KR100307639B1 - Current / temperature measurement optical sensor using multi-wavelength light source and its method - Google Patents

Abstract

The present invention is intended to provide an optical sensor and a current and temperature measuring method capable of simultaneously measuring a magnetic field (or current) without being affected by temperature and simultaneously measuring temperature. In the present invention, by utilizing the fact that the Verdet constant of the Faraday device changes not only with temperature but also with respect to the wavelength of light, it is possible to measure an accurate magnetic field (or current) excluding the influence of temperature without attaching a separate temperature sensor A multi-wavelength light source having at least two wavelengths, the temperature of which can be measured at the same time; A Faraday element for allowing linearly polarized multi-wavelength light to pass through the inside thereof; Means for detecting a linear polarization rotation angle of light passing through the Faraday element for each wavelength; And the signal processing means for detecting the magnitude and the temperature of the magnetic field applied to the Faraday element from the correlation of the rotation angles according to the wavelengths, it is possible to detect without being influenced by the temperature, reduce the electrical insulation cost, It is easy to implement a reliable overcurrent protection relay and metering system that is resistant to electromagnetic noise or surge.

Description

Current / temperature measurement optical sensor using multi-wavelength light source and its method

The present invention analyzes an angle of rotation of linearly polarized light of light passing through light of various wavelengths of a Faraday element and analyzes the mutual relationship therebetween to obtain an accurate magnetic field regardless of a temperature change The present invention relates to a current / temperature measuring optical sensor using a multi-wavelength light source capable of measuring temperature as well as a magnitude of current.

Current meters are used in many parts of the power line for metering or protection relays. The iron-core-wire-type current transformer, which has been mainly used so far, detects a current in the form of magnetic field induction by winding a coil on a primary conductor through which a large current flows. On the secondary side, Are directly excited or converted to voltage and used in stationary or digital signal processing. The secondary side current is usually set to 5A, but if a short circuit or a ground fault occurs in the power system, the current size increases from several times to several tens times. At this time, the conventional current transformer deteriorates over time, so that the performance deteriorates and causes various electric failures. In addition, it has structural problems of electrical devices such as waveform distortion due to magnetic saturation and harmonics, and surge and noise. Further, the insulation equipment for measuring the transmission and distribution voltage as the voltage of the transmission and distribution becomes super-high pressure needs to be strengthened. For this purpose, the size of the insulation device is increased, the cost for insulation is increased, and it is difficult to handle.

In particular, optical fibers can be used to send and receive light to and from a sensor, and thus, it is possible to use a copper wire And the dynamic range of the current is wide. Among the advantages of the sensor, it is attractive from the point of view of the electric power company.

However, since the Verdet constant and the length of the Faraday device are changed according to the change of the temperature, an error occurs in the measured value, so that the practical application has a difficulty in terms of reliability.

The optical sensor technology using the Faraday device capable of measuring the temperature and the magnetic field (or current) conventionally proposed is as follows.

One is to use a thermocouple metal coil next to the Faraday element to sense the temperature and rotate the linearly polarized rotating part at an appropriate angle according to the sensed temperature. The temperature compensated magnetic field (or current) can be measured by compensating the variation of the rotation angle of the polarization due to the change of the Verdet constant or the Faraday element length depending on the temperature by the rotation of the linearly polarized light rotating part.

Another technique is to have a temperature sensor next to the Faraday device and pass the temperature sensor through a different light than the light passing through the Faraday device. In this temperature sensor, the light transmittance changes according to the temperature. Therefore, the detector senses the temperature to determine the temperature, and the optical signal emitted from the Faraday element is analyzed in consideration of the temperature to measure the correct magnetic field (or current).

The problem of the existing technology is that a separate temperature sensor is needed first. This leads to a complicated configuration of the system, which causes difficulties in manufacturing. Particularly, when a thermocouple metallic coil is used, rotation of the linearly polarized light rotation part is caused, so that movement is generated in the sensor, so reliability is lowered and power supply for rotation is required.

