JP2996775B2 - Optical magnetic field sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field sensor for detecting a magnetic field strength by applying the Faraday effect.

[0002]

2. Description of the Related Art A magnetic field sensor of this type is disclosed in
The thing described in 9-159076 is known conventionally. 3 and 4 show the prior art disclosed in this publication. FIG. 3 shows a magnetic field sensor for measuring the magnetic field strength H itself, and FIG. 4 shows a current I flowing through a conductor. The present invention is applied to a current transformer in which the intensity H of a magnetic field formed by the above is measured and the current I is to be measured thereby.

In FIG. 3, light emitted from a light emitting section 1 composed of a light emitting diode or the like is guided to a condenser lens 3 via an optical fiber 3, and is converted into light close to parallel light by the condenser lens 3 to be polarized. The polarized light that is incident on the polarizer 4 and extracted by the polarizer 4 is incident on the magneto-optical element 5. The magneto-optical element 5 is formed of a material exhibiting a so-called Faraday effect depending on the intensity H of the placed magnetic field (in the direction of the arrow in the figure), for example, a lead glass or a magnetic film. Therefore, the polarization plane of the polarized light incident on one end face of the magneto-optical element 5 is rotated by θ in proportion to the magnetic field strength H and is emitted from the other end face. The emitted light is composed of a polarizing prism or a polarizing beam splitter, etc., and is incident on an analyzer 7 whose main axis is set at 45 ° with respect to the polarizer 4. Here, as shown in FIG. , Y components). From FIG. 5, each vector component is represented by the following equation. Ex = E · sin (45 ° + θ) (1) Ey = E · cos (45 ° + θ) (2)

These vector lights become light quantity signals Px and Py condensed by condensing lenses 8 and 9, respectively.
The light is guided to the light receiving elements 12 and 13 via the optical fibers 10 and 11. Here, since the light amount is the square of the magnitude of the vector, the light amount signals Px and Py are as follows. Px = Ex ² = E ² ・ Sin ² (45 ° + θ) = (E ² / 2) · (1 + sin2θ) (3) Py = Ey ² = E ² ・ Cos ² (45 ° + θ) = (E ² / 2) · (1-sin2θ) (4)

The light receiving elements 12 and 13 are formed of, for example, photodiodes, and receive light amount signals Px and Px.
This is a photoelectric converter that outputs a current signal proportional to y. Taking the case where the magnetic field is an alternating magnetic field as an example, this current signal is converted by the current-voltage conversion amplifiers 14 and 15 into the following equations (5) and (6).
Are converted into the voltage signals Vx and Vy shown in FIG. Note that K _{1 in} the equation is a constant. Vx = K ₁ (1 + sin 2θ) (5) Vy = K ₁ (1-sin 2θ) (6)

The voltage signal Vx is supplied to analog adders 16 and 17
And the voltage signal Vy is input to the + input terminal of the analog adder 16 and the − input terminal of the analog adder 17, respectively. The output of the analog adder 17 is input to a denominator input terminal of a divider 18. As a result, the signal V ₀ output from the divider 18 is represented by the following equation (7). V ₀ = (Vx−Vy) / (Vx + Vy) = sin2θ (7) In the expression (7), when θ is sufficiently small, the following expression (8) is obtained.
Holds. V ₀ = 2θ = K ₂ · H (8) (where K ₂ is a proportionality constant, and V ₀ = 2θ is an approximate value.) That is, as is apparent from the equation (8), the output to the divider 18 is obtained. The magnetic field strength H is detected by the signal V ₀ .

FIG. 4 shows an example in which the magnetic field sensor is applied to a current transformer as described above, and detects an alternating current I flowing through the conductor 6. In this example, a hole through which the conductor 6 penetrates is formed in the magneto-optical element 5, and the light emitted from the polarizer 4 passes through the optical path indicated by a dotted line in the magneto-optical element 5 and passes through the analyzer 7. It is led to. Otherwise, the configuration is the same as that of the magnetic field sensor shown in FIG.

Accordingly, the polarization plane of the polarized light transmitted through the magneto-optical element 5 is rotated in proportion to the intensity H of the magnetic field generated in proportion to the current I, and the output V _{0 of the} divider 18 becomes This is the same as (7), and the following expression (9) is obtained in a range where θ is sufficiently small, so that the current I flowing through the conductor 6 is detected. V ₀ = 2θ = K ₃ · H (9) (where K ₃ is a proportionality constant, and V ₀ = 2θ is an approximate value.)

