JPH01237477A - fiber optic sensor - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical fiber sensor that measures an alternating magnetic field or an alternating current using the Faraday effect.

[Conventional technology]

FIG. 3 is a system diagram showing the connection system of the optical path and electric path of a conventional optical fiber sensor disclosed in Japanese Patent Publication No. 45-35250, and FIG.
It is a characteristic curve diagram showing the relationship between the Verdet constant and temperature at a wavelength of 778 nm of light of 85Mn 0.15 Te. In Figure 3, (1) is a light source consisting of a light emitting diode that emits light with a predetermined emission spectrum, (2) is a polarizer that converts the light emitted by this light source into linearly polarized light, and (3) is a straight line from this polarizer. A Faraday element that rotates the polarization plane of polarized light in response to the strength of the magnetic field, (4) an analyzer that converts the rotation angle of linearly polarized light from this Faraday element into light intensity, and (5) from this analyzer. (6) is a bandpass filter that passes the alternating current component of the electrical signal from this light-receiving element; (7) is the light-receiving element (5) that converts the light into an electrical signal;
), which passes the DC component of the electrical signal from
(8) is a division circuit that divides the AC component of the electric signal that has passed through the bandpass transducer (6) by the DC component of the electric signal that has passed through the DC filter (7), and 00 is the polarizer (2
), a Faraday element (3), and an analyzer (4).
Q''4 is a second optical fiber that optically connects the analyzer (4) and the light receiving element (5).

A conventional optical fiber sensor is constructed as described above. For example, when measuring the current of a high-potential AC circuit, a magnetic field probe is placed near the conductor of the AC circuit in the air gap of a C-shaped iron core that the conductor passes through. (10 is placed to match the direction of the magnetic field of this air gap with the direction of the light passing through the Faraday element (3), and the light source (1), light receiving element (5), band p-wave generator (6), Place the device (7) and the divider circuit (8) at ground potential, and connect the light source (1) and the polarizer (2) of the magnetic field probe Q0.
between the analyzer (4) of the magnetic field probe 00 and the light receiving element (
5) between the first optical fibers αη of electrical insulation.
and a second optical fiber (2). light source(
The light with a predetermined emission spectrum emitted by 1) is propagated within the core while repeating total reflection at the boundary between the core and cladding of the first optical fiber (11), and passes through the polarizer (of the magnetic field probe a).
2). This light is converted into linearly polarized light by a polarizer (2), and then by a Faraday element (3), the plane of polarization of this linearly polarized light is rotated in accordance with the strength of the magnetic field. The rotation angle θ of this plane of polarization is determined by the distance H between the magnetic field strength H in which the Faraday element (3) is placed and the transmission distance H that linearly polarized light passes through the crystal.
It has something to do with VHL. The proportionality constant ■ is called the Verdet constant and indicates the magnitude of the Faraday effect specific to the Faraday element (3). When the linearly polarized light whose plane of polarization has been rotated by the Faraday element (3) enters the analyzer (4), it undergoes intensity modulation corresponding to the rotation angle. The linearly polarized light that has undergone intensity modulation exits the analyzer (4), propagates within the core of the second optical fiber (a), enters the light receiving element (5), and is converted into an electrical signal. By the way, the transmission loss of the first optical fiber αυ and the second optical fiber θ group changes due to bends in the wiring, so the intensity of the linearly polarized light incident on the light receiving element (5) also changes, causing an error in the measurement of the magnetic field. there is a possibility. Since the transmission loss due to the bending of the first optical fiber αυ and the second optical fiber @ is constant regardless of the presence or absence of a magnetic field in each measurement, the electric signal output from the light receiving element (5) corresponds to the magnetic field. When measurements are performed based on the ratio of the AC component to the DC component corresponding to the absence of a magnetic field, the first optical fiber (1
1) Errors due to bending of the second optical fiber can be eliminated. Therefore, the electrical signal output from the light receiving element (5) is separated into an AC component and a DC component by a band R wave unit (6) and a DC F wave unit (7), respectively, and input to a dividing circuit (8). A magnetic field signal corresponding to the ratio obtained by dividing the current by the DC component is detected, and the current in the AC circuit is measured based on this magnetic field signal.

[Problem to be solved by the invention]

For example, when measuring the current of an outdoor AC circuit, the conventional optical fiber sensor described above uses a magnetic field probe α.
Since the magnetic field probe 00 is installed near the AC circuit, the temperature of the magnetic field probe 00 may fluctuate from 120°C to +100°C due to the influence of temperature, solar radiation, heat generated by the conductor of the AC circuit, etc. However, the Verdet constant, which indicates the magnitude of the Faraday effect of the Faraday element (3) that constitutes the magnetic field probe 00, changes with temperature as shown in Figure 4, so the polarization plane of the linearly polarized light incident on the Faraday element (3) is the magnetic field. There was a problem to be solved in that the current in the AC circuit could not be accurately measured due to an error in the rotation angle corresponding to the strength of the current.

This invention was made to solve this problem, and a magnetic field probe (10 is the temperature,
The purpose of the present invention is to obtain an optical fiber sensor that can accurately measure the current in an AC circuit even if its temperature fluctuates due to the influence of sunlight, heat generation of conductors in the AC circuit, etc.

