SU560193A1 - Magnetic field measurement method - Google Patents

Description

The invention relates to magnetic measurements and can be used in the construction of primary measuring transducers, preferably a weak constant or slow magnetic field into an electrical signal, geophysical and navigation devices.

There is a known method for measuring a magnetic field, in which a magnetic conductor with a signal winding and an auxiliary alternating field distributed along it, or a constant and alternating fields simultaneously distributed, is magnetised under a magnetic field. As a result of magnetization, the magnetic permeability of the body of the magnetic circuit changes, and consequently, the magnetic permeability of the body of the magnetic core for an external measurable field. A change in the magnetic permeability of the body of the magnetic circuit leads to a modulation of the measured magnetic flux in it with a frequency that coincides with the frequency of the bias field, or twice the frequency. The magnitude of the measured floor is judged by the magnitude of the EMF in the signal winding with the frequency of the magnetizing field or twice the frequency. The method is implemented using both closed and open magnetic circuits Ij.

However, the magnetic field of the magnetic core body for an external magnetic field and the magnetic flux in the magnetic core body are related to the magnetic permeability of the material of the magnetic circuit by nonlinear dependence and from the small pulses in smaller

absolute and relative limits. This reduces the robustness, sensitivity and thus the measurement accuracy of this method. In addition, in the case of registration of EMF in the signal winding, which varies with

doubled in comparison with the bias frequency field, the corresponding secondary transducers are complicated.

The closest technical solution to the invention is the method of measuring the magnetic field with the help of a sensitive element in the form of a closed magnetowire with a signal winding distributed over it, which consists in periodically magnetising opposite areas

magnetic and izmereniya EMF in the signal winding 2.

However, when measured by this method, the magnetic permeability. The magnet body in the measuring direction changes according to a law that is nonlinearly related to the change in the permeability of the material of the sections. This leads to harmful modulation of the measured magnetic flux through the body.

nonlinear law, and therefore to by in

the higher harmonic components in the output emf.

The purpose of the invention is to improve measurement accuracy.

This is achieved by the fact that according to the proposed method, the opposite sections of the magnetic circuit are placed in auxiliary constant fields of the same magnitude and direction, as well as in variable fields of the same magnitude, but in different directions, or in variable fields of the same magnitude and direction and in constant fields of the same magnitude, but different voltage.

FIG. 1 shows the sensing element; in fig. 2 and 3 are curves of changes in the differential magnetic permeability of the material of the sections for the case of antiphase biasing along one branch and different branches of the magnetization curve, respectively; FIG. 4 - equivalent circuit of magnetic flux in the magnetic core.

Example 1. For the measurement, a sensitive element (Fig. 1) was used in the form of a closed magnetic circuit 1 with a signal winding 2 distributed over a closed circuit. Each of the opposite sections 3 and 4 was placed into the gap of a separate electromagnet. Through the windings of electromagnets, direct current of the same magnitude and sign was passed, and alternating current of the same magnitude but of a different sign was passed. The sensing element was placed in a reference field with known strength and direction and oriented until the longitudinal axis of the magnetic circuit coincided with the direction of the field. The EMF was measured in the signal winding and the coefficient determining the sensitivity of the measurement as a quotient of the division of the output EMF was found by the magnitude of the polarity of the field.

The sensing element was placed in a measurable field and oriented with the longitudinal axis in the direction of measurement, the output emf was measured. To find the magnitude of the field in the direction of measurement, the resulting emf value was divided by the coefficient that determines the sensitivity of the measurement.

FIG. 2, curve 5 depicts the change in the differential magnetic permeability of the magnetic core material as a function of the bias field strength. Sections 3 and 4 in the gaps of electromagnets are under the action of a constant field with the strength Hi (both portions) and an alternating field with a strength varying in time along curves 6 and 7, respectively. The permeability of the material of sections 3 and 4 varies with time according to antiphase curves 8 and 9.

Example 2. For the measurements, the sensitive element shown in FIG. 1. Each section 3 and 4 were placed in the gap of a separate electromagnet. Through the windings of electromagnets, a constant current of the same magnitude, but of a different sign, and an alternating current of the same magnitude and sign were passed.

