UA54354C2 - Method for testing powder materials by eddy currents - Google Patents

Abstract

The proposed method for testing powder materials by eddy currents consists in placing the material sample to be tested into a cylindrical sampler made of insulating material, creating alternating magnetic field for generating eddy currents in the sample, and measuring the impedance of the measuring coil at different frequencies and at two different distances between the end surface of the measuring coil and the surface of the sample. The first of the said distances exceeds the double radius of the measuring coil. The second distance is equal to the thickness of the base of the sampler. Inside of the measuring coil, a compensating coil is arranged coaxially. From the results of the measurements of the impedance at the said distances between the end surface of the measuring coil and the surface of the sample, and at the presence and absence of load in the circuit of the measuring coil, the introduced resistance of the measuring coil is determined that is reduced to the inductive reactance of the coil. The said measurement procedure is repeated at different values of the thickness of the material sample layer and different frequencies of the magnetic field in the sampler. The measurement data are compared with consideration for correcting effect of the compensating coil that is determined from the change of the measurement results when changing the tested material sample in the sampler. The comparison results are used for determining the working frequency at which the testing of a series of the powder material samples will be accomplished as well as for determining the conductivity of the material in testing at the working frequency. The present invention provides the possibility to enhance the reliability of the measurement results when measuring conductivity of powder materials.

Description

Description of the invention

The invention relates to the electrical engineering industry, in particular to the field of measuring the electrical properties of 2 powdered materials used in the production of chemical current sources, and relates to a method of measuring or controlling their electrical conductivity.

Known devices for measuring the electrical resistance of granular media, such as grain, by contact methods: for example, Japanese patents UR 3048006826294764A "Grain moisture meter with resistance measurement"

Zayake Topipiko and others. from 05.06.200 Or.; OP. 3048377824058143 "Device for measuring grain moisture", Capeko 70 Ayigo, etc. from 05.06.200OR; US patent 5 6076396A "Humidity sensor", YuOadasnpnapgpi and others. from 20.06.200O0r.

In patent OP 304800682694764A, grains are sequentially passed between the rollers, which also act as electrodes. The amount of moisture of each grain is determined on the basis of the measured value of the electrical resistance of the grain at the time of its crushing under pressure.

In patent UR 3048377824058143A, a logarithmic diode is included in the measuring circuit A. At output 19 of circuit A, the electrical resistance of the grains moving between the rollers, which also act as electrodes, is determined. This resistance is converted into voltage and subjected to a logarithmic transformation. Reference circuit B is used to determine humidity.

The general drawback of the patents discussed above is the low accuracy of the measurement, because the grains differ in size, shape and mechanical characteristics, while the contact area between the electrodes and the grain remains unknown. The variability of the contact resistance, which depends on the shape of the grain, its position between the contact rollers, the strength and moisture content of each grain, also contributes to the overall measurement error.

The control methods described in the patents are used for granular materials with fairly large grains. They are unsuitable for finely dispersed powdery materials such as carbon black or graphite, whose particle size does not exceed a few tens of micrometers. Gee)

In patent O5 6076396A, two spiral electrodes, isolated from each other and in contact with the granular material, are used to control the moisture content of grain or other granular materials located in a cylindrical sampler. The electrodes are connected to the measuring circuit.

The shortcoming of this patent, as well as the general shortcoming of contact measurements of granular and powdered Z materials, is the lack of reliable and stable ohmic contact between the electrode and the material, the dependence (0) of the contact resistance on the pressure of the electrode against the sample surface. In US patent 5 5859537A "Electrochemical sensor for corrosion research and adhesion of painted metal structures", YuOamii Siu O, et al., dated 12.01.1999, investigated the impedance spectra of two- and three-electrode contact sensors sensitive to "I water absorption and corrosion. 3o Electrochemical impedance spectra of the investigated materials depend on the type of sensors. They were used about gold, platinum, nickel and carbon electrodes.The patent materials note that unlike metal electrodes, the use of carbon electrodes does not allow unambiguous restoration of the impedance spectrum.

Low repeatability of results. The authors of the patent explain the discrepancies in the results, in particular, by the fact that "graphite particles in the electrode material are surrounded by an insulating epoxy polymer (binder), while with 50, many insulating layers are formed between the conductive grains. c In the case of contact measurement of the conductivity of powdered materials, the number of powder particles, their total surface area in contact with the electrode varies from experiment to experiment, introducing a significant error in the measurement results, even if the density of the material is kept constant.

Therefore, it is advisable to use non-contact methods for measuring the electrical conductivity of powdered materials, which are used to control various materials. i-th As a representative of the class of non-contact capacitive methods, we will consider the German patent OE "" 19833331A1 "Sensor of humidity of a layer of material, Vgapaeik A, etc., dated February 10, 2000. The sensor contains two parallel electric conductors connected by a cable to a measuring device that measures the dielectric permeability, and provides measurement without contact with the material of the layer, for which both electrical conductors 20 are covered with an insulating layer, and on the side opposite to the controlled layer, they are shielded from electromagnetic interference with a metal screen. according to the task of controlling powdery materials are the following.

First, the results of measurements of the electrical properties of the material layer depend on the geometric 29 dimensions, dielectric constant, and tangent of the dielectric loss angle of the insulating gasket located between

HF) electrode and the surface of the material layer. It is quite difficult to establish the dielectric properties of the gasket, because they, as a rule, change with frequency. If the properties of the gasket are not precisely established, but remain unchanged from experiment to experiment, relative measurements can be made by comparing the tested materials with each other: absolute measurements, which allow, for example, to determine the specific electrical conductivity of the controlled material at a given frequency of the alternating field, are possible only using the standard.

The second disadvantage concerns the most frequently used designs of overhead capacitors, the electrodes of which are located in the same plane, that is, coplanar. Such capacitors provide the possibility of control with unilateral access to the object of control, which is an important technological advantage. However, if, for example, the controlled powdery material is in a sampler, which is a dielectric beaker mounted on an overhead capacitor, then the lines of force of the potential electric field of the capacitor will be largely closed through the bottom of the beaker. The field strength in the material will be significantly weakened.