[Means to solve the problem]

The optical fiber sensor according to the present invention makes light of a predetermined wavelength emitted by a light source at ground potential pass through a first optical fiber and enter a magnetic field probe installed near a high potential AC circuit. The polarization plane of the linearly polarized light is changed to linearly polarized light by rotating it using the Faraday element of the magnetic field probe in response to the alternating magnetic field of the AC circuit, and the intensity modulation of the DC polarized light is performed using the analyzer of the magnetic field probe in accordance with the angle at which the polarization plane is rotated. This intensity-modulated linearly polarized light is incident on a light-receiving element at ground potential via a second optical fiber and converted into an electrical signal, and this electrical signal is divided into AC and DC components corresponding to the presence or absence of an alternating magnetic field. A temperature sensor that is located near a magnetic field probe and detects a temperature light signal corresponding to the temperature of the magnetic field probe in a device that measures an alternating magnetic field based on the ratio of an alternating current component and a direct current component, and the output of this temperature sensor. A third optical fiber transmits a temperature optical signal to be transmitted, and data stored in advance indicating the relationship between the Verdet constant specific to the Faraday element and temperature, and the relationship between the Verdet constant and the wavelength of light transmitted through the Faraday element, A temperature compensation circuit that detects a wavelength signal corresponding to the temperature electric signal based on the temperature electric signal obtained by photoelectrically converting the temperature light signal from the optical fiber, and emits light of a wavelength corresponding to the wavelength signal output from this temperature compensation circuit. It is equipped with a light source.

[Effect]

In this invention, a temperature sensor located near the magnetic field probe detects a temperature optical signal corresponding to the temperature of the magnetic field probe, transmits it to a temperature compensation circuit via a third optical fiber, and the temperature compensation circuit photoelectrically converts this temperature optical signal. A temperature electrical signal is generated based on the temperature electrical signal and data stored in advance in this temperature compensation circuit indicating the relationship between the Verdet constant unique to the Faraday element and temperature, and the relationship between the Verdet constant and the wavelength of light transmitted through the Faraday element. A wavelength signal corresponding to the wavelength signal is detected, and a light source emits light of a wavelength corresponding to this wavelength signal.

[Embodiments of the invention]

FIG. 1 is a system diagram showing the connection system of the optical path and the electric path in one embodiment of the present invention, and FIG.
FIG. 2 is a characteristic curve diagram showing the relationship between the Verdet constant and the wavelength of transmitted light at 20° C. for 85Mn 0.15'l'e. In FIG. 1, (2) to (8) and α0 to (6) are exactly the same as the conventional optical fiber sensor described above. Reference numeral (21) is a temperature sensor made of an optical semiconductor whose absorption edge wavelength changes with temperature, and is located near the magnetic field probe α0 and detects a temperature optical signal corresponding to the temperature. (
b) is a temperature compensation circuit which includes the Faraday element (3)
Data showing the relationship between the Verdet constant and temperature specific to , and the relationship between this Verdet constant and the wavelength of light transmitted through the Faraday element (3) are stored in advance, and this data and the temperature light from the temperature sensor ■υ are stored in advance. Based on the temperature electric signal obtained by photoelectrically converting the signal, a wavelength signal corresponding to this temperature electric signal is detected. A) is a light source that consists of a light emitting element with a wide emission spectrum and an optical filter that continuously changes the wavelength of transmitted light by rotating.This optical filter is activated by the wavelength signal from the temperature compensation circuit (a). It is rotated to emit light of a predetermined wavelength. 6◇ is a third optical fiber that optically connects the temperature sensor Q]) and the temperature compensation circuit (A).

In the optical fiber sensor configured as described above, for example, when measuring the current of a high-potential AC circuit, a magnetic field probe αQ is placed near the conductor of the AC circuit in the air gap of the C-shaped iron core that the conductor passes through. is placed so that the direction of the magnetic field in this gap matches the direction of the light passing through the Faraday element (3), and a temperature sensor (c) is installed near the magnetic field probe αQ. And temperature compensation circuit (a), light source (a)
, photodetector (5), band-pass transducer (6), DC transducer (7)
), the divider circuit (8) is placed at ground potential, and the magnetic field probe (1) is placed between the light source (2) and the polarizer (2) of the magnetic field probe α0.
0 analyzer (4) and light receiving element (5), temperature sensor Q
1) and the temperature compensation circuit (a) are optically connected by a first optical fiber a1), a second optical fiber @, and a third optical fiber eυ made of electrical insulators, respectively. Magnetic field probe α0
The temperature of the magnetic field probe αQ fluctuates due to the effects of air temperature, solar radiation, heat generated by the conductors of the AC circuit, etc., so the temperature sensor Q installed near the magnetic field probe H detects a temperature optical signal corresponding to the temperature of the magnetic field probe αQ. . This temperature light signal propagates through the third optical fiber 0υ and enters the temperature compensation circuit (a) where it is photoelectrically converted into a temperature electric signal. Temperature compensation circuit (a)
Now let's look at the relationship between the pre-stored Verdet constant specific to Faraday element (3) and temperature (see Figure 4) and the relationship between this Verdet constant and the wavelength of light transmitted through Faraday element (3) (
A wavelength signal corresponding to the temperature electrical signal is detected based on the temperature electrical signal and data indicating the temperature (see FIG. 2). The light source (c) rotates its optical filter based on this wavelength signal and emits predetermined light. This light is transmitted through the first optical fiber αυ
The electric signal propagates and enters the polarizer (2) of the magnetic field probe θQ, and finally the AC component of the electric signal corresponding to the strength of the magnetic field received by the Faraday element (3) is divided by the DC component in the divider circuit (8). A magnetic field signal corresponding to the ratio is detected, but the operation during this period is the same as that of the conventional optical fiber sensor described above, so a description thereof will be omitted. If the current of the AC circuit is measured based on the magnetic field signal detected by the divider circuit (8), accurate measurement can be performed without errors due to temperature fluctuations of the magnetic field probe 00.

