JPH0432991B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a magnetic field sensor that detects the rotation angle of a plane of polarization rotated by a magnetic rotator having the Farade effect, and thereby detects the magnetic field strength. Regarding.

[Background of the invention]

This type of magnetic field sensor is shown in Figure 1 or Figure 2.
What is proposed is shown in the figure. The one shown in Figure 1 measures the strength H of the magnetic field itself, and the one shown in Figure 2 measures the strength H of the magnetic field formed by the current I flowing through a conductor, thereby determining the current This is an example of a current transformer that attempts to measure I.

As shown in FIG. 1, light emitted from a light emitting unit 1 consisting of a light emitting diode or the like is guided to a condenser lens 3 via an optical fiber 2, and is converted into nearly parallel light by the condenser lens 3. The polarized light is incident on a polarizer 4, and the polarized light extracted by the polarizer 4 is made incident on a magnetic optical rotator 5. The magnetic optical rotator 5 is placed under the intensity H of the magnetic field (in the direction of the arrow shown)
It is made of a material that exhibits the so-called Farade effect, such as lead glass or a magnetic film.
Therefore, the plane of polarization of the polarized light incident on one end face of the magnetic optical rotator 5 is rotated by θ in proportion to the magnetic field strength H, and is emitted from the other end face. This emitted light is incident on an analyzer 7 consisting of a polarizing prism or a polarizing beam splitter, etc., where the two orthogonal components (X
component, Y component). These vector lights are condensed by condensing lenses 8 and 9, respectively, and are converted into light quantity signals P _X ,
P _Y and is guided to light receiving elements 12 and 13 via optical fibers 10 and 11. The light receiving elements 12 and 13 are formed of photodiodes, for example, and are photoelectric converters that output current signals proportional to the received light amount signals P _X and P _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 equation:
It is designed to be converted into voltage signals V _X and V _Y shown in (1) and (2). Note that K ₁ in the equation is a constant.

V _X = K ₁ (1 + sin2θ) ... (1) V _Y = K ₁ (1 - sin2θ) ... (2) The voltage signal _V
The voltage signal V _Y is input to the +input end of the analog adder 16 and the -input end of the analog adder 17, respectively. Analog adder 1
The output of the analog adder 16 is input to the numerator input terminal of the divider 18, and the output of the analog adder 16 is input to the denominator input terminal of the divider 18. By this, divider 1
The signal V ₀ output from 8 is expressed by the following equation (3).

V ₀ =V _{X −V Y} / _V In addition, _K2 in the same formula is a proportionality constant.

V ₀ ≒2θ=K ₂・H ...(4) That is, as is clear from equation (4), the magnetic field strength H is detected by the output signal V ₀ of the divider 18. be.

FIG. 2 is an example of a case where a magnetic field sensor is applied to a current transformer as described above. That is, the purpose is to detect the alternating current I flowing through the conductor 6. A hole through which a conductor 6 passes is formed in the magnetic optical rotator 5, and the light emitted from the polarizer 4 is guided to an analyzer 7 through an optical path shown by a dotted line inside the magnetic optical rotator 5. It's becoming like that. In other words, the light is transmitted through the conductor 6
It is beginning to circulate around the world. The rest of the structure is the same as the example shown in FIG.

Therefore, the plane of polarization of the polarized light transmitted through the magnetic optical rotator 5 is rotated in proportion to the intensity H of the magnetic field generated in proportion to the current I, and the output of the divider 18 is
V ₀ is the same as the previous equation (3), and in the range θ<<1, it becomes as shown in the following equation (5). During the same ceremony
K ₃ is a proportionality constant.

V ₀ ≒2θ=K ₃ ·I (5) In this way, the current I flowing through the conductor 6 is detected.

However, in the case shown in FIG. 1 or 2, the characteristics of the optical system such as the optical fibers 10 and 11 and the light source 1 may vary, and
An imbalance of characteristics may occur between
The light amount signals P _X and P _Y may contain noise as an error signal. For example, a difference may occur in the transmission of the light amount signal, and the signal V _Y may become as shown in the following equation (6).

