JPS59670A - Optical fiber magnetic field sensor - Google Patents

Abstract

PURPOSE:To reduce a measurement error and to improve reliability by propagating plural light beams with different wavelengths in the same optical path on time-division basis, and processing the difference in the influence of a magnetic field upon those light beams. CONSTITUTION:This system consists of a light source means 11 which has peaks for two wavelengths of lambda1 and lambda2 and sends out light beams with the wavelengths on time-division basis, an optical fiber 12, a polarizer means 13, a magnetooptic effect means 14, a photodetecting means 15, an optical fiber means 16, etc. The light beams of the lambda1 and lambda2 emitted from the light source 11 alternately for tens of mus by a signal from a control means 17 are varied in level and supplied to a photodetecting means 18 as outputs P1 and P2 of electric power. The photodetecting means 18 detects their levels synchronously with the generation timing of those two wavelengths and the results are processed by an analog or digital arithmetic means 19 to find a magnetic field H. Thus, the measurement error is reduced and the reliability is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an optical fiber magnetic sensor that is applied to current measurement in a high voltage region, etc., using the magneto-optic effect in which the plane of polarization rotates in response to changes in the magnetic field. .

When the light emitted from a light source is made into a certain polarized state by a polarizer means and then transmitted through the inside of a so-called Faraday effect element, which is a type of magneto-optic effect element such as lead glass, 9
Since the polarized light is modulated in accordance with the surrounding magnetic field, when the light is passed through the analyzer means, there is a change in optical power corresponding to the change in polarized light. The magnetic field can be determined by converting this into an electrical signal using a photodetector such as a photodiode. This measurement method is widely known.

Fiber optic magnetic field sensors combine this measurement method with highly electrically insulating optical fibers.

Since it is possible to measure ultra-high voltage power equipment of hundreds of thousands to 100 volts, it has been put into practical use to the extent that it has been studied for a long time.

However, in the above-mentioned optical fiber magnetic field sensor, since the output signal is the output optical power of the analyzer means, optical coupling loss between each component and optical transmission loss within the optical fiber are affected by temperature fluctuations and optical fibers. Bending or other changes in the fiber immediately lead to measurement errors, making it difficult to obtain accurate results and lacking long-term measurement reliability.

Therefore, an object of the present invention is to obtain a highly reliable optical fiber magnetic field sensor in which the above-mentioned measurement error in the optical fiber magnetic field sensor is minimized.

The present invention focuses on the fact that the above-mentioned modulation of polarized light differs depending on the wavelength of the propagating light, and by propagating a plurality of lights with different wavelengths in the same optical path, the difference in the influence of the magnetic field H on these lights is calculated. The purpose of this method is to calculate the magnetic field by calculating the .

That is, according to the present invention, means for time-divisionally transmitting polarized light of a plurality of wavelengths, magneto-optic effect means for changing the polarized light passing therethrough in response to changes in an external magnetic field, and analyzer means. , an optical fiber means, a light detection means, and a calculation means for computing the output electric signal of the light detection means based on the correspondence with the light wavelength to obtain the magnetic field. A fiber magnetic field sensor is obtained. In addition to the above-mentioned light transmitting means to light detecting means, there is also a light branching means for branching part of the output or internal light of the light transmitting means, and a monitor light detecting means for detecting a part of the branched light. An optical fiber magnetic field sensor is obtained, which includes arithmetic processing means for calculating the magnetic field by performing arithmetic processing using the output electric signal detected by the monitor light detection means and the output electric signal emitted by the light detection means.

Next, a detailed explanation will be given with reference to the drawings.