Although the above embodiment describes the case where the current in an AC circuit is measured, it goes without saying that the intended purpose of the present invention can be achieved even when a magnetic field generated in an AC circuit is measured.

〔Effect of the invention〕

As explained above, this invention makes light of a predetermined wavelength emitted by a light source at ground potential pass through a first optical fiber and enter a magnetic field probe installed near a high potential AC circuit, and the polarizer of the magnetic field probe linearly polarizes the light. The Faraday element of the magnetic field probe rotates the polarization plane of the linearly polarized light in response to the alternating magnetic field of the AC circuit, and the analyzer of the magnetic field probe modulates the intensity of the linearly polarized light in response to the rotated angle of the polarization plane. The linearly polarized light that has undergone intensity modulation is incident on a light receiving element at ground potential via a second optical fiber, where it is converted into an electrical signal, and this electrical signal is separated into alternating current and direct current components, each corresponding to the presence or absence of an alternating magnetic field. In devices that measure alternating magnetic fields based on the ratio of AC and DC components, a temperature sensor located near the magnetic field probe detects a temperature optical signal corresponding to the temperature of the magnetic field probe, and the temperature is measured via a third optical fiber. Photoelectrically converts the temperature optical signal and data indicating the relationship between the Verdet constant specific to the Faraday element and temperature and the relationship between the Verdet constant and the wavelength of light transmitted through the Faraday element, which are transmitted to the compensation circuit and stored in advance in the temperature compensation circuit. A wavelength signal corresponding to the temperature electrical signal is detected based on the temperature electrical signal, and the light source emits light with a wavelength corresponding to this wavelength signal, eliminating errors due to temperature fluctuations of the magnetic field probe and accurately controlling the magnetic field. It has the effect of being measurable.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing the connection system of the optical path and the electric path in one embodiment of the present invention, and FIG.
A characteristic curve diagram showing the relationship between the Verdet constant of 85Mn 0.15 Te and the wavelength of transmitted light, Figure 3 is a system diagram showing the connection system of the optical path and electric path of a conventional optical fiber sensor, and Figure 4 is a diagram showing the connection system of the optical path and electric path of a conventional optical fiber sensor. Effective CdO,85MrI0,
FIG. 3 is a characteristic curve diagram showing the relationship between the Verdet constant and temperature of 15Te. In the figure, (2) is a polarizer, (3) is a Faraday element,
(4) is an analyzer, (5) is a light receiving element, (6) is a band F-wave device, (7) is a DC F-wave device, (8) is a divider circuit, θO is a magnetic field probe, and αυ is the first Optical fiber, (6) is the second optical fiber, 01) is the temperature sensor, (a) is the temperature compensation circuit, (d) is the light source, and 0◇ is the third optical fiber. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] Light of a predetermined wavelength emitted by a light source at ground potential is incident on a magnetic field probe installed near a high-potential AC circuit via a first optical fiber, and is converted into linearly polarized light by a polarizer of the magnetic field probe. The plane of polarization of the linearly polarized light is rotated by a Faraday element in accordance with the alternating magnetic field of the AC circuit, and the analyzer of the magnetic field probe performs intensity modulation of the linearly polarized light in accordance with the angle at which the plane of polarization is rotated. The intensity-modulated linearly polarized light is incident on a light-receiving element at ground potential through a second optical fiber, where it is converted into an electrical signal. a temperature sensor that is located near the magnetic field probe and detects a temperature light signal corresponding to the temperature of the magnetic field probe, in which the alternating magnetic field is measured based on the ratio of the alternating current component to the direct current component; , a third optical fiber that transmits the temperature optical signal output from the temperature sensor, a pre-stored relationship between the Verdet constant unique to the Faraday element and temperature, and a relationship between the Verdet constant and the wavelength of light transmitted through the Faraday element. and a temperature electrical signal obtained by photoelectrically converting the temperature optical signal from the third optical fiber, the temperature compensation circuit detects a wavelength signal corresponding to the temperature electrical signal; An optical fiber sensor comprising the above light source that emits light of a wavelength corresponding to a wavelength signal to be output.