Sensor Noise Compensation Method with Convergent Polarization Interference and Merging Unit Synchronous Sampling

Abstract

The present invention proposes a sensor noise compensation method that combines convergent polarization interference and synchronous sampling of a unit. The light from a light source passes through a polarizer to form linearly polarized light. Under the action of a magnetic field to be measured, the linearly polarized light passes through a magneto-optical thin film, and its polarization plane rotates by α. Then, it enters a uniaxial crystal through a converging lens, where birefringence occurs and it is decomposed into an o-ray and an e-ray with vibration directions perpendicular to each other and a fixed phase difference, forming a convergent polarization interference image. When there is no temperature drift or vibration, in the convergent polarization interference image corresponding to the zero-crossing of the alternating current to be measured, the Faraday magneto-optical rotation angle α The center position of the bright fringe of the corresponding interference spot is at y axis; in the case of temperature drift or vibration, the rotation angle of the interference spot of the convergent polarization interference image corresponding to the zero-crossing of the alternating current to be measured relative to the y axis is the corresponding temperature drift noise γ , which is detected by positioning the spot characteristics γ and compensated to achieve the purpose of eliminating γ ; the present invention can extract and compensate the interference amount formed by stress-induced birefringence.

Description

Technical Field

[0001] The present invention relates to the technical field of voltage measurement, in particular to a sensor noise compensation method for convergent polarization interference and merging unit synchronous sampling, that is, an optical current sensor temperature drift noise compensation method based on convergent polarization interference and merging unit synchronous sampling. Background Art

[0002] Optical current sensors effectively overcome the inherent defects of traditional electromagnetic current transformers and have received extensive attention and research for decades. In practical engineering applications, affected by factors such as temperature changes and vibrations, magneto-optic materials and transmission fibers generate random stress line birefringence, that is, temperature drift noise, making it difficult for the measurement accuracy and stability of optical current sensors to meet practical requirements. At the same time, temperature drift noise is also considered to be one of the key problems restricting the practical application of optical current sensors for many years.

[0003] Existing optical current sensors are mostly based on Malus' law, that is, the Faraday magneto-optic rotation angle is approximately linearly measured by detecting the output light intensity of the sensor. This measurement mode has disadvantages such as light source power dependence and non-linear demodulation, making the Faraday magneto-optic rotation angle and temperature drift noise mixed together, difficult to separate and eliminate, which is also the crux of the problem that has not been effectively solved for temperature drift noise. Summary of the Invention

[0004] The present invention proposes a sensor noise compensation method for convergent polarization interference and merging unit synchronous sampling, which can extract and compensate the interference caused by stress line birefringence formed by temperature drift or vibration when the alternating current passes through zero.

[0005] The present invention adopts the following technical solutions.

[0006] A sensor noise compensation method for convergent polarization interference and merging unit synchronous sampling, which is used for an optical current sensor based on the Faraday magneto-optic effect to detect the temperature drift noise γ corresponding to the stress line birefringence caused by temperature drift or vibration of the optical fiber and magneto-optic crystal of the optical current sensor, and includes the following steps;

[0007] Step S1: The light emitted by the light source passes through a polarizer to form linearly polarized light. Under the action of the magnetic field to be measured, the linearly polarized light passes through the magneto-optical thin film, and its polarization plane rotates by α, which is the Faraday magneto-optical rotation angle. Then it passes through a converging lens (4) for focusing and enters a uniaxial crystal (5). Birefringence occurs in the uniaxial crystal, and it is decomposed into an o-ray and an e-ray with vibration directions perpendicular to each other and a fixed phase difference. After being processed by a collimating lens (6) and an analyzer (7), a converging polarized light interference image (8) that can be detected by the merging unit synchronous sampling device (9) is formed. When there is no temperature drift or vibration in the environment where the optical current sensor is located, in the converging polarized light interference image (10) corresponding to the zero-crossing of the alternating current to be measured, the center position of the bright fringe of the interference spot corresponding to the Faraday magneto-optical rotation angle α is on the y-axis;

[0008] Step S2: When there is temperature drift or vibration in the environment where the optical current sensor is located, the temperature drift noise γ is superimposed on α, resulting in a total rotation of the polarization plane of the output linearly polarized light by an angle of α + γ. The rotation angle of the polarization plane of the linearly polarized light is directly and linearly measured by detecting the rotation angle of the spot;

[0009] Step S3: In the converging polarized light interference image (11) corresponding to the zero-crossing of the alternating current to be measured under the condition of temperature drift or vibration, α = 0. At this time, the output signal of the optical current sensor is the temperature drift noise γ, and the rotation angle (11) of the interference spot relative to the y-axis corresponds to the temperature drift noise γ. By locating the spot characteristics, γ is detected and compensated to achieve the purpose of eliminating γ.

