JPH0361152B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention provides a fluxgate magnetic detector, particularly two
The present invention relates to a method of constructing a compact and highly accurate magnetic field vector detector having an axis detection system. Generally, as a method of detecting a weak magnetic field, a high permeability magnetic core with rectangular hysteresis characteristics is excited with alternating current until it reaches saturation, and a second harmonic component of the excitation frequency proportional to the applied external magnetic field component during magnetic flux change is generated. A so-called flux gate method is used to extract the FIG. 1 is a diagram showing the operating principle of this fluxgate type magnetic detector. Figure 1-1 is a system diagram showing the configuration of a fluxgate magnetic detector. In the figure, 1 indicates a ring-shaped magnetic core with high magnetic permeability, and 3
The excitation coil is uniformly wound. (The figure shows only a part of it.) Reference numeral 4 denotes a driver for alternating current excitation of the magnetic core 1, which generates an excitation field H _Dr alternately in the ○→←● direction as shown in the figure. In the figure, reference numerals 2 and 2' indicate detection coils for detecting changes in magnetic flux in the magnetic core, and in this figure, the coils are wound so as to interlink with the magnetic flux in portions A and B of the magnetic core. Now, external magnetic field
When H _S does not exist, the magnetic cores A and B portions draw B-H curves in opposite directions with respect to the detection coils 2 and 2', and are symmetrical with respect to the excitation field. The curve shown by the thin solid line in FIG. 1-2 (the horizontal axis is the excitation field H _and the vertical axis is the magnetic flux B) shows this situation. Externally applied magnetic field
When H _S exists at an angle θ with respect to the central axis of the detection coil as shown in the figure, the B-H curve in FIGS. 1-2 is biased as shown by the broken line and becomes an asymmetrical curve. The thick solid line in FIG. 1-2 is an example of the state of magnetic flux change at this time for explanation, and FIG.
corresponds to the conditions in the table below.

[Table] The magnetic core sections A and B continuously repeat the states of ~ according to the temporal change of the excitation field. In the above table, when both magnetic cores are saturated, there is no change in magnetic flux, so no voltage is induced in the detection coil, and both magnetic cores are in a non-saturated state, and the amount of change in magnetic flux is equal and in opposite directions. Therefore, the induced voltage is canceled out in the detection coil. One of the magnetic cores is in a saturated state and the other is in a non-saturated state, and a signal is induced in the detection coil that is proportional to the external magnetic field and has a frequency component twice the excitation field. Note that if there is no external magnetic field Hs, the state does not exist. Reference numerals 5 and 5' in FIG. 1-1 indicate band-pass filters for extracting a double frequency component proportional to an externally applied magnetic field. The center frequency of the bandpass filter is set to ₂₀ , where _f0 is the excitation frequency. 7 and 7' in Figure 1-1 indicate phase detectors,
Detecting the phase of the output of the bandpass filters 5 and 5',
Convert to DC Hs ^E. 8 in Figure 1-1 is the frequency
2 ₀ oscillator, converted to ₀ frequency by 6 frequency divider, driver 4, phase detector 7, 7' respectively.
supply to. Note that the output of the detector is expressed as follows. E(f)=K ₁ N [S _A dB _A (f)dt −S _B dB _B (f)/dt] ...(1) N: Winding B _A (f), B _B (f ): Magnetic flux density S _A , S _B of core A, B: Cross-sectional area K ₁ : amplitude constant Various solutions are given depending on the difference, but the solution when the driving magnetic field is assumed to be a triangular wave that increases and decreases with time is shown below. E(f)=K ₂ N・S ₀ μd/(1+kμd) Hs……
(2) N: Number of turns of detection coil ₀ : Excitation frequency S: Cross-sectional area, when S _A = S _B μd: Differential magnetic permeability μd = dB: dH K: Demagnetization constant H _S : Applied external magnetic field The above is the flux This is the operating principle of a magnetic detector known as a gate type, and various structures have been put into practical use. In particular, if the magnetic core is ring-shaped (or rectangular), two orthogonal
