JPH04286974A - Optical type magnetic field sensor - Google Patents

Abstract

PURPOSE:To enable a wide-range magnetic field to be measured by reducing the number of optical parts to be used as much as possible and performing assembly as one sensor without dividing light. CONSTITUTION:An optical type magnetic sensor measures a magnetic field by allowing light from a light source 1 to be passed from a polarizer 7 to a Faraday element 8 in sequence. The Faraday element 8 consists of a first Faraday element 8a consisting of a magnetic body which is placed on a same light path and a second Faraday element 8b consisting of a non-magnetic body.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical magnetic field sensor that optically measures a magnetic field using a Faraday element having a Faraday effect.

0002

2. Description of the Related Art Conventionally, the above-mentioned optical magnetic field sensor for measuring current, for example, has generally been constructed as shown in FIG.

That is, it mainly consists of a light source 1 that emits light such as a light emitting diode (LED), a sensor head 2, and an optical receiver 3. It is connected to the machine 3 through optical fibers 4a and 4b, respectively. One end of each of the optical fibers 4a, 4b is connected to the sensor head 2 via microlenses 6a, 6b attached to the case 5 of the sensor head 2. A polarizer 7, a Faraday element 8, an analyzer 9, and a reflecting mirror 10 are arranged on the same optical path along the direction. On the other hand, the optical receiver 3 is mainly composed of a light receiving element 11 and a detection electric circuit 12 that outputs an output according to the light that has entered the light receiving element 11.

[0004] As a result, the light emitted from the light source 1 is
The light is guided into the sensor head 2 by the optical fiber 4a, made into parallel light by the microlens 6a, bent by 90 degrees by the polarizer 7, and introduced into the Faraday element 8 as a linearly polarized light wave. In this Faraday element 8, the plane of polarization is rotated according to the external magnetic field H, and the rotated emitted light is changed into light intensity by an analyzer 9, and a reflection mirror 10
After being reflected by the microlens 6b and the optical fiber 4
The light is guided to the light receiving element 11 through the light receiving element 11, and the light intensity is measured and outputted by the electric circuit 12. As a result, the external magnetic field H
The size of can be measured.

When measuring current using the optical magnetic field sensor, the sensor head 2 is attached to the gap 14a of the iron core 14 installed around the electric wire 13, as shown in FIG. The current flowing through the electric wire 13 was measured from the magnitude of the external magnetic field H measured at this time.

[0006] Here, when the current measured by the above optical magnetic field sensor ranges from a small current to a large current such as several tens of kA, that is, from a low magnetic field to a high magnetic field, it is necessary to prepare two optical magnetic field sensors. was there. i.e. small current (low magnetic field)
In order to obtain a Faraday rotation angle that can be measured with , it is necessary to use a Faraday element made of a magnetic material with a large Verdet constant. Therefore, it is not possible to measure large currents. For this reason, a separate optical magnetic field sensor having a Faraday element made of a non-magnetic material with a small Verdet constant is required for measuring large currents (high magnetic fields).

[0007] For this reason, two sensor heads are arranged within the gap of the same core (for example, see Japanese Patent Laid-Open No. 1-75696), or a plurality of Faraday elements made of magnetic material are used (similarly, , Japanese Patent Publication No. 2-103
484 Publication), which can measure from low magnetic fields to high magnetic fields by dividing the light into two beams using a polarizer, introducing them into separate Faraday elements, and detecting them with separate light receiving elements (Similarly, Japanese Patent Application Laid-Open No. 60-375) and the like have been developed.

[0008]

[Problems to be Solved by the Invention] However, as described in the above-mentioned Japanese Patent Application Laid-Open No. 1-175696, when two sensor heads are arranged in the gap of the same iron core, if they are arranged in series, this cap becomes wide. If you try to arrange them in parallel, you will need to make the iron core wider. When the gap becomes wider in this way, it becomes more susceptible to the influence of external magnetic fields, and measurement accuracy deteriorates. Moreover, since two sensor heads are required, two sets of optical fibers and other optical components are required.

Furthermore, as described in Japanese Patent Application Laid-open No. 2-103484, when only a Faraday element made of a magnetic material is used, as mentioned above, the magnetic field exceeding the saturation magnetic field of the magnetic material,
That is, it is not possible to measure large currents.

Furthermore, as described in Japanese Patent Application Laid-Open No. 60-375, when splitting the light into two beams using a polarizer, two sets of analyzers and light-receiving optical fibers are required, and in order to incorporate them, There was a problem that the sensor head became quite complicated.

In view of the above, it is an object of the present invention to reduce the number of optical parts used as much as possible, and to provide a sensor that can be assembled into a single sensor without dividing the light, and can measure a wide range of magnetic fields. This is the purpose.

0012

[Means for Solving the Problems] In order to achieve the above object, an optical magnetic field sensor according to the present invention is an optical magnetic field sensor that measures a magnetic field by sequentially passing light from a light source through a polarizer and a Faraday element. In the magnetic field sensor, the Faraday element is composed of a first Faraday element made of a magnetic material and a second Faraday element made of a nonmagnetic material, which are arranged on the same optical path.