V _Y = K ₁ (1-δ) (1-sin2θ) ...(6) As a result, the output signal V ₀ becomes the following equation (7), which has the disadvantage of causing a large error. .

V ₀ ≒ 2θ (1 + δ/2) ...(7) [Object of the Invention] The object of the present invention is to eliminate errors caused by variations in the characteristics of optical systems such as optical fibers, and to provide a stable and highly accurate magnetic field sensor. It lies in what we are trying to provide.

[Summary of the invention]

The present invention converts a light quantity signal emitted from an optical fiber into an electrical signal, subtracts each average value from this electrical signal, further divides each by the average value, and calculates the difference between the signals obtained by this division. By detecting the rotation angle of the plane of polarization based on the angle of rotation of the polarization plane, errors caused by variations in the characteristics of optical systems such as optical fibers are removed, and stable and highly accurate detection is attempted.

[Embodiments of the invention]

Hereinafter, the present invention will be explained based on examples.

FIG. 3 shows a first embodiment of the present invention. This embodiment corresponds to the conventional example shown in FIG. 1, and the optical system has the same configuration, so a description thereof will be omitted.

As shown in FIG. 3, the current signals converted by the light-receiving elements 12 and 13 are converted into voltage signals V _X and V _Y by current-voltage conversion amplifiers 14 and 15, respectively, and are passed through a low-pass filter 19. , 20 and the +input terminals of analog adders 21 and 22. The outputs of the low-pass filters 19 and 20 are sent to the analog adder 2.
1 and 22 and the denominator input terminals of dividers 23 and 24, respectively. This divider 2
The analog adder 2 is connected to the numerator input terminals 3 and 24.
1 and 22 are input, and the divider 23,
The outputs of 24 are input to the - input terminal and the + input terminal of an analog adder 25, respectively.

The operation of the signal processing circuit configured in this way will be described below. If the magnetic field is an alternating magnetic field,
Output signals V _X of current-voltage conversion amplifiers 14 and 15,
X _Y is expressed by the previous equations (1) and (2). Low-pass filters 19 and 20 are input signals
The alternating current components of V _X and V _Y are removed to obtain average values _X and _Y , which are further inverted and output. Note that the average value _X ,
V _Y will be equal to K ₁ . Analog adder 2
The output signals of 1 and 22 are (V _X − _X ) and (V _Y −
_Y ), and the output signals S ₁ and S ₂ of the dividers 23 and 24 are
are expressed by the following equations (8) and (9), respectively.

_{S 1 = V X −V _ _} Output signal of device 25
V ₀ is expressed by the following equation (10).

V ₀ =S ₂ −S ₁ ≒4θ≒K ₂ ·H (10) Here, it will be explained that according to this embodiment, it is possible to eliminate errors caused by variations in the characteristics of the optical system.

First, error factors in the optical system can be broadly divided into two types. One is that the optical transmission loss of the optical fibers 10 and 11 deteriorates over time, making the transmission characteristics of the two fibers non-uniform, or that the transmission characteristics of the two fibers become non-uniform due to different temperature characteristics. This is a case where very slow fluctuations in light amount occur. The other case is when optical components are mechanically distorted or vibrated, which essentially causes a farade rotation phenomenon, resulting in rapid light intensity fluctuations. These error factors have been confirmed both experimentally and theoretically.

If the error signal due to the very slow fluctuation in light amount is included, the outputs V _X and X _Y of the amplifiers 14 and 15 will be expressed by equations (11) and (12), respectively.

V _{X = K 1 ・ (} 1 _{− δ} 19 and 20, the values are expressed by equations (13) and (14).

_{X = K 1} (1 _{- δ}
3 and 24, the signal is obtained by extracting the AC signal component and calculating the ratio to the average value.
S ₁ and S ₂ are expressed by the above equations (8) and (9), and the error factors δ _X and δ _Y are removed.

On the other hand, if error _{components δ
The outputs V _} It has become a thing.

