RU2582488C1 - Two-wire differential magnetoimpedance sensor - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention relates to a measuring technique and provides a two-wire differential magnetoimpedance sensor. Detector comprises two magnetoimpedance sensors manufactured by frameless winding technology, that is, detecting coils of detectors are wound directly on magnetoimpedance conductors themselves with a layer of protective masks each. Detecting coils of detectors are connected oppositely, wherein magnetoimpedance conductor of one of detectors is not excited, and is closed on itself.

EFFECT: high output signal amplitude of sensor, reduced temperature dependence of output signal, high accuracy of measurements and wider range measuring scale.

1 cl, 5 dwg

Description

The invention relates to the field of construction of highly sensitive magnetic sensors based on the magneto-impedance (MI) effect.

The effect of magnetic impedance has been well known for quite some time, but the strongest interest in it has arisen relatively recently, due to an increase in the general level of development of sensor technologies in industry. The MI effect is expressed in the dependence of the surface impedance on the magnetic structure of the conductor. The surface impedance is a proportionality coefficient in the vector ratio between the tangential components of the electric and magnetic fields on the surface of the conductor and determines the generalized voltage taken directly from the conductor or from a coil wound on the conductor. The principle of operation of the sensor is based on measuring the dependence of this voltage on external factors, for example, on an external magnetic field. At the same time, sensors that are not equipped with an operational amplifier have an extremely small amplitude of the output signal, and the use of an operational amplifier with a large gain leads to amplification of not only the useful signal, but also noise, which greatly reduces the measurement accuracy.

The design of the sensor, most similar to the device under development, is described in the analogue (Patent US 8587300 B2, publ. November 19, 2013, Magneto-impedance element and its production). This patent discusses single-wire and multi-wire sensor designs with various ways of arranging magneto-impedance conductors. The main disadvantages of which are low sensitivity, design complexity and temperature instability.

The closest analogue (prototype) is the multi-wire design described in the patent (US 8587300 B2, publ. 11/19/2013, Magneto-impedance element and its manufacture), works as follows: through the MI conductors pass a high-frequency pulse current (exciting signal); an external magnetic field acting on the MI conductor and causing a reversal of static magnetization changes its surface impedance, as a result of which an induced signal arises on the detection coil. Since the signal amplitude is very small, it must be amplified with an operational amplifier.

The design of the above sensor is assembled on a substrate with previously applied conductive conductors and pads. MI conductors are glued onto the substrate with epoxy resin, after which the conductors are sprayed, forming the second half of the detection coils. Coils and MI conductors are switched by means of conductors and contact pads of the substrate according to FIG. one.

The disadvantage of this development is the high temperature instability. As a result, the sensor output is highly dependent on changes in ambient temperature.

This technical solution is aimed at increasing the amplitude of the output signal of the sensor by changing the design of the most sensitive element of the sensor.

The technical result of the invention is as follows: increasing the amplitude of the output signal of the sensor, improving the signal-to-noise ratio, improving temperature stability, simplifying assembly technology in an industrial environment.

The technical result is achieved as follows. Two-wire magneto-impedance sensor, contains two magneto-impedance detectors. The detectors are made using frameless winding technology and included in the opposite direction. The design feature is that the detecting coil is wound directly on the magneto-impedance conductor itself with a layer of a protective mask, and the coils of the magneto-impedance detectors are turned on in the opposite direction, and the MI conductor of one of the detectors is not excited, but closed to itself.

The invention is illustrated by drawings, where in FIG. 1 shows the design of a magneto-impedance detector which shows: 1 - a glass shell, 2 - a MI conductor, 3 - a protective mask, 4 - a detecting coil. In FIG. 2 shows a block diagram of a two-wire differential magneto-impedance element, which shows: 5 - direct current for magnetization, 6 - excitation signal, 7 - MI conductor in glass insulation and mask, 8 - magnetizing coil, 9 - first detecting coil, acts as a signal detection , further in the text “detection coil”, 10 - the second detection coil, performs the role of noise compensation in the signal, further in the text “compensation coil”. 11 - output signal output. In FIG. 3 shows the design of a two-wire differential magnetic impedance element, which shows: 7 - MI conductor in glass insulation and mask, 8 - magnetizing coil, 9 - detecting coil, 10 - compensation coil. " In FIG. Figure 4 shows the dependence of the amplitude of the output signal on the magnitude of the magnetic field, which shows two curves: 12 - before the heat treatment, 13 - after the heat treatment. In FIG. Figure 5 shows the dependence of the amplitude of the output signal in relative units on the temperature, on which two curves are shown: 14 - before the heat treatment, 15 - after the heat treatment.

The technical solution of the invention is as follows. A design of a frameless MI detector is proposed (Fig. 1). In this design, the detection coil is wound directly on the MI conductor itself on a winding machine. An amorphous wire in glass insulation was chosen as the MI conductor, the winding wire was copper in varnish insulation. It was observed that the winding of the detection coil causes damage to the glass shell of the MI microwire even with minimal tension on the copper conductor. Damage occurs due to physical contact and friction of the conductors. To prevent damage to the shell of the MI conductor before winding the coil, a thin layer (≈5 μm) of the protective mask is applied to its surface, which eliminates the occurrence of friction between the conductors. The protective mask is made on a polyurethane basis, has high elasticity, does not have magnetic properties and electrical conductivity. The mask is dried under an IR heater at a temperature of + 40 ... + 60 ° C for 10 minutes. The detector can be supplemented with an additional magnetizing coil, which is wound on top of the detection coil. This coil creates a constant magnetic field and is designed to expand the limits of the measuring scale of the sensor and to provide feedback.

