RU2012009C1 - Method of measuring parameters of continuous cylindrical electroconducting objects - Google Patents

Abstract

FIELD: non-destructing control. SUBSTANCE: uniform alternate axially symmetric magnetic field is excited. Frequency of the magnetic field is changed till achieving maximal value of phase angle of total magnetic flux. Value of normalized total magnetic flux of maximal phase angle of the total magnetic flux is carried, as well as frequency of probing magnetic field. Parameters of continuous cylindrical conducting objects are determined from the set relations. EFFECT: improved precision of measurement. 3 dwg

Description

 The invention relates to non-destructive testing and can be used to measure the parameters of ferromagnetic cylindrical electrically conductive objects.

 A known method of non-contact measurement of electrical conductivity and magnetic permeability of cylindrical electrically conductive objects, which consists in the fact that the controlled object is placed in a uniform variable axisymmetric magnetic field, the amplitude and phase of the normalized total emf of the measuring winding are measured, which, using the established dependencies, determine these two parameters (Golotsvan S. B., Gorkunov B. M., Sebko V. P. Investigation of electromagnetic transducer with cylinder // eskim product of the universities. Instrument, 1988, t. XXXI, N 7, pp. 53-59). In these measurements, the radius of the cylindrical object is assumed to be known.

 The disadvantage of this method is the low number of measured parameters.

 The closest in technical essence to the claimed is a method of measuring the parameters of cylindrical conductive products, which consists in the fact that the monitored object is exposed to a uniform variable axisymmetric magnetic field, by changing the frequency of the probe magnetic field, the maximum value of the imaginary part of the introduced magnetic flux is achieved, the amplitude and phase of the normalized introduced magnetic flux and the established ratios determine the magnetic permeability, specific electric pr water productivity and radius of the controlled product (ed. St. N 1672340, class G 01 N 27/72, 1987).

 The disadvantage of this method is the complexity of its implementation and low measurement accuracy associated with the influence of the error of compensation of the magnetic flux of the converter without the product on the measured value of the introduced magnetic flux.

 The purpose of the invention is to improve the accuracy of measuring magnetic permeability, electrical conductivity and radius of continuous cylindrical electrically conductive objects.

 The goal is achieved in that the known method, including the action of a uniform variable axisymmetric magnetic field on the controlled object, changing the frequency of the acting magnetic field, is supplemented by the fact that the maximum phase angle of the total magnetic flux is fixed, the value of the total normalized magnetic flux is measured at a frequency corresponding to the maximum value of the phase angle of the total magnetic flux, and the established dependencies determine the magnetic permeability, specific electric conductivity and radius of continuous cylindrical electrically conductive objects.

 The novelty of the proposed method lies in the fact that changing the frequency of the acting magnetic field to achieve the maximum phase angle of the total magnetic flux, measuring the value of the total normalized magnetic flux at a frequency corresponding to the maximum value of the phase angle of the total magnetic flux, and measuring this maximum phase angle, using the established dependencies allows to increase the accuracy of measuring magnetic permeability, electrical conductivity and for whiskers of continuous cylindrical electrically conductive objects. Since in the known analogues are not found distinctive features of the claimed device, the authors and the applicant believe that the invention meets the criterion of "significant difference".

 In FIG. 1 presents an electrical diagram of an installation that implements the inventive method; in FIG. 2 is a vector diagram of magnetic fluxes; in FIG. 3 is a graph of the dependence of the maximum phase angle of the total magnetic flux and the generalized control parameter.

 The installation that implements the inventive method consists of a sequence of connected variable voltage generator 1, an ammeter 2, an eddy current transformer 3 of a transformer type with a controlled object 4 placed in it, and a mutual inductance coil 5. The measuring circuit of the installation consists of a voltmeter 6 and a phase meter 7 connected to the measuring winding of the converter 3, the reference input of which is connected to the output of the secondary winding of the coil 5.

The vector diagram shows the vector Ф _о of the probe magnetic flux through the measuring winding of the transducer 3 without a controlled object, the vector Ф _{Σ of the} total magnetic flux, which is the vector sum of the flux Ф _{1 of the} probing magnetic field in the gap between the controlled object 4 and the measuring winding of the transducer 3 and the flux F ₂ magnetic field in the controlled object. The vector diagram shows the maximum phase angle φ _omax between the flows Ф _о and Ф _Σ . In addition, the hodograph of the vectors Φ _Σ and Φ _{2 is given} , which is obtained by changing the frequency of the probe magnetic field from zero to infinity.

 The essence of the method of non-contact measurement of cylindrical solid conductive objects is as follows.