The disadvantages of the non-contact capacitive method listed above are not inherent in the non-contact eddy current control method, where a eddy magnetic field is used as a probe

Inductance coils.

Close in technical essence to the proposed invention are: US patent 05 4303885 "Multi-frequency eddy current device and method", Oamizv, eai., dated 01.12.1981; US patent 5 5077525 "Electrodeless conductivity sensor with a changing surface", U/ezi ei ai., dated 12/31/1991; US patent 05 5889401 "Method and apparatus for determining the thickness of several layers located on a substrate", dog aaiip, ei. AI., dated 30.03.1999; /o US patent Z 6288536 "Eddy current transmitter", Mapa), ei. a!., from 11.09.2001

In patent 5 4303885, the eddy current method is used for absolute and differential measurements of discontinuity parameters. Excitation of the magnetic field of the eddy current sensor (inductance coil) is carried out at a number of frequencies. The sensor impedance value measured at these frequencies is used to detect discontinuity parameters and correct the influence of interfering factors, such as changes in the distance between the sensor and the surface of the control object.

The advantage of the method is the multi-frequency mode of operation, which allows obtaining more information about the object under study. However, the direct application of this method for the control of powdery materials encounters serious difficulties, because the powder, which is a collection of conductive particles that are partially in contact with each other and partially separated by air gaps, can be represented electrically in the form of a complex resistive-capacitive, distributed in the space of an equivalent circuit with random connections. The frequency characteristics of such a circuit are random, and the use of only a change in the frequency of the magnetic field that probes the material is clearly insufficient.

In patent OZ 5077525, the electrodeless transmitter of liquid conductivity includes a circuit for generating a variable primary magnetic field, an inductance coil that performs conductivity measurements by fixing the secondary magnetic field, which is induced by eddy currents excited in the liquid by the primary magnetic field. The sensor contains an elastic membrane made of vulcanized rubber, which separates it from the surface of the liquid. and)

The advantage of this sensor, which has a clearly expressed technological nature, is that by vibrating the membrane, you can clean its surface from the resulting sediment. The sensor is thus self-cleaning.

In a similar way, it is possible to measure the electrical conductivity of powders. The disadvantage of the sensor is that, due to the elasticity of the membrane, the outer surface of the controlled liquid, or, for example, of a powdery material, may differ from a flat one. This does not allow the application of existing calculation models to determine the absolute value of electrical conductivity; only relative c measurements of material samples of the same density and volume are possible here.

In patent 05 5889401, the method of eddy current control of at least one layer, located on the substrate, is considered. At a minimum, either the layer or the substrate conducts an electric current. A parametric eddy current transducer (inductance coil) is used as a source of the primary field and a measurer of the secondary field formed by eddy currents induced in the conductive layer or substrate. The primary magnetic field is generated at least at two frequencies. The electromagnetic properties of the substrate and the layer are measured, which are used to determine the thickness of the layer. "

The advantage of the method described in patent OZ 5889401 is the two-frequency mode of operation of the eddy current pt") with given. However, as already noted above, when analyzing patent 05 4303885, the presence of only a multi-frequency mode is insufficient for measuring the electrical conductivity of a powdered material. ;" Patent 5 6288536 proposes an eddy current sensor having an AC-powered inductance measuring coil and a measuring circuit. To compensate for the effect of environmental temperature changes on the impedance of the measuring coil, a compensating coil is used, which, like the measuring coil, has a cylindrical shape and is located coaxially with the measuring coil. The fields of the measuring and compensation coils are orthogonal to each other. The advantage of this invention is the use of an additional coil, which allows you to receive an independent signal, which is used to compensate for the interfering factor, in this case, a change in temperature of 50o of the environment. o The disadvantage of this sensor is the presence of a relationship between the fields of the measuring and compensating coils. This leads to the fact that the signal of the compensation coil also depends on the information signal of the measuring coil. As a result, the sensitivity of the eddy current sensor decreases.

The closest technical essence to the proposed invention is the US patent 5 6479990 "Eddy current sensor for the analysis of the object under study and the method of its operation)), by Meapik, ei ai, dated 11.12.2002.

F) The eddy current sensor contains measuring and compensating coils, as well as a measuring circuit and is used to determine the properties of the material of the object under study or its geometric parameters.

The principle of operation of the sensor includes the location of the object at a given distance from the measuring and compensating coils, the measurement of the impedance of the measuring coil at the first and second set frequencies, the calculated determination of the material properties based on the measurement results and the geometrical parameters of the object. Calculations are based on measured impedance values, including compensation for the temperature effect on the measuring coil using a compensation coil. The compensating coil is spatially smaller than the measuring coil and is located inside the measuring coil, coaxial with it. The principle of placement of the compensation coil 65 practically ensures the independence of its impedance from the investigated object. The geometric shapes of the coils are identical. Temperature compensation consists in subtracting the complex impedance of the compensation coil from the complex impedance of the measuring coil. To determine the properties of the material, as well as the geometric parameters of the object, first the object is located from the measuring coil at a distance that exceeds its double radius, while the impedance of the coil is determined. Then the object approaches the measuring coil and is located at a distance less than twice the radius of the coil, and its impedance is determined again. Based on the obtained values determined at each of the control frequencies, the properties of the material, as well as the geometric parameters of the object, are calculated.

The main advantage of this method, compared to the previous one, is the use of two control frequencies, which allows measurements to be made at different depths of field penetration into the material. Thereby, it enables some 7/0 Measure to take into account the geometrical parameters of the sensor-object of control system when calculating, for example, the electrical conductivity of the material of the controlled object.

The main disadvantages of this method and the eddy current sensor in relation to the control of powdered materials are: an insufficient number of operating frequencies, which does not allow determining the change in the gradient of the frequency characteristic of the impedance component of the measuring coil. This does not make it possible to eliminate the ambiguity /5 of the measurement results. In addition, as already mentioned above, measurements of powder properties only with frequency variation do not provide reliable information about these properties.