The next problem is that although the temperature sensor is close to the Faraday element, it is installed separately, so that the actual Faraday element temperature may be different from the temperature sensed by the temperature sensor. In this case, the correction of the magnetic field (or current) with respect to temperature becomes inaccurate, and an error occurs when measuring the magnetic field (or current). In addition, a separate temperature sensor is attached to the linearly polarized light rotation part, which is a core part of the system, so that the configuration becomes complicated and the volume becomes large.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems of the prior art and to provide a Faraday device having a Verdet constant that depends on the wavelength and temperature of light, By passing the light through the Faraday device and measuring the angle of linear polarization for each wavelength and analyzing it through signal processing, it is possible to measure the exact magnetic field (or current) and temperature simultaneously without being influenced by the temperature change. A current / temperature measuring optical sensor and a method thereof.

Accordingly, the present invention can fundamentally eliminate the disadvantages of the prior art technologies by using the physical properties of the Faraday element itself without using a separate temperature sensor. The fundamental measurement principle of this will be described in detail through examples.

In order to eliminate the dependency of the existing Faraday sensor on the temperature, the present invention uses a light source having two or more wavelengths to measure the rotation angle of polarization with respect to light of each wavelength, It is possible to prevent an error in the measured value of the measurement value.

In addition, since the temperature can be measured anywhere in a magnetic field, it can be used as a temperature sensor at the same time. Particularly, unlike the conventional temperature compensated Faraday's magnetic field (or current) sensor, the present invention does not have a separate temperature sensor, so that the configuration of the linearly polarized light rotating part is simple and an error due to the temperature difference between the temperature sensor part and the Faraday element Eliminate the possibility.

Another advantage of the present invention is that temperature can be measured wherever a magnetic field (or current) is present. If the temperature needs to be measured, the temperature can be measured by creating a magnetic field through the supply of permanent magnet or current. Since the linearly polarized light rotating part of the present invention can be manufactured in a very small size, it can be installed easily wherever temperature measurement is required. For example, the system of the present invention can be installed at a portion where a lot of heat is likely to occur, such as a junction portion of a power line, and current and temperature can be simultaneously measured.

This new idea solves the fundamental problems of existing optical magnetic field (or current) sensors and realizes the measurement of the current without temperature influence and the simultaneous measurement of temperature by implementing the multi-wavelength light source, the linearly polarized light rotating part, The effect can be obtained.

1 is a block diagram of a current and temperature optical sensor constructed from a multi-wavelength light source of the present invention.

2 is a view showing an embodiment of a current and temperature measuring optical sensor using multi-wavelengths according to the present invention.

3 (a) to 3 (c) are diagrams showing a configuration example of a multi-wavelength light source according to the present invention.

4 (a) and 4 (b) illustrate examples of means for keeping the intensity of linearly polarized light coming from the polarizer of the present invention constant.

5 (a) to 5 (c) illustrate examples of wavelength separating means for detecting a linear polarization rotation angle according to wavelengths of the present invention.

Description of the Related Art

100: Multi-wavelength light source 110: ₁ FP-LD

120: Wavelength ₂ FP-LD 130: Fiber optic optical coupler

200: linear polarization rotation unit 210: optical splitter

220: selfoc lens 230: PBS polarizer

240: Faraday element 300: linear polarization rotation angle detector

310: PBS analyzer 320: selfoc lens

330: optical connector 340: fiber optic splitter

350: Photodiode ( ₁ ) 360: Photodiode ( ₂ )

400: signal processing unit (SPU) 500: optical fiber

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a current and temperature optical sensor composed of a multi-wavelength light source according to the present invention. As shown in FIG. 1, a multiwavelength light source 100 A polarizer for receiving the optical signal generated from the multi-wavelength light source 100 through an optical fiber and linearly polarizing the optical signal; a Faraday device for changing the rotation angle according to the current and temperature of the object to be detected by the linearly polarized multi- A rotation angle detector 300 for detecting a linearly polarized light rotation angle of light passing through the Faraday element by each wavelength, and a rotation angle detector 300 for detecting a rotation angle of the wavelength, And a signal processing unit (SPU) 400 for detecting the magnitude and temperature of the magnetic field applied to the Faraday element from the relationship.