The MI detectors thus obtained are mounted on the sensor substrate, two in one sensor. The detection coil, in addition to detecting the useful signal, also detects external noise and radio noise. To compensate for the induced interference, a sensor design with two MI detectors was developed, shown in FIG. 2.

In this design, the windings of the MI detectors are turned on and opposed parallel to each other, and the excitation current is passed through only one MI detector. It is he who registers the magnetic field, and the second MI detector acts as a compensator for external interference, in which the conclusions of the MI conductor are closed to each other by the conducting conductor of the substrate. Since the circuit uses two completely identical windings, the external noise induced in them compensates each other as accurately as possible, which can significantly reduce the level of interference. The arrangement and connection of MI detectors in the sensor is shown in FIG. 3.

To increase the sensitivity of the magnetic sensor, its temperature treatment was proposed, which results in the relaxation of mechanical stresses in the MI conductor obtained during the assembly of the MI detector and the sensor as a whole. A fully assembled sensor is subjected to processing. Processing temperature is 200 ° C, processing time 5 minutes. The curves of the dependence of the sensor output signal on the magnetic field before (curve 1) and after heat treatment (curve 2) are shown in FIG. four.

The relaxation of mechanical stresses in the MI conductor, carried out by annealing the entire design of the sensor, also significantly reduces the temperature instability of the sensor. With the appropriate selection of the annealing regime, a multiple decrease in the level of temperature instability is possible. The curves of the change in the output signal (in percent) versus temperature for the same sensor before (curve 3) and after heat treatment (curve 4) are shown in FIG. 5.

The reproducibility of the results of the experiment on thermal processing was confirmed on 5 samples; the spread of parameters did not exceed 10%.

Thus, we can note the following distinctive features of the proposed sensor design and method of its manufacture:

- increase in the output signal and sensitivity to the magnetic field;

- improved temperature stability;

- increase the level (or degree) of interference compensation.

The use of these distinctive features to achieve the goal previously unknown to the authors.

Example 1

The design of the MI detector, assembled on an MI amorphous conductor in glass insulation with a cross section of 40 μm, with a protective mask of 5 μm thick and a detection coil of copper wire in varnish insulation with a cross section of a metal core of 40 μm and a number of turns equal to 60. The two-wire sensor is used in the design two elements with counter-activated coils. In this case, the excitation signal is turned on to one of the detectors, while the second detector is closed to itself. To improve the characteristics of the sensor, the entire structure is heat treated after assembly. The main technical characteristics of the design are: the operating frequency of the excitation signal is 20 MHz, the MI sensitivity of the element is 500 mV / O, the maximum amplitude of the output signal is 770 mV, the limit of the measuring scale is 1.5 E.

In FIG. Figure 4 shows the dependence of the amplitude of the output signal (in relative units) on the magnitude of the external field (curve 1 — before heat treatment, curve 2 — after heat treatment).

Example 2

The design of the MI detector, assembled on an MI amorphous conductor in glass insulation with a cross section of 40 μm, with a protective mask of 5 μm thick and a detection coil of copper wire in varnish insulation with a cross section of a metal core of 7 μm and a number of turns equal to 80. The two-wire sensor is used in the design of a two-wire sensor two elements with counter-activated coils. In this case, the excitation signal is turned on to one of the detectors, while the second detector is closed to itself. To improve the characteristics of the sensor, the entire structure is heat treated after assembly. The main technical characteristics of the design are: the operating frequency of the excitation signal is 20 MHz, the MI sensitivity of the element is 700 mV / O, the maximum amplitude of the output signal is 900 mV, the limit of the measuring scale is 1.3 E.

Example 3

The design of the MI detector, assembled on the MI amorphous conductor in glass insulation with a cross section of 40 μm, with a protective mask of 5 μm thick and a detection coil of copper wire in varnish insulation with a cross section of a metal core of 40 μm and a number of turns equal to 60. On top of the detection coil is the same with a wire, as the detecting coil, a magnetizing coil containing 120 turns is wound in 2 layers. The design of a two-wire sensor uses two elements with counter-activated coils. In this case, the excitation signal is turned on to one of the detectors, while the second detector is closed to itself. To improve the characteristics of the sensor, the entire structure is heat treated after assembly. The main technical characteristics of the design are: the operating frequency of the excitation signal is 20 MHz, the maximum MI sensitivity of the element is 500 mV / O, the maximum amplitude of the output signal is 770 mV, the limit of the measuring scale is 5 E.

Claims (1)

A two-wire magneto-impedance sensor containing two magneto-impedance detectors made according to a frameless winding technology and turned on in the opposite, characterized in that the detection coil is wound directly on the magneto-impedance conductor with a layer of a protective mask, and the coils of the magnetic impedance detectors are turned on and one of the detectors is not excited, but on himself.

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