CN111624390A - Optical fiber reflection type current sensor, system and method based on magnetic fluid - Google Patents
Optical fiber reflection type current sensor, system and method based on magnetic fluid Download PDFInfo
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- CN111624390A CN111624390A CN202010537195.9A CN202010537195A CN111624390A CN 111624390 A CN111624390 A CN 111624390A CN 202010537195 A CN202010537195 A CN 202010537195A CN 111624390 A CN111624390 A CN 111624390A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/24—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices
- G01R15/245—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect
- G01R15/246—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using light-modulating devices using magneto-optical modulators, e.g. based on the Faraday or Cotton-Mouton effect based on the Faraday, i.e. linear magneto-optic, effect
Abstract
The invention provides an optical fiber reflection type current sensor, a system and a method based on magnetic fluid. The current sensor includes: the optical fiber comprises a capillary tube and an optical fiber, wherein magnetic fluid is filled in the capillary tube, and ports at two ends of the capillary tube are sealed through colloid; one end of the optical fiber is inserted into the capillary, and the other end of the optical fiber is exposed out of the capillary; the end face of the optical fiber in the capillary is formed by cutting the optical fiber along the direction perpendicular to the axis of the optical fiber. The sensing structure in the sensor provided by the invention mainly comprises the optical fiber, and the optical fiber has the characteristics of insulation, corrosion resistance and high temperature resistance, and can adapt to the complex environment of a high-voltage strong magnetic field of a convertor station; by utilizing the refractive index controllable characteristic of the magnetic fluid, the refractive index of the magnetic fluid is very sensitive to the change of a current magnetic field, so that the sensitivity of the sensor to the current change is very high.
Description
Technical Field
The invention relates to the technical field of optical sensing, in particular to an optical fiber reflection type current sensor, a system and a method based on magnetic fluid.
Background
The flexible direct-current transmission technology is a new generation transmission technology which has the most potential for realizing direct-current power grid and new energy grid connection after alternating-current transmission and conventional direct-current transmission, and consists of a flexible direct-current converter station and a direct-current transmission line. The flexible direct current converter station mainly completes the mutual conversion of alternating current and direct current, the core equipment of the flexible direct current converter station is a bipolar transistor (IGBT), and the size of direct current of a copper bar connected with the IGBT is monitored in real time, so that the flexible direct current converter station is of great importance to the safe and stable operation of the whole converter station.
At present, an electromagnetic current transformer is mainly used for monitoring current in an electric power system, but on one hand, the electromagnetic current transformer has the problems of poor transient response and unstable signals, so that the current measurement precision can be influenced; on the other hand, the insulation device also has the problem of difficult insulation, is easy to malfunction and even can cause electric power accidents. Therefore, a novel current sensing method capable of replacing the electromagnetic current transformer is imperative for maintaining the safe and reliable operation of the whole power system.
In the research on high-voltage current optical measurement of magnetic fluid sheets [ J ] optical science report, 2007,27(6): 1049-. However, the manufacturing process of the magnetic fluid film structure is complex and strict in requirements, the thickness of the magnetic fluid film needs to be in the micron order, the situation of non-uniformity of the magnetic fluid is easy to occur in the manufacturing engineering, the current measurement result is influenced, and the structure is not easy to install in the engineering.
Disclosure of Invention
The invention provides an optical fiber reflection type current sensor, a system and a method based on magnetic fluid, aiming at solving the problems of poor transient response, unstable signal and difficult insulation of the existing current sensor.
The invention provides an optical fiber reflection type current sensor based on magnetic fluid, which comprises: the optical fiber comprises a capillary tube and an optical fiber, wherein magnetic fluid is filled in the capillary tube, and ports at two ends of the capillary tube are sealed through colloid; one end of the optical fiber is inserted into the capillary, and the other end of the optical fiber is exposed out of the capillary; the end face of the optical fiber in the capillary is formed by cutting the optical fiber along the direction perpendicular to the axis of the optical fiber.
Further, one end of the optical fiber inserted into the capillary is located at 1/3 within the capillary.
Further, the magnetic fluid is Fe3O4A water-based magnetic fluid.
