RU2075757C1 - Sensor of induced magnetic fields (variants) - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: sensor is designed to measure quasi-constant and variable magnetic fields of low levels and unspecified shape. Sensor of induced magnetic fields has inductor, case, permanent magnet and magnetic circuit located in case, magnetic screen housing C-shaped magnet and measurement winding so installed that section of sensor surface on side of poles of magnet and face surface of magnetic circuit are not screened. Poles are oriented relative to inductor and opposite face surface of magnetic circuit is matched with inner surface of magnet in point of its crossing with common symmetry axis of magnet and magnetic circuit. Measurement winding is uniform, its electric parameters are chosen in compliance with working range of measurement frequencies with account of given relationships. In agreement with another variant measurement winding placed inside magnetic screen is so mounted that section of surface of sensor on side of poles of C-shaped magnet and face surface of magnetic circuit oriented towards inductor are not screened. Opposite face surface of magnetic circuit is matched with inner surface of magnet in point of its crossing with common symmetry axis of magnet and magnetic circuit. Measurement winding is uniform and has electric parameters chosen in accord with same relationships. EFFECT: expanded application field thanks to enhanced sensitivity and widened measurement frequency range. 9 cl, 4 dwg

Description

 The invention relates to sensors designed to measure quasi-constant and variable magnetic fields of low levels of arbitrary shape in various fields of technology, in particular arising from certain technological processes of purification and separation of waste emulsions stabilized by mechanical impurities in water-oil and water-oil emulsions in environmental protection systems.

 Sensors of various types are known for measuring quasi-constant and variable magnetic fields of low levels in the range from millitesla units and below. When using semiconductor-type sensors for these purposes based on Hall, magnetoresistive, and other effects, the need arises for highly stabilized power sources, correction devices to compensate for imperfections in manufacturing technology and the influence of temperature and other environmental factors, there is a significant dependence of the conversion coefficient on the size of the sensitive element . Carrying out such measurements using induction-type sensors, in addition to the limitations associated with direct magnetic field measurements by the direct method and restrictions on the overall mass characteristics, has several advantages. These are: the absence of external power sources, the linear dependence of the output signal voltage in a wide range of measurement levels and frequencies, the possibility of achieving significant levels of conversion coefficient with comparatively small sizes of the sensitive element, and the simplicity of the design.

 A known type of inductance sensor [1] under the name "Ferrite Magnetic Modulation Parametric Sensor", designed to measure low-frequency, as well as constant magnetic fields of low levels. Signal measurements are carried out by modulating the magnetic permeability (magnetic resistance) of the composite magnetic circuit by the field of the magnetization reversal circuit. The result is amplitude modulation at the magnetization reversal frequency and amplitude-frequency modulation and amplification at the frequency of parametric resonance. By tuning the frequency of the circuit, consisting of the inductance of the measuring winding and the output capacitance, the voltage of the signals is emitted at the frequencies of parametric resonance, which correspond to even harmonics of the magnetization reversal current. However, the use of a well-known technical solution for measuring variable low-level magnetic fields is limited by the discrete nature of the spectrum of amplified signals and narrow frequency tuning bands of parametric resonance, significant levels of nonlinear distortion, as well as significant, about tens of centimeters, overall dimensions of the sensor magnetic circuit.

 Of the known technical solutions, the sensor closest in technical essence to the claimed one is a sensor [2]. The sensor contains an inductor, a housing and a permanent magnet and a magnetic core located in the housing. The axis of maximum sensitivity of the sensor, which coincides with the magnetization axis of a rectangular magnet, is oriented in the direction of measurement along the radius of the inductor made of ferromagnetic material. The magnetic flux from the magnet pole closest to the inductor is closed through successive sections of the sensor’s magnetic circuit: magnetic pole structural elements of the magnetic circuit in the form of two extreme longitudinal ones with a jumper and a third middle longitudinal one from the middle of the jumper; the free end of the third element working air gap inductor; inductor ambient sensor medium opposite pole of the magnet. Measuring windings are placed on the jumper between the two extreme and middle longitudinal elements. By means of an inductor, the magnetic resistance of the working gap is modulated. The result is a variable component of the flux of induction of a permanent magnet, accompanied by the voltage of the signal EMF induction at the output of the measuring winding. The sensitivity value of the sensor is determined by the magnitude and rate of change of the gradient of the field flow in the working gap.

