CN101598748A - A temperature-compensated current sensor head and an alternating current measurement method and system - Google Patents

Abstract

The invention relates to a temperature-compensated current sensing head and an alternating current measurement method and system. The current sensing head is placed in the magnetic field generated by the alternating current to be measured, and the fiber grating FPI pasted on the magnetostrictive material Sensing the temperature and the magnitude of magnetic induction in the surrounding environment. The optical signal emitted by the monochromatic light source enters the fiber grating F-P cavity of the fiber grating Fabry-Perot interferometer, and forms an approximately double-beam interference signal output after interference. According to the double-beam interference signal, the cavity length variation of the fiber grating FP cavity of the fiber grating Fabry-Perot interferometer is obtained, and then the measured value of the alternating current is obtained through the linear relationship between the cavity length variation and the current. Finally, the actual value of the alternating current is obtained by using the temperature compensation relationship between the measured current value and the actual measured value. The performance of the original current sensor is improved, the manufacturing process is relatively simple, and the simultaneous measurement of temperature and alternating current can be realized.

Description

A temperature-compensated current sensor head and an alternating current measurement method and system

technical field

The invention relates to a temperature-compensated current sensor head and an alternating current measurement method and system, belonging to the field of optical fiber sensing and optical measurement.

Background technique

The principle of the fiber grating sensor is to convert the measured value into the drift of the fiber grating Bragg wavelength. It is simple to manufacture, but its wavelength modulation characteristic brings certain difficulties to signal demodulation. Ordinary fiber optic Fabry-Perot interferometer (FPI) sensor utilizes the principle of optical fiber light transmission and F-P interference, and has high measurement accuracy, but the manufacturing process is relatively difficult. Fiber Bragg grating FPI is composed of two identical fiber gratings written in the same fiber, which combines the advantages of fiber Bragg grating and fiber FPI. The advantages of the all-fiber structure can reach the measurement accuracy of the traditional fiber-optic FPI sensor, which has attracted more and more attention.

In the power system, it is particularly important to monitor parameters such as voltage, current, and power of transmission and transformation lines. With the continuous increase of grid voltage, traditional electromagnetic sensors are increasingly unable to meet the requirements due to poor insulation, complex structure, and high cost. For this reason, the all-fiber high-voltage current sensor has become one of the research hotspots. At present, the measurement methods used in fiber optic current sensors include: optical polarization state measurement method, wavelength modulation measurement method and optical interferometry method. Among them, the principle of optical interferometry is to use the external field to change the phase difference of coherent light for measurement, such as the "interferometric fiber optic current sensor" in the fourth issue of "Instrument Technology and Sensors" in 2006. The interferometer structure used in the interferometric fiber optic current sensor mainly includes Mach-Zehnder (M-Z) interferometer, Michelson interferometer and FPI. The structure of the Mach-Zehnder interferometer is basically the same as that of the Michelson interferometer, consisting of a signal arm fiber and a reference arm fiber. Since the sensing beam and the reference beam of the optical fiber current sensor with this structure are transmitted in two optical fibers, the interference of birefringence, ambient temperature, vibration, bending and other factors inside the optical fiber will seriously affect the performance of the sensor. The sensing beam and reference beam of the FPI fiber optic current sensor are transmitted in the same optical fiber, which effectively solves the problems of birefringence, vibration and bending of the optical fiber, but the influence of temperature cannot be solved.

Contents of the invention

technical problem to be solved

In order to avoid the deficiencies of the prior art, the present invention proposes a temperature-compensated current sensor head and an alternating current measurement method and system, which improves the performance of the original current sensor, and the manufacturing process is relatively simple, which can achieve temperature and Simultaneous measurement of alternating current.

Technical solutions

The current sensing head proposed by the present invention is characterized in that it includes a fiber grating Fabry-Perot interferometer 12, a magnetostrictive material 8, and 2 permanent magnets 7; 2 permanent magnets 7 are placed relatively parallel to the magnetostrictive On both sides of the material 8, the fiber grating F-P cavity of the fiber grating Fabry-Perot interferometer 12 is pasted on the magnetostrictive material 8; the length of the magnetostrictive material 8 is the fiber grating F-P cavity length or less than the fiber grating F-P cavity length 1.5 times; the length of the two permanent magnets 7 is greater than or equal to the length of the fiber grating F-P cavity length; the fiber grating F-P cavity is located between the two sections of the fiber grating 6 of the fiber grating Fabry-Perot interferometer.