The invention provides an optical fiber reflection type current sensing system based on a magnetic fluid, which comprises a light source, a circulator, a sensing probe, a photoelectric detector, a signal processing unit and a PC (personal computer) end, wherein the light source, the circulator and the sensing probe are sequentially connected through optical fibers; the sensing probe adopts the optical fiber reflection type current sensor based on the magnetic fluid.
Further, the current sensing path is: light beams emitted by the light source enter the sensing probe through the circulator, the light beams reflected by the sensing probe reach the photoelectric detector through the circulator again, the photoelectric detector transmits detection signals to the signal processing unit to perform signal processing to obtain current signals of the circuit to be detected, and the PC side displays the current signals.
Furthermore, the signal processing unit comprises a singlechip, a driving circuit, an I/U conversion and operational amplifier circuit, an A/D converter and a power supply; the single chip microcomputer is connected with the input end of the driving circuit, and the output end of the driving circuit is connected with the light source to drive the light source to emit light beams; the output end of the photoelectric detector is connected with the input end of the I/U conversion and operational amplifier circuit, the output end of the I/U conversion and operational amplifier circuit is connected with the input end of the A/D converter, and the output end of the A/D converter is connected to the single chip microcomputer.
Further, the light source is a DFB laser.
The invention provides a manufacturing method of an optical fiber reflection type current sensor based on magnetic fluid, which comprises the following steps:
step 1: selecting a capillary tube, wherein one end of the capillary tube is an open end, and a first hole and a second hole are respectively formed in two ends above a tube body of the capillary tube;
step 2: selecting an optical fiber, and cutting one end of the optical fiber along the direction vertical to the axis of the optical fiber to form an optical fiber end face;
and step 3: inserting one end of the optical fiber forming the end face of the optical fiber into the capillary from the open end of the capillary along the axial direction of the capillary;
and 4, step 4: sealing the ports at the two ends of the capillary tube through the colloid, and fixing the optical fiber;
and 5: injecting magnetic fluid into the capillary through the first hole, and simultaneously exhausting air in the capillary through the second hole;
step 6: and sealing the first hole and the second hole, thereby forming the optical fiber reflection type current sensor based on the magnetic fluid.
The invention provides an optical fiber reflection type current sensing method based on magnetic fluid, which comprises the following steps:
step 1: obtaining the intrinsic reflected light power P of the system according to the formula (6) by adopting a known sample calibration method0：
Wherein S is an optical fiberEffective cross-sectional area of end face, PaAnd PwThe reflected light power, n, measured by placing the pre-packaged fiber in a first sample and in a second sample, respectivelyf、naAnd nwThe refractive indexes of the fiber core, the first sample and the second sample are respectively;
step 2: according to the intrinsic reflected light power P0Calculating according to the formula (7) to obtain the reflected light power P of the optical fiber in the magnetic fluidMFAnd refractive index n of magnetic fluidMFThe relation of (1):
wherein k isMFThe attenuation coefficient of the magnetic fluid;
and step 3: calculating the refractive index n of the magnetic fluid according to the formula (8)MF：
And 4, step 4: and calculating to obtain magnetic field information according to the relationship between the refractive index of the magnetic fluid and the magnetic field defined by the Langmuim function, and obtaining the current of the circuit to be tested according to the relationship between the magnetic field information and the current defined by the Biot-Saval law.
The invention has the beneficial effects that:
1. safe insulation: the sensing structure in the sensor provided by the invention mainly comprises the optical fiber, and the optical fiber has the characteristics of insulation, corrosion resistance and high temperature resistance, and can adapt to the complex environment of a high-voltage strong magnetic field of a convertor station.
2. The transient response is fast, and the signal is stable: the magnetofluid material has the characteristics of no hysteresis effect and quick response, so the sensor based on the magnetofluid provided by the invention has quick transient response and stable signals.
3. The sensitivity is high: the refractive index of the magnetic fluid is very sensitive to the change of the current magnetic field, and the sensor provided by the invention utilizes the controllable refractive index characteristic of the magnetic fluid, so that the sensor has very high sensitivity to the current change.