The basis of the invention is the task of obtaining reliable results of measuring the absolute values of electrical conductivity of powdered materials at a given frequency and rejecting materials based on the obtained value of electrical conductivity.

The task is achieved by the fact that in the method of eddy current control of powder materials, which includes the location of the tested material in a dielectric sampler that has the shape of a cylinder, the excitation of the probing eddy magnetic field and the measurement of the impedance of the measuring coil at several frequencies at two different distances between the surface of the material in the sampler and the working end of the measuring coil, and the first distance exceeds its double radius, the location inside the measuring coil of the coil, the compensating coil coaxial with it, which has the same shape, according to the invention, the second distance is set equal to the thickness of the sampler base, according to the results of measurements at two distances for, i) respectively, the unloaded and loaded coil determine the active resistance introduced into the measuring coil, normalized to its own reactive resistance, repeat this process at different thicknesses of the layer of powder material in the sampler for each frequency of the probing field i, compare the obtained results with each other with "g" taking into account the corrective effect of the compensation coil caused by changing the material sample in the sampler, based on the results of the comparison, find the operating frequency at which the mass measurements of the samples are made, determine the absolute electrical conductivity of the powder material at the operating frequency, material samples are rejected according to this parameter.

From this batch of samples of powder materials, for which conductivity measurement and rejection are carried out, the first test sample is arbitrarily selected, the study of which is carried out using three different thicknesses of the layer of this material in the sampler.

At a number of discrete frequencies, the introduced resistances of the measuring coil for the minimum thickness of the material layer are determined, the obtained values are memorized, the corrective effects are determined at the same frequencies using a compensating coil, and this process is repeated for the average and maximum thickness of the layers. "

The operating frequency is chosen as the frequency at which the differences between the corrected input resistances of the measuring coil for the maximum and average, as well as the average and minimum layer thicknesses are positive and as close as possible to each other, while the largest value of the input resistance is preferred. ;" Conditional differences should differ no more than three times.

The thicknesses of the layers of powder material in the sampler are chosen in the range from 0.1 to 0.5 radius

Measuring coil, the difference between the thicknesses is kept constant. c All remaining samples of this lot are monitored at the operating frequency using a layer of medium thickness. According to the values of the input resistances of the measuring coil for a layer of medium thickness, corrected by 2) using a compensation coil, as well as taking into account the geometrical parameters of the measuring coil, 5p of the thickness of the material layer in the sampler and the operating frequency, determine the absolute electrical conductivity o of each sample of powder material at this frequency . The rejection of samples is carried out according to the value of the absolute electrical conductivity of the material relative to the average value for the entire batch, moreover, the samples found outside the tolerance are subjected to the same research procedure as the first washed sample, but at the operating frequency, and are finally rejected, in If the aforementioned conditions for the difference of the input resistances are met. If the number of samples whose electrical conductivity is outside the tolerance limits and which do not satisfy the conditions for the differences of the introduced resistances exceeds 1095

Ф) from the total number of samples, then, using the entire array of samples of this batch, a test group of samples is formed, in which each sample is examined according to the procedure outlined for the first test sample, and the new operating frequency is determined as the average value of the operating frequencies for all samples in the group , while repeating the procedure of control and rejection of samples.

The radius of the compensating coil is set p times less than the radius of the measuring coil (p-1.5-2), the field frequency of the compensating coil is chosen 4 times greater than the operating frequency (4-4-8), and the working end of the compensating coil is placed at a distance reduced by P times to the nearest surface of the material layer in the sampler compared to the distance from the working end of the measuring coil. 65 The number of turns of the compensating and measuring coils is set equal, the lengths of the coils are set not exceeding their diameters, the winding of the coils is carried out closely, while taking into account the diameter of the winding wire, the function of the influence of the gap of the measuring and compensating coils is determined.

After removing another sample of powder material from the sampler, the bottom of the sampler is mechanically cleaned, and measurements of the introduced resistance of the loaded compensating coil are carried out by placing the sampler without material on the working end of the compensating coil.

The axis of symmetry of the cylindrical sampler is connected to the axis of symmetry of the coil system, the diameter of the material layer in the sampler is set at least twice the diameter of the measuring coil, while the correction is carried out by subtracting from the relative introduced resistance of the measuring coil the relative introduced resistance of the compensating coil, multiplied by a factor , which is equal to the product rg/d by 70 The ratio of the functions of the influence of the gap and the inverse ratio of the inductances of the measuring and compensating coils.

During measurements, the density of the material in the sampler is maintained at a given level for all samples, regardless of the thickness of the layers. The powdery material used for measurements is classified by the size of the granules.

The proposed method, in comparison with the prototype, makes it possible to obtain reliable results of measuring the absolute electrical conductivity of powdery materials at a given frequency and to carry out testing of materials according to the obtained value of electrical conductivity, by measuring the frequency characteristics of the introduced impedance of the measuring coil for three thicknesses of the material layer, comparing the values obtained at each frequency with each other taking into account the corrective effect of the compensation coil, the determination of the operating frequency, and the absolute electrical conductivity of the material at this frequency, the rejection of material samples according to this parameter.

The search conducted by the applicant on the sources of scientific and technical and patent information, the analysis of the analogs and prototypes selected as a result of the search showed that the proposed method of eddy current control of powdery materials meets the criteria of the invention "novelty" and "technical level".

The essence of the proposed method is explained by the graphs shown in Fig. 1 - 5. Ha

Fig.1. Dependence of the normalized value A/z of the vector potential of the magnetic field of the coil in free space on the ratio 2/K at p-K. Here K is the radius of the turn, p and 2 are the coordinates of the cylindrical coordinate system. i9)

Fig. 2. Dependences of Ke of (6, 7) on the parameter v- v esco for three different values of the plate thickness d4-1mm (curve 1), a-2mm (curve 2), d-Zmm (curve 3); the radius of the measuring coil is equal to K-7.25 mm, the corresponding - 20 values of s 2 are equal to: 0.27; 0.55 and 0.83. Эе ив)

Fig. 3. Experimental dependences of the relative active resistance introduced into the measuring coil on the frequency of the initial powdery material of manganese dioxide for three layer thicknesses: a-1mm (1), a-2mm (2), a-Zmm (3). "

Fig. 4. Scheme of placement of the sampler on the coil system: 1 - sampler body; 2 - a cavity in which the powdered material is located; C - fiberglass membrane; 4 - dielectric washers; 5 - fastening screws; 6 - turns of the measuring coil; 7 - turns of the compensation coil.