The two permanent magnets 7 are vertically fixed at both ends of the magnetostrictive material 8 .

The reflectivity of the fiber grating Fabry-Perot interferometer is less than 5%.

The magnetostrictive material 8 adopts piezoelectric ceramics 11 of equal length, and the permanent magnet 7 adopts a mutual induction coil 10 and a transmission line 9 ; the mutual induction coil 10 is connected with the piezoelectric ceramics 11 through the transmission line 9 .

A method for measuring alternating current using any of the above-mentioned current sensing heads, characterized in that the steps are as follows:

Step 1: Place the current sensing head in the magnetic field generated by the alternating current to be measured, input an optical signal with a wavelength of λ and a light intensity of I ₀ , and the current sensing head outputs a double-beam interference signal with a light intensity of I ;

其中R_λ为光纤光栅FPI对波长为λ的单色光强度的峰值反射率，为光纤光栅F-P腔干涉信号的初相位，n为光纤纤芯的折射率；Step 2: Obtain the fiber grating Fabry-Perot interferometer fiber grating FP cavity length variation according to the two-beam interference signal whose light intensity is I:

where R _λ is the peak reflectance of the fiber grating FPI to the intensity of monochromatic light at wavelength λ, is the initial phase of the fiber grating FP cavity interference signal, n is the refractive index of the fiber core;

其中A为比例系数由常规实验定标的方式得到；Step 3: According to the linear relationship between Δh and current intensity, the measured value i' of current intensity is obtained as

Among them, A is the proportional coefficient obtained by conventional experimental calibration;

其中κ₂为磁致伸缩材料的温度磁场强度交叉灵敏度系数，C_eff为磁致伸缩材料的磁致伸缩系数，且κ₂和C_eff两个系数值由常规实验定标的方式得到。Step 4: According to the compensation relationship between the measured value i' and the actual value i to the temperature $i=\frac{C_{\mathrm{eff}}}{C_{\mathrm{eff}}+{\mathrm{\κ}}_2\&Center\; Dot;\mathrm{\ΔT}}{i}^{\′},$ The actual value of the current measured in the environment is obtained

Among them, κ ₂ is the temperature and magnetic field intensity cross-sensitivity coefficient of the magnetostrictive material, C _eff is the magnetostriction coefficient of the magnetostrictive material, and the two coefficient values of κ ₂ and C _eff are obtained by conventional experimental calibration.

A system for realizing the above method of measuring alternating current, characterized in that: the current sensing head is connected to one port on one side of the fiber coupler 4 through a single-mode fiber 3, and the other port is placed in a refractive index matching port through a single-mode fiber 3 In the liquid 5; the two ports on the other side of the fiber coupler 4 are respectively connected to the monochromatic light source 1 and the photodetection device 2.

Beneficial effect

The temperature-compensated current sensing head provided by the present invention can implement the method and system for measuring alternating current by the current sensing head of the present invention. The method and system of the invention solve the temperature and current cross-sensitivity problem of the traditional current sensor, realize the compensation measurement of the temperature to the current, and improve the measurement accuracy. The present invention can also improve the sensitivity and range of current measurement by improving the effect of current on the magnetostrictive element and the fiber grating F-P cavity being limited by the length of the magnetostrictive element. At the same time, the invention has the advantages of small size, simple structure, low cost, stable performance, high sensitivity, good electrical insulation and corrosion resistance, and can work under harsh conditions.

Description of drawings

Figure 1: Schematic diagram of the structure of the fiber Bragg grating FPI current measurement device in Embodiment 1 of the present invention

Figure 2: Schematic diagram of the structure of the fiber Bragg grating FPI current measurement device in Embodiment 2 of the present invention

Figure 3: Schematic diagram of the structure of the fiber Bragg grating FPI current measurement device in Embodiment 3 of the present invention

Figure 4: It is the relationship curve of monochromatic light intensity peak reflectance R _λ and temperature, the abscissa is temperature, and the ordinate is R _λ

1. Monochromatic light source; 2. Photoelectric detection device; 3. Single-mode optical fiber; 4. Fiber coupler; 5. Refractive index matching liquid; , Permanent magnet; 8, Magnetostrictive material; 9, Transmission line; 10, Mutual induction coil; 11, Piezoelectric ceramics; 12, Fiber Bragg grating Fabry-Perot interferometer.