When the light incident from the light source 100 passes through the linearly polarized light rotating part 200, if the magnetic field is applied parallel to the traveling direction of the light, the polarization direction of the linearly polarized light is rotated differently depending on the magnitude and temperature of the magnetic field and the wavelength of the light . The different linearly polarized light rotation angles are detected by the linear polarization rotation angle detector 300 for each wavelength. The signal processing unit 400 extracts information on the magnitude and temperature of the magnetic field (or current) staked on the linear polarization rotation unit 200 from the linear polarization rotation angles of the respective wavelengths detected by the linear polarization rotation angle detection unit 300.

2 is a configuration diagram of a current and temperature measuring optical sensor using two wavelengths according to an embodiment of the present invention. First, as the multi-wavelength light source 100, ₁ , An optical coupler for transmitting optical signals; (Fabry-Perot Laser Diode FP-LD) 110, 120) and the laser diodes 110 and 120 to the optical fiber 500 (the two laser diodes having a _second 130).

The linearly polarized light rotation unit 200 includes an optical connector 210 for receiving a multi-wavelength optical signal through the optical fiber 500 and outputting an optical signal through a lens (selfoc lens) 220, a PBS polarizer 230 for linearly polarizing an optical signal that has passed through the optical fiber 500 through a selfoc lens 220 and a polarizer 230 which is proportional to the magnitude of a magnetic field flowing in parallel with the traveling direction of the linearly polarized light in the PBS polarizer 230 And a Faraday element 240 in which linearly polarized light is rotated.

The rotation angle detector 300 includes a PBS detector 310 for detecting the rotation angle of the multi-wavelength light rotated in proportion to the magnitude of the magnetic field of the measurement object from the Faraday element 240, An optical coupler 330 for receiving the light detected by the optical fiber 310 in the optical fiber 310 through a lens (selfoc lens) 320 and transmitting the light to the optical fiber 500, And two photodiodes 350 and 360 for converting the light separated by the wavelength separator 340 into electric signals by wavelengths, respectively.

Meanwhile, when the temperature is measured even in a place where no separate magnetic field is formed, a means for supplying a separate magnetic field to the Faraday element 240 of the linear polarization rotary part 200 is further provided.

In the embodiment using the two wavelengths, the two lasers 110 and 120 generate light of different wavelengths and transmit the generated light of different wavelengths to the optical fiber optical coupler 130 and the optical fiber 500, To the optical connector 210. [ The light input to the optical coupler 210 is linearly polarized in the PBS polarizer 230 through the lens 220 and passes through the inside of the Faraday element 240. At this time, the Faraday element 240 rotates the linearly polarized light passing through in proportion to the magnitude of the magnetic field flowing in the measurement object. In the analyzer 310, the rotation angle of linearly polarized light is converted into light intensity, and light enters the optical fiber through the lens 320 and the optical connector 330. The tube-wave wavelength separator 340 separates the two wavelengths of light and sends them to the photodiodes 350 and 360, respectively. The photodiodes 350 and 360 transmit a current or a voltage proportional to the intensity of the detected light to the signal processing unit 400 and the signal processing unit 400 receives the linearly polarized light from the linear polarization rotation unit 200, (Or current) and the temperature of the magnetic field (or current).

FIG. 3 shows a configuration example of a multi-wavelength light source, and various methods of constructing a multi-wavelength light source are presented.

Fig. 3 (a) ₁ , ..., _N , and the light of the plurality of light sources is combined through one optical coupler and is transmitted to the optical fiber. That is, light coming from a light source having a different wavelength is combined using an optical coupler.

FIG. 3 (b) shows a configuration in which light having different wavelengths is sent one by one using an optical switch instead of the optical coupler.

3C shows a case in which a broadband light source having a very wide spectrum is provided and a tunable optical filter is installed in front of the broadband light source to transmit light of a desired wavelength with time .

In addition, a multi-wavelength light source may be constructed using a tunable laser whose wavelength is varied in time.

FIG. 4 shows a method for making the intensity of linearly polarized light emitted from a polarizer of the linearly polarized light rotating unit of the present invention constant. When light emitted from a multi-wavelength light source is linearly polarized light and travels along the optical fiber, It shows two ways to keep the light intensity constant.