=

(1-η)+

(1) где η - коэффициент заполнения измерительной обмотки преобразователя
η = a² / a_c ² , (2) а - радиус контролируемого объекта; а_с - радиус измерительной обмотки преобразователя; μ_r - относительная магнитная проницаемость контролируемого объекта;

- комплексная эффективная магнитная проницаемость, которая для случая сплошного цилиндрического объекта в продольном осесимметричном магнитном зондирующем поле может быть записана как (Приборы для неразрушающего контроля материалов и изделий. Справ. : В 2-х кн. /Под ред. В. В. Клюева. М. : Машиностроение, 1986, с. 352):

=

, (3) где I_o, I₁ - модифицированные функции Бесселя первого рода нулевого и первого порядков соответственно; х - обобщенный параметр контроля,
x =

; (4) σ - удельная электрическая проводимость контролируемого объекта; ω - круговая частота зондирующего магнитного поля; μ_o - магнитная постоянная; i - мнимая единица.In an eddy current transducer, a time-varying magnetic field is excited. The controlled object is placed in the working cavity of the converter. In this case, the measuring winding of the eddy current transducer penetrates the total flux of an alternating magnetic field Φ _Σ associated with the flux Φ _{about the} ratio:

=

(1-η) +

(1) where η is the fill factor of the measuring winding of the transducer
η = a ² / a _c ² , (2) a is the radius of the controlled object; and _with - the radius of the measuring winding of the Converter; μ _r is the relative magnetic permeability of the controlled object;

- complex effective magnetic permeability, which for the case of a continuous cylindrical object in a longitudinal axisymmetric magnetic sounding field can be written as (Devices for non-destructive testing of materials and products. Reference: In 2 books / Ed. by V.V. Klyuyev. M.: Mechanical Engineering, 1986, p. 352):

=

, (3) where I _o , I ₁ are the modified Bessel functions of the first kind of zero and first orders, respectively; x is a generalized control parameter,
x =

; (4) σ is the electrical conductivity of the controlled object; ω is the circular frequency of the probe magnetic field; μ _o is the magnetic constant; i is the imaginary unit.

The phase shift between the magnetic fluxes Ф _о and Ф _Σ is due to the second term in the right-hand side of equation (1), which is the magnetic field flux in the product - Ф ₂ . Therefore, the hodograph of the vector Φ _Σ and the hodograph of the vector Φ ₂ coincide and are equal to the hodograph of μ _eff (accurate to a constant factor), which is tabulated in (Devices for non-destructive testing of materials and products. Reference: In 2 books / Ed. V.V. Klyueva. M.: Mechanical Engineering, 1986, p. 352).

. (5) Так как каждая точка годографа соответствует строго определенному значению обобщенного параметра контроля х, то выражение (5) позволяет, воспользовавшись аппаратом специальных функций, определить зависимость φ_оmax = f(x), что было сделано авторами. График этой зависимости приведен на фиг. 3. Аналитически эту зависимость можно записать как:
φ_omax= arctg

, (6) где A = ber₁(x) . ber_o(x) + bei₁(x) . bei_o(x);
B = ber_o(x) . bei₁(x) - bei_o(x) . ber₁(x);
C = ber_o ²(x) + bei_o ²(x);
ber_n, bei_n - функции Бесселя первого рода n-го порядка, "штрих" обозначает производную по х.When the frequency of the probe magnetic field ω changes from zero to infinitely large values, the vector Φ _Σ runs along the hodograph and at some point the phase angle φ _o between the fluxes Φ _o and Φ _Σ becomes maximum. It is seen that at this point the vector Φ _{Σ is} tangent to the hodograph. The latter allows you to write the ratio
φ _omax = arctg

. (5) Since each point of the hodograph corresponds to a strictly defined value of the generalized control parameter x, expression (5) allows, using the apparatus of special functions, to determine the dependence φ _{о max} = f (x), which was done by the authors. A graph of this relationship is shown in FIG. 3. Analytically, this dependence can be written as:
φ _omax = arctg

, (6) where A = ber ₁ (x). ber _o (x) + bei ₁ (x). bei _o (x);
B = ber _o (x). bei ₁ (x) - bei _o (x). ber ₁ (x);
C = ber _o ² (x) + bei _o ² (x);
ber _n , bei _n are the Bessel functions of the first kind of the nth order, the “prime” denotes the derivative with respect to x.

) и Im(

). По зависимости
a = a

(7) определяют радиус контролируемого объекта а. По зависимости
μ_r=

(8) определяют относительную магнитную проницаемость объекта и из соотношения
σ =

(9) определяют удельную электрическую проводимость контролируемого объекта.Thus, by changing the frequency of the probe magnetic field, the maximum value of the phase angle φ _{o is} achieved, the frequency values of the probe magnetic field I and φ _{о max} , and also the fluxes Ф _Σ and Ф _о are measured. After that, according to the dependence, inverse dependence (6) (graphically, according to the table or numerically), the value of the generalized control parameter x corresponding to the given value φ _{о max is determined} , and from it using the well-known dependence (3) - the values of Re (

) and Im (

) According to
a = a

(7) determine the radius of the controlled object a. According to
μ _r =

(8) determine the relative magnetic permeability of the object and from the relation
σ =

(9) determine the electrical conductivity of the controlled object.