 In the absence or low modulation frequency, the output signal determined by the contribution due to the inductive component of the winding resistance will be equal to or close to zero. For small working gaps, starting from a certain threshold frequency value, the output voltage will change in proportion to the modulation frequency. By modulating an external source of the field flux through the measuring winding, in addition to frequency, it is possible to measure variable values of magnetic fields with magnitude of levels and in the frequency range determined by the sensitivity threshold and calibration errors of the frequency response of the sensor in terms of the amplitude and frequency of the measured signals. Limitations when using the known technical solution are: the frequency dependence of the conversion coefficient, a low sensitivity threshold in the frequency range of the signals up to 40-50 Hz, a significant decrease in sensitivity with an increase of more than 1 mm in the working air gap, as well as the influence of external noise due to the absence of magnetic shielding sensor circuit.

 The problem to which the invention is directed, is to expand the scope by increasing the sensitivity and expanding the frequency range of measurements.

где Ω_в и Ω_н частоты верхнего и нижнего рабочих диапазонов измерений соответственно;
L, R и C_o индуктивность, сопротивление и межвитковая емкость измерительной обмотки соответственно;
r и c сопротивление и емкость выходного импеданса датчика.First option. The problem is solved due to the fact that in the known sensor of induced magnetic fields containing an inductor, a housing and a permanent magnet and a magnetic circuit housed in the housing, the magnetic circuit is provided with a magnetic screen, inside which a magnet made C-shaped, and a measuring winding installed in this way that the portion of the sensor surface from the side of the magnet poles and the end surface of the magnetic circuit oriented towards the inductor is unscreened, the opposite end surface of the magnetic circuit is compatible Even with the inner surface of the magnet at the point of its intersection with the common axis of symmetry of the magnet and the magnetic circuit, and the measuring winding is made uniform with electrical parameters selected in accordance with the operating range of measurement frequencies according to the relations:

where Ω _in and Ω _{n are the} frequencies of the upper and lower working ranges of measurements, respectively;
L, R and C _o inductance, resistance and inter-turn capacitance of the measuring winding, respectively;
r and c are the resistance and capacitance of the output impedance of the sensor.

 In addition, a ferrite core was used as a magnetic core, and the body is made of caprolon.

где Ω_в и Ω_н частоты верхнего и нижнего рабочих диапазонов измерений соответственно;
L, R и C_o индуктивность, сопротивление и межвитковая емкость измерительной обмотки соответственно;
r и c сопротивление и емкость выходного импеданса датчика.The second option. The problem is solved due to the fact that in the known sensor of induced magnetic fields, containing an inductor, a housing and a permanent magnet and a magnetic circuit housed in the housing, the magnetic circuit is provided with a magnetic screen, inside which a measuring winding is placed, so that a portion of the sensor surface is on the pole side a magnet made with a C-shaped and the end surface of the magnetic circuit oriented towards the inductor is unshielded, the opposite end surface of the magnetic circuit is aligned with the inner surface of the magnet at the point of intersection of the common axis of symmetry of the magnet and the magnetic circuit, and the measuring winding is made uniform with electrical parameters selected in accordance with the operating range of measurement frequencies according to the ratios:

where Ω _in and Ω _{n are the} frequencies of the upper and lower working ranges of measurements, respectively;
L, R and C _o inductance, resistance and inter-turn capacitance of the measuring winding, respectively;
r and c are the resistance and capacitance of the output impedance of the sensor.

 In addition, a ferrite core was used as a magnetic core, the housing is made of caprolon, the measuring winding is made in length less than the length of the magnetic core.

 In addition, the magnetic screen near the poles of the magnet is made composite in generators of different diameters from n-sections, where n≥2, electrically isolated from each other and offset in diameter by the amount of clearance between them.

 In FIG. 1 shows the first and second versions of the design of the sensor in the context.

 Designations: A, B first sensor variant, C, D second sensor variant, 1 measuring winding, 2 C-shaped permanent magnet, 3 magnetic core, 4 magnetic screen, 5 inductor. In FIG. 1 additionally shown: 6 measuring coil frame, 7 sensor housing made of non-magnetic material such as caprolon, 8 extraction column with walls of non-magnetic material in section (fragment), 9 direction of pulsations among the extraction; 10 clearance, 11 electrical insulation between sections of the screen.

 In FIG. 2 shows a generalized diagram of the magnetic circuit of the sensors.