[0010] The magneto-optical crystal is the magneto-optical thin film (3); the linearly polarized light is generated by processing the optical signal emitted by the laser source (1) through the polarizer (2).

[0011] The method obtains the output signal of the optical current sensor by the merging unit synchronous sampling method of the merging unit synchronous sampling device, and samples through the whole station merging unit accessing the unified synchronous clock to improve the synchronization accuracy, and thus determines the zero-crossing point of the alternating current to be measured.

[0012] In Step S3, the compensation for the temperature drift noise is calculated based on the Jones matrix. The specific method is as follows: A coordinate system is established with the transmission axis direction of the analyzer as the x-axis. When the linearly polarized light passes through the crystal, it is decomposed into an o-ray and an e-ray along the normal and tangent directions of the conical light circle. Among them, P1 is the azimuth of the transmission axis of the polarizer, P2 is the azimuth of the transmission axis of the analyzer, θ1 is the angle from the x-axis to the e-axis, and θ2 is the angle between the transmission axis of the polarizer P1 and the transmission axis of the analyzer P2;

[0013] In the o-e coordinate system, the Jones matrix E of the elliptically polarized light is:

[0014]

[0015] where δ is the phase difference between the o-ray and the e-ray introduced by the crystal:

[0016]

[0017] Where: n o is a constant and is the refractive index of the o-ray; n e (θ) is the refractive index of the e-ray, which varies with the incident angle θ of the light beam; d is the thickness of the crystal in the optical transmission direction; λ is the wavelength of the laser;

[0018] Transforming Equation (1) to the x-y coordinate system gives:

[0019]

[0020] Equation (3);

[0021] The Jones vector after passing through the analyzer is:

[0022]

[0023] The expression for the output light intensity is:

[0024]

[0025] Equation (5);

[0026] Performing partial differential operations on Equation (5) to obtain the positions of the maximum or minimum brightness of the interference fringes:

[0027]

[0028] Equation (6);

[0029] Since sin 2 δ / 2 is not zero, so θ2 = 2θ1;

[0030] The relationship between the sum of the Faraday rotation angle of the incident light and the temperature drift noise α + γ and the rotation angle θ of the interference fringes is: α + γ = 2θ Equation (7);

[0031] The result of the linear measurement of the optical current sensor is the linear superposition of α and γ. According to the Faraday magneto-optical effect, the measured magnetic field H and α satisfy

[0032] α = VHL M Equation (8);

[0033] where V is the Verdet constant, L M is the optical path length of the magneto-optical material along the magnetic field direction; when H = 0, α = 0, that is, at the moment when the alternating current passes through zero, the output signal α' of the optical current sensor is γ / 2, and γ is detected and compensated at this moment.

[0034] In step S3, the rotation angle of the light spot is detected by a CMOS area array camera to achieve direct linear measurement of α + γ.

[0035] This invention patent obtains the output signal of the optical current sensor based on the merging unit synchronous sampling method. Sampling is achieved by connecting the whole station merging unit to a unified synchronous clock, which has a high synchronous accuracy, and thus determines the zero-crossing of the alternating current to be measured. Description of the Drawings

[0036] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments:

[0037] Att Figure 1a is a schematic diagram of the principle of the method of the present invention;

[0038] Att Figure 1b is a comparison schematic diagram of the convergent polarized light interference images before and after the environment generates temperature drift or vibration;

[0039] Att Figure 2 is a schematic diagram of the light intensity distribution vector;

[0040] Att Figure 3 is a three-dimensional and top view schematic diagram of the interference light spot when the sum of the Faraday rotation angle and the temperature drift noise is 0°;

[0041] Att Figure 4 is a schematic diagram of the output light spot of the optical current sensor;

[0042] In the figure: 1 is a laser, 2 is a polarizer, 3 is a magneto-optical thin film, 4 is a converging lens, 5 is a uniaxial crystal, 6 is a collimating lens, 7 is an analyzer, 8 is a convergent polarized light interference image, 9 is a merging unit synchronous sampling device,

[0043] 10 is the convergent polarized light interference image corresponding to the zero-crossing of the alternating current to be measured when the environment where the optical current sensor is located does not generate temperature drift or vibration,