4 (a) shows a method of disposing a depolarizer such as a Lyot depolarizer between the linearly polarized light rotating unit and the light source to remove the degree of polarization of the light up to the moment before entering the linearly polarized light rotating unit The polarized light generated in the wavelength light source 100 is converted into the polarized light by the polarized light eliminator 231 and the linearly polarized light having a constant intensity is input to the polarizer 230 So that it can be obtained.

4B shows a state in which the linearly polarized light generated from the multi-wavelength light source 100 is transmitted to the polarizer 230 of the linearly polarized light rotating unit while maintaining the polarization state through a polarization maintaining fiber (PMF) I have shown how to do it.

FIG. 5 shows a wavelength separation method for detecting a linear polarization rotation angle per wavelength, and shows various means for separating wavelengths.

5 (a) shows a method of using an optical filter that divides light into various paths in the optical isolator 340 and allows only specific wavelengths to pass through the respective paths, and FIG. 5 (b) FIG. 5 (c) shows a method of passing multi-wavelength light having a variable rotation angle through a wavelength tunable optical filter through a wavelength tunable optical filter. FIG. 5C shows a method of grating or arrayed waveguide grating ) Is used to spatially separate the light according to the wavelength using the color dispersing element 343 having a large chromatic dispersion characteristic.

Hereinafter, the operation of the present invention will be described.

In the embodiment shown in FIG. 2, the multi-wavelength light source 100 has wavelengths of ₁ = 450 nm and Two FP LDs (Fabry-Perot Laser Diodes) 110 and 120 with a wavelength of ₂ = 520 nm were used. The light emitted from the two lasers 110 and 120 enters the optical fiber 500 and joins together through the optical fiber optical coupler 130 and proceeds along the optical fiber to enter the linear polarization rotator 200. The light of each wavelength in the linearly polarized light rotating unit 200 has linear polarization in the same direction through the polarizer 230 made of PBS (Polarizing Beam Splitter), and the direction of the polarized light propagates through the Faraday element 240 The Faraday element 240 rotates in proportion to the magnitude of the magnetic field applied thereto. At this time, since the Verdet constant differs for each wavelength, the magnitude of the rotation angle also changes.

The rotation angle of the linearly polarized light changes with the power of the light passing through the analyzer 310 made of PBS and the two wavelengths are separated from each other by the optical fiber wavelength separator 340 to form photodiodes 350 and 360, Respectively.

The photodetector outputs a current or a voltage proportional to the intensity of light and is input to a signal processing unit (SPU) 400. In the signal processing unit 400, from the information about the rotation angle of linearly polarized light with respect to two wavelengths, And the magnitude of the magnetic field (or current). This process is described in more detail as follows.

Speaking of the Faraday element 240 passes while θ the angle of light polarization is rotated _F a, θ _F is proportional to the size of B, the length 1, the product of the Verdet constant of the Faraday element of the magnetic field as shown in Equation 1 below.

θ _F ( ,T) -V(,T) ㆍl(T) ㆍB(Equation 1)

(Equation 1), T stands for temperature. As shown in (Equation 1), the Verdet constant is a function of wavelength and temperature, and is a function of Faraday element length 1 degree temperature.

In the magnetic field sensor using the Faraday element 240, the magnitude of the magnetic field B (or the magnitude of the current in the same sense) is inverted to find θ _F by measuring the intensity of the light passing through the analyzer 310 by knowing V and 1 . If the temperature T is changed, V and l are changed. Therefore, even if there is a magnetic field of a certain magnitude, an incorrect result appears as if θ _F has changed.

Here, since two wavelengths are used, the angle &thetas; _F at which the polarization rotates when the temperature of the current Faraday element 240 is T is expressed by the following equation (2) for each wavelength.

θ _F ( ₁ , T ) - V ( ₁ , T ) 占1 ( T ) 占B (Equation 2-1)

θ _F ( ₂ , T ) - V ( ₂ , T ) 占1 ( T ) 占B (Equation 2-2)

Assuming that the polarization axis of the analyzer 310 and the polarization axis of the polarizer 230 form an angle of γ with respect to each other, the intensity of light passing through the analyzer 31 is cos ² [ - ? _F ( ₁ , T )], cos ² [ - ? _F ( _2, T)] in proportion, so equation (2-1) and equation (2-2) in the θ _F ( ₁ , T ) and ? _F ( ₂ , T ) can be easily determined by analyzing the current or voltage of the photodetector.