[0013]

[Operation] According to the present invention configured as described above, light passing through the polarizer passes through the first Faraday element made of a magnetic material and the second Faraday element made of a non-magnetic material. For low magnetic fields, the rotation angle of a Faraday element made of a non-magnetic material is small, but the rotation angle of a Faraday element made of a magnetic material with a large Verdet constant increases; , the rotation angle of the Faraday element made of magnetic material does not exceed a certain value, but the rotation angle of the Faraday element made of non-magnetic material advances,
As a result, although the output is not linear, it is possible to detect from a low magnetic field to a high magnetic field with one sensor.

[0014]

[Embodiment] An embodiment of the present invention will be explained below with reference to FIG.

In this embodiment, light emitted from a light source 1, such as a light emitting diode with a wavelength of 1.3 μm, is guided into the sensor head 2 by an optical fiber 4a, and is converted into parallel light by a microlens 6a. , is bent by 90 degrees by a polarizer (polarized beam splitter) and becomes a linearly polarized light wave, which is constructed by arranging a Faraday element 8a made of a magnetic material and a Faraday element 8b made of a non-magnetic material on the same optical path. It is introduced into the Faraday element 8. Within this Faraday element 8, the plane of polarization of each Faraday element 8a, 8b is rotated according to the external magnetic field H, and the rotated output light has a transmission polarization direction of 4 with respect to a linear polarization direction.
The light intensity is changed by an analyzer 9 installed at an angle of 5 degrees, and after being reflected by a reflection mirror 10, a microlens 6b
The light is guided through an optical fiber 4b to a light receiving element 11 made of a photodiode, and the light intensity is measured by an electric circuit 12 and output. This allows the magnitude of the external magnetic field H to be measured.

Here, as the Faraday element 8a made of the magnetic material, one in which a thin film of Y3 Fe5 O12 is formed with a thickness of 50 μm on a crystal substrate that is transparent at the operating wavelength where there is almost no Faraday effect is also used. The Faraday element 8b of the body is made of ZnSe and has a thickness of 1.7 m.
m are used respectively, and which Faraday element 8a
, 8b are also polished on both sides to be optically flat.

FIG. 2 shows the results of measuring the output from the electric circuit 12 with the sensor head 2 configured as described above placed in a magnetic field.

As a result, in a low magnetic field of 0 to about 2 kOe, the Faraday element 8a made of a magnetic material can provide a highly sensitive output based on the rotation angle, and in a high magnetic field of several tens of kOe, the Faraday element made of a non-magnetic material can produce a highly sensitive output. It can be seen that an output based on the rotation angle at 8b can be obtained.

This is because the light that has passed through the polarizer 7 passes through the Faraday element 8a made of a magnetic material and the Faraday element 8b made of a non-magnetic material in sequence.
For low magnetic fields, a Faraday element 8 made of non-magnetic material
Although the rotation angle b is small, the rotation angle of the Faraday element 8a made of a magnetic material with a large Verdet constant increases, and in response to a high magnetic field higher than the saturation magnetic field of this magnetic material, the Faraday element 8a made of a magnetic material This is because although the rotation angle does not exceed a certain value, the rotation angle of the Faraday element 8b made of a non-magnetic material advances, resulting in a curve that is bent near the saturation magnetic field of the magnetic material. Thereby, magnetic fields ranging from low magnetic fields to high magnetic fields can be detected with one sensor.

When measuring current using the optical magnetic field sensor, the sensor head 2 is attached to the gap 14a of the iron core 14 installed around the electric wire 13, as shown in FIG. The current flowing through the electric wire 13 is measured from the magnitude of the external magnetic field H measured at this time. It becomes possible to measure up to large currents.

In this embodiment, a thin film of Y3 Fe5 O13 is used for the Faraday element 8a made of a magnetic material, and ZnSe is used for the Faraday element 8b made of a non-magnetic material. Of course, the material is not limited, and by using a Faraday element made of a magnetic material with a large Verdet constant, it is also possible to detect a magnetic field as low as several tens of Oe.

Furthermore, the order in which the Faraday elements 8a and 8b are installed may be reversed, or the two Faraday elements 8a and 8b may be integrated with adhesive or the like. Furthermore, by a thin film forming method such as sputtering method on a non-magnetic Faraday element or other optical components,
It is also possible to form a thin film of Y3 Fe5 O13 or the like.

[0023]

[Effects of the Invention] Since the present invention has the above structure,
It has high detection sensitivity in low magnetic fields, and can also measure magnetic fields in high magnetic fields that would saturate magnetic materials.This allows a single sensor to measure magnetic fields over a wide range from low to high magnetic fields. can do.

Moreover, the number of optical parts can be reduced as much as possible, and the light can be assembled as a single sensor without splitting, which has the effect of making the structure relatively simple and inexpensive to manufacture. There is.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one embodiment of the present invention.

FIG. 2 is a graph showing the output of the embodiment shown in FIG. 1;

FIG. 3 is a schematic diagram showing current measurement conditions.

FIG. 4 is a schematic diagram showing a conventional example.

[Explanation of symbols]

1 Light source (light emitting diode) 2 Sensor head 3 Optical receivers 4a, 4b Optical fibers 6a, 6b Microlens 7 Polarizer 8 Faraday element 8a Faraday element 8b made of magnetic material Faraday element 9 made of non-magnetic material Analyzer

Claims (1)

[Claims] 1. An optical magnetic field sensor in which a magnetic field is measured by passing light from a light source sequentially through a polarizer and a Faraday element, wherein the Faraday element is a first magnetic field sensor made of a magnetic material disposed on the same optical path. An optical magnetic field sensor comprising: a Faraday element and a second Faraday element made of a non-magnetic material.