[0009]

However, the conventional optical magnetic field sensor shown in FIGS. 3 and 4 has a drawback that linearity can be obtained only in a range where θ is sufficiently small as described above. . For example, the range of θ satisfying the accuracy of 1% is slightly within ± 7.0 °. Further, as known from the equations (3), (4) and (5) and (6), the ratio (modulation degree) of the signal component to be measured to the bias component included in the light quantity signal is only 24% when θ = 7 °. Absent. This means that when trying to measure a low magnetic field region, the signal / noise ratio is small and sufficient measurement accuracy cannot be obtained. As described above, the conventional optical magnetic field sensor has a disadvantage that it can measure only a magnetic field in a very narrow range. The present invention
The present invention has been proposed to solve the above-described problems of the related art, and has as its object to provide an optical magnetic field sensor having a wide measurement range.

[0010]

According to another aspect of the present invention, there is provided an optical magnetic field sensor having a Faraday effect in which a plane of polarization rotates in proportion to the strength of a measured magnetic field. An optical element, a polarizer disposed on the light source side of the magneto-optical element, and a detector configured to receive light transmitted through the magneto-optical element and to determine the direction of the main axis so as to form a specific angle with the main axis of the polarizer. A photon, a light receiving element that receives light transmitted through the analyzer and converts the light into an electric signal, and separates the electric signal output from the light receiving element into a component that changes according to a DC bias component and rotation of the polarization plane. Means, a divider that divides a component that changes according to the rotation of the polarization plane by the DC bias, an A / D converter that converts the divider output into a digital signal, and the A / D converter. The inverse Sin function value of the output value of the vessel Luo and a beforehand stored to keep the memory element, be sequentially read by outputting a value corresponding to the output value of the A / D converter from the storage element, characterized by.

[0011]

According to the optical magnetic field sensor of the present invention, the output of the divider can be obtained without receiving the characteristic fluctuation of the light emitting portion and the characteristic fluctuation of the optical fiber and the current-voltage conversion amplifier. The signal is converted into a digital signal by an A / D converter. Then, a previously stored inverse S corresponding to the output value from the A / D converter is stored from the storage element.
The in function value is read out at a high speed by one correspondence.

[0012]

【Example】

(1) First Embodiment Hereinafter, a first embodiment of the present invention will be specifically described with reference to FIG.

Reference numeral 1 denotes a light emitting unit including a light emitting element such as an LED and a driving circuit; 2, an optical fiber for guiding light from the light emitting unit;
Is a condensing lens for converting light emitted from the optical fiber 2 to be spread into substantially parallel rays, 4 is a polarizer for converting light from the condensing lens 3 into linearly polarized light, and 5 is a magnetic field to be measured acting thereon. A magneto-optical element 7 whose polarization plane rotates in proportion to the intensity of H is another analyzer arranged such that the direction of the main axis is at 45 ° with respect to the main axis of the polarizer.

Reference numeral 8 denotes a condenser lens, and reference numeral 10 denotes an optical fiber. Parallel rays emitted from the analyzer 7 are converged by the condenser lens 8 and enter the optical fiber 10. The other end of the optical fiber 10 is coupled to the light receiving element 12, and the light quantity signal having passed through the optical fiber 10 is converted into a current, and then the output of the current / voltage tube amplifier 14 is input to the signal processing circuit 19, and the output signal is output. V
_{Get 0} .

The configuration of the signal processing circuit 19 is as follows. That is, 20 is a high-pass filter, and 21 is a low-pass filter that divides an input signal into an AC signal component to be measured and a DC bias signal component. Reference numeral 18 denotes a divider connected so as to divide the output of the high-pass filter 20 by the output of the low-pass filter 21. 22 is A to be done later
High-frequency rejection filter as a preceding stage of / D conversion;
/ D converter. 24 is the so-called Read on
This is a storage element called a memory (ROM). This storage element 24 has a one-to-one correspondence with the input digital signal value (A).
The value of sin ^-1 (A) corresponding to is stored in advance,
This is read out and output at high speed according to the input value. Reference numeral 25 denotes a D / A converter for converting a digital output signal from the ROM into an analog signal. The operation of the magnetic field sensor thus configured will be described below.