4. The structure is light and handy, easily preparation and installation: the sensor of the invention is composed of the optical fiber, the magnetic fluid and the capillary, has simple structure composition, simple manufacturing method and small volume, is easy to arrange and install in the complex structure of the power equipment, and hardly occupies the space of the power system.
5. The application prospect is wide: the current sensor, the system and the method provided by the invention can be suitable for power equipment in multiple application occasions, and can be applied to power equipment in application scenes of chemical plants, petroleum pipelines, automobile equipment and the like besides a converter station.
Drawings
Fig. 1 is a schematic structural diagram of a magnetic fluid-based optical fiber reflective current sensor according to an embodiment of the present invention;
fig. 2 is a second schematic structural diagram of a magnetic fluid-based optical fiber reflective current sensor according to an embodiment of the present invention;
FIG. 3 is a schematic end view of an optical fiber positioned within a capillary according to an embodiment of the present invention;
FIG. 4 is a schematic view of a first hole and a second hole above a body of a capillary tube provided by an embodiment of the present invention;
FIG. 5 is a schematic structural diagram of a magnetofluid-based optical fiber reflective current sensing system according to an embodiment of the present invention;
fig. 6 is a second schematic structural diagram of a magnetic fluid-based optical fiber reflective current sensing system according to an embodiment of the present invention;
fig. 7 is a schematic circuit structure diagram of a single chip microcomputer in the signal processing unit according to the embodiment of the present invention;
fig. 8 is a schematic diagram of an I/U conversion and operational amplifier circuit in a signal processing unit according to an embodiment of the present invention;
fig. 9 is a schematic diagram of an a/D converter circuit in the signal processing unit according to the embodiment of the present invention;
fig. 10 is a schematic diagram of a circuit structure of a light source in a signal processing unit according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The magnetic fluid, also called magnetic liquid, is a stable colloidal system that possesses both the magnetic properties of solid magnetic materials and the fluidity of liquids. The composition of the magnetic particle dispersion liquid comprises three parts of magnetic particles, a surfactant and a carrier liquid, wherein nano-scale ferromagnetic solid particles (the diameter is about 10nm generally) are uniformly dispersed in a certain carrier liquid under the coating of the surfactant. As a special novel intelligent nano material, the magnetic fluid has some special optical characteristics, such as the magnetic control refractive index characteristic (namely the characteristic that the refractive index can change along with the change of a magnetic field) of the magnetic fluid. The invention designs a novel current sensor by utilizing the magnetic control refractive index characteristic of the magnetic fluid.
Example 1
As shown in fig. 1 to 3, an embodiment of the present invention provides a fiber-optic reflective current sensor based on a magnetic fluid, including: the device comprises a capillary tube 1 and an optical fiber 2, wherein magnetic fluid 3 is filled in the capillary tube 1, and ports at two ends of the capillary tube 1 are sealed through colloids 4; one end of the optical fiber 2 is inserted into the capillary 1, and the other end of the optical fiber 2 is exposed out of the capillary 1; the optical fiber end face 5 in the capillary 1 is formed by cutting the optical fiber 2 in a direction perpendicular to the axis of the optical fiber 2. As shown in FIG. 2, as an embodiment, one end of the optical fiber 2 inserted into the capillary 1 is located at 1/3 in the capillary 1, and the magnetic fluid is Fe3O4A water-based magnetic fluid.
The optical fiber is inserted into 1/3 of the capillary, so that the end face of the optical fiber can be completely immersed in the environment of the magnetic fluid, the optical fiber has a certain margin in the capillary, the contact surface between the colloid and the optical fiber can be increased, and the optical fiber is not easy to fall off from the capillary; in addition, on the basis of ensuring that the optical fiber has certain allowance in the capillary, the optical fiber waste caused by overlong inserted optical fiber is avoided to a certain extent, and the using amount of the optical fiber is saved. Compared with other types of magnetic fluids, the water-based magnetic fluid adopts deionized water as a base fluid, has stable and safe performance and low cost, and is easy to manufacture.