Further measurements were made as described above. The measurement results are the same. Sections 3 and 4 in the gaps of electromagnets were under the action of constant fields with intensity and -HI, respectively, and variable zero of one direction (curves 6 and 6). The permeability of the material of sections 3 and 4 changed over time according to antiphase curves 8 and 9, respectively.

Example 3. For measurements, the sensitive element shown in FIG. 1. In each of the opposite portions 3 and 4, a hole was made in which the bias winding was placed. The current was supplied to the bias windings and further measurements were carried out in accordance with examples 1 and 2. The measurement results coincide. The following is a characteristic of the sensing element, the measurement results of examples 1, 2 and 3 and the mathematical analysis of the proposed method.

The magnetic core of the sensing element is made of permallo sheet thickness

0.05 mm with a set of 1.2 mm, a magnetic core length of 90 mm and after heat treatment were placed in a protective dielectric cover (signal winding 400 turns, bias winding 50 turns on each electromagnet or in each hole). A constant current of 9 ma and an alternating current of 2 ma at a frequency of 5 kHz were applied to the bias winding.

Obtained by the value of the output electromotive force with a frequency of 5 KHz - 10 MB for a field with a unit strength of 1 a / and in the range of measured fields from 0 to 50 a / m. The nonlinear distortion of the output signal (harmonic ratio) in a field with a voltage of 25 a / m is less than 2%, the residual signal at a zero value of the measured field strength is 1.5 m / v, the output impedance of the sensing element in the signal winding is 250 ohms. Selection in examples 1, 2 and 3 of the direct current bias (current magnitude) and alternating current (amplitude and current waveform) modes can provide a sinusoidal change in the magnetic permeability of the material of sections 3 (jii)

and 4 (| i2). In this case, curves 8 and 9 mathematically can be written as

| 1 g IJ. + sin Q (;

lij a - yes sin Qi

where | .i and A) i is the average value and amplitude of the increment of the magnetic permeability of the material of the sections; Q-circular frequency; t - time

It is obvious that the magnetic conductivity of the material of the magnetic conductor m in the direction of measurement, and therefore the magnetic conductivity of the body of the magnetic conductor gt in the external field of this direction, and the magmatic flux Yao through the body of the magnetic conductor

uh

of the measured floor remain unchanged in time and are equal

5 jJ-oPЯ gi + Я2 (0 (g + H-a)

zT I

 YAL

ST

/

where gi and g2 are the magnetic conductivity of the material of sections 3 and 4;

But the absolute magnetic permeability of the vacuum;

1-1т - magnetic permeability of the body of the magnetic core;

HO is the intensity of the measured magnetic field;

/ and 5 - the length and cross-sectional area of the magnetic circuit.

The flux Fo from the measured magnetic field is distributed over sections 3 and 4 of the closed magnetotherm according to their magnetic conductivity determined by the magnetic permeability of the material of the sections. Flows F1 and F2 in sections 3 and 4 can be found according to the first Kirchhoff's law for magnetic circuits and are equal to

.sinQ.

F

1o o

22a

0, .. sinQ.

22; a

The equivalent circuit of magnetic fluxes operating in the magnetic circuit is shown in FIG. 4, where 10 and 11 are sources of variable flows.

F „Di

sinQ.

and

It can be seen from the diagram that the magnetic flux acting in the magnetic core from the measured field can be represented as a constant flux Fo uniformly distributed over

sections 3 and 4 and a closed variable magnetic flux. The flow along the closed circuit of the magnetic circuit () can be found as the difference of the magnetic fluxes F1 and F

F Fo - Sin Yg sin Ш,

and.

and EMF (e) in the signal winding with the number of turns W

JF,

- WQy., I.H, S - cos Q.

e - W

It is clear from the latter that the output emf is related to the strength of the measured field in terms of constant coefficients and has a harmonic character with a harmonic antiphase law of change in the magnetic permeability of the material of opposite sections of the magnetic conductor.

Claims (2)

1. Afanasyev Yu. V. Ferrozond, L., “Energie, 1969, p. 14-39. 2. Auth. St. M 352238, cl. G 01R 33/00, 15.03.71. t