[0044] 11 is the convergent polarized light interference image corresponding to the zero-crossing of the alternating current to be measured when the environment where the optical current sensor is located generates temperature drift or vibration. Specific Embodiments

[0045] As shown in the figure, the sensor noise compensation method for convergent polarized light interference and merging unit synchronous sampling is for an optical current sensor based on the Faraday magneto-optical effect, and is used to detect the temperature drift noise γ corresponding to the stress line birefringence caused by temperature drift or vibration of the optical fiber and magneto-optical crystal of the optical current sensor, and includes the following steps;

[0046] Step S1: The light emitted by the light source passes through a polarizer to form linearly polarized light. Under the action of the magnetic field to be measured, the linearly polarized light passes through the magneto-optical thin film, and its polarization plane rotates by α, which is the Faraday magneto-optical rotation angle. Then it is focused by the converging lens 4 and enters the uniaxial crystal 5. Birefringence occurs in the uniaxial crystal, and it is decomposed into an o-ray and an e-ray with vibration directions perpendicular to each other and a fixed phase difference. After being processed by the collimating lens 6 and the analyzer 7, a converging polarized light interference image 8 that can be detected by the merging unit synchronous sampling device 9 is formed; when there is no temperature drift or vibration in the environment where the optical current sensor is located, in the converging polarized light interference image 10 corresponding to the zero-crossing of the alternating current to be measured, the center position of the bright fringe of the interference spot corresponding to the Faraday magneto-optical rotation angle α is on the y-axis.

[0047] Step S2: When there is temperature drift or vibration in the environment where the optical current sensor is located, the temperature drift noise γ is superimposed on α, resulting in a total rotation of the polarization plane of the output linearly polarized light by an angle of α + γ. The rotation angle of the polarization plane of the linearly polarized light is directly and linearly measured by detecting the rotation angle of the spot.

[0048] Step S3: In the converging polarized light interference image 11 corresponding to the zero-crossing of the alternating current to be measured under the condition of temperature drift or vibration, α = 0. At this time, the output signal of the optical current sensor is the temperature drift noise γ, and the rotation angle (11) of the interference spot relative to the y-axis corresponds to the temperature drift noise γ. The γ is detected and compensated by positioning the spot characteristics to achieve the purpose of eliminating γ.

[0049] The magneto-optical crystal is the magneto-optical thin film 3; the linearly polarized light is generated by processing the optical signal emitted by the laser source 1 through the polarizer 2.

[0050] The method obtains the output signal of the optical current sensor by the merging unit synchronous sampling method of the merging unit synchronous sampling device, samples through the whole station merging unit accessing the unified synchronous clock to improve the synchronization accuracy, and thereby determines the zero-crossing point of the alternating current to be measured.

[0051] In step S3, the compensation for the temperature drift noise is calculated based on the Jones matrix. The specific method is: a coordinate system is established with the transmission axis direction of the analyzer 7 as the x-axis. When the linearly polarized light passes through the crystal, it is decomposed into an o-ray and an e-ray along the normal and tangent directions of the conical light circle, as shown in the appendix. Figure 2 Among them, P1 is the azimuth of the transmission axis of the polarizer, P2 is the azimuth of the transmission axis of the analyzer, θ1 is the angle from the x-axis to the e-axis, and θ2 is the angle between the transmission axis of the polarizer P1 and the transmission axis of the analyzer P2;

[0052] In the o-e coordinate system, the Jones matrix E of the elliptically polarized light is:

[0053]

[0054] Among them, δ is the phase difference between the o-ray and the e-ray introduced by the crystal:

[0055]

[0056] Where: n o is a constant and is the refractive index of the o-ray; n e (θ) is the refractive index of the e-ray, which varies with the incident angle θ of the light beam; d is the thickness of the crystal in the light-passing direction; λ is the wavelength of the laser;

[0057] Transforming Formula One into the x-y coordinate system gives:

[0058]

[0059] Formula Three;

[0060] The Jones vector after passing through the analyzer is:

[0061]

[0062] The expression for the output light intensity is:

[0063]

[0064] Formula Five;

[0065] Performing partial differential operations on Formula Five to obtain the positions of the maximum or minimum brightness of the interference fringes:

[0066]

[0067] Formula Six;

[0068] Since sin 2 δ / 2 is not zero, so θ2 = 2θ1;

[0069] The relationship between the sum of the Faraday rotation angle and the temperature drift noise α + γ of the incident light and the rotation angle θ of the interference fringes is: α + γ = 2θ Formula Seven;

[0070] When the initial azimuth of the analyzer's light-transmitting axis is 0° and α + γ = 0°, the 3D image of the light spot and its top view are as shown in the appendix Figure 3 as follows.