Fig. 5. Dependence of the normalized value A/5 of the vector potential of a magnetic half turn in free space on the ratio p/K at 2/K-0. Here K is the radius of the turn; 27, p - coordinates of the cylindrical coordinate system. "

The method is as follows. From the batch of samples of materials for which the conductivity measurement and rejection rate are measured, the first sample is randomly selected for testing. Sample powder. of material, pre-weighed, taking into account the diameter of the cylindrical sampler and the required thickness of the first layer, is placed in the sampler. The sampler has the shape of a short cylinder.

The probing vortex magnetic field is excited using a short cylindrical

Inductance coils at the first frequency of the frequency range. This coil is a parametric eddy current transducer, i.e., it is both exciting and measuring at the same time.

The measurement of the impedance of the measuring coil is carried out at two different distances between the surface of the layer of material in the sampler closest to the coil and the working end of the coil. The first distance exceeds the diameter 2) of the coil, while the material practically does not affect the impedance of the coil, it is unloaded. This is considered in more detail in example 1. Fig. 1 shows the dependence of the normalized value of the vector potential about the coil on the distance along the normal to the plane of its first turn.

T" For an unloaded coil, its own parameters are determined, that is, its inductance and active resistance at the control frequency (Go and Io).

The second distance is set equal to the maximum thickness of the base of the sampler, that is, in fact, two samplers are set on the working end of the measuring coil, while it is loaded. At the same time, the inductance Я and the active resistance г are determined. Based on the obtained data, the active resistance introduced into (Ф, the measuring coil, normalized to its own reactive resistance (di /uI0) is calculated. This process is described in more detail in example 2,

A compensating coil, having the same shape, is placed inside the measuring coil, coaxial with it. The radius of the compensating coil is set to P times less than the radius of the measuring coil (p-1.5-2), and the frequency of the probing field of the compensating coil is chosen to be 4 times greater than the frequency of the field of the measuring coil. The working end of the compensating coil is placed at a distance reduced by P times to the nearest surface of the material layer in the sampler compared to the distance from the working end of the measuring coil.

Measurements with the help of measuring and compensating coils are carried out independently of each other. 65 Measurement with the help of a measuring coil is carried out when a layer of the investigated powdered material, for example, of minimum thickness, is located in the sampler. Measurements for this layer are carried out at a number of discrete frequencies. After that, the sampler is freed from the powder. Mechanically, with the help of a brush, the base of the sampler is cleaned from particles of powder stuck to it. After that, a measurement is made with a compensation coil at the same discrete frequencies. As mentioned above, the sampler is made of dielectric. This dielectric must have a small loss tangent in the range of meter wavelengths and good strength, because the base of the sampler must have a small thickness so that the distance from the working end of the measuring coil to the surface of the material is minimal. These requirements are well met by, for example, glass-textolite. The investigated powder, for example, MpO 5, graphite, carbon black, etc. lingers on the irregularities of the microrelief of the sampler base in the open pores, "lubricates" its surface. As 7/0 experience shows, it is impossible to completely remove it from the surface of the base, and this is true for different types of dielectric from which the base of the sampler was made. The thickness of this diffusion layer is small, but due to the sufficient conductivity of the particles and the high control frequency, the presence of this diffusion layer introduces a significant error into the measurement results.

From the theory of eddy current control, it is known (1) that with a small thickness of the conducting layer in comparison with /5 the diameter of the coil and the depth of penetration of the plane wave, the introduced active resistance of the coil is determined as follows: zv (U

Evn- 721077 ro ev OV ooo, de do - Yak. 10-7Hn/m is the magnetic constant, MU is the number of turns of the coil, y is the distance from the first turn of the coil to the surface of the material, K is the radius of the coil, o is the circular frequency, y is the thickness of the layer, c is the specific electrical conductivity of the layer material.

This formula is close to the formula previously obtained by Levy |2). The number of turns of the measuring and compensating coils is set equal. The value of the exponent e/"" for a coil consisting, for example, of three turns, (5) is determined by averaging the values of the three exponents. Coils are wound close together, that is, turn to turn, without a gap between them. Then, if the diameter of the wire of the measuring coil is equal to, then we denote the corresponding averaged exponent as E(u) and call it the function of the influence of the gap for the measuring coil.

Similarly, we determine the function of the influence of the gap for the compensating coil - K(a.). Due to the different distance from the first turn of the measuring coil and the first turn of the compensating coil to the nearest surface of the material layer in the sampler, the value of the exponent for the first turns of these coils is the same.

The introduced resistance of the measuring coil is defined as the sum of the introduced resistance given by the layer (ze) of the controlled material and the introduced resistance given by the diffusion layer. We write down the relative introduced resistance for the diffusion layer based on (1) in the form:

IC c)

Nv 2 og(fty i, id z « de K-72.1077. pu M2.y.s - с t0 In the case of a compensating coil, a similar expression of masses is: z vni. K (i). -ao. Z le P «sl The relative resistance (3) will be equal to (2) under the condition: schi vno Ve (in? new) Ya o sid o | Ya Go EI) s 50

T» The calculation of the adjustment coefficient in square brackets is given in example 3.

The correction is carried out by subtracting from the relative measured resistance of the measuring coil the relative measured resistance of the compensating coil, multiplied by a factor equal to the product p/4 by the ratio of 5 functions of the gap effect and by the inverse ratio of the inductances of the measuring and compensating coils.