It is also possible to install two main detection coils 2, 2', each detecting a component of the applied external magnetic field perpendicular to the coil axis, as seen above. That is, a two-dimensional magnetic field vector detector can be easily constructed, and the characteristics of the detection system can also be constructed to have an orthogonal coordinate system. The present invention provides a highly accurate and economical magnetic detector in which the detector forms an orthogonal coordinate system with respect to an externally applied magnetic field. Although arranging the axes of the detection system perpendicular to each other is the most common and simple method, it has the following drawbacks. Even if the detection coil axes are geometrically orthogonal, the electrical detection system does not become orthogonal. The explanation will be given according to FIG. Broken lines 20 and 22 in the figure indicate detection coils, respectively, and have x and y axes whose central axes are perpendicular to each other. 21 and 23 are the number of turns N
indicates the central axis of the y, x detection coil, and has error angles Δθyi and Δθxi with respect to the orthogonal axes y, x. This can be easily understood from the fact that the detection coil is wound with a large number of wires in order to increase the detection sensitivity, and therefore, the wires are wound with a width relative to the central axis. Furthermore, the smaller the detector is, the greater the problem of this error angle becomes. From equation (2), the outputs Vsx and Vsy of the detectors x and y are as follows, respectively. Vsx=K ₂ S・₀ μd/(1+kμ ₀ ) _N 〓 ⁱ⁼¹ cosθxiHscosθ ……(3) Hscosθ=Hsx _N 〓 ⁱ⁼¹ cosθxi=Ncosδx then =K ₂ S・₀ , μd.N/( 1+kμ ₀ ) Hsx・cosδx…
…(3)′ Similarly, if we set Hssinθ=Hsθ _N 〓 ⁱ⁼¹ cosθyi=Ncosδθ, then Vsy=K ₂ S・₀・μd/(1+k ₀ μ ₀ ) _N 〓 〓 ⁱ⁼¹ cosθyi・Hssinθ=K ₂ S・₀・μd・N/(1+kμ
₀ ) Hsx・cosδx...(4) That is, it has error angles δx and δy. Therefore, the detection system constitutes an oblique coordinate system. If there is a slight non-uniformity in the magnetic properties of the magnetic cores in opposing parts of the detection coil and a slight intersection of the cross-sectional areas, the output due to the magnetic flux change of the excitation field, which is much stronger than the externally applied magnetic field, will be canceled out by the detection coil. Instead, its second harmonic component is output. That is, there is an offset component that produces an output even in the absence of an externally applied magnetic field. As described above, FIG. 3 shows how the characteristics of a magnetic detector having axes geometrically orthogonal to the detection coil axis form an eccentric oblique system. In the figure, x and y are orthogonal coordinate axes passing through the geometric center O of the magnetic detector, hx and hy are the axial components of the magnetic field vector Hs, and x' and y' are the offset component Ho.
It shows an oblique coordinate system that is eccentric due to the existence of (x, y-axis direction components hox, hoy), and has respective axial direction components hy', hx' of the magnetic field vector Hs. The error angles for the orthogonal system are δx and δy, respectively. It is expressed as hx=Hscosθ, hy=Hssinθ, and the azimuth angle θ is obtained as θ=tan ⁻¹ hx′/hy′. However, for such a detector, hx′=Hscos(θ−δx)−hox hy′=Hssin(θ
+δy)−hoy, and the azimuth θ′ is θ′=tan ^-1 Hssin(θ−δx)−hox/Hssin(θ+δy
)−hoy becomes cosδx, cosδy1, sinδx, sinδyδx, δy
Then, the azimuth error θ−θ′ θ−θ′=tan ^-1 Hscosθ／Hssinθ −tan ^-1 Hscosθ−δxsinθ−hox／Hssinθ＋δycos
θ−hoy. The above-mentioned drawbacks become more pronounced as the magnetic detector becomes smaller. In other words, there are problems with the geometric accuracy of the detection coil, the winding width and diameter of the coil,
The non-uniformity of magnetic properties occurring at the winding start and winding end of a high magnetic permeability annular wound iron core, which is commonly used as a ring core magnetic core, cannot be ignored, and it becomes difficult to construct a detector with orthogonality. In the present invention, the detection coil is configured with a main winding of the detection coil that surrounds the magnetic core, and an auxiliary winding that is magnetically linked to both sides or one side of the main winding,
It is characterized by determining the turn ratio of the main winding and the auxiliary winding so that the directivity of each detection coil is orthogonal. This will be explained below with reference to the attached drawings. FIG. 4 shows an embodiment of the present invention. In the figure, x and y are an orthogonal coordinate system passing through the geometric center of the magnetic detector, and may or may not coincide with the geometric center of the sensing coil. 42 and 43 are the main windings of the detection coil, respectively, and the directivity axes 44 and 45 are x, respectively.
It has error angles δx and δy with respect to the y-axis. 47,
Reference numeral 46 indicates an auxiliary winding of the main winding 43, and the basic axis 48 of the directivity has an angle of θsy with respect to the y-axis.