Example 2
Correspondingly, the embodiment of the invention also provides a manufacturing method of the optical fiber reflection type current sensor based on the magnetic fluid, which comprises the following steps:
s101: selecting a capillary tube 1, wherein one end of the capillary tube 1 is an open end, and a first hole 6 and a second hole 7 are respectively formed at two ends above a tube body of the capillary tube 1, as shown in fig. 4;
specifically, a polyimide capillary having a diameter of 3mm and a length of 5cm may be used.
S102: selecting an optical fiber, and cutting one end of the optical fiber along the direction vertical to the axis of the optical fiber to form an optical fiber end face;
specifically, an FC-6S fiber cleaver may be used to cleave the fiber, leaving the fiber end face to be flattened. The optical fiber adopts single-mode optical fiber, the mode dispersion of the single-mode optical fiber is very small, and the optical fiber is suitable for long-distance transmission.
S103: inserting one end of the optical fiber forming the end face of the optical fiber into the capillary from the open end of the capillary along the axial direction of the capillary;
s104: sealing the ports at the two ends of the capillary tube through the colloid, and fixing the optical fiber;
in particular, the colloid may use UV glue.
S105: injecting magnetic fluid into the capillary through the first hole 6, and simultaneously exhausting air in the capillary through the second hole 7;
it should be noted that the injection of the magnetic fluid should avoid the generation of air bubbles, and therefore the second hole 7 is provided for exhausting the air in the capillary. The magnetic fluid adopts Fe3O4Water based magnetic fluid, such as EMG 605.
S106: and sealing the first hole 6 and the second hole 7, thereby forming the optical fiber reflection type current sensor based on the magnetic fluid.
As can be seen from the above, compared with a current sensor that optically measures high-voltage current by using a magnetic fluid thin film, the optical fiber reflective current sensor based on magnetic fluid provided by the embodiment of the present invention has a capillary structure in which an optical fiber end surface is disposed in a magnetic fluid environment, so that the magnetic fluid environment is stable, and the stability of a measurement result can be effectively ensured; the sensing probe has a tiny structure, is beneficial to installation in engineering, has strong survivability in a narrow space, is insulated and safe in material and stable in performance, and can effectively meet the strict requirements of engineering; the manufacturing process is simple and is beneficial to batch production.
Example 3
As shown in fig. 5, an embodiment of the present invention further provides an optical fiber reflective current sensing system based on a magnetic fluid, including a light source, a circulator, a sensing probe, a photodetector (also referred to as PD for short), a signal processing unit, and a PC terminal, where the light source, the circulator, and the sensing probe are sequentially connected by an optical fiber, the signal processing unit provides a driving signal for the light source, the circulator is further connected with the photodetector by an optical fiber, and the photodetector, the signal processing unit, and the PC terminal are sequentially electrically connected; the sensing probe adopts the optical fiber reflection type current sensor based on the magnetic fluid in the embodiment 1.
In particular, in use, it is necessary to place the sensing probe in the magnetic field generated by the circuit under test (e.g. the energized copper bar). The current sensing path of the current sensing system provided by the embodiment of the invention is as follows: light beams emitted by the light source enter the sensing probe through the circulator, the light beams reflected by the sensing probe reach the photoelectric detector through the circulator again, the photoelectric detector transmits detection signals to the signal processing unit to perform signal processing to obtain current signals of the electrified copper bar to be detected, and the PC side displays the current signals.
As shown in fig. 6, the signal processing unit in the embodiment of the present invention includes a single chip, a driving circuit, an I/U conversion and operational amplifier circuit, an a/D converter, and a power supply; the single chip microcomputer is connected with the input end of the driving circuit, and the output end of the driving circuit is connected with the light source to drive the light source to emit light beams; the output end of the photoelectric detector is connected with the input end of the I/U conversion and operational amplifier circuit, the output end of the I/U conversion and operational amplifier circuit is connected with the input end of the A/D converter, and the output end of the A/D converter is connected to the single chip microcomputer. As an implementation manner, as shown in fig. 7 to 10, the power supply adopts a ± 5V voltage source to provide a ± 5V voltage for the whole circuit system; the type of the singlechip is AT89C 51; a drive chip in the drive circuit adopts an ULN2003 power consumption drive chip; the A/D converter adopts ADC 0809; the light source adopts a DFB laser with the wavelength of 1550 nm; an AD626 operational amplifier is adopted in the I/U conversion and operational amplifier circuit, and the AD626 operational amplifier specifically comprises two AD 626: the first AD626 is connected with a resistor to be used as a trans-resistance amplifier to realize I/U conversion and amplify voltage at the same time, and the second AD626 is used as a voltage follower.