The light from the light emitting section 1 reaches the collective lens 3 through the optical fiber 2, where it becomes substantially parallel rays. This light becomes linearly polarized light by the polarizer 4 and passes through the magneto-optical element 5. During this time, if the magnetic field H acts in the direction of the arrow shown in FIG. 1, the polarization plane rotates by θ in proportion to the strong field intensity. The light emitted from the magneto-optical element 5 passes through the analyzer 7. Since the main axis of the analyzer 7 is arranged so as to form an angle of 45 ° with the main axis of the polarizer 4, as can be seen from the light vector diagram shown in FIG. You. Ex = E · sin (45 ° + θ) (10)

The beam diameter of this light is reduced by the condenser lens 8, becomes a light amount signal Px, and is guided to the light receiving element 12 through the optical fiber 10. Since the light amount is the square of the magnitude of the vector, it is as follows. Px = Ex ² = E ² ・ Sin ² (45 ° + θ) = (E ² / 2) · (1 + sin2θ) (11)

The light receiving element 12 is a photoelectric converter which is formed of, for example, a photodiode and outputs a current signal proportional to the received light amount signal Px. Taking the case where the magnetic field is an alternating magnetic field as an example, this current signal is converted into a voltage signal Vx by the current-voltage conversion amplifier 14. Vx = K ₁ (1 + sin 2θ) (12) (where K ₁ is a constant).

The voltage signal Vx is supplied to the high-frequency pass filter 20
And the low-frequency pass filter 21. Therefore, the output Vx _A high frequency pass filter 20, (1
The DC bias component of equation (2) is removed, and the following equation is obtained. The output Vx _D of _{Vx A = K 1 sin2θ (13} ) low-pass filter 21, the AC component is removed, the following equation. Vx _D = K ₁ (14)

Vx _A is applied to the numerator input terminal of the
Since x _D is input to the denominator input terminal of the divider 18, the output signal Vx ₀ of the divider is represented by the following formula (15). Vx ₀ = sin2θ (15)

The signal represented by the equation (15) is converted into a digital signal by an A / D converter after a high frequency is removed by a high frequency blocking filter. This signal, in the memory device 24, by reading Vx ₀ and advance so stored values of theta one-to-one correspondence to which a high speed by the relationship (15), enter the Vx _0, theta Will be output in real time. At this stage, the output is sufficient, but in the embodiment shown in FIG. 1, the analog output V ₀ is obtained via the D / A converter 25. Therefore, in the present embodiment, the detectable range of θ is −90 ° ≦ 2θ ≦ 90 °, and thus −45 ° ≦ θ ≦ 45 °, which makes it possible to detect a range approximately six times that of the related art.

As is apparent from the equation (15), the characteristic fluctuation of the light emitting section 1, the optical fibers 2 and 10, the light receiving element 1
2. It is not affected by the characteristic fluctuation of the current-voltage conversion amplifier 14. Furthermore, there are only two optical fibers, 2 and 10, and the optical system is simpler than the three optical fibers of the prior art.

(2) Second Embodiment FIG. 2 shows a second embodiment of the present invention. In the configuration of the second embodiment, between the light emitting unit 1 and the current-voltage conversion amplifier 14,
This is the same as the first embodiment. In the second embodiment, the output of the current-voltage conversion amplifier 14 is input to the low-frequency pass filter 21, while the output of the low-frequency pass filter 21 is fed back to the light emitting unit as a signal for controlling the amount of light emission. . The output of the current-voltage conversion amplifier 14 is input to the A / D converter via the high-frequency rejection filter 22 at the same time. 24 is a one-to-one relationship with the input digital signal value (A).
This is a storage element (ROM) in which a value of sin ^-1 (A / k-1) corresponding to the data is stored in advance and read out at a high speed in accordance with an input value. Reference numeral 25 denotes a D / A converter for converting a digital output signal from the ROM into an analog signal.