Designations: ΔZ _o (t) and Z _{i are the} variable and constant components of the magnetic resistance, Δφ (t) and φ $\genfrac{}{}{0ex}{}{\text{o}}{\text{j}}$ variable and constant components of magnetic fluxes of scattering, U _{k the} magnetomotive force of the magnet, U (t) voltage EMF induction of the measuring winding, i, j, k designation indices: i 0, 1, 2, 3, 4, 5; j 0, 1, 2 and K 1, 2. Designations with the corresponding indices refer to: 0 to the parameters of interaction with the inductor, 3 to the magnetic resistance of the magnetic circuit, 4 to the magnetic resistance of the scattering fields of the magnet of the first sensor variant, 5 to the magnetic resistance of the scattering fields of the magnet of the second sensor options; 1, 2 to the parameters of interconnected sections of the magnetic circuit; a, b and c are points of the magnetic circuit in the plane of the poles of the magnet.

 In FIG. 3 shows a block diagram of measurements using the first and second sensor variants. Designations: 12 sensitive element, including the measuring winding and the sensor magnetic circuit, 13 - amplifier-converter, 14 registrar.

напряжение эквивалентного генератора (индуктора) сигналов, Ζ_g(jω) импеданс чувствительного элемента, Z_вых(jω) выходной импеданс датчика, Z_вх(jω) выходной импеданс усилителя-преобразователя, ω круговая частота измерений.In FIG. 3 additionally shown:

voltage of the equivalent generator (inductor) of the signals, Ζ _g (jω) impedance of the sensor, Z _o (jω) output impedance of the sensor, Z _I (jω) output impedance of the amplifier-transducer, ω circular measurement frequency.

In FIG. Figure 4 shows typical dependences on the frequency of measurements of conversion coefficients of sensors of the MPF type. Designations: I sensor MPF-01, II sensor MPF-07, III sensor MPF-06. Each of the sensor options is used as follows. The sensor is placed at a controlled point near the inductor 5, carrying out its "capture" by the magnetic field of the "probe" flow of the scattering field. For this, the axis of the maximum sensitivity of the sensor, which coincides with the common axis of symmetry of the magnet 2 and the magnetic circuit 3, is chosen in the direction normal to the measurement plane. By selecting the distance between the inductor 5 and the sensor, a threshold flux linkage between them is reached, at which the probe flow is modulated by the scattering resistance of the interaction space. In accordance with FIG. 2 due to the occurrence of a variable component of the magnetic resistance DZ _o (t) there is a redistribution of the components of the flow φ $\genfrac{}{}{0ex}{}{\text{o}}{\text{o}}$ at points a, b and c of the plane of the poles of the magnet and the passage of the flux signal Δφ (t) through the portion of the magnetic circuit with magnetic circuit 3. The signal Δφ (t) induces voltage U (t) at the output terminals of the measuring winding 1.

где K₁ коэффициент преобразования магнитной схемы,
K₂ коэффициент преобразования чувствительного элемента,
Δφ(0),ΔZ_o(0), U(0) амплитудные значения соответствующих переменных составляющих Δφ(t),ΔZ_o(t) и U(t);
μ_o и S_g магнитная проницаемость вакуума и площадь поверхности неэкранированного участка поверхности датчика соответственно.We determine the conversion coefficient of the sensor in the form of a product of factors:

where K ₁ the conversion coefficient of the magnetic circuit,
K ₂ the conversion coefficient of the sensing element,
Δφ (0), ΔZ _o (0), U (0) the amplitude values of the corresponding variable components Δφ (t), ΔZ _o (t) and U (t);
μ _o and S _{g the} magnetic permeability of the vacuum and the surface area of the unscreened portion of the surface of the sensor, respectively.

Пусть в момент времени t = 0 φ $\genfrac{}{}{0ex}{}{\text{0}}{\text{2}}$ > φ $\genfrac{}{}{0ex}{}{\text{0}}{\text{1}}$ . Тогда для переменной и постоянной составляющих магнитных потоков имеем:

В линейном приближении теории возмущений при

, используя соотношения (2) и (3), а также полагая, что U₁ U₂, Δφ = 0, φ $\genfrac{}{}{0ex}{}{\text{0}}{\text{1}}$ Z₁≪ φ $\genfrac{}{}{0ex}{}{\text{0}}{\text{0}}$ Z₀~2U₁, Z₄>Z₅≫ Z₃= Z_u, получаем следующее выражение для коэффициента K₁ соотношения (1):