Detailed ways

Now in conjunction with embodiment, accompanying drawing, the present invention will be further described:

A kind of temperature compensation type alternating current sensing head of the embodiment of the present invention, wherein comprises fiber grating Fabry-Perot interferometer 12, magnetostrictive material 8 and 2 permanent magnets; 2 permanent magnets are placed opposite On both sides of the magnetostrictive material 8 , the fiber grating FPI formed between the two sections of fiber grating 6 of the fiber grating Fabry-Perot interferometer is pasted on the magnetostrictive material 8 . The sensor head can also replace the magnetostrictive material 8 and two permanent magnets with piezoelectric ceramics 11, mutual induction coil 10 and transmission line 9; the mutual induction coil 10 connects the output voltage signal to the input piezoelectric ceramics 11 through the transmission line 9 .

The basic method of measuring the alternating current proposed by the embodiment of the present invention is: place the current sensing head in the magnetic field generated by the alternating current to be measured, and the fiber grating FPI attached to the magnetostrictive material senses the temperature in the surrounding environment and the magnitude of the magnetic induction. The optical signal emitted by the monochromatic light source enters the fiber grating F-P cavity of the fiber grating Fabry-Perot interferometer, and forms an approximately double-beam interference signal output after interference. According to the double-beam interference signal, the cavity length variation of the fiber grating F-P cavity of the fiber grating Fabry-Perot interferometer is obtained, and then the measured value of the alternating current is obtained through the linear relationship between the cavity length variation and the current. Finally, the actual value of the alternating current is obtained by using the temperature compensation relationship between the measured current value and the actual measured value.

The realization device of this method is that the fiber grating FPI of the fiber grating Fabry-Perot interferometer is pasted on the magnetostrictive material, and it is connected with a port of the fiber coupler through a single-mode fiber, and the monochromatic light source and the photoelectric The detection device is connected with the other two ports of the fiber coupler, and the fourth port of the fiber coupler is inserted into the refractive index matching liquid through a single-mode fiber.

Embodiment 1: Referring to accompanying drawing 1, it is a structural schematic diagram of the fiber grating FPI current measuring device. The fiber grating FPI12 is pasted on the magnetostrictive material 8, and the permanent magnet 7 is fixed on both sides of the magnetostrictive material 8 in parallel. The refractive index matching liquid 5 is connected, and the two ports on the other side of the fiber coupler 4 are respectively connected with the monochromatic light source 1 and the photodetection device 2 .

The F-P cavity of the fiber grating FPI12 is constrained by the magnetostrictive material 8, and the two fiber grating parts 6 are placed freely; the reflectivity of the fiber grating FPI12 is less than 5%.

The monochromatic light source emits an optical signal with a wavelength of λ and a light intensity of _I0 , which is transmitted to the fiber grating FPI sensor probe through a coupler. Since the reflectivity of the fiber grating FPI is less than 5%, the reflected optical signal is approximately a two-beam interference signal, which can be approximately expressed as

表示光纤光栅FPI干涉信号的初相位，对测量结果没有影响，为一常值。由此得到到光纤光栅F-P腔的腔长变化量Δh为In the formula, R _λ represents the peak reflectance of the fiber grating FPI to the intensity of monochromatic light with a wavelength of λ during the cavity length change process, which is determined by the fiber gratings at both ends of the fiber grating FPI; n represents the refractive index of the fiber core; Δh represents the cavity long stretch;

Indicates the initial phase of the fiber grating FPI interference signal, which has no influence on the measurement results and is a constant value. From this, the cavity length variation Δh of the fiber grating FP cavity is obtained as

时，且光纤光栅F-P腔的腔长变化量Δh与电流强度i的关系为线性关系The magnetostrictive material works in the linear region under the action of the permanent magnet. The magnetic field around the alternating current acts on the magnetostrictive material, causing the length of the magnetostrictive material to change periodically. The fiber grating FP cavity is deformed accordingly. The influence of deformation on the fiber is divided into two parts: one is the change of the core refractive index caused by the elastic-optic effect; the other is the change of the fiber length caused by the strain. The combined effect of the two causes periodic changes in the optical path of the optical signal transmitted in the FPI, resulting in periodic changes in the reflected light intensity. The alternating current to be measured is