V _X = K ₁・(1−δ _X ′)・(1+sin2θ)≒K
₁・(1+2θ−δ _X ′)……(15) V _Y =K ₁・(1−δ _Y ′)・(1+sin2θ)≒K
₁・(1−2θ−δ _Y ′)……(16) Therefore, the output signals S ₁ of the dividers 23 and 24,
S ₂ and the output signal V ₀ of the analog adder 25 are shown in equations (17), (18), and (19), respectively.
Their waveforms are shown in FIG. 4b, d, and e.

S ₁ =V _{X −V X / −V X ≒} − ₍ 2θ _{− δ} 4θ+(δ _Y ′−δ _X ′) …(19) As shown in equation (19), the error term (δ _Y ′−δ _X ′)
remains, but the _optical fiber ₁ is
By selecting cables with the same characteristics of 0 and 11 as possible and installing them within the same cable, it is possible to eliminate errors caused by mechanical vibrations and the like. In other words, focusing on the fact that the true signal component of the light intensity signal is in opposite phase and the error component is in phase, the signal is differentially processed to increase the signal component and reduce the error component, resulting in high-precision detection. We are making it possible to do this.

Further, according to the present invention, since the signal processing circuit performs analog processing, there is also the effect that alternating magnetic fields with frequencies over a wide band can be detected at high speed.

A second embodiment of the invention is shown in FIG. This embodiment corresponds to the conventional example shown in FIG.
The signal processing circuit portion has the same configuration as the first embodiment. Therefore, according to this embodiment, the same effects as those of the first embodiment can be obtained, and the alternating current flowing through the conductor can be detected stably and with high accuracy.

FIG. 6 shows a third embodiment of the present invention. FIG. 6 shows only a portion of the signal processing circuit of the present invention. As shown in the figure, the _output signals _V
6 and 27 into digital signals, which are input to a digital arithmetic unit 28 formed by a microprocessor or the like. This arithmetic unit 28 calculates the average value _{of the} input signals _V It is now output to .
Thereby, the output signal of the D/A converter 29 can obtain an output voltage proportional to the magnetic field strength H or the current I.

Therefore, according to this embodiment, since the signals are digitally processed, the accuracy in signal processing is further improved, and the magnetic field or current can be detected with even higher precision. In addition, the signal required for detection is a sine function such as sin2θ, but it is an arc sine function.
Since signal processing with calculation elements such as sin ^-1 (X) can be easily executed, θ<<1
It becomes possible to detect a wide range without being limited to a certain range.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to eliminate errors caused by variations in the characteristics of optical systems such as optical fibers, and thereby it is possible to detect magnetic fields or currents stably and with high precision. .

[Brief explanation of drawings]

FIGS. 1 and 2 are block diagrams showing an example of an optical magnetic field sensor, FIG. 3 is a block diagram of a first embodiment of the optical magnetic field sensor of the present invention, and FIGS. 4 a to 4 e illustrate the embodiment. FIG. 5 is a block diagram of the second embodiment of the optical magnetic field sensor of the present invention, and FIG. 6 is a block diagram of the main parts of the third embodiment of the optical magnetic field sensor of the present invention. be. 4... Polarizer, 5... Magnetic rotator, 6... Conductor, 7... Analyzer, 10, 11... Optical fiber,
12, 13... Light receiving element, 14, 15... Current voltage conversion amplifier, 19, 20... Low pass filter, 2
1, 22...analog adder, 23, 24...divider, 25...analog adder, 28...digital arithmetic device.

Claims (1)

[Claims] 1. A magnetic optical rotator having a Farade effect in which the plane of polarization rotates in accordance with the applied magnetic field strength, and the polarized light transmitted through the magnetic optical rotator is split into vector optical signals of two orthogonal components. an analyzer, a light-receiving element that receives the optical signal via an optical fiber and converts it into an electrical signal, and detects the rotation angle of the polarization plane using the electrical signal output from the light-receiving element to determine the magnetic field strength. a signal processing circuit for detecting, the signal processing circuit subtracts each average value from the input signal, further divides by each of the average values, and calculates the rotation based on the difference between the signals obtained by the division. An optical magnetic field sensor configured to detect corners. 2 In the invention described in claim 1,
An optical magnetic field sensor characterized in that the magnetic optical rotator is disposed close to a conductor and is provided in a magnetic field that changes depending on the current flowing through the conductor.