JP2979003B2 - DC magnetic field detector - Google Patents

Description

The present invention relates to a direct current magnetic field detection device.

(B) Conventional technology A conventional direct-current magnetic field detecting device is disclosed in Japanese Patent Publication No. 38-16943. That is, in the DC magnetic field detecting device shown in this figure, a hole is provided in a saturable rod-shaped magnetic core excited by an AC primary coil, and a secondary coil is wound around each of magnetic paths formed on both sides of the hole. ing. A rectifier is provided in each secondary coil circuit.
The two rectifiers are arranged so as to generate a magnetic field (bias magnetic field) that rotates in one direction around a hole formed in the magnetic core when a current flows therethrough. In such a case, the DC magnetic field applied from the outside is detected by differentially detecting the DC of both secondary coils. That is, in a state where there is no external DC magnetic field in the axial direction of the magnetic core, the bias magnetic fields acting on the two secondary coils are equal, and the rectified currents in the circuits of the two secondary coils are equal to each other and appear at the output terminal. The voltages are also equal. On the other hand, if there is an external DC magnetic field to be measured in the axial direction of the magnetic core, the magnetomotive force acting on one magnetic path is reduced by the amount of the existing DC magnetic field, and the magnetomotive force acting on the other magnetic path is conversely reduced by the DC magnetic field. It increases by the amount of. When the bias magnetic field due to the AC primary current and the DC magnetic field to be measured are in the same direction, the magnetic path approaches the saturation point, while the DC magnetic field to be measured is in the opposite direction to the bias magnetic field due to the AC primary current. Is set to be away from the saturation point, so that the magnetic flux saturation state is different between one magnetic path and the other magnetic path, and the secondary coil of one magnetic path and the secondary coil of the other magnetic path Different DC voltages are generated. The strength of the magnetic field in the axial direction of the magnetic core can be measured from the difference between the DC voltages.

(C) Problems to be Solved by the Invention However, the above-described conventional DC magnetic field detection apparatus has a problem that there is a limit in accuracy due to an error in manufacturing a magnetic path of a magnetic core. In other words, the cross-sectional area of the magnetic path formed by machining a hole in the rod-shaped magnetic core cannot be completely the same for both magnetic paths due to unavoidable manufacturing errors. The characteristics are asymmetric. For this reason, when a compass was configured using this DC magnetic field detection device, a direction error of about 10 ° had to be allowed. Further, since the DC magnetic field detection apparatus of this system is of a self-bias type, harmonics generated when the power supply output of the high-frequency oscillator fluctuates affect the bias set value, which also causes an increase in measurement error. An object of the present invention is to solve such a problem.

(D) Means for Solving the Problems The present invention solves the above problems by providing means for adjusting the output from the secondary coil. That is, the DC magnetic field detecting device according to the present invention has a primary coil (12) connected to an AC power supply (14) and a magnetic core (10) excited by the primary coil, and the magnetic core has a direction perpendicular to the axis. Are provided with two saturable magnetic paths (18 and 20) separated from each other by a hole in the axial direction of the magnetic core.
The secondary coils (22 and 24) are wound, and the wires (25 and 27) drawn from one end of both secondary coils are grounded, and the wires (30 and 27) drawn from the opposite ends of both secondary coils are grounded.
34) are respectively connected to both ends of a variable resistor (44) for bias adjustment and an output resistor (38) via rectifiers (32 and 36), and both rectifiers are connected to each magnetic path when current flows through them. The output resistor is provided with a baseline adjustment slider (40) whose contact position is variable about the midpoint of the output resistor. Connected to terminal (42).

The wires (25 and 27) taken out from the one end side of the secondary coil are wound around a magnetic core and the feedback coil (26
And 28) can also be configured.

In addition, the code | symbol in a parenthesis shows the corresponding member of the Example mentioned later.

(E) Operation When the AC power supply is operated and the AC power supply is supplied to the primary coil, an AC magnetic field acts on the magnetic path around which the secondary coil is wound, and
An alternating current is generated in the next coil. A rectifier is provided in each of the circuits of the two secondary coils. Both rectifiers are arranged in such a manner that when a current flows through them, a magnetic field (bias magnetic field) that rotates in one direction around a hole provided in the magnetic core is generated. When a DC magnetic field to be measured externally acts on the magnetic core in this state, the magnetic field is strengthened when the directions of the magnetic field generated by the AC power supply and the DC magnetic field match, and the magnetic field is weakened in the opposite case. By setting the magnetic path closer to the saturation point when the magnetic field is strengthened and away from the saturation point when the magnetic field is weakened, a difference occurs between the output voltages of the two secondary coils. The strength of the magnetic field in the axial direction of the magnetic core is detected from the difference between the output voltage and the voltage.