The working process of the optical fiber reflection type current sensing system based on the magnetofluid provided by the embodiment of the invention is as follows: the whole system is started by turning on a power supply, AT89C51 outputs current through a P2.0 port, then outputs large current through ULN2003, further drives the DFB laser to emit a 1550nm light beam, the 1550nm light beam enters a sensing probe through a circulator, the sensing probe reflects the entered light beam, and a photoelectric detector detects the light intensity of the light beam reflected by the sensing probe to obtain a current signal corresponding to the light intensity; the current signal output by the photoelectric detector is converted into a voltage signal through an I/U conversion and operational amplifier circuit; then the voltage signal is converted into a digital signal through an ADC 0809; then the digital signal is transmitted to AT89C51 through ports P1.0 to P1.7, AT89C51 substitutes the received digital signal (i.e. light information data) into a formula to calculate (i.e. a related algorithm formula of current is calculated according to light intensity, which will not be described in detail in embodiment 4 below), obtains a current value of the energized copper bar to be tested AT the moment, and displays the current value AT the PC end in real time, and simultaneously, the PC end compares the current value with a set current threshold, and if the current value exceeds the threshold, an alarm is sent out AT the PC end to prompt relevant workers to perform follow-up maintenance.
Example 4
The embodiment of the invention measures the current by utilizing the magnetic control refractive index characteristic of the magnetic fluid. It is known from biot-savart law that a magnetic field is generated around a current-carrying conductor and varies with a change in current. The magnetic control refractive index characteristic of the magnetic fluid can be expressed by a langevin function, and the refractive index of the magnetic fluid can be changed along with the change of a magnetic field according to the langevin function, so that the change condition of the current can be obtained by measuring the change of the refractive index of the magnetic fluid.
The magnetic control refractive index characteristic of the magnetic fluid is expressed by a langevin function, and the refractive index of the magnetic fluid can be expressed as follows:
wherein n isMFThe refractive index of the magnetic fluid is shown, and H represents the magnetic induction intensity; hc,nIs nMFCritical magnetic induction at which a change begins; n is0Is magnetic field smaller than Hc,nThe refractive index of the lower magnetic fluid; n issIs the saturation index, α is the tuning coefficient, and T is the ambient temperature.
The embodiment of the invention realizes the measurement of the refractive index of the magnetic fluid based on the Fresnel reflection theory: when a light beam is incident on the interface of two media with different refractive indexes, a part of the light will be reflected back. For the absorption medium and the magnetic material, the reflectance (r) of the electric field amplitude can be obtained assuming that the light beam is incident from the medium 1 to the interface with the medium 2s,rp) The expression of (a) is as follows:
wherein E issAnd E'sElectric field amplitude of incident and reflected light, respectively, of a component s of the light beam perpendicular to the plane of incidence, EpAnd E'pElectric field amplitudes of incident light and reflected light, which are components p of the light beam parallel to the incident surface, respectively;
and
complex amplitudes, n, of media 1 and 2, respectively1And n2Refractive indices, k, of media 1 and 2, respectively1And k2Attenuation coefficients, k, of Medium 1 and Medium 2, respectively1＝α1λ/4πk2＝α2λ/4π，α1And α2The absorption coefficients of the medium 1 and the medium 2 are respectively, and lambda is the wavelength of the light beam; mu.s1And mu2Relative magnetic permeability of medium 1 and medium 2, respectively; i.e. i1And i2Respectively, angle of incidence and angle of reflection.