The auxiliary windings 46 and 47 are wound differentially with respect to the driving magnetic field, and their relationship to the winding direction of the main winding is determined by the relationship between δy and θsy, and may be in the same or opposite direction. Note that the excitation winding is omitted in this figure. Further, the offset of the second harmonic component of the excitation field caused by non-uniform magnetic properties of the magnetic core and variations in cross-sectional area can be canceled by the auxiliary winding as follows. That is, from equation (1), the above non-uniform components are expressed as follows. _{ΔVox ＝ K 1 (} N _AX S _AX −N _{BX S BX ) dΔB} ΔVox, ΔVoy are 42, 43, 50 and 51, 4
6,47 offset voltages, S _AX , S _BX , S _Ay , S _By
represent the cross-sectional area of the opposing portions of the detection coil, and ΔBx and ΔBy represent the difference in magnetic properties between the opposing portions. N _AX , N _BX , N _Ay , N _By are the combined number of turns of the main winding and auxiliary winding, and N _AX =
N _X +m _1X N _BX =N _X +m _2X N _Ay =N _y +m _1y N _By =N _y
It is expressed as +m _2y . (N _x : number of turns 42, N _y : 4
3 turns, m _1X : 50 turns, m _2X : 51 turns,
m _1y : Number of turns of 46, m _2y : Number of turns of 47) Set the number of turns so that N _AX S _AX = N _BX S _BX , N _Ay S _Ay = N _By S _By using equations (7) and (8). In this case, the offset is zero, that is, the output is zero when there is no external magnetic field. The difference in the number of turns between m _1X and m _2X is Δmx = m _1X − _{m 2X} , and the difference between m _1y and m _2y is Δm _y =
If m _{1y −m 2y} , then S _AX ／ _{S B} = N _X ＋m _{2X ／ N X} ＋ _{m 1X} = N _X ＋ _{m 1X −Δm} (K _3X −1) (N _X +m _1X ) Similarly, Δm _y =
(K _3y −1)(N _y +m _1y ). That is, the offset can be removed by providing a difference Δm _x and _Δmy in the number of turns of the auxiliary winding. Reference numerals 50 and 51 denote auxiliary windings of the main winding 42, and the basic axis 49 of the directivity has an angle θsx with respect to the x-axis.
The relationship with the winding direction of the main winding 42 is determined by the relationship between δa and δsx. In addition, 42, 51, 50 and 43,
46 and 47 respectively constitute the same detection coil, the main winding being wound so as to wrap around the magnetic core, and the auxiliary windings being wound so as to interlink with the magnetic core. If the output of the detector is expressed as equation (2), then 42,5
The output Vsx of 0,51 is obtained from (3): Vsx=K ₂ S ₀ μd/(1+kμ ₀ ) _N 〓 ⁱ⁼¹ Hscos (θ−θi) + _n 〓 ^j=1 Hscos (θ−θj) K ₂ S ₀ μd/(1+kμ ₀ )(N+m _X )cos
θ−(Nδx+m _X θsx) sinθ……(5) N: Number of turns of main winding 42, _m
If the number of turns is 51, and θ is the azimuth angle of the magnetic field Hs, _mX = -Nδx/θsx, then the error term can be eliminated and the basic axis of directivity coincides with the x-axis. As for the difference direction of the auxiliary winding, if δx and θsx have the same sign, it is sufficient to wind them m times in opposite directions or in the same direction with different signs. Similarly, the output θsy of 43, 47, and 46 is VsyK ₂ S ₀ μd/(1+kμ ₀ )(N+m _y sin
θ−(Nδy+ _my θsy) cosθ……(6) N: Number of turns of main winding 43, m _y : Auxiliary winding 46,
If the number of turns m _y =−Nδy/θsy of 47 is set, the error term is canceled and the directivity coincides with the y-axis. As described above, a detection system whose directivity is orthogonal to each other is constructed by the auxiliary winding. FIG. 5 shows an example of the winding in the case of FIG. Reference numeral 53 indicates a ring core magnetic core, and the excitation winding is omitted. The main winding 54 and auxiliary windings 56 and 57 constitute a y-side detection coil 51, and the main winding 58 and auxiliary windings 60 and 61 constitute an x-side detection coil 52. As stated above, the number of turns and winding direction of the auxiliary winding are determined by the error angle and offset. FIG. 6 shows an embodiment in which the auxiliary winding is divided into both ends of the main winding. In the figure, the main winding 63 and auxiliary windings 67, 69, 70, 72 constitute a y-side detection coil, and the main winding 65 and auxiliary windings 73, 75, 77,
78 constitutes an x-side detection coil. This figure shows an example in which the basic axes of the main windings are obliquely crossed, and the basic axes 63 and 66 of the directivity are δx and 66, respectively, with respect to the orthogonal coordinate axes.