When measuring the earth's magnetic field with this DC magnetic field detection device, the slider for adjusting the baseline is used when the operating magnetic field is maximum (when the magnetic field acts in the core axis direction, that is, when the magnetic core moves north (90 °) and south (270 °) Output is the same, and no magnetic field is applied by the bias adjusting variable resistor (the core is east (0 °) and west (180 °)).
The phase of the output in the case of ゜) is adjusted so that the output in both directions matches the zero value, so that even if the cross-sectional area of the magnetic path is slightly different, an output value corrected for this is obtained. That is, the output sine wave can be normalized.

When the rectified current obtained by the secondary coil is negatively fed back to the magnetic core by the feedback coil, the influence of harmonic components is removed, the output from the secondary coil is stabilized, and the input magnetic field changes rapidly. Hysteresis error in the case is also reduced. As a result, the DC magnetic field can be detected with high accuracy despite the simple configuration as described above.

(F) Embodiment (First Embodiment) FIG. 1 shows a first embodiment of the present invention. The magnetic core 10 made of a rectangular thin plate is made of saturable ferrite, and can be excited by a primary coil 12 wound around the core. Primary coil 12
Is connected to an AC power supply 14. The oscillation frequency of the AC power supply 14 is 2 to 4 MHz. Core 10 is 0.5mm thick and 15mm long
And a width of 5 mm.
A hole 16 of mm is provided. This hole 16 forms narrow magnetic paths 18 and 20 on both sides thereof. The smallest cross-sectional area of the magnetic paths 18 and 20 is 0.5 × 0.5 mm ² . 2 in magnetic path 18
A secondary coil 22 is wound, and a secondary coil 24
Is wound. The secondary coils 22 and 24 have the same winding direction and the same number of turns. The wires 25 and 27 on the left side of the secondary coils 22 and 24 in FIG. 1 are both grounded. Secondary coil 22
A rectifier 32 is provided on a line 30 taken out from the right end side in FIG. 1, while a rectifier 32 is provided on a line 34 on the secondary coil 24 side.
36 are provided. Output resistors terminated at lines 30 and 34
38 are connected to both ends. The rectifier 32 and the rectifier 36, when a current flows in these possible directions,
The secondary coils 22 and 24 are arranged so that magnetic fields in opposite directions are generated (so that a magnetic flux that rotates in one direction in the circumferential direction of the hole 16 is formed). The output resistor 38 is provided with a base line adjustment slider 40 that can be swiveled about the midpoint. The base line adjustment slider 40 is connected to the output terminal 42. A variable resistor 44 for bias adjustment is connected between the line 30 and the line 34 so as to be in parallel with the resistor 38. The lines 30 and 34 are grounded via capacitors 46 and 48, respectively.

Next, the operation of this embodiment will be described. AC power supply 14
When a high-frequency AC current is caused to flow through the primary coil 12, an alternating magnetic flux equal to the magnetic paths 18 and 20 is generated. As a result, an alternating electromotive force is induced in the secondary coils 22 and 24, and a current flows through the lines 30 and 34. Line 30 and
Since 34 has rectifiers 32 and 36 respectively,
The flowing current is rectified in one direction. In this case, since the secondary coil 22 and 24 has a magnetic path 18 and 20 as a magnetic core each have a predetermined inductance L ₁ and L _2. Since the magnetic paths 18 and 20 have saturable magnetism,
The inductance of the secondary coils 22 and 24 is variable depending on the saturation state. If the inductance of the magnetic paths 18 and 20 in the saturation region is generally expressed as L, and the DC magnetic field in the axial direction of the magnetic paths 18 and 20 is generally expressed as H, the relationship between the DC magnetic field H and the inductance L is saturable. As shown in FIG. Since the rectifier 32 and 36 as described above are arranged to produce a magnetic field opposite to the magnetic path 18 and 20, the magnetic path 18 and the presence reverse DC bias magnetic field h ₁ and h ₂ are mutually the 20 Will do. Therefore, the characteristics of the inductance L ₁ and L ₂ of the secondary coil 22 and 24, indicating to the DC magnetic field H to the horizontal axis, so that the third view. h ₁ and h ₂ are the magnetic paths 18 and
When the 20 features are equal, h ₁ = h ₂ , and the maximum values L ₁₀ and L ₂₀ of the inductances L ₁ and L ₂ are L ₁₀ = L ₂₀ . In this state, when the magnetic actuation field F is externally in the axial direction of the magnetic core 10, the magnetic field F is added to the magnetic field H _1, depending on the direction of the external magnetic field F for example magnetic path 18 side acting, whereas the magnetic path 20 the magnetic field of H ₂ side field F is subtracted. Thus for the inductance L ₁ side, whereas H ₁ = h ₁ + F, with respect to the inductance L ₂ side and H ₂ = h ₂ -F. Here, when L ₁ −L ₂ = ΔL, the relationship between ΔL and F is shown as shown in FIG. That is, the inductance difference ΔL changes according to the magnitude of the magnetic field F. Since current flows through the lines 30 and 34 according to the difference ΔL between the two inductances, a voltage signal corresponding to the magnetic field F is output to the output terminal 42. When h ₁ = h ₂ and L ₁₀ = L ₂₀ , the baseline adjustment slider 40 may be set at the middle point of the output resistor 38. The capacitors 46 and 48 have a function of bypassing the AC component of the secondary current flowing through the lines 30 and 34 and outputting only the DC component to the output terminal 42.