In the optical fiber reflective current sensing system based on the magnetic fluid provided in embodiment 3, the end face of the optical fiber of the sensing probe located in the magnetic fluid is specially cut flat (i.e. the optical fiber is cut along the direction perpendicular to the optical fiber axis), so that the incident light and the reflective interface satisfy the normal incidence condition, i.e. i1And i2Are both 0. The light source is selected to be near infrared light with single wavelength, and has relative permeability mu for medium 1 and medium 21And mu2May be 1. Therefore, the electric field amplitude reflectivity relationships (1) and (2) can be simplified as follows:
wherein, the fiber core is used as medium 1, the attenuation coefficient is very small, and k is takenf0, refractive index thereof
Magnetic fluid as medium 2, refractive index of which
The total reflected light power R can be expressed as:
in the formula (5), nfKnown attenuation coefficient k of magnetic fluidMF＝αMFLambda/4 pi, absorption coefficient of magnetofluid αMFIs 4600cm-1λ is the beam wavelength; from the formula (5), the refractive index n of the magnetic fluid can be calculated by measuring RMFThe size of (2).
Based on the above concept, corresponding to the magnetofluid-based optical fiber reflective current sensing system provided in embodiment 3, an embodiment of the present invention provides an optical fiber reflective current sensing method based on a magnetofluid, including the following steps:
s201: obtaining the intrinsic reflected light power P of the system according to the formula (6) by adopting a known sample calibration method0：
Specifically, the reason why step S201 is provided is that there are cases where: the optical fiber is inserted into the solution to be measured, and under the condition that no light source is provided, the reflected light power which is not zero can be actually detected, namely, the intrinsic reflection phenomenon exists in the system. In order to solve the problem, the known sample calibration method is adopted in the step, namely the intrinsic reflected light power of the system is indirectly obtained by measuring the reflected light power of two samples through the two samples with known refractive indexes, so that the interference caused by the intrinsic reflection can be eliminated.
As an implementation mode, the air and the deionized water are used as the calibration samples in the embodiment of the invention. In order to eliminate the influence of other light intensity parameters incident on the interface, the intrinsic reflection and the refractive index of the magnetofluid are calculated by using a proportional algorithm in step S201. At one standard atmosphere, room temperature T ═ 20 ℃, for near infrared light, the refractive indices of air and deionized water were: n isa1.00027 and nw1.333, their attenuation coefficient is ka＝kw0, so
The intrinsic reflected light power P can be obtained from the formula (5)0The relationship of (A) is as follows:
wherein S is the effective cross-sectional area of the fiber end face, PaAnd PwThe reflected light power measured with the pre-packaged fiber in air and water, respectively.
S202: according to the intrinsic reflected light power P0Calculating according to the formula (7) to obtain the reflected light power P of the optical fiber in the magnetic fluidMFAnd refractive index n of magnetic fluidMFThe relation of (1):
s203: calculating the refractive index n of the magnetic fluid according to the formula (8)MF：
S204: and calculating to obtain magnetic field information according to the relation between the refractive index of the magnetic fluid and the magnetic field defined by the Langmuim function, and obtaining the current of the electrified copper bar to be tested according to the relation between the magnetic field information and the current defined by the Biot-Saval law.
In fact, as can be seen from the formula (7), for each PMFAre all correspondingly provided with two nMFThe value, and therefore the negative sign between the first and second terms of the polynomial in equation (8), is due to: the first term of the polynomial in the formula (8) is constantly larger than nfThe second term is non-negative, and the magnetic fluid used in the present embodiment is Fe3O4And the actual refractive index of the water-based magnetic fluid is slightly less than that of the fiber core, so that the second term of the formula (8) takes a negative sign.
In the formula (7), PMFThe light intensity is detected by a photoelectric detector, i.e. the optical fiber is placed in the magnetic fluid and reflected from the end faceThe optical power, formula (8), is obtained by combining formulas (6) and (7).
Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (9)
1. Optical fiber reflective current sensor based on magnetic fluid, characterized in that includes: the optical fiber comprises a capillary tube and an optical fiber, wherein magnetic fluid is filled in the capillary tube, and ports at two ends of the capillary tube are sealed through colloid; one end of the optical fiber is inserted into the capillary, and the other end of the optical fiber is exposed out of the capillary; the end face of the optical fiber in the capillary is formed by cutting the optical fiber along the direction perpendicular to the axis of the optical fiber.