Practically, the operating frequency of the compensating coil is selected in the range of 150-300 MHz. The compensating coil (F) has greater sensitivity to the diffusion layer of the powder than the measuring coil. d) After using a measuring coil at a number of discrete frequencies to control the layer of material with the minimum thickness, at the same frequencies control the layers of material with an average and up to maximum thickness. Determine the corresponding values of the relative active resistance introduced into the measuring coil at each discrete frequency for each layer thickness. The thicknesses of the layers of powdered material in the sampler are chosen in the range from 0.1 to 0.5 of the radius of the measuring coil, the difference between the thicknesses is kept constant. The obtained values are corrected using a compensation coil.

Determine the difference between the relative introduced resistances for the maximum and average, as well as the average and minimum thickness of the layers at each frequency. b5 It is known from the theory of eddy current control |1) that the impedance introduced by the conducting non-magnetic plate

the radial dimensions of which are at least twice the diameter of the measuring coil can be approximately determined by the expression:

K! - zn yar (5) 2 Yavn- 48107 yuvuue U Ve p 9--hidr zani av zIvnisov dp 2 vir de o - 2p / K, p - distance from the first turn of the coil to the surface of the material layer, K - radius of the measuring coil; E2-2a/K, where 4 is the thickness of the plate; district of Osno, where Fo is the frequency, c is the specific electrical conductivity of the material of the plate, the nose is 1077Hn/m.

To determine the active resistance introduced into the coil, it is necessary to divide (5) into real and imaginary parts.

Denoting the fraction in (5) as φ (is, В), we obtain - 2 (6)

Kk and 10 Ov

Avn Zv lo7 ov ME (bo) o) kefiv,c) si p Ha de I - inductance of the measuring coil, 2 (7

VO.

Befig, vi- ' ve ota s de o o - zid? 1 sov 9. with vaA DE vipeya- vip -1VA soev (A? NI « zo Ve ato - 2A soz tsiv|il|- 48 - ВИ)

IF) zva? 1 owl 0-12 Poison? Vol. 2 2 (ze) I12A DE vip dviplyu zv sov |y « 2 2

And c) with ik2 Vi appeared

From Fe 4 4 - pov e- 4 R

A shchy ev -y PE vip to IDI- iv, rot ad -a-V- R uvsno.

P 2 "

Figure 2 shows the dependence of Kef on B for three different thickness values of plate 4-1; 2 and Zmm, K-7.25mmM 70 (yen027; 0.55; 0.83). The fraction u(6 b and Befvvve these Z c (2-0.27; 0.55; 0.83). The fraction in expression (6) is a constant, therefore the dependences of Kerf on B and y fully characterize the corresponding dependences of Kevn/oiYo . As shown by the results of experimental studies conducted with "z" powdery materials, the use of introduced reactive resistance Хвн/оио for powder control is impractical. The value of Хвн/оио is determined by the strength of the magnetic field of the eddy current circuit induced by the primary field in the controlled material. In the case of no the eddy current density of a solid powder-like "sl" material is insignificant, in addition, it is subject to significant changes due to changes in the contact between powder particles. Accordingly, the value of Hvn/oi o. оз In the initial to extreme part of the graphs, an increase in the thickness of the layer increases the active resistance introduced into the coil sl 50. An increase in the electrical conductivity of the layer, which increases in elichynu r-r sno, also leads to the growth of Kvn/o/ o. In the area after the extremum, the picture changes. Here, the increase in conductivity leads to

T» decrease Kvn/oi o, and as the thickness of the plate increases, the value of the active introduced resistance decreases. Near the extremum, a situation is observed when plates of different thicknesses can give the same values of K vrn/oi o.

The noted regularity is qualitatively confirmed in the study of layers of powdery materials. 99 The corresponding results obtained by us for manganese dioxide are given in example 4.

GF) Thus, there is an ambiguity. From the measured value of Квн/оЙ о, we cannot determine from the value of В, and, accordingly, s, because we have two of these values, one in before the extreme, and the other in after the extreme region of the dependence of Kef on В. In addition, for powdered materials have their own specificity compared to solid materials.

For solid material, maximum dependence Kvn/o! o from B is due to the following. With an increase in the frequency of the field or conductivity of the material within small values of the parameter B, the density of eddy currents induced by the field of the coil in the volume of the sample increases. As a result, field power losses in the sample increase and, accordingly, the active resistance introduced into the transducer increases. With a further increase in the electrical conductivity of the material or b5 current frequency, the intensity of the field of eddy currents acting against the primary field of the coil becomes noticeable and the inductance of the coil decreases. Starting from a certain value of the product co, the inductive resistance of the sample to eddy currents becomes equal to the active resistance and the introduced active resistance stops growing. Phenomena of the surface effect caused by the field of eddy currents displace the field and currents to the surface of the sample and also contribute to the reduction of the relative resistance Kvn/o| at.

Heterogeneous powdery material can be represented by a distributed capacitive-resistive equivalent circuit with random parameters due to the active resistance of solid powder particles to the eddy current, ohmic contact between particles, as well as capacitances representing non-conductive layers in a heterogeneous medium.

As the field frequency increases, reactive capacitive resistances decrease, the density of eddy currents increases 7/0 In solid powder particles. This process is superimposed on the phenomena described above for continuous media, dragging the maximum to the side of higher frequencies. The extrusion of eddy currents to the surface of the powder-like material increases the influence of the coarseness and density of the powder in the near-surface layer (in the thickness of the material, this influence is largely averaged out). This process increases the instability of the results of measurements obtained for powder-like materials in the extreme region of the dependence of K vn/oY on V. Therefore, it is advisable to carry out measurements in the region of lower frequencies, to the extremum, where an increase in the layer thickness and electrical conductivity gives an unambiguous increase in the relative, active resistance Kvn/o/ o, introduced into the measuring coil.

