achieved by the appropriate placement and orientation of the frames 1 and 8.

и $${\underset{\_}{U}}_{Д}$$

, получаемых при перемещении проволоки 12 через полость каркаса 1 вихретокового преобразователя, выполняется известным образом, например, амплитудно-фазовым способом [1. Неразрушающий контроль: справ.: В 7 т. / т. 2. Кн. 2: Вихретоковый контроль / Ю.К. Федосенко, В.Г. Герасимов, А.Д. Покровский, Ю.Я. Останин / Под. общ. ред. В.В. Клюева. М.: Машиностроение, 2004 с. 473-474, рис. 8.5-8.6).Signal processing $${\underset{\_}{U}}_{\mathrm{BUT}}$$

and $${\underset{\_}{U}}_D$$

obtained by moving the wire 12 through the cavity of the frame 1 of the eddy current transducer, is performed in a known manner, for example, by the amplitude-phase method [1. Non-Destructive Testing: Ref.: 7 t / t 2. Book. 2: Eddy current control / Yu.K. Fedosenko, V.G. Gerasimov, A.D. Pokrovsky, Yu.Ya. Ostanin / Under. total ed. V.V. Klyueva. M .: Engineering, 2004 p. 473-474, fig. 8.5-8.6).

The claimed eddy current transducer, in contrast to the known ones, allows one to record changes in the copper / non-copper ratio in a wire with a diameter of less than 1 mm such as stabilized Nb ₃ Sn superconductors with a copper shell and a core made of niobium-tin alloy during long-term measurements. The inventive eddy current transducer allows you to simultaneously detect defects such as pores and inclusions of various metals. In addition, it allows you to determine the value of the parameter Cu / nonCu at each point of the long wire, which is confirmed by the dependence shown in figure 4.

The results of eddy current control were verified by metallographic studies. It was found that the error in measuring the percentage of copper / non-copper is not more than 3%, while defects of the type of inclusions with an equivalent volume of the order of 0.03 mm ³ in a superconducting wire based on the Nb ₃ Sn compound with an external diameter of 0.82 mm are reliably detected Thus, the information content and threshold sensitivity of the control of stabilized superconductors with a diameter of less than 1 mm based on the Nb ₃ Sn compound are increased.

Claims (4)

1. An eddy current transducer of a bushing type, comprising a first hollow cylindrical frame with a solenoidal exciting coil placed on it, a second hollow cylindrical frame with first and second identical measuring inductors located in axial clearance and connected in series, in the opposite direction, the first frame is placed symmetrically inside the second frame with it, characterized in that it is equipped with a third measuring coil located on the first frame and wound bifilarly with the exciting coil inductance, while the eddy current transducer is equipped with a potentiometer, a third, identical to the first, cylindrical frame with bifilar fourth and fifth inductors placed on it and wound bifilarly, similar to the exciting inductor and the third measuring inductor, respectively, but with a large number of turns W ₄ = W ₅ = (1.1 ... 1.3) W _in , where W ₄ , W ₅ and W _in are the number of turns of the fourth, fifth and exciting inductors, respectively, the fourth inductor is connected in series with the choke inductor, and the fifth inductor is connected in parallel with a potentiometer connected by its middle output to the output of the third measuring inductance coil. 2. The eddy current transducer of passage type according to claim 1, characterized in that the diameter d _and wires of the third and fifth measuring coils are selected from the conditions d _and <0.8d _in , where d _in is the diameter of the wire of the exciting inductor. 3. Eddy current transducer of a bushing type according to claim 1, characterized in that the first and second frames are made with the possibility of mutual axial movement and rotation. 4. The eddy current transducer of the bushing type according to claim 1, characterized in that the width b, the outer diameter D _n , the inner diameter D _{in the} first and second measuring coils and the axial clearance Z between their centers satisfy the ratios 0.3 <b / D _in <0.4; 1.3 <D _n / D _at <1.4; 0.75 <Z / D _at <0.85.

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