2. The fiber optic reflective magnetic fluid-based current sensor according to claim 1 wherein the end of the optical fiber inserted into the capillary is located at 1/3 within the capillary.
3. The fiber optic reflective magnetic fluid-based current sensor according to claim 1, wherein the magnetic fluid is Fe3O4A water-based magnetic fluid.
4. The optical fiber reflection type current sensing system based on the magnetofluid comprises a light source, a circulator, a sensing probe, a photoelectric detector, a signal processing unit and a PC (personal computer) end, and is characterized in that the light source, the circulator and the sensing probe are sequentially connected through optical fibers, the signal processing unit provides a driving signal for the light source, the circulator is further connected with the photoelectric detector through the optical fibers, and the photoelectric detector, the signal processing unit and the PC end are sequentially and electrically connected; the sensing probe adopts the optical fiber reflective current sensor based on magnetofluid according to any one of claims 1 to 3.
5. The fiber optic reflective magnetic fluid-based current sensing system according to claim 4, wherein the current sensing path is: light beams emitted by the light source enter the sensing probe through the circulator, the light beams reflected by the sensing probe reach the photoelectric detector through the circulator again, the photoelectric detector transmits detection signals to the signal processing unit to perform signal processing to obtain current signals of the circuit to be detected, and the PC side displays the current signals.
6. The optical fiber reflection type current sensing system based on magnetic fluid according to claim 4, wherein the signal processing unit comprises a single chip microcomputer, a driving circuit, an I/U conversion and operational amplifier circuit, an A/D converter and a power supply;
the single chip microcomputer is connected with the input end of the driving circuit, and the output end of the driving circuit is connected with the light source to drive the light source to emit light beams; the output end of the photoelectric detector is connected with the input end of the I/U conversion and operational amplifier circuit, the output end of the I/U conversion and operational amplifier circuit is connected with the input end of the A/D converter, and the output end of the A/D converter is connected to the single chip microcomputer.
7. The fiber optic reflective magnetic fluid-based current sensing system according to claim 4, wherein the light source is a DFB laser.
8. The manufacturing method of the optical fiber reflection type current sensor based on the magnetic fluid is characterized by comprising the following steps of:
step 1: selecting a capillary tube, wherein one end of the capillary tube is an open end, and a first hole and a second hole are respectively formed in two ends above a tube body of the capillary tube;
step 2: selecting an optical fiber, and cutting one end of the optical fiber along the direction vertical to the axis of the optical fiber to form an optical fiber end face;
and step 3: inserting one end of the optical fiber forming the end face of the optical fiber into the capillary from the open end of the capillary along the axial direction of the capillary;
and 4, step 4: sealing the ports at the two ends of the capillary tube through the colloid, and fixing the optical fiber;
and 5: injecting magnetic fluid into the capillary through the first hole, and simultaneously exhausting air in the capillary through the second hole;
step 6: and sealing the first hole and the second hole, thereby forming the optical fiber reflection type current sensor based on the magnetic fluid.
9. The optical fiber reflection type current sensing method based on the magnetic fluid is characterized by comprising the following steps:
step 1: obtaining the intrinsic reflected light power P of the system according to the formula (6) by adopting a known sample calibration method0：
Wherein S is the effective cross-sectional area of the fiber end face, PaAnd PwThe reflected light power, n, measured by placing the pre-packaged fiber in a first sample and in a second sample, respectivelyf、naAnd nwThe refractive indexes of the fiber core, the first sample and the second sample are respectively;
step 2: according to the intrinsic reflected light power P0Calculating according to the formula (7) to obtain the reflected light power P of the optical fiber in the magnetic fluidMFAnd refractive index n of magnetic fluidMFThe relation of (1):
wherein k isMFThe attenuation coefficient of the magnetic fluid;
and step 3: calculating the refractive index n of the magnetic fluid according to the formula (8)MF：
And 4, step 4: and calculating to obtain magnetic field information according to the relationship between the refractive index of the magnetic fluid and the magnetic field defined by the Langmuim function, and obtaining the current of the circuit to be tested according to the relationship between the magnetic field information and the current defined by the Biot-Saval law.
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