Comparing the frequency characteristics for layers with thicknesses, for example, O.1K, 0.2K, and 0.3K, they find the frequency where the differences between the adjusted values of the introduced resistances for layers 0.ZK and 0.2K, as well as 0.2K and 0LK are as close as possible to each other ( at least differ no more than three times). At the same time, preference is given to larger values of the introduced resistance. In example 4, using the graphs of Fig. 3 obtained for manganese dioxide powder, the procedure for determining the operating frequency is illustrated.

After that, all selected samples of this batch are controlled at the operating frequency using a layer of medium thickness. These results are given when considering example 5. for the same manganese dioxide powder.

Based on the introduced resistances of the measuring coil, corrected with the help of a compensation coil, and also taking into account the geometrical parameters of the measuring coil (number of turns MU, radius of the coil K, diameter o of the winding wire k), the thickness of the material layer in the sampler and the operating frequency of the control determine the absolute electrical conductivity of each samples of powdered material at the operating frequency.

The values obtained for all tested samples are averaged and samples are rejected based on the deviation of their absolute conductivity from the average value. The procedure for calculating the absolute conductivity and the rejection procedure are illustrated in example 5.

Samples that are outside the tolerance are additionally tested using the same test procedure as was used for the first test sample, but at the same operating frequency. If the conditions for the differences between the introduced resistances of the measuring coil, determined for the maximum and average, average and minimum thickness of the layers, specified above, are fulfilled, then the samples are finally rejected. WITH

If the number of samples, the electrical conductivity of which is outside the tolerance limits and the difference of the introduced resistances, for which the above conditions are not satisfied, exceeds 1095 of the total number of samples of this batch, then using the entire array of samples of this batch, form a test group of samples, in which each sample is examined according to by the same method as the first trial. At the same time, the new value of the operating frequency " is determined as the average value of the operating frequencies for all sample samples in the test group. After that, the final procedure of control and rejection of samples is repeated. - c During measurements, the sampler is placed on the system of measuring and compensation coils so that the axis of symmetry of the cylindrical sampler coincides with the axis of symmetry of the coil system (see Fig. 4). The diameter of the "" material layer in the sampler is set at least twice the diameter of the measuring coil.

At the same time, the tangential field component of the coil practically does not go beyond the radial boundaries of the layer. The corresponding calculations are given in example 6 and illustrated by the graph in Fig.5. 1 The sampler has an adjustable cavity height. The thickness of the layer of powdered material in the cavity of the sampler varies discretely, by installing or removing washers 4 (see Fig. 4). Before pouring the next sample of powder into the sampler, it is weighed and the density of the material in the cavity is brought to the specified (95) level, which is the same for all samples, regardless of the thickness of the layers. In addition, the powdered material used for measurements is classified according to the size of the granules. The following examples illustrate the essence of the invention.

I" Example 1.

The vector potential of the magnetic field of a coil with a harmonic alternating current in free space, in the case when the center of the cylindrical coordinate system is placed in the center of the coil, can be represented as |11.; and TV (8)

F An oE of the name) oh, with y

Where /-deoi is the current in the coil, B is the radius of the coil, sho is DC. 10-"Hn/m is the magnetic constant, ) is the Bessel function of the first order, 7 is the transformation parameter; p, 2 are the coordinates of the cylindrical coordinate system. The integral in (8) is expressed in terms of complete elliptic integrals of the first E and second K , the tables of which are contained in a number of mathematical reference books, including IZ): b5

In | in t

AN DA KE,

LE Per 2 2. 4AEr dk tov (B vv nt

The electric field strength is directed along the F coordinate and is proportional to the vector potential / magnetic field. The emf induced by the magnetic field of the coil in any circuit coaxial with it, which is equal to the circulation of the vector E along this circuit, is also proportional to the vector potential. Thus, the value A is a convenient characteristic of the field of a turn and, accordingly, of a low-turn measuring coil. Figure 1 shows the dependence of the value A/5, where 5-tsd/x -sopvi, on the ratio 2/kK, calculated according to formula (9). As follows from the graph, at 2/Ki-1, the value of the vector potential decreases by approximately 10 times from 75 of the maximum value observed at 2-0, at 2/2K 1, the value of the vector potential decreases by approximately 40 times, that is, it is approximately 2.595 of the maximum . The same situation is approximately preserved for the low-turn coil. All this is well confirmed experimentally.

Thus, it can be assumed that if the distance between the end of the measuring coil and the boundary of the material is two or more radii of the coil, then the material has practically no effect on the impedance of the coil.

Example 2

Measurements of the input impedance of the measuring coil for relatively weakly conductive powders used in chemical current sources are carried out in the high-frequency range using Q-factor meters, the basis of which is the resonance method of measurements.

For an unloaded measuring coil at the operating frequency, its own Q-factor Об and capacitance Со сч of the resonant circuit are fixed: о 1 po) to -- - вд и - 5. ! Z zo de go is the own active resistance of the coil winding. From here we determine: ив) 1 11 ше ше со will go " and according to Thompson's formula for the resonance circuit: юю в - 1 х2 --я-- ух

Gi 0 « where o is the operating frequency. With c For a loaded measuring coil, i.e. a measuring coil with a sample at the same operating frequency "» fix the Q factor value: n 1 (13) with pt persons vnu slvia same VN t" where Kvn is the active resistance introduced into the measuring coil; a also the value of the capacity: (95) si 1 (14) 1 1 that the navel is in the same vn) s» where I vn is the inductance introduced into the measuring coil.

It follows from expressions (12) and (14) that

It is taken) and taking into account the fact that at resonance it 1 si -8E- -- 60 th

Kvno en - boss (16)

Phys sia b5 and y

Using formula (16), the results given in examples 4, 5 regarding the experimental study of manganese dioxide powder were calculated.

Example 3.

Let's consider the method of calculating the adjustment coefficient in expression (4). Let's denote it as: 17 in-vo viv) 77 a So Ri) where p is the ratio of the radii of the measuring and compensating coils, 4 is the ratio of the operating frequencies 70 of the compensating and measuring coils.

The inductance of the measuring coil is determined according to expression (12), where о is the operating frequency, and Со is the capacitance of the resonance circuit of the Q-factor meter, measured when resonance is reached on the scale of the device.