где: l_g,μ,Z_u,Ω длина в пределах размеров измерительной обмотки, относительная магнитная проницаемость, магнитное сопротивление магнитопровода и частота измеряемого сигнала соответственно.As can be seen from FIG. 2, the sensor magnetic circuit can be represented as consisting of three interconnected circuits of scattering fluxes: the circuit sNSn forming the probing flux, and two circuits csb and bna connected through the magnetic circuit 3 to the measuring winding 1 and forming a differential conversion circuit. The external circuit includes both series-connected magnetomotive forces U _k , each of the internal one of them. The circulation of the magnetic field vector He along each of the circuits L _Σ of the sensor magnetic circuit will be equal to:

Let at time t = 0 φ $\genfrac{}{}{0ex}{}{\text{0}}{\text{2}}$ > φ $\genfrac{}{}{0ex}{}{\text{0}}{\text{one}}$ . Then for the variable and constant components of the magnetic fluxes we have:

In the linear approximation of perturbation theory for

using relations (2) and (3), and also assuming that U ₁ U ₂ , Δφ = 0, φ $\genfrac{}{}{0ex}{}{\text{0}}{\text{one}}$ Z ₁ ≪ φ $\genfrac{}{}{0ex}{}{\text{0}}{\text{0}}$ Z ₀ ~ 2U ₁ , Z ₄ > Z ₅ ≫ Z ₃ = Z _u , we obtain the following expression for the coefficient K _{1 of} relation (1):

where: l _g , μ, Z _u , Ω is the length within the dimensions of the measuring winding, the relative magnetic permeability, magnetic resistance of the magnetic circuit and the frequency of the measured signal, respectively.

где Ω_o резонансная частота датчика,
a и b коэффициенты.We use the block diagram of FIG. 3. It can be shown that for Z _in (ω) ≫ Z _out (ω), the transformation coefficient K ₂ (Ω) of relation (1) will be characterized by the values:

where Ω _{o the} resonant frequency of the sensor,
a and b coefficients.

,
выполненной равномерной, рабочий диапазон частот измерений может быть определен из соотношения:

Из соотношений (1), (4) и (5) следует, что увеличение чувствительности датчика может быть достигнуто использованием дифференциальной схемы преобразования, уменьшением магнитного сопротивления магнитопровода, увеличением отношения

. Частотный диапазон измерений на низких частотах приближается к 0 Гц. Расширение диапазона измерений на высоких частотах может быть достигнуто за счет уменьшения параметров L, C, C_o и выбора материала магнитопровода обмотки, обеспечивающего μ(Ω) = const при Ω _→ Ω_в. Влияние значений параметров C, C_o и r зависит от уровня технологии изготовления датчика и величины импеданса усилителя-преобразователя.When the values of the electrical parameters of the measuring winding 1, satisfying the conditions:

,
made uniform, the operating range of measurement frequencies can be determined from the ratio:

From relations (1), (4) and (5) it follows that an increase in the sensitivity of the sensor can be achieved using a differential conversion circuit, a decrease in the magnetic resistance of the magnetic circuit, and an increase in the ratio

. The frequency range of measurements at low frequencies approaches 0 Hz. The extension of the measurement range at high frequencies can be achieved by reducing the parameters L, C, C _o and choosing the material of the winding magnetic circuit, providing μ (Ω) = const as Ω _ → Ω _c . The influence of the values of the parameters C, C _o and r depends on the level of manufacturing technology of the sensor and the magnitude of the impedance of the converter amplifier.

 In the first and second versions of the sensor, a ferrite core is used as the material of the magnetic circuit.

 The use of a magnetic screen allows measurements of low level magnetic fields in the event of interference. In the second version of the sensor, the reduction of the shunt effect of the magnetic screen by the sensitivity threshold of the differential conversion circuit is achieved by the fact that the measuring winding is made along a length less than the length of the magnetic circuit. The shunting effect is also achieved by the fact that the magnetic screen near the poles of the magnet is made composite by generators of different diameters from n sections, where n≥2 are electrically isolated from each other and offset in diameter by the amount of clearance between them.