FIG. 1 is a diagram illustrating a conventional fiber optic magnetic field sensor with a -4 compensation. In FIG. 1, light emitted from a light source 1 such as a laser diode (LD) or a light emitting diode (LED) is guided to a magneto-optic effect means 4 such as lead glass through an optical fiber 2 and a polarizer 3, and its output light is is converted into a stain signal and outputted by the light detection means 7 via the analyzer means 5 and the optical fiber 6. Assuming that the length of the magneto-optic effect means 4 is l, and that it is placed in a magnetic field having a magnetic field component H parallel to the light beam, the light linearly polarized by the polarizer 3 becomes α= due to the so-called Faraday effect. VH1”
......The plane of polarization is rotated by the angle α expressed in (1). Here, V is called the Verdet constant, and is a constant representing the strength of the influence of the magneto-optic effect, which varies depending on the material. As can be seen from equation (1), the magnetic field H
The relationship of α to the change in is a linear relationship. As a result of this rotation, the output light level Po of the analyzer means 5 depends on the input to the magneto-optic effect means 4, that is, the polarization direction of the output light of the polarizer means 3 and the setting of the polarization direction of the analyzer means 5. shows a unique relationship with changes in

Figure 2 shows the polarization rotation angle α and the output light level Pa explained above.
FIG. 3 is a diagram showing the relationship between the magnetic field H and the magneto-optical effect of the magnetic field sensor. By using these relationships and placing this sensor in a magnetic field H generated by an ultra-high voltage current I, it is possible to measure the magnetic field H and therefore the current ■ by measuring the output light level Po. . Optical fibers 2 and 6 are typically used for insulation in this configuration.

Here, the polarizer means 3 is used if the light source 1 is an LD or IIe-N.
If the e-laser already has sufficient polarization characteristics and its polarized light can be directly introduced into the magneto-optic effect element 4 without using the fiber 2, or by using a special polarization-maintaining fiber, etc. Although it can be omitted if the polarization is sufficiently maintained, it is usually necessary.

Now, in the optical fiber magnetic field sensor with the above configuration, the output signal is the output light level itself, so as briefly explained earlier, for example, the optical fiber 6 may be bent or changed in temperature, resulting in propagation loss. This has the disadvantage that if there is a change in the coupling loss between the various means, this will immediately result in a measurement error.

FIG. 3 is a diagram explaining the present invention in detail. In FIG. 3, λl on the incident side for simplicity.

The light levels of the two wavelengths of λ2 are both P as shown in the same figure (A).
o, the output side is usually on the short wavelength side (λ1)
Since the Verdet constant is larger, the λl side is more susceptible to the influence of the magnetic field, resulting in the result shown in FIG. Now the wavelength λl
, the Verdet constant for λ2 is ■I + v2, and further P=f(α)・Po−=f(VHl)・P.

If there is a relationship *Vt7 = K+ + V2
1 = as 2.

P+=f(α1)・Po=f(V+H6)Po=f(K
tH)P.

P2=f(α2) Po=f(V2Hl) Po
= f (K2H) P.

The ratio of the outputs of both Ymi Pl/P2 is Y”” f(KtH)/f(K2H)...Song...
(2) Hail. Since f(α) is usually a sine or cosine function, the value of Y in equation (2) becomes a monovalent nonlinear function with respect to H within the measurement range, and there is a one-to-one relationship between Y and H. Therefore, by measuring the ratio Y of both forces, the magnetic field H can be determined. Moreover, in this case, since errors caused by loss fluctuations in the fiber system and its coupling portion can be removed, the magnetic field H can be determined more accurately than in the past.

FIG. 4 is a diagram showing the configuration of an embodiment of the present invention. First, to give an overview, 11 is λ1. 2 of λ2
A light source means having a peak wavelength and transmitting these two wavelengths in a time-divisional manner as described later.

12 to 16 are optical fibers similar to the conventional example shown in FIG.

Polarizer means, magneto-optic effect means, analyzer means and optical fiber means are provided respectively. In this system, depending on the signal from the control means 17, the light λ1 and λ2 emitted from the open light source 11, for example, alternately for several tens of microseconds, undergo level changes and have an optical power Pl.