In the second embodiment, the operation from the light emitting section 1 to the current / voltage conversion amplifier 14 is the same as that of the first embodiment shown in FIG. However, since the signal from which the AC component has been removed by the low frequency pass filter 21 is fed back to the light emitting unit as a signal for controlling the light emission amount, (1)
The constant K ₁ in the equation (2) is controlled so that K ₁ = K (constant), and the voltage signal Vx is not affected by the characteristic fluctuation from the light source unit 1 to the current-voltage conversion amplifier 14. Vx = K (1 + sin2θ) (16)

The signal represented by the equation (16) is converted into a digital signal by an A / D converter after the high frequency is removed by a high frequency blocking filter. This signal is input to the storage element 24. In the storage element 24, Vx
The value of θ corresponding to one-to-one is stored in advance, and by reading this at high speed, Vx is input and θ is output in real time. Although the output is sufficient at this stage, in the other embodiment shown in FIG.
An analog output V ₀ is obtained via the converter 25.

In the second embodiment, similarly to the first embodiment, the detectable range of θ is −45 ° ≦ θ ≦ 45.
°, the optical system is simple without being affected by the characteristic fluctuation between the light emitting unit 1 and the current-voltage conversion amplifier 14.
In addition, there is an effect that the signal processing circuit is simplified by the necessity of the high frequency pass filter 20 and the divider 18 in the first embodiment.

[0027]

As described above, according to the present invention, the inverse Sin function corresponding to the digital input value obtained by converting the signal from the light receiving element is stored in the storage element in advance, and the output of the digital input value is stored in the storage element. The optical magnetic field that can detect a wide range of magnetic fields with high accuracy without having to use an approximation formula or being strictly limited to the rotation angle θ of the polarization plane as in the past, because it is read out sequentially according to A sensor can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an optical magnetic field sensor according to the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the optical magnetic field sensor of the present invention.

FIG. 3 is a configuration diagram showing an example of a conventional optical magnetic field sensor.

FIG. 4 is a configuration diagram showing a state in which the optical magnetic field sensor of FIG. 3 is applied to a current transformer.

FIG. 5 is a vector diagram for explaining the operation of a polarizer and an analyzer.

[Description of Signs] 4 ... Polarizer 5 ... Magneto-optical element 7 ... Analyzer 12 ... Light receiving element 14 ... Current / voltage conversion amplifier 18 ... Divider 19 ... Signal processing circuit 20 ... High frequency pass filter 21 ... Low frequency pass filter 22 ... High frequency rejection filter 23 ... A / D converter 24 ... Storage element

──────────────────────────────────────────────────続 き Continuation of the front page (72) Takashi Nakajima 2-1 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Hamakawasaki Plant of Toshiba Corporation (56) References JP-A 1-191062 (JP, A) JP-A-63-85463 (JP, A) JP-A-64-26168 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 33/00-33/18

Claims (2)

(57) [Claims] 1. A magneto-optical element having a Faraday effect in which a plane of polarization rotates in proportion to the strength of a magnetic field to be measured, a polarizer disposed on a light source side of the magneto-optical element, and a light transmitted through the magneto-optical element. An analyzer that receives the transmitted light and determines the direction of the main axis so as to form a certain angle with the main axis of the polarizer; a light receiving element that receives the light transmitted through the analyzer and converts the light into an electric signal; Means for separating the electric signal output from the component into a DC bias component and a component that varies according to the rotation of the polarization plane; and a divider that divides the component that varies according to the rotation of the polarization plane by the DC bias component. An A / D converter that converts the output of the divider into a digital signal; and a storage element that stores an inverse Sin function value of an output value of the A / D converter in advance. A / D converter output value Light type magnetic field sensor that can be characterized to sequentially read by outputting a Flip value. 2. A magneto-optical element having a Faraday effect in which the plane of polarization rotates in proportion to the strength of a magnetic field to be measured, a polarizer disposed on the light source side of the magneto-optical element, and a light transmitted through the magneto-optical element. An analyzer that receives the transmitted light and determines the direction of the main axis so as to form a certain angle with the main axis of the polarizer; a light receiving element that receives the light transmitted through the analyzer and converts the light into an electric signal; Means for extracting a DC bias component from the electrical signal output from the controller, control means for changing the light emission amount of the light source so that the extracted DC bias component has a constant value K, and an electrical signal output from the light receiving element. An A / D converter for converting into a digital signal; and an inverse S of (A / K-1) for an output value A of the A / D converter.
a storage element for storing an in-function value in advance, wherein a value corresponding to an output value A of an A / D converter is sequentially read from the storage element and output as an output.