It shows that δy is tilted. As understood from the above description, it is not necessary for the main windings to be geometrically orthogonal, and it is clear that the orthogonality correction and offset correction can be performed by dividing the auxiliary windings into left and right sides using the same principle. FIG. 7 shows the winding side of the configuration shown in FIG. 6, where 80 indicates the magnetic core and the excitation winding is omitted. In the figure, a main winding 81 and auxiliary windings 82, 83, 84, 85 constitute a y-side detection coil, a main winding 86, an auxiliary winding 87,
88, 89, and 90 constitute an x-side detection coil. The number of turns and the winding direction of the auxiliary winding are determined by the offset of the angle of the base axis of the auxiliary coil and the angle of the directivity base axis of the main coil (with respect to the orthogonal coordinate axis). As described above, according to the present invention, a detector having the same directivity axis as the orthogonal reference coordinate system passing through the geometric center of the magnetic detector can be configured with an extremely simple configuration. Furthermore, orthogonality of the detection coil and its accuracy are not required. Furthermore, it is possible to construct a highly accurate magnetic detector without requiring a high degree of uniformity of the magnetic core.Although we have not mentioned the sensitivity coefficient (swing constant) of the detection coil until now, the detection coil Matching the amplitude constants of the coils is shown in Figure 1 1-1.
In the operating principle diagram, the x-side and y-side band filters,
This can be easily done by adjusting the amplification factors of the 5, 5' phase detectors 7, 7', and the directivity of the detection coil can be made into an orthonormal coordinate system by the above method. Additionally, the effects and implementation modes of the present invention are as follows. With this magnetic detector, if the position and angle of the auxiliary winding are determined, the number and direction of the auxiliary winding can be determined from the measured values at the stage when the main winding is installed. By configuring them with the same wire, you can easily create an auxiliary coil when processing the coil terminals. Geometric precision of the magnetic detector and uniformity of the magnetic core are not required, and a small magnetic detector can be constructed at low cost.

[Brief explanation of drawings]

FIG. 1 shows a diagram for explaining the operating principle of a fluxgate type magnetic detector having a ring core type magnetic core, and FIG. 1-1 is a configuration diagram thereof. In the figure, 1 is the ring core magnetic core, 2 is the X side main detection coil, and 2' is the Y
Side main detection coil, 3 is excitation winding, 4 is drive circuit,
5 is an X-side bandpass filter, 5' is a Y-side bandpass filter, 6 is a frequency divider, 7 is an X-side phase detector,
7' is a Y-side phase detector, and 8 is an oscillator.
In the figure, H _Dr is the AC excitation field, Hs is the externally applied magnetic field, and Hs ^E
indicates DC output. Figure 1-2 shows the B-H curves of the magnetic cores A and B in Figure 1-1. In the figure, the thin solid line is when no externally applied magnetic field exists, the broken line is when an external magnetic field is present, and the thick solid line is the change in magnetic flux. Indicates the condition.
FIG. 1-3 shows a characteristic diagram in which the thick solid line portion of FIG. 1-2 is extracted. Figure 2 shows an example of a magnetic detector in which the geometrical axes of the detection coils are orthogonal;
Reference numeral 2 indicates the main detection coil, and 21 and 23 indicate the central axes of the respective coils, which are shown to be inclined at Δθyi and Δθxi with respect to the geometric orthogonal coordinates x and y of the coils. In the diagram
Hsx and Hsy are the x and y direction component forces of the applied magnetic field Hs. FIG. 3 shows the relationship between the geometric orthogonal axes x, y and the directivity base axes x', y' of the magnetic detector shown in FIG. FIG. 4 is a block diagram showing an embodiment of the present invention, 42, 4 in the figure.
3 is the main winding of the detection coil, 46, 47, 50, 5
1 indicates the auxiliary winding, 45 and 44 indicate the main winding directivity base axes, and 48 and 49 indicate the directivity base axes of the auxiliary windings.
It has a slope of θsy. FIG. 5 shows another embodiment of the configuration shown in FIG. FIGS. 6 and 7 show still other embodiments of the present invention.

Claims (1)

[Claims] 1. In a fluxgate type magnetic field vector detector having a ring-shaped or square magnetic core with two main detection coils that detect magnetic fields in the orthogonal X and Y directions, each of the main detection coils is adjacent to one or both sides. and an auxiliary coil is provided, and the auxiliary coil is connected in series to each adjacent main detection coil, and the X-direction main detection coil and the Y-direction main detection coil have an electrical output proportional to the external magnetic field. The number of turns of the auxiliary coil is selected so that the auxiliary coil has the same sensitivity, and the main detection coil in the X direction and the main detection coil in the Y direction have an output proportional to an electrically corrected external magnetic field in the orthogonal axis direction. A magnetic field vector detector characterized in that the polarity of the auxiliary coil is selected and connected so that the auxiliary coil is connected.