The inductance I of the compensating coil is determined in a similar way.

We will consider the method of calculating the function of the influence of the gap K(to) on an example.

Let the radius of the measuring coil be K-7.25 mm, the thickness of the bottom of the sampler at the location of the turns of the measuring coil n-0.5 mm, the diameter of the coil winding wire d9-1.5 mm, the number of turns M/-3. The value of K(to) is defined as the average value of three exponents:

From (18) svoe K

R

Here n is the distance from each turn to the surface of the material, i.e. for the first turn n - 0.5mm, for the second n-0.5vad-2mm, for the third turn n-0.542a0-3.5mm. The corresponding value of K(ar) is equal to: s z 1Y 05 a j o geo TB ve! nat (se

In a similar way, the influence function K(a 4) of the compensating coil is calculated, taking into account the thickness of the lens of the sampler at the location of the turns of the compensating coil and the diameter of the wire of its winding.

Example 4.iv)

A sample of powdered material (manganese dioxide) used in the co-production of cathodes of electrochemical current sources was tested. The measuring coil contained three turns (MU - Z) of copper wire with a diameter of 40-1.5 mm. The outer diameter of the coil is 1mm, the inner diameter is 1mm. "

The average radius of the coil, thus, is equal to K-7.25mm. yu

The sample was selected from the original industrial batch, fraction 40 μm. Layers with a thickness of 1 mm, 2 mm and 3 mm were used for the study. Dependencies of the relative active resistance entered into the measuring coil on the frequency for this material are shown in Fig.3.

The frequency at which the differences between the introduced resistances of the measuring coil for "20 maximum and average, as well as the average and minimum thickness of the layers are positive and close to each other to the maximum degree is chosen as the working frequency, while preference is given to larger values of the introduced resistance. These conditions correspond to the T1-140 MHz frequency, which was chosen as the working frequency. The magnitude of the corrective impact from the compensatory side;" coil at this frequency was (Evni/oi o)correP-0.02.1033. Thus, the method of determining the operating frequency is illustrated.

Example 5. c A batch of 8 samples of the original manganese dioxide powder, fraction 4Ωm, was formed. Samples are numbered. Formally, a Mob sample was selected from this batch. This sample was examined using three layers according to the method described above. The results of the study are given in example 4, the frequency 2) characteristics are shown in Fig.3. The operating frequency is chosen equal to 140MHz. The value of the introduced resistance for the 5th layer of a-2mm thickness at this frequency, taking into account the correction of the compensation coil and Vvni/oi-0-1.12.107, "z" Using expression (6), we determine the value of Kef:

Can her (18)

Bver-Fa o 481077 vu vi ime) Щ Щ y . sh. . . . where K-7.25mm, M/-3, the impact function is defined in the example of ZE(40)-0.49. The self-inductance of the measuring coil is determined by Thompson's formula (see example 2, expression 12) and is equal to I 00.24.10 Hn,

Substituting these values in (19), we obtain Ke F-0.16.107. According to expression (7) and graph 2 in Fig.2, this corresponds to B-0.21. Knowing the value of B, we will determine the value of electrical conductivity: v- or "vtvsmm 65 KD

The other 7 samples of this batch were tested at a frequency of 140 MHz using a layer with a thickness of 2 mm.

The values of their conductivity are given in Table 1. и ов оо | tv with with || oh | tv here oyu la in | oyu oo zv 15 in ov ol vo

The average value of conductivity ssr-0.79Sm/m. The absolute and relative values of the errors are given in Table 1

Let's set the tolerance to 1095. Samples Mo7 and Mo8 are located outside this tolerance. For them, control was carried out using the same procedure as for the first Mob sample (using three layers), but at the same 20 operating frequency. For the Mo7 sample, the differences in the applied resistances for the layers with 4-Z3mm and 4-2mm, as well as a-2mm and a-1mm, respectively, were: l.-0.18.107 and d»-0.25.1073; for sample Mo8: A.-0.18.1073 and A/-0.36.1073. At the same time, the condition that the differences should differ by no more than three times is fulfilled, samples Mo7 and Mo8 are rejected.

Example 6.

The results of calculating the vector potential A/z depending on the radial coordinate (r/k, according to formula c 29 (9) given in example 1, are shown in Fig. 5. The graph is shown for the field in free space. Ge)

The graph shows that at a distance from the center of the turn (p/K-2, the value of A/5 is approximately 1295 from the maximum. The same situation is approximately preserved for a low-turn coil. In a conducting medium, the field decays faster than in free space, and the decay rate along the radial coordinate increases with the increase in the product of the field frequency by the conductivity of the material. Thus, if the diameter of the material layer in the sampler 30 is twice the diameter of the measuring coil, then at the outer radial boundary of the layer, the value of the vector potential of the field is less than 1095 of the maximum, which is permissible, and the value of the diameter of the material layer can be considered as satisfying the measurement conditions for accuracy.

Sources. ch.i

UR 3048006826294764А, dipe 05, 2000, Zagake Tozpipiko ei ai. oyu 35 UR 3048377824058143А, dipe 05, 2000, Capeko AiYigo ei ai.

ОЗ 6076396А, dipe 20, 2000, Yuadasnagpi ei ai.

OZ 5859537A, dapyagu 12, 1999, Yuamia Siu Oei ai.

OE 19833331A1, Rergiagu 10, 2000, Vgapaeiik A ei ai. « 4303885, Oesetrbeg 01, 1981, Yuamiz ei ai. -o to tsy5 5077525, Oesetreg 31, 1991, Uuevi ei a. with OB 5889401, Magsy 30, 1999, Khdotsgaaip ei ai. :z» Ob6288536, Zerietrbeg 11, 2001, Map) ей ай. 5 6479990, Mometreg 12, 2002, Meapikom ei ai. 1. Sobolev V.S., Shkarlet Yu.M., "Wearable and Touchable Sensors", Novosibirsk, "Nauka", 1967, 149bs. page 395 2. Hemu 5. EIesigotadpeyis zspiyeeidipud oeyesi oi ap o ipbipie oriape sopacysipud vzpeei riasey bBeimeep sigsetsiag soahiai soiYiv. Rgos. IKE, 1936, 24, Mob

ChK» Z. MUpeeiop A.O. Tariez oi zittabrie zegiev apa ipiedgaie ipmoimipd Vevzze! Typsiopv. Zap Egapsivso:

Noidep Wow Ips., 1968.