When the magnetic field F is the earth's magnetic field, the output voltage obtained at the output terminal 42 becomes the maximum value of positive and negative when the magnetic core 10 faces north and south, and becomes 0 when the magnetic core 10 faces east and west. A sine waveform as shown in FIG. Therefore, if a pair of magnetic cores 10 having the configuration shown in FIG. 1 are arranged orthogonally to each other, one output voltage becomes a sine wave and the other output voltage becomes a cosine wave. Therefore, taking the ratio of both, sin θ / cos θ = tan θ, and the azimuth angle θ can be obtained.

The above description is for the case of h ₁ = h ₂ and L ₁₀ = L ₂₀ as described above. However, in actuality, the asymmetry of the inductances L ₁ and L ₂ due to the manufacturing error of the magnetic core 10 and the like Occurs.
That is, the magnetic path 18 and the magnetic path 20 formed by providing the hole 16 have a minimum cross-sectional area of 0.5 × 0.5 mm ² in design as described above. Since the above error always occurs, a deviation occurs in the cross-sectional area of the magnetic paths 18 and 20. Therefore, as shown in FIG. 6 L ₁₀ and L ₂₀
Deviation occurs. As a result, the characteristic of the inductance difference ΔL with respect to the magnetic field becomes asymmetric as shown in FIG. 7, and the output diagram does not have a correct sine waveform as shown in FIG. In the present embodiment, the asymmetry is corrected by the variable resistor 44 for bias adjustment and the slider 40 for baseline adjustment. That is, during the assembling process of the apparatus shown in FIG. 1, with the longitudinal axis of the magnetic core 10 facing south and north, the base line is set so that the positive and negative output voltages of the output terminal 42 in both cases are equal. The base line position is adjusted by the adjustment slider 40. Next, with the axis of the magnetic core 10 facing east and west, the phase is adjusted by the bias adjusting variable resistor 44 so that the output voltage in both cases becomes zero. By repeating the above adjustment operation, the output voltage at the north position (90 ° position) and the maximum value at the south position (270 ° position) coincide with each other, and the output at the west position (0 ° position) and the east position (180 ° position). Accurate determination of the zero value of the voltage and the orthogonality between the east-west direction and the north-south direction, that is, sine wave normalization adjustment is possible. Thus, by combining the two normalized DC magnetic field detecting devices, a compass with an azimuth accuracy of ± 1 ° can be obtained.

(Second Embodiment) FIG. 9 shows a second embodiment. In the second embodiment, feedback coils 26 and 28 are added to the configuration of the above-described first embodiment, and the other configuration is the same as that of the first embodiment. That is, wires 25 and 27 from the secondary coils 22 and 24 are wound around the magnetic core 10 as feedback coils 26 and 28, respectively.

