JP2514338B2 - Current detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention detects a magnetism of the core which is changed by applying a detected DC current to a coil wound around a ferromagnetic core or an electric wire passing through the coil. The present invention relates to a current detector for detecting a direct current.

[Conventional technology]

FIG. 7 is a block diagram showing an example of a conventional current detector. In the figure, 31 is a ring-shaped ferromagnetic core, and a magnetic gap 32 is provided in a part of a magnetic path having a circumferential shape. In this magnetic gap 32, a magnetic sensing element such as a Hall element
33 is fixedly provided with resin or the like. A coil 35 through which a current to be detected flows is wound around the magnetic path of the ferromagnetic core 31. The magnetic field proportional to the measured current is the magnetic gap 32
An electric signal generated therein and proportional to the magnetic field is guided by the magnetic sensitive element 33 through the lead wire 34 to a signal processing circuit (not shown).

[Problems to be Solved by the Present Invention] In the current detector having the above structure, since the magnetic sensitive element 33 is placed in the magnetic gap 32 provided in the ferromagnetic core 31, the magnetic gap is reduced.
The length of 32 must be larger than the thickness of the magnetic sensing element 33. In the magnetic circuit shown in FIG. 8, the magnetic field Ho generated in the magnetic gap 32 is HoNI / lg, where N is the number of coil turns I, the measured current is lg, and the magnetic gap length is inversely proportional to the magnetic gap length.

When the current to be measured is small, it is necessary to increase the number of turns of the coil 35 or greatly amplify the signal from the magnetic sensitive element 33. Therefore, the impedance or shape of the coil becomes large, or the SN ratio deteriorates. Problems such as occur. In order to solve these problems and generate a large magnetic field with a small current, the length lg of the magnetic gap 32 must be reduced, and it is difficult to detect a small current with the conventional structure.

[Purpose of the present invention]

An object of the present invention is to provide a small-sized current detector which can generate a large magnetic field with a small current and can be converted into an electric signal by a magnetic sensing element.

[Means for solving problems]

The current detector according to the present invention detects the leakage magnetic flux from the magnetic gap by the magnetic sensitive element by reducing the length of the magnetic gap as much as possible in order to increase the magnetic field generated in the magnetic gap of the ferromagnetic core. Is. That is, in a current detector composed of a ferromagnetic core in which a magnetic gap is provided in a part of a magnetic path having a circular shape and a magnetic sensitive element, the magnetic sensitive element is placed near the outside of the magnetic gap of the ferromagnetic core. It is a current detector arranged. A magnetoresistive sensor including a magnetoresistive element can be used as the magnetic sensitive element, and a DC magnetic field different from the magnetic field generated by the measured current may be applied to the magnetic sensitive element.

〔Example〕

Next, embodiments according to the present invention will be described with reference to the drawings. 1 and 3 (a) are structural views of a current detector showing an embodiment of the present invention. In FIG. 1, a coil 4 in which a current to be measured flows is wound around a circumferential ferromagnetic core 1 having a magnetic gap 2. The magnetically sensitive portion of the magnetically sensitive element 3 including a Hall element or a magnetoresistive element is arranged so as to be located near the outside of the magnetic gap. FIG. 2 shows the magnetic field distribution near the upper end of the magnetic gap as a vector locus. The x-component magnetic field parallel to the width direction of the gap is strong near the center axis of the magnetic gap, and the y-component magnetic field perpendicular to this is strong distribution on the end face of the magnetic gap. A signal corresponding to the magnetic field component in each direction can be taken out by the magnetic sensing element.

FIG. 3 (a) shows the structure of another embodiment of the present invention when a magnetoresistive element is used as the magnetic sensing element. Two U-shaped strong cores 11, 11 'are combined, and one end of the matching portion is aligned with a spacer 12 made of a non-magnetic material to form a magnetic gap.
The other end penetrates through the hollow of the bobbin 14 around which the coil 13 is wound and is aligned. The two U-shaped ferromagnetic cores 11, 11 'are fixed by a core holder 16 made of resin or metal, and a leaf spring 24 is used for the case.
It is mechanically held at 22. The magnetoresistive element 15 is a leaf spring.
It is fixed to 17 and is pressed mechanically by the leaf spring 17 so that the magnetic sensitive part is located at the center of the magnetic gap on the upper end surface of the core. The alignment of the center of the magnetic sensitive portion of the magnetoresistive element 15 and the center of the magnetic gap is adjusted by an adjusting screw 23 embedded in the case 22. A signal from the magnetoresistive element 15 is connected from a terminal 19 via a lead wire 18 to a circuit mounting board 20 on which a signal processing circuit is mounted, and the signal is taken out through an input / output terminal 21.

The signal processing circuit is provided with an adjusting resistor 25 in order to suppress variations in the magnetic sensing element. After the adjustment screw 23 and the adjustment component 25 are adjusted, resin potting is performed to prevent displacement due to mechanical vibration or shock.

 An example of the signal processing circuit is shown in FIG.