, and the relationship between the cavity length variation Δh of the fiber grating FP cavity and the current intensity i is linear

In the formula, A is a proportional coefficient, which can be measured through experiments. Therefore, without considering the influence of temperature, the measured value of the current is equal to the actual value i, which can be expressed as

It can be seen from the above formula that if the frequency of the current to be measured is ω and nAi ₀ >λ, the frequency characteristic of the reflected light signal I is only related to the amplitude i ₀ of the current. Therefore, the alternating current i' to be measured can be obtained by analyzing the frequency characteristics of the reflected light signal I.

The fiber grating FP cavity is deformed under the influence of ambient temperature. The influence of temperature on optical fiber is mainly reflected in the change of fiber length caused by the thermal expansion effect of the fiber and the change of the refractive index of the fiber core caused by the thermo-optic effect of the fiber. The combined effect of the two causes the change of the FBG reflectivity at both ends of the FPI, which leads to the change of R _λ . Please refer to Figure 4 for R _λ versus temperature. When measuring temperature, R _λ is required to change in a monotonous interval. In order to obtain the maximum temperature measurement range, it is necessary to select a suitable operating point. The specific method is as follows: determine the variation range of the temperature to be measured, and select a suitable operating wavelength so that R _λ is half of the maximum reflectance at the intermediate temperature.

Since the temperature change will change the properties of the magnetostrictive material, and then affect the measurement of the current. Therefore, the current value needs to be corrected. On the one hand, when the temperature is constant, the elongation of the magnetostrictive material is proportional to the magnetic field strength of the material; on the other hand, when the magnetic field is constant, the elongation of the magnetostrictive material is also proportional to the temperature. Therefore, it can be assumed that the strain ε of the magnetostrictive material after being subjected to temperature and magnetic field is

$\mathrm{<span\; class="notranslate">\; \&epsiv;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; \&Delta;L</span>}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; eff</span>}}\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&kappa;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;T</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&kappa;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; H\&Delta;T</span>}$

In the formula, κ1 is the sensitivity coefficient of strain to temperature of magnetostrictive material, κ2 is the cross-sensitivity coefficient of temperature and magnetic field strength of magnetostrictive material, and Ceff is the magnetostrictive coefficient of magnetostrictive material at a certain constant temperature. The three coefficient values can be obtained by means of experimental calibration. Therefore, through analysis, the relationship between the actual correction value i of the current and the measured current value i′ is as follows:

$\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; eff</span>}}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; eff</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&kappa;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>\mathrm{<span\; class="notranslate">\; \&Delta;T</span>}}{\mathrm{<span\; class="notranslate">\; i</span>}}^{<span\; class="notranslate">\; \&prime;</span>}$

Therefore, the simultaneous measurement of current and temperature can be realized by detecting the intensity and frequency characteristics of the output optical signal, and then the actual current value after temperature compensation can be obtained.

Embodiment 2: Referring to accompanying drawing 2, the difference from Embodiment 1 is that the two permanent magnets 7 are respectively fixed at both ends of the magnetostrictive material.

Embodiment 3: Referring to FIG. 3 , the difference from Embodiment 1 is that the driving element for periodically changing the cavity length of the fiber grating FPI12 includes a transmission line 9 , a piezoelectric ceramic 11 and a mutual induction coil 10 . The output of the mutual induction coil 10 is connected to the piezoelectric ceramic 11 through the transmission line 9 .

The mutual induction coil converts the current in the busbar into a voltage, and loads it on the piezoelectric ceramic through the transmission line. Driven by the voltage, the piezoelectric ceramic deforms and acts on the F-P cavity of the fiber grating, causing the F-P cavity of the fiber grating to deform.