The light enters the light detection means 18 as P2. Light detection means 18
The magnetic field H is determined by detecting the respective levels in synchronization with the timing of generation of the two wavelengths by the control means 17 for λl and λ2, and calculating the results by the digital calculation means 19 such as an analog or microcomputer. can be found.

Needless to say, if the interval at which λl and λ2 occur alternately is short, the influence of disturbance on the fiber etc. can be ignored.

Next, to explain partially, the light source means 11 has a wavelength λ
The LEDs and LDs emit 1 and λ2, respectively, and are designed to output alternately by rectangular lights. FIG. 5 is a diagram showing another example of the light source means 11, in which λl, λ2
The control means 17 controls the light from the two light sources 23a and 23b.
The high-speed optical switch 24 alternately switches the signals based on the signals and couples them to the optical fiber 12. The above two examples are currently practical. In the future, it will be possible to control one emission wavelength, and it is thought that D and LEDs will be developed and available.

Returning to FIG. 4, the light detection means 18 is connected to the optical fiber 1.
The level P1+P1 is detected by using a photodetecting element 31 such as a photodiode (PD) coupled to the output terminal of the control means 17, and a demultiplexer 32 which operates according to a signal from the control means 17. The output of this photodetection means 18 is also the signal of the control means 17, and the data corresponding to the wavelengths λl and λ2 is in analog or digital form in the calculation means 19.
is input and processed.

FIG. 6 is a diagram showing another example of the photodetection means 18, in which the output of the photodetection element 33 (same as 31) is sent to the A/D conversion circuit 35 via the sample and hold circuit 34. It has become. The output of this circuit is sent to arithmetic means, in this case digital.

FIG. 7 is a diagram showing still another example of the photodetecting means 18, in which the optical fiber demultiplexer 36 separates the light into wavelengths of λ1 and λ2, and controls the outputs of the photodetecting elements 37a and 37b. Means 17
A sample hold circuit 38a that operates based on the signal of
The signal is output to the calculation means 19 via 38b.

Returning to FIG. 4 again, the device shown in FIG. 4 is equipped with a polarizer 13, but if the light source 11 has certain polarization characteristics such as an LD and the optical fiber 12 maintains polarization. If it is a polarized optical fiber and the light sent to the magneto-optic optical element is polarized light.

The polarizer 13 does not necessarily need to be provided.

FIG. 8 is a diagram showing the configuration of another embodiment of the present invention. This embodiment is particularly intended to improve measurement accuracy. That is, in the example shown in FIG. 4, the incident levels of the two wavelengths of light to the magneto-optic effect means 14 are both set to be the same as Po, but this is actually quite difficult to adjust, and furthermore, the optical Like the optical fiber 16, the γ fiber 12 is also subject to variations in propagation characteristics due to temperature changes. In this case, if the two wavelengths are close to each other to some extent, the change in the level of one optical signal is not a problem because the effect will cancel out, but the effect of rotation of the plane of polarization in the optical fiber 12, etc. can be measured. directly affect the results.

Therefore, in the embodiment shown in FIG. 8, in order to eliminate such problems, the incident light is branched at the input side of the magneto-optic effect means 14 by a branch 41, and a monitor light detection means 42 for monitoring the level thereof is installed. The data is input to the calculation means 43. The calculation means 43 normalizes the output of the light detection means 18 by dividing it by the output of the monitor light detection means 42, and calculates the magnetic field H from this normalized value.

Here, it is preferable that the monitor light detection means 42 be capable of independently detecting the two wavelengths λl and λ2 with the same configuration as the light detection means 18 in response to the signal from the control means 17; .

It is also possible to detect and use the average level of any one wavelength of λ2 or the sum of the wavelengths.