 From the above algorithms for the functioning of the sensors, it can be seen that, in contrast to the known field of use of the claimed technical solution can be expanded. Due to the high sensitivity and uniformity of the characteristics in a wide range of frequencies, it becomes possible to measure, in addition to the modulation frequency (magnetic resistance) of solid-state inductors, the frequency and amplitude of modulation of liquid inductors, as well as the frequency, magnitude and direction of various other radiation sources of low-level quasi-constant and variable magnetic fields at distances exceeding more than an order of magnitude the distance of a known technical solution.

 The findings are confirmed by experimental results. From FIG. Figure 4 shows that when using the claimed technical solution, an increase in sensitivity and an extension of the frequency range of measurements can be achieved both towards low frequencies up to 0 Hz and frequencies above 10 kHz. Further (curve 3 in Fig. 4) the expansion of the frequency range is provided by the use of a ferrite rod 3 as a magnetic circuit.

в пределах, соответствующих экспериментальным зависимостям фиг. 4, могут быть получены оценочные расчетные значения электрических параметров датчиков.Within the operating range of measurement frequencies, the frequency response does not exceed ± 0.5 dB. Overall and mass parameters of the sensor with an operating frequency range of 0-80 kHz: external diameter 8 mm, length 1.5 mm, weight 10 g, magnet weight 30 g. The accuracy of calculating the electrical parameters of the sensors is limited by technological ambiguity in the choice of parameter values C _o , C and r. Using relation (6) for a given frequency range ΔΩ and relative values

within the limits corresponding to the experimental dependences of FIG. 4, estimated design values of the electrical parameters of the sensors can be obtained.

 Based on the foregoing, the claimed technical solution in comparison with the known allows: to increase the sensitivity; expand the frequency range of measurements; ensure high frequency response uniformity in the operating frequency range; measure the modulation frequency, frequency, magnitude and direction of quasi-constant and variable magnetic fields of low levels; take measurements with solid-state and liquid inductors; significantly increase the measurement distance; take measurements under external interference and environmental factors; carry out evaluative calculations of electrical and other parameters of the sensors.

Claims (8)

1. A sensor of induced magnetic fields, comprising an inductor, a housing and a permanent magnet and a magnetic circuit housed in the housing, characterized in that it is provided with a magnetic screen, inside which a C-shaped magnet is placed, and a measuring winding arranged so that a surface section the sensor from the side of the magnet poles and the end surface of the magnetic circuit oriented towards the inductor is unscreened, the opposite end surface of the magnetic circuit is aligned with the inner surface of the magnet at its intersection with the common axis of symmetry of the magnet and the magnetic circuit, and the measuring winding is made uniform with electrical parameters selected in accordance with the operating range of measurement frequencies according to the ratios

ΔΩ = Ω _in -Ω _n ,
where Ω _in and Ω _n are the frequencies of the upper and lower working range of measurements, respectively;
L, R and C _about inductance, resistance and inter-turn capacitance of the measuring winding, respectively;
r and C are the resistance and capacitance of the output impedance of the sensor.  2. The sensor according to claim 1, characterized in that a ferrite core is used as a magnetic core.  3. The sensor according to claim 1, characterized in that the housing is made of caprolon. 4. A sensor of induced magnetic fields, comprising an inductor, a housing and a permanent magnet and a magnetic circuit housed in the housing, characterized in that it is equipped with a magnetic screen, inside which a measuring winding is placed, installed so that the surface area of the sensor from the side of the magnet poles made With -shaped, and the end surface of the magnetic circuit oriented towards the inductor is unscreened, the opposite end surface of the magnetic circuit is aligned with the inner surface of the magnet at the point cross-sections with a common axis of symmetry of the magnet and the magnetic circuit, and the measuring winding is made uniform with electrical parameters selected in accordance with the operating range of measurement frequencies according to the ratios

ΔΩ = Ω _in -Ω _n ,
where Ω _in and Ω _n are the frequencies of the upper and lower working range of measurements, respectively;
L, R and C _about inductance, resistance and inter-turn capacitance of the measuring winding, respectively;
r and C are the resistance and capacitance of the output impedance of the sensor.  5. The sensor according to claim 4, characterized in that a ferrite core is used as a magnetic circuit.  6. The sensor according to claim 4, characterized in that the housing is made of caprolon.  7. The sensor according to claim 4, characterized in that the measuring winding is made in length less than the length of the magnetic circuit.  8. The sensor according to claim 4, characterized in that the magnetic screen near the poles of the magnet is made integral in generators of different diameters from n sections, where n ≥ 2, are electrically isolated from each other and offset in diameter by the amount of clearance between them.

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