The optical signal is separated by using the wavelength separator 340 without using the optical detector 310 and the optical detectors 350 and 360 and then analyzed by a polarization analyzer to directly detect the rotation angle of the linearly polarized light have.

In the signal processing unit (SPU) (400) so the detected θ _F ( ₁ , T ), &thetas; _F ( ₂ , T ). For example, as shown in (Equation 3) below, (T)

When Tb ₂ Al ₅ O ₁₂ is used as a constituent of the Faraday device, it has the characteristic of Verdet constant as shown in Table 1. Therefore, at T = 300 K (T) = 0.0686, at T = 77 K (T) = 0.0335.

Conversely, (T) =0.068, T = 300 K, (T) =0.0335, it can be seen that T = 77K. At this point, one thing to note is that what we actually measureV ( , T)Notθ _F (,T), The moment the magnetic field becomes zero, the denominator becomes zero in the case of (Equation 3) (T)The error occurs. Once you know this temperature, the next thing you knowV ( _One , T)ㆍ (T)orV ( ₂ , T)ㆍ (T)(2) to calculate the magnitude B of the magnetic field. Therefore,V ( _One , T)ㆍ (T)WowV ( ₂ , T)ㆍ (T)If you know,θ _F ( _One,T)Wowθ _F ( ₂,T(Or current) excluding the influence of temperature from the magnetic field (or current).

Of course, there is one prerequisite. Characteristic function (T) is a monotonic increasing function or a monotonic decreasing function with respect to the temperature T, this signal processing is possible only in the temperature range. If this is not satisfied, It is difficult to determine the temperature because two or more temperatures can be matched with respect to the temperature (T) value. However, (T) is not necessarily set as shown in equation (3) given V ( ₁ , T), V ( ₂ , T) , it can be defined to be a simple increase or a simple decrease function in a wide temperature range. For example, V ( ₂ , T) is a simple increase function with a positive value in a certain temperature range (T) is defined as the following equation (4) (T) as a simple increase function.

(4), a, b, and c are determined to satisfy the following conditions in the temperature range given by a constant.

Here, A and B are functions defined as follows.

A = ㆍ V ( ₁ , T) + V ( ₂ , T) (Equation 5-3)

B = b V ( ₁ , T) + V ( ₂ , T) + c (Equation 5-4)

Further, when using more N wavelengths, the further obtained functions V ( ₃ , T) , ..., V ( _N , T) . (T) to define one (T) may correspond to one T alone.

If this sensor is installed for the first time and has a constant temperature and the SPU keeps track of subsequent increases and decreases in temperature, The temperature and the magnetic field (or current) can be accurately measured even when the temperature T does not satisfy the above-mentioned condition.

The sensor system described above can be applied when the change of the magnetic field is slow enough than the response time of the sensor. The response time of the sensor is comprehensively determined by the time taken to measure the linear polarization rotation angle for light of various wavelengths, the time required for signal processing, the speed of the photodetector, and the reaction speed of the Faraday element. In the case of alternating current, if the period is sufficiently longer than the response speed of this optical sensor system, the above-mentioned principle is applied as it is, so the alternating current and temperature can be measured.

Therefore, since the present invention can detect without being influenced by temperature, the problem of saturation occurring in the iron core-wire type current modifying apparatus is solved and the signal is transmitted to the optical fiber, so that the electrical insulation cost is reduced, It is possible to realize an overcurrent protection relay and a metering system which are highly reliable against noise or surge caused by the overcurrent protection relay and the metering system.

In addition, since the operation range of the optical sensor is wide, it is necessary to set up the respective tabs according to the current capacity of the existing transformer, while it can be designed to be set directly on the control panel, so that the maintenance and operation of the system is very simple Loses.