[0071] The convergent polarized light interference images when α + γ are 0°, 60°, 90°, and 150° respectively are as shown in the appendix Figure 4 as follows. It can be seen that θ is half of α + γ.

[0072] The result of the linear measurement of the optical current sensor is the linear superposition of α and γ. According to the Faraday magneto-optical effect, the measured magnetic field H and α satisfy

[0073] α = VHL M Formula Eight;

[0074] where V is the Verdet constant, and L M is the optical path length of the magneto-optical material along the magnetic field direction; when H = 0, α = 0, that is, when the alternating current passes through zero, the output signal α' of the optical current sensor is γ / 2. At this moment, γ is detected and compensated for.

[0075] In step S3, the rotation angle of the light spot is detected by a CMOS area array camera to achieve a direct linear measurement of α + γ.

[0076] Embodiment:

[0077] In this example, an optical current sensor temperature drift noise compensation method based on convergent polarized light interference and synchronous sampling of a merging unit is shown in Figure 1. The optical signal emitted by the laser source 1 passes through the polarizer 2 to obtain linearly polarized light. The linearly polarized light passes through the magneto-optical thin film 3, and under the action of the magnetic field, the polarization plane of the polarized light rotates, and the rotation angle is the Faraday magneto-optical rotation angle α.

[0078] However, temperature changes and vibrations generate stress line birefringence, that is, temperature drift noise γ, in the magneto-optical thin film and the transmission optical fiber, and it is superimposed on α, resulting in the polarization plane of the output linearly polarized light rotating a total of α + γ angles.

[0079] The linearly polarized light passes through the converging lens 4 and is focused into the uniaxial crystal 5, where birefringence is generated and decomposed into an o-ray and an e-ray with vibration directions perpendicular to each other and having a fixed phase difference. After passing through the collimating lens 6 and the analyzer 7, a convergent polarized light interference image 8 is formed. The interference image rotates synchronously with the change of the polarization plane of the linearly polarized light, and the direct and linear measurement of the rotation angle of the polarization plane of the linearly polarized light can be achieved by detecting the rotation angle of the light spot.

[0080] According to the Faraday magneto-optical effect, when the alternating current to be measured passes through zero, α = 0, and at this time, the output signal of the sensor is γ. Based on the synchronous sampling of the merging unit, the output signal of the optical current sensor is obtained, and the zero-crossing point of the alternating current is determined. At this moment, the center position of the bright fringe of the interference light spot corresponding to α is on the y-axis, and the rotation angle of the interference light spot output by the optical current sensor is γ. By positioning the light spot, γ can be detected and compensated for to achieve the purpose of eliminating γ.

[0081] In this example, the laser is a helium-neon laser produced by Pulei Optoelectronics, with a light wave wavelength of 632.8 nm; the magneto-optical thin film is of the Bi-Gd-YIG type; the electro-optic crystal is an LN crystal, with transverse modulation and a half-wave voltage of the crystal of 720 V; another LN crystal is a uniaxial crystal for convergent polarized light interference, and the crystal plane is perpendicular to the optical axis; a high-sensitivity CMOS camera is used to continuously collect the spot images; a high and low temperature alternating humidity test chamber is used to provide different temperature environments, with a temperature range of -40°C to 85°C and a temperature fluctuation of ±0.5°C. In the example, the optical path of the optical current sensor is placed in the inner cavity of the incubator, and a temperature cycle experiment is carried out in the range of -40°C to 85°C. The zero-crossing detection circuit is used to detect the zero-crossing point, determine the stress-induced birefringence introduced in each cycle and compensate for it. Finally, the basic accuracy of the optical current sensor is recorded by a calibrator, as shown in Table 1. Under the temperature cycle conditions, the optical current sensor can meet the accuracy requirements of class 0.5.