The potential at the midpoint of the magnetoresistive element indicated by the dotted line is 1/2 Vcc when the measured current flowing through the coil 13 is zero, but the leakage flux from the magnetic gap increases as the measured current increases,
The midpoint potential of the magnetoresistive element changes accordingly. By amplifying the difference voltage between the midpoint potential and the reference voltage (1/2 Vcc), the output signal according to the measured current can be obtained.

The magnetoresistive element is a magnetic sensor that utilizes the phenomenon that the resistance value changes depending on the direction of the external magnetic field due to the anisotropic magnetoresistive effect of the ferromagnetic thin film, and the pattern length of the magnetoresistive element is perpendicular to the magnetic flux direction. When the resistance value becomes low. NiCo
A magnetoresistive element using an alloy has a saturation magnetic field of 50 to 1000e and a resistance change rate of 4.5 to 6%.

3 is a circuit diagram of the 3-terminal magnetoresistive element shown in FIG. Magnetoresistive element is the same resistor with magnetoresistive effect
R _A and R _B are arranged orthogonal to each other and connected in series. R
_When a voltage of Vcc is applied to both ends of _A and R _B, the midpoint potential shows a value of 1/2 Vcc when the applied magnetic field H is zero as shown in Fig. 3 (c). _{The A} resistance decreases and the midpoint potential Vo increases. The midpoint potential Vo becomes stable above the saturation magnetic field Hs.

Next, the operation of the current detector according to the present invention shown in FIG. 3 (a) will be described.

By passing a current to be measured to the coil 13 through the lead wire 19 to the external input terminal 21, the current to be measured was measured inside and outside the magnetic gap provided in the magnetic path of the circular ferromagnetic core 11 according to the current to be measured. A magnetic field is generated. The resistance of the pattern orthogonal to the upper surface direction of the ferromagnetic core of the magnetoresistive element 15 changes according to the leakage magnetic flux from the magnetic gap. This resistance change is taken out as a voltage signal from the terminal 19 and led through the lead wire 18 to the signal processing circuit including the circuit mounting board 20 of FIG. The signal amplified by the signal processing circuit can be taken out through the external input / output terminal 21.

FIG. 4 shows a characteristic diagram when the output from the magnetoresistive element is amplified and taken out by combining a ferromagnetic core with a magnetic coil of 300 turns and a magnetic gap of 100 μm in FIG. The output increases as the measured current flowing through the coil increases and reaches saturation at a measured current of 4 mA. The current flow direction was reversed, and the same results were obtained for currents of opposite polarity, which were symmetrical with respect to the I = 0mA axis.

FIG. 5 is a configuration diagram of another embodiment according to the present invention. The difference from the above-described embodiment is that the magnet 105 is fixed to the surface of the magnetic sensing element 103 facing the magnetic gap 102.
In addition to the magnetic field created by the current to be measured, a DC magnetic field is applied to 103. In the figure, the magnet 105 creates a DC magnetic field as a bias, but a coil can also create a magnetic field having the same function.

FIG. 6 is a diagram showing output voltage characteristics when a magnetoresistive element is used as the magnetic sensing element in the embodiment of FIG. The magnetic field applied to the magnetoresistive element is a combined magnetic field of the magnetic flux created by the magnet 105 and the leakage flux from the magnetic gap created by the measured current, and an output voltage corresponding to the polarity of the measured current is obtained.

〔The invention's effect〕

As is clear from the above description, according to the present invention, since a large magnetic field can be created with a small current, a small current to be measured can be faithfully detected. Moreover, the shape of the ferromagnetic core is small, and it is possible to provide a small and inexpensive current detector.

[Brief description of drawings]

In addition to FIG. 1, FIG. 3 (a) shows the structure of a current detector showing an embodiment of the present invention. FIG. 2 shows a magnetic field distribution diagram near the magnetic gap. 3 (b) is a signal processing circuit, FIG. 3 (c) is a characteristic diagram of the 3-terminal type magnetoresistive element shown in FIG. 3 (d), and FIG. 3 (d) is a 3-terminal type magnetoresistive element. Show. FIG. 4 shows a characteristic diagram of measured current vs. output voltage. FIG. 5 shows another embodiment of the present invention in which a magnet is fixed to the surface facing the magnetic gap, and FIG. 6 shows its characteristic diagram. FIG. 7 shows a conventional current detector, and FIG. 8 shows a diagram for explaining a magnetic field in a magnetic gap. In the figure, 1,11,31,101 is the ferromagnetic core, 2,32,102 is the magnetic gap 3,
33 and 103 are magnetic sensitive elements, and 105 is a magnet.

Claims (3)

(57) [Claims] 1. A current detector comprising a ferromagnetic core having a magnetic gap provided in a part of a magnetic path having a circular shape and a magnetic sensitive element, wherein the magnetic sensitive element is outside the magnetic gap of the ferromagnetic core. A current detector characterized by being arranged in the vicinity of. 2. The current detector according to claim 1, wherein a magnetoresistive sensor having a magnetoresistive element is used as the magnetic sensing element. 3. The current detector according to claim 1 or 2, wherein a DC magnetic field is applied to the magnetic sensing element in addition to the magnetic field generated by the current to be measured.