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Claims (1)

The formula of the invention 1. The method of eddy current control of powdery materials, which includes the location of the tested material in a dielectric sampler that has the shape of a cylinder, the excitation of the probing eddy magnetic field and the measurement of the impedance of the measuring coil at several frequencies at two different ts distances between the surface of the material in the sampler and the working the end of the measuring coil, and the first "" distance exceeds its double radius, the location inside the measuring coil, coaxial with it, " of the compensating coil, which has the same shape, which differs in that the second distance is set equal to the thickness of the sampler base, according to the results of measurements at at two distances for the correspondingly unloaded and loaded coil, determine the active resistance introduced into the measuring coil, normalized to its own reactive resistance, repeat this process with different thicknesses of the layer of powder material in the sampler for each frequency of the probing field, compare the obtained and the results among themselves, taking into account the corrective effect of the compensation coil, which is determined when changing the material sample in the sampler, based on the results of the comparison, find the working frequency at which the mass measurements of the samples are made, determine the absolute electrical conductivity of the powder material at the working frequency, carry out sample rejection material according to this parameter. 2. The method according to claim 1, which is characterized by the fact that from a given batch of samples of powdered materials for which conductivity and rejection are measured, the first test sample is arbitrarily selected, the research of which is carried out using three different thicknesses of layers of this material in a 2o sampler . o C. The method according to claims 1, 2, which differs in that at a number of discrete frequencies, the introduced resistances of the measuring coil for the minimum thickness of the material layer are determined, the obtained values are memorized, o the corrective effects are determined at the same frequencies using a compensation coil and repeated this process is for the average and maximum thickness of the layers. 60 4. The method according to claims 1-3, which differs in that the working frequency is chosen as the frequency at which the differences between the adjusted input resistances of the measuring coil for the maximum and average, as well as the average and minimum thickness of the layers are positive and as close as possible to each other, while the largest value of the applied resistance is preferred. 5. The method according to claims 3, 4, which differs in that the differences determined according to claim 4 must differ 65 no more than three times. b. The method according to claims 1-5, which differs in that the thicknesses of the layers of powdery material in the sampler are chosen in the range from 0.1 to 0.5 of the radius of the measuring coil, the difference between the thicknesses is kept constant. 7. The method according to claims 1-6, which differs in that all remaining samples of this batch are monitored at the operating frequency using a layer of medium thickness. 8. The method according to claims 1-7, which is distinguished by the fact that the values of the input resistances of the measuring coil for a layer of medium thickness, adjusted with the help of a compensating coil, as well as taking into account the geometric parameters of the measuring coil, the thickness of the material layer in the sampler and the operating frequency, determine the absolute electrical conductivity of each sample of powdered material at this frequency. 70 9. The method according to claim 8, which is characterized by the fact that the rejection of samples is carried out according to the value of the absolute electrical conductivity of the material in relation to the average value for the entire batch, and the samples that are outside the tolerance are subjected to the same research procedure as for the first test sample , but at the operating frequency, and are finally rejected if the conditions of claims 4-5 are fulfilled for them. 10. The method according to claims 1-9, which differs in that, if the number of samples whose electrical conductivity is outside the tolerance limits and which do not satisfy the conditions of claims 4-5 exceeds 1095 of the total number of samples, then, using the entire array of samples of this batch , form a test group of samples, each of which is examined according to the procedure set forth in claims 1-5, and the new operating frequency is determined as the average value of the operating frequencies for all samples in the group, while repeating the sample control procedure according to claims 7-8 and the procedure rejection according to claims 9-10. 11. The method according to claims 1-10, which differs in that the radius of the compensating coil is set p times less than the radius of the measuring coil (p-1.5-2), the frequency of the field of the compensating coil is chosen 4 times greater than the operating frequency (d-4 -8), and the working end of the compensating coil is placed at a distance reduced by P times to the nearest surface of the material layer in the sampler compared to the distance from the working end of the measuring coil. high school 12. The method according to claims 1-11, which differs in that the number of turns of the compensating and measuring coils is set equal, the lengths of the coils are set not exceeding their diameters, the winding of the coils is carried out close to each other, while taking into account the diameter of the winding wire, the functions of the influence of the gap of the measuring and compensation coils. 13. The method according to claims 1-12, which is distinguished by the fact that after removing the next sample of the powder-like material from the sampler, the bottom of the sampler is mechanically cleaned, and the measurement of the introduced resistance of the loaded compensating coil is carried out by placing the sampler without material on the working end of the compensating coil. with 14. The method according to claims 1-13, which differs in that the axis of symmetry of the cylindrical sampler is connected to the axis of symmetry of the coil system, the diameter of the material layer in the sampler is set at least twice - zv5 exceeding the diameter of the measuring coil, while the correction is carried out by subtracting from the value of the relative input resistance of the measuring coil to the value of the relative input resistance of the compensating coil, multiplied by a factor equal to the product p"/4 by the ratio of the gap influence functions and the inverse ratio of the inductances of the measuring and compensating coils. " 15. The method according to claims 1-14, which is characterized by the fact that during measurements, the density of the material in the sampler 70 is maintained at a given level for all samples, regardless of the thickness of the layers. - c 16. The method according to claims 1-15, which differs in that the powdery material used for these measurements is classified by the size of the granules. and? Official bulletin "Industrial Property". Book 1 "Inventions, useful models, topographies of integrated microcircuits", 2005, M Z, 15.03.2005. The State Department of Intellectual Property of the Ministry of Education and Science of Ukraine. sh» (95) s 50 s» F) ime) 60 b5