The realization device of this method is that the fiber grating FPI of the fiber grating Fabry-Perot interferometer is pasted on the magnetostrictive material, and it is connected with a port of the fiber coupler through a single-mode fiber, and the monochromatic light source and the photoelectric The detection device is connected with the other two ports of the fiber coupler, and the fourth port of the fiber coupler is inserted into the refractive index matching liquid through a single-mode fiber. During the measurement, the alternating current sensing head is placed in the magnetic field generated by the alternating current to be measured. The center wavelength of the fiber grating FPI used at room temperature (20°C) is around 1550nm, and the bandwidth is less than 0.2nm. The reflectivity is less than 5%, and the F-P cavity is pasted on the surface of the magnetostrictive material with modified acrylate glue, and the distance between the two pasting points is 6cm. When the current value to be measured changes, the narrow-band light emitted by the monochromatic light source is emitted through the fiber grating FPI, and then the signal detected by the photoelectric detection device will change the period of the measurement waveform displayed on the oscilloscope. The magnitude of the current value is obtained according to the different periodic characteristics of the waveform; when the ambient temperature changes, the amplitude of the waveform displayed on the oscilloscope will change, and then the temperature can be obtained according to the magnitude of the amplitude. Finally, the temperature-compensated current value is obtained from the relationship between the actual correction value i of the current and the measured current value i′.

Claims (6)

1. A temperature-compensated current sensing head is characterized in that it comprises a fiber grating Fabry-Perot interferometer (12), a magnetostrictive material (8) and 2 permanent magnets (7); 2 permanent magnets The magnet (7) is relatively parallel placed on both sides of the magnetostrictive material (8), and the fiber grating F-P cavity of the fiber grating Fabry-Perot interferometer (12) is pasted on the magnetostrictive material (8); The length of the fiber grating F-P cavity of the stretchable material (8) is long or less than 1.5 times of the fiber grating F-P cavity length; the length of the two permanent magnets (7) is greater than or equal to the length of the fiber grating F-P cavity length; the fiber grating F-P cavity is located Between two sections of fiber gratings (6) of the fiber grating Fabry-Perot interferometer. 2. The temperature-compensated current sensing head according to claim 1, characterized in that: the two permanent magnets (7) are vertically fixed at both ends of the magnetostrictive material (8). 3. The temperature-compensated current sensing head according to claim 1, characterized in that: the reflectivity of the fiber grating Fabry-Perot interferometer is less than 5%. 4. The temperature-compensated current sensing head according to claim 1 or 3, characterized in that: the magnetostrictive material (8) adopts equal-length piezoelectric ceramics (11), and the permanent magnet adopts a mutual induction coil (10) and a transmission line (9); the mutual induction coil (10) is connected to the piezoelectric ceramic (11) through the transmission line (9). 5. A method for measuring alternating current using any one of the temperature-compensated current sensor heads described in claims 1 to 4, characterized in that the steps are as follows: Step 1: Place the current sensing head in the magnetic field generated by the alternating current to be measured, input an optical signal with a wavelength of λ and a light intensity of I ₀ , and the current sensing head outputs a double-beam interference signal with a light intensity of I ; Step 2: Obtain the fiber grating Fabry-Perot interferometer fiber grating FP cavity length variation according to the two-beam interference signal whose light intensity is I:

where R _λ is the peak reflectivity of the fiber grating FP cavity to the intensity of monochromatic light at wavelength λ,

is the initial phase of the fiber grating FP cavity interference signal, n is the refractive index of the fiber core; Step 3: According to the linear relationship between Δh and current intensity, the measured value i' of current intensity is obtained as Among them, A is the proportional coefficient obtained by conventional experimental calibration; Step 4: According to the compensation relationship between the measured value i' and the actual value i to the temperature $i=\frac{C_{\mathrm{eff}}}{C_{\mathrm{eff}}+{\mathrm{\&kappa;}}_2\&Center\; Dot;\mathrm{\&Delta;T}}{i}^{\&prime;},$ The actual value of the current measured in the environment is obtained

Among them, κ ₂ is the temperature and magnetic field intensity cross-sensitivity coefficient of the magnetostrictive material, C _eff is the magnetostriction coefficient of the magnetostrictive material, and the two coefficient values of κ ₂ and C _eff are obtained by conventional experimental calibration. 6. A system for realizing the method for measuring alternating current according to claim 5, characterized in that: the current sensing head is connected to one port on one side of the fiber coupler (4) through a single-mode optical fiber (3), and the other The port is placed in the refractive index matching liquid (5) through the single-mode optical fiber (3); the two ports on the other side of the fiber coupler (4) are respectively connected to the monochromatic light source (1) and the photoelectric detection device (2).

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