FIG. 9 is a diagram showing the configuration of still another embodiment of the present invention. When using this type of device to measure ultra-high voltage power equipment, polarizer 13. Magneto-optic effect element 14. and the analyzer 15 are integrated and installed in the high pressure part. Therefore, while being aware of the deterioration of the polarization characteristics caused by the optical fiber 12, the optical fiber 12 is arranged not on the input side of the magneto-optic effect means 14 but on the output side of the light source 52, and the monitor light detection means 53 is connected to this branch 51.
is arranged. Of course, in this configuration, the measurement accuracy decreases by the amount of the optical fiber 12, but as mentioned earlier, when the light source 11 itself has a certain polarization characteristic like an LD and the optical fiber 12 has polarization preservation property, This configuration is effective because there is only a slight decrease in measurement accuracy. Moreover, in this case, the polarizer 13 does not need to be provided.

FIG. 10 is a diagram showing the configuration of another embodiment of the present invention. In the apparatus shown in FIG. 10, the two orthogonal output lights of the analyzer means 61 are divided into, for example, V-polarized light and H-polarized light, and the two are controlled by the control means 17 through separate optical fiber means 62a and 62b, respectively. set of light detection means 63a
, 63b, and λ1. Each V polarization of λ2, H
The polarized wave component data is obtained and processed by the calculation means 64, which is further controlled by the control means 17, to obtain the magnetic field H.

In the above explanation, for convenience of explanation, the wavelength is λ1. Although two wavelengths λ2 are used, increasing the number of wavelengths within a practical range and increasing the calculation input data is useful for improving measurement accuracy and is in line with the gist of the present invention.

Note that descriptions of lenses, optical phase plates, etc. that are not directly related to the description of the present invention have been omitted. Furthermore, the configuration of the present invention can adopt various forms depending on the combination of the selection of the hardware, the timing of the generation of the optical wavelength, the signal output of each photodetecting means, and the timing of the arithmetic circuit.

In addition, in the above explanation, a lead glass block was shown as an example of the magneto-optic effect means, but this also applies even if it is made of other materials or has a structure or form different from the above example, such as an optical fiber. are included in the present invention. Further, as described in the explanation regarding FIG. 4, a polarizer is not necessarily required.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a conventional optical fiber magnetic field sensor, FIG. 2 is a diagram explaining the magneto-optical effect in the above-mentioned magnetic field sensor, and FIG. 3 is a diagram explaining the present invention in detail. , FIG. 4 is a diagram showing the configuration of an embodiment of the present invention, FIG. 5 is a diagram illustrating an example of the configuration of a light source means suitable for the present invention,
FIG. 6 is a diagram illustrating an example of the configuration of a light detection means suitable for the present invention, FIG. 7 is a diagram illustrating another example of the configuration of a light detection means suitable for the present invention, and FIG. 8 is a diagram illustrating an example of the configuration of a light detection means suitable for the present invention. FIG. 9 is a diagram showing the configuration of still another embodiment of the present invention, and FIG. 10 is a diagram showing the configuration of another embodiment of the present invention.

Claims (1)

[Claims] 1. Means for time-divisionally transmitting polarized light of a plurality of wavelengths;
Magneto-optical effect means for changing the polarization of light passing therethrough in response to changes in an external magnetic field, analyzer means, optical fiber means, and light detection means. An optical fiber magnetic field sensor comprising a calculation means for calculating the magnetic field by processing the output electric signal of the photodetection means in correspondence with the optical wavelength and calculating the magnetic field. 2. A light transmitting means that transmits polarized light of a plurality of wavelengths in a time-division manner, and a magneto-optic effect means that changes the polarized light passing therethrough in response to changes in an external magnetic field. Analyzer means, optical fiber means, and light detection means. a light branching means for branching a part of the output or internal light of the light sending means; a monitor light detection means for detecting the branched part of the light; an output electric signal detected by the monitor light detection means; 1. An optical fiber magnetic field sensor comprising: arithmetic means for performing arithmetic processing using an output electric signal emitted by a light detection means to obtain the magnetic field.