[0082] Table 1 Basic accuracy experimental data

[0083]

[0084] Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Claims

1. A sensor noise compensation method for convergent polarized light interference and synchronous sampling of a merging unit, which is applicable to an optical current sensor based on the Faraday magneto-optic effect and is used to detect the temperature drift noise γ corresponding to the stress line birefringence caused by temperature drift or vibration of the optical fiber and magneto-optic crystal of the optical current sensor, and is characterized in that: Including the following steps; Step S1: The light emitted by the light source passes through a polarizer to form linearly polarized light. Under the action of the magnetic field to be measured, the linearly polarized light passes through the magneto-optical thin film, and its polarization plane rotates by α, which is the Faraday magneto-optical rotation angle, and is focused by the converging lens (4), and then enters the uniaxial crystal (5). Birefringence is generated in the uniaxial crystal and decomposed into an o-ray and an e-ray with mutually perpendicular vibration directions and a fixed phase difference, and then passes through the collimating lens (6) and the analyzer (7) for processing to form a converging polarized light interference image (8) that can be detected by the merging unit synchronous sampling device (9); when there is no temperature drift or vibration in the environment where the optical current sensor is located, in the converging polarized light interference image (10) corresponding to the zero crossing of the alternating current to be measured, the center position of the bright fringe of the interference spot corresponding to the Faraday magneto-optical rotation angle α is on the y-axis; Step S2: When there is temperature drift or vibration in the environment where the optical current sensor is located, the temperature drift noise γ is superimposed on α, resulting in a total rotation of the polarization plane of the output linearly polarized light by an angle of α + γ. The rotation angle of the polarization plane of the linearly polarized light is directly and linearly measured by detecting the rotation angle of the spot. Step S3: In the converging polarized light interference image (11) corresponding to the zero crossing of the alternating current to be measured under the condition of temperature drift or vibration, α = 0. At this time, the output signal of the optical current sensor is the temperature drift noise γ, and the rotation angle of the interference spot relative to the y-axis corresponds to the temperature drift noise γ. By positioning the spot characteristics, γ is detected and compensated to achieve the purpose of eliminating γ. In step S3, the compensation for the temperature drift noise is calculated based on the Jones matrix. The specific method is as follows: A coordinate system is established with the transmission axis direction of the analyzer as the x-axis. When the linearly polarized light passes through the crystal, it is decomposed into an o-ray and an e-ray along the normal and tangent directions of the conical light circle. Among them, P1 is the azimuth of the transmission axis of the polarizer, P2 is the azimuth of the transmission axis of the analyzer, θ1 is the angle from the x-axis to the e-axis, and θ2 is the angle between the transmission axis of the polarizer P1 and the transmission axis of the analyzer P2; In the o-e coordinate system, the Jones matrix E of the elliptically polarized light is: where δ is the phase difference between the o-ray and the e-ray introduced by the crystal: Where: n o is a constant and is the refractive index of the ordinary ray; n e (θ) is the refractive index of the extraordinary ray, which varies with the incident angle θ of the light beam; d is the thickness of the crystal in the optical transmission direction; λ is the wavelength of the laser; Transforming formula one to the x-y coordinate system, we get: The Jones vector after passing through the analyzer is: The expression of the output light intensity is: Perform partial differential operations on formula five to obtain the position of the maximum or minimum brightness of the interference fringes: Since sin 2 δ / 2 is not zero, so θ2 = 2θ1; The relationship between the sum of the Faraday rotation angle of the incident light and the temperature drift noise α + γ and the rotation angle θ of the interference fringes is: α + γ = 2θ formula seven; The linear measurement result of the optical current sensor is the linear superposition of α and γ. According to the Faraday magneto-optical effect, the magnetic field H to be measured and α satisfy α = VHL M Formula VIII; where V is the Verdet constant and L M is the optical path length of the magneto-optic material along the magnetic field direction; when H = 0, α = 0, that is, when the alternating current passes through zero, the output signal α' of the optical current sensor is γ / 2. At this moment, γ is detected and compensated for.

2. The sensor noise compensation method for convergent polarized light interference and synchronous sampling of a merging unit according to claim 1, characterized in that: The magneto-optical crystal is the magneto-optical thin film (3); the linearly polarized light is generated by processing the optical signal emitted by the laser source (1) through the polarizer (2).

3. The sensor noise compensation method of convergent polarized light interference and synchronous sampling of a merging unit according to claim 1, characterized in that: The method obtains the output signal of the optical current sensor by the merging unit synchronous sampling method of the merging unit synchronous sampling device, and improves the synchronization accuracy by accessing the unified synchronous clock through the substation merging unit for sampling, and thereby determines the zero crossing of the alternating current to be measured.

4. The sensor noise compensation method for convergent polarized light interference and synchronous sampling of a merging unit according to claim 1, wherein: In step S3, the rotation angle of the spot is detected by a CMOS area array camera to achieve the direct linear measurement of α + γ.

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