Claims (8)

A multi-wavelength light source for generating an optical signal having at least two wavelengths; A polarizer that receives the optical signal generated from the multi-wavelength light source through the optical fiber and linearly polarizes the optical signal; a Faraday rotator including a Faraday element that changes the rotation angle according to the current and temperature of the object to be detected by the multi-wavelength light with linear polarization; A rotation angle detector for detecting a linear polarization rotation angle of light passing through the Faraday element and separating the linear polarization rotation angle by wavelength; A signal processor for detecting a magnitude and a temperature of a magnetic field applied to the Faraday element from the correlation of the rotation angles of the respective wavelengths detected by the rotation angle detector; And an optical sensor for measuring current and temperature using the multi-wavelength light source. The polarized beam splitter as claimed in claim 1, further comprising a polarizer or polarizer for removing polarized light between the multi-wavelength light source and the linearly polarized light rotating unit so that the polarization state of linearly polarized light input to the Faraday element is kept constant, And a polarization maintaining optical fiber (PMF) for light induction for maintaining the polarization state of the light. The optical sensor according to claim 1, further comprising a magnetic field supply unit for supplying a separate magnetic field to the Faraday element of the linearly polarized light rotating unit. A method for measuring a current and a temperature using a Faraday element, the method comprising: a multi-wavelength light output step of generating multi-wavelength light through a multi-wavelength light source having at least two wavelengths and sequentially outputting the multi- The multi-wavelength light output from the step is linearly polarized through the linear polarizer and then passed through the Faraday element to output a light having a variable linear polarization rotation angle in proportion to the magnitude of the magnetic field of the object to be measured A rotation angle detecting step of detecting a rotation angle variable amount of the multi-wavelength optical signal having the variable linear polarization angle of rotation by the optical intensity and separating the optical signal by the wavelength, detecting the optical signal separated by the wavelength, The Faraday element includes a plurality of Faraday elements for detecting the magnitude and temperature of the magnetic field applied thereto, And the current and temperature measurement method using a light source comprising a. The method as claimed in claim 4, wherein the rotation angle detection step comprises a step of detecting a rotation angle &thetas; _F (&thetas; ₁ , T ), ..., &thetas; _F ( _N , T ) was measured with a PBS analyzer to determine the intensity P ( ₁ , T ), ..., P ( _N , T ), where θ _F is the angle at which the polarization of light is rotated, B is the magnitude of the magnetic field, L is the length of the Faraday element, V is the Verdet constant, T is the temperature, ₁ ... _{And N} represents a wavelength). The optical signal is detected by each wavelength in each path by dividing the optical signal whose rotation angle of the linearly polarized light is changed into the light intensity by a plurality of paths, and measuring the current and temperature using the multi-wavelength light source. The method of claim 4, wherein the step of detecting the size and temperature of the magnetic field, the rotation angle per wavelength θ _F ( ₁ , T ), ..., &thetas; _F ( _N , T ) in the required temperature range, (T) is calculated as θ _F ( ₁ , T ), ..., &thetas; _F ( _N , T ) One of the (T) is defined so as to correspond to only one T, and the intensity of light for each wavelength is detected to obtain a temperature. Based on the detected temperature, θ _F ( , T ) = V ( , T) ㆍ (T) 占 B (Equation 1) (Where, θ _F are each, B is the magnetic field size, L is the length of the Faraday element, V is the Verdet constant, T is the temperature, λ ₁ ... λ _N of the light polarization is rotated represents the wavelength) And the magnitude of the magnetic field (or current) B is obtained. The method as claimed in claim 4, wherein the step of detecting the magnitude and temperature of the magnetic field comprises: setting a sensor to be installed for a first time and having a predetermined temperature; (T) have a maximum value or a minimum value, and some functions having no maximum value or minimum value at a temperature having a maximum value or a minimum value As appropriate (T) to continuously track the temperature, Further comprising a temperature tracking step of measuring a temperature and a magnetic field (or current) even when the temperature (T) is not a simple increase or a simple decrease function. The method according to claim 6, wherein, in the measurement of the alternating magnetic field (or current), the rotation angle detecting step divides the magnitude of the AC component of the signal from the photodetector by the magnitude of the DC component, Further comprising the step of preventing erroneous measurement results due to a change in the current and temperature of the multi-wavelength light source.