Next, the operation of the feedback coils 26 and 28 will be described. When an alternating current flows through the primary coil 12, the magnetic core
An alternating magnetic field acts on 10, and a rectified current flows through the secondary coils 22 and 24, which also flows through the feedback coils 26 and 28. The magnetomotive force generated by the feedback coils 26 and 28 is opposite to the magnetomotive force of the secondary coils 22 and 24, thereby giving a negative feedback action to the secondary coils 22 and 24. The rectified current flowing through the secondary coils 22 and 24 includes a DC component and an AC component including harmonics. The DC component is directly involved in determining the bias position, while the AC component has nothing to do with the bias position determination, but rather acts to prevent normal bias operation. In particular, the harmonics cause the output to be unstable as noise. Both the direct current component and the alternating current component provide a negative feedback action to the secondary coils 22 and 24 through the feedback coils 26 and 28. In this case, the direct current component has a reduced output magnitude as predetermined and the accuracy is increased accordingly. . Also,
The size of the AC component is also reduced, and the output stability is increased accordingly. In particular, harmonics are likely to occur greatly when the output of the high-frequency power supply fluctuates, but the reduction due to the feedback has a remarkable effect on stabilization of the output when the power supply fluctuates. Note that both the DC component and the AC component pass through the feedback coils 26 and 28, thereby transmitting the magnetomotive force to the secondary coils 22 and 24. However, there is a difference in the transmission efficiency between the two. That is, the AC component decreases rapidly with an increase in the feedback coefficient, but the DC component decreases only slightly. For example, if the number of turns of the feedback coils 26 and 28 is 25 turns, the DC component is 70%
However, the AC component attenuates to 7% or less. As described above, since the attenuation of the DC component is small, a decrease in gain is prevented. Also, the hysteresis error of the magnetic core 10 is reduced by this feedback.

(G) Effect of the Invention As described above, according to the present invention, a variable resistor for bias adjustment and an output resistor with a slider for baseline adjustment are provided in parallel with the line connected to the secondary coil, Since the output voltage is taken out from the adjustment slider,
Even when the magnetic path around which the secondary coil is wound has asymmetry, the output signal can be normalized by correcting this asymmetry, thereby improving the accuracy of magnetic field measurement. Further, when the feedback coil connected to the secondary coil is provided on the outer periphery of the magnetic core, the influence of the harmonic noise included in the high-frequency power supply output is removed from the rectifier circuit, the output stability at the time of power supply fluctuation is improved, and Hysteresis at the time of a rapid change of the input is reduced, and highly accurate magnetic field measurement becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention, FIG. 2 is a diagram showing a general relationship between a magnetic field and an inductance, and FIG. 3 is a relationship between a magnetic field and an inductance in an embodiment of the present invention. FIG. 4 is a diagram showing the relationship between the measured symmetric magnetic field and the difference in inductance, FIG. 5 is a diagram showing the characteristics of the output voltage corresponding to the earth magnetic field, and FIG. 6 is a diagram showing the case where the magnetic path is asymmetric. FIG. 7 shows the relationship between the magnetic field and the inductance, FIG. 7 shows the relationship between the asymmetric magnetic field obtained in the state shown in FIG. 6 and the difference in inductance, and FIG. 8 shows the relationship in the state shown in FIG. FIG. 9 is a diagram showing characteristics of the output voltage with respect to the obtained earth magnetic field, and FIG. 9 is a diagram showing the second embodiment. 10 ... magnetic core, 12 ... primary coil, 14 ... AC power supply, 16 ...
... Hole, 18 ... Magnetic path, 20 ... Magnetic path, 22 ... Secondary coil, 24
…… Secondary coil, 26 …… Feedback coil, 28 ……
Feedback coil, 30… wire, 32… Rectifier, 34…
... Wire, 36 ... Rectifier, 38 ... Output resistor, 40 ... Base line adjustment slider, 42 ... Output terminal, 44 ... Bias adjustment variable resistor, 46 ... Capacitor, 48 ... Capacitor.

Claims (2)

(57) [Claims] The present invention has a primary coil connected to an AC power supply and a magnetic core excited by the primary coil, and the magnetic core has two narrow core axial directions separated from each other by holes perpendicular to the axis. A saturated magnetic path is provided, a secondary coil is wound around each of the magnetic paths, and a wire drawn from one end of each of the secondary coils is grounded, and the opposite ends of the secondary coils are connected to each other. Are connected to both ends of a variable resistor for bias adjustment and an output resistor via a rectifier, and both rectifiers are connected in such a direction as to generate magnetic fields in opposite directions in each magnetic path when current flows through them. Has been
A DC magnetic field detecting device in which a base adjustment slider whose contact position is variable around the midpoint of the output resistor is provided, and the base adjustment slider is connected to an output terminal. 2. The DC magnetic field detecting device according to claim 1, wherein a wire taken out from said one end of each of said secondary coils is wound around a magnetic core.