 Improving the accuracy of measuring three parameters of continuous cylindrical electrically conductive objects is achieved due to the absence of influence on the measurement results of the errors of compensation of the magnetic flux of the probe field without the product, which are inevitably present when measuring the introduced fluxes. In addition, increasing accuracy is achieved by direct measurement of the parameter taking the maximum value, and not by indirect measurement characteristic of the prototype method (the prototype determines the maximum product of the amplitude of the introduced stream by the sine of its phase angle).

 The proposed method of non-contact measurement of the parameters of cylindrical continuous electrically conductive objects was implemented as follows.

 Measure the parameters of a cylindrical solid product with a radius of 6.563 mm, made of paramagnetic cast iron.

 Measurements are carried out using an eddy current transducer with the following parameters: the number of turns of the measuring winding is 800; radius of the measuring winding - 9.27 mm; the number of turns of the magnetizing winding - 190; the radius of the magnetizing winding is 10.56 mm. As measuring equipment, a GZ-112 generator, a F2-34 phase meter, a B7-16 voltmeter and a precision shunt with a nominal value of 1 Ohm are used.

) = 0,493068 и Im(

) = -0,358122. Воспользовавшись соотношением
Ф =

(10) где Е - ЭДС, наводимая магнитным потоком в соленоиде; W_изм - количество витков измерительной обмотки, можно записать

=

(11) и поэтому можно измерять непосредственно значения ЭДС, которые составили E_Σ= 451,201 мВ, Е_о = 493,829 мВ.The controlled product is placed in the working cavity of the eddy current transducer, its magnetizing circuit is supplied with a current of 9 mA and the frequency of the probing field is changed until the phase angle reaches its maximum value. In this case, the value of φ _omax amounted to - 17.34 ^about at a frequency of the probing field of 14.9462 kHz. The value of the generalized control parameter x = 3.02957 and the values of Re (

) = 0.493068 and Im (

) = -0.358122. Using the ratio
F =

(10) where E is the EMF induced by the magnetic flux in the solenoid; W _ISM - the number of turns of the measuring winding, you can write

=

(11) and therefore it is possible to directly measure the EMF values, which were E _Σ = 451,201 mV, E _о = 493,829 mV.

From relation (7), the radius of the test object is determined a = 6.57303 mm, from relation (8), the relative magnetic permeability μ _r = 1.51240, and from relation (9), the specific electrical conductivity σ = 0.119027 ˙10 ⁷ S / m

 A comparison of the results with the measurement results by control methods, which were used differential ballistic (error not more than 1%), contract bridge (error not more than 0.3%) and micrometric (error not more than 0.1%), showed that measurement errors were: radius - 0.16%, magnetic permeability - 0.637%, specific electric permeability - 0.927%.

 Compared with the prototype method, which was implemented in a facility that used a converter with a compensation error not exceeding 0.5%, the proposed method made it possible to increase the accuracy of measuring radius by 1.25%, magnetic permeability by 0.45%, and electrical conductivity - by 2.5%.

 Using the proposed method will allow to obtain reliable values of magnetic permeability, electrical conductivity and radius of continuous conductive cylindrical objects, which is important in areas such as input control of metal rods, selection of optimal materials for such structures as shafts of submersible electric motors, details of field-forming physical installations, etc. . d.

Claims (1)

METHOD FOR MEASURING THE PARAMETERS OF A SOLID CYLINDRICAL ELECTRIC CONDUCTING OBJECTS, including exposure to a measured object with a homogeneous variable axisymmetric magnetic field, characterized in that, in order to improve accuracy, measure the normalized magnetic flux through the measuring winding with the measured object and the measured magnetically frequency of the acting magnetic field, change the frequency of the magnetic field until the phase angle between the measured and the acting magnetic fluxes of the maximum value, fix the maximum value of this phase angle φ _{0 max} , the corresponding normalized magnetic flux Φ _Σ ^* through the measuring winding with the measured object and the frequency ω of the acting magnetic field, and the relative magnetic permeability, electrical conductivity and radius of the object are determined from the following system of equations
φ _omax = arctg

,
a = a

,
μ = Φ $\genfrac{}{}{0ex}{}{\text{*}}{\text{Σ}}$

,
Where

=

;
x = a

;
j ₀ , j ₁ - modified Bessel functions of the first kind of zero and first orders;
Φ $\genfrac{}{}{0ex}{}{\text{*}}{\text{Σ}}$ , φ _omax is the amplitude and phase of the normalized magnetic flux of an alternating magnetic field through a measuring winding with an object Φ $\genfrac{}{}{0ex}{}{\text{*}}{\text{Σ}}$ = Φ _Σ / Φ _o ;
Φ _o - magnetic flux in the measuring winding without an object;
μ _c is the relative magnetic permeability of the object;
σ is the electrical conductivity of the object;
a, a _c are the radii of the object and the measuring winding;
ω is the frequency of the acting magnetic field;
μ _o is the magnetic constant.

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