Current measuring device

Abstract

[Problem] To provide a current measurement device that makes it possible to achieve high-frequency current measurement and to perform current measurement for devices that operate at higher switching frequencies, without using a division means. [Solution] According to the present invention, a current measurement device includes an optical fiber for a sensor, a light source, two variable optical attenuators, and a signal processing circuit that comprises two photoelectric conversion elements. The signal processing circuit comprises the two photoelectric conversion elements and a current / voltage conversion circuit. The two photoelectric conversion elements are connected in series. An optical signal is inputted into the variable optical attenuators then into the two photoelectric conversion elements and converted to a first photocurrent and a second photocurrent. The photocurrents are fed back to the variable optical attenuators, the amount of light that is inputted into the two photoelectric conversion elements is adjusted, and the DC components of the photocurrents are equalized. At the same time, the difference in the photocurrents is inputted into the current / voltage conversion circuit, the DC components of the photocurrents are offset, the AC components are outputted as a difference, and a current to be measured that is flowing in a conductor is converted to an electrical signal and measured.

Description

Technical Field

[0001] The present invention relates to a current measuring device.

Background Art

[0002] As a current measuring device that utilizes the Faraday effect of an optical fiber, for example, Patent Document 1 can be cited.

[0003] In the current measuring device of Patent Document 1, an optical fiber is provided around a current-carrying conductor. Laser light from a semiconductor laser light source is converted into linearly polarized light and propagated through this optical fiber. The polarization plane of this linearly polarized light changes in polarization angle due to the current flowing through the current-carrying conductor. Next, the light emitted from the optical fiber is separated into a p-wave and an s-wave, and is converted into voltage signals by two photodiodes. Further, it is separated into an AC component and a DC component by the separation means of the arithmetic processing unit, and the first component ratio and the second component ratio of the AC component and the DC component are respectively obtained by two division means, and the difference is calculated by the arithmetic means. Finally, the value of the current flowing through the current-carrying conductor is measured from the output of the arithmetic means.

[0004] Also, the current measuring device is used for the evaluation and inspection of power semiconductors that control and supply power (electric power).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when using division means in the signal processing unit as in the current measuring device described in Patent Document 1, due to the bandwidth limitation of the division means, it becomes difficult to measure high-frequency (several M (Hz) to several hundred M (Hz)) currents.

[0007] Furthermore, with improvements in power semiconductor performance, there is a growing need to measure the current of devices operating at higher switching frequencies.

[0008] The present invention has been made in view of the above problems, and aims to provide a current measuring device that does not use a division means in the current measuring device, thereby enabling high-frequency current measurement and current measurement of devices operating at higher switching frequencies. [Means for solving the problem]

[0009] The aforementioned problems are solved by the present invention as follows. That is, the current measuring device of the present invention includes at least a sensor optical fiber, a light source, two optical variable attenuators, and a signal processing circuit comprising two photoelectric conversion elements, wherein the sensor optical fiber is installed around the outer circumference of a conductor through which the current to be measured flows, and an optical signal emitted from the light source is propagated into the sensor optical fiber, and the polarization plane of the optical signal is rotated by the Faraday effect occurring in the optical signal propagating within the sensor optical fiber, thereby measuring the current to be measured flowing through the conductor, and furthermore, the signal processing circuit comprises at least two photoelectric conversion elements and a current-voltage conversion circuit, wherein the two photoelectric conversion elements are connected in series, and the optical signal The light is injected into a variable optical attenuator, then into two photoelectric conversion elements, where it is converted into a first photocurrent and a second photocurrent. Either the first or second photocurrent is fed back to each variable optical attenuator, adjusting the amount of light injected into the two photoelectric conversion elements. The DC components of the first and second photocurrents become equal, and the difference between the first and second photocurrents is input to a current-voltage conversion circuit. The DC components of the first and second photocurrents cancel each other out, and the AC component is output as a difference. The current flowing through the conductor is then converted into an electrical signal and measured.

[0010] In other words, the current measuring device of the present invention is configured without a division means. [Effects of the Invention]

[0011] According to the current measuring device of the present invention, the DC component of the photocurrent of the two photoelectric conversion elements is made identical, and the difference between the first photocurrent and the second photocurrent in the two photoelectric conversion elements is input to the current-voltage conversion circuit, thus eliminating the need for a divider in the signal processing circuit. Furthermore, it is possible to simultaneously eliminate common-mode noise (light source noise that enters both photoelectric conversion elements simultaneously) and achieve output from the current measuring device.

[0012] Furthermore, by canceling out the DC component and inputting only the AC component into the current-to-voltage conversion circuit, it becomes possible to increase the amplification factor in the current-to-voltage conversion circuit. Consequently, as the amplification factor of the current-to-voltage conversion circuit improves, it becomes possible to reduce the number of amplifiers and thus reduce manufacturing costs by reducing the number of components in the signal processing circuit.

[0013] Furthermore, by eliminating the use of a divider, the bandwidth limitation imposed by the divider is removed, and the current measurement bandwidth becomes dependent on the performance of the current-to-voltage conversion circuit. This makes it possible to measure currents in the high-frequency range (several MHz to several hundred MHz).

[0014] Furthermore, it becomes possible to measure the current of devices operating at higher switching frequencies. [Brief explanation of the drawing]

[0015] [Figure 1] This is an explanatory diagram showing the configuration of a current measuring device according to an embodiment of the present invention. [Figure 2] This is an explanatory diagram that shows in detail the configuration of the signal processing circuit in Figure 1 and the connection status of each element. [Figure 3] This is a waveform diagram of the output result according to an embodiment of the present invention. [Modes for carrying out the invention]

[0016] The first feature of this embodiment is that the current measurement device includes at least an optical fiber for a sensor, a light source, two optical variable attenuators, and a signal processing circuit including two photoelectric conversion elements. The optical fiber for the sensor is wound around the outer periphery of a conductor through which the measured current flows, propagates the optical signal emitted from the light source into the optical fiber for the sensor, and rotates the polarization plane of the optical signal due to the Faraday effect generated in the optical signal propagating through the optical fiber for the sensor, thereby measuring the measured current flowing through the conductor. Further, the signal processing circuit includes at least two photoelectric conversion elements and a current-voltage conversion circuit. The two photoelectric conversion elements are connected in series. The optical signal is incident on the optical variable attenuator and then on the two photoelectric conversion elements, and is converted into a first photocurrent and a second photocurrent. The first photocurrent or the second photocurrent is fed back to each optical variable attenuator to adjust the amount of light incident on the two photoelectric conversion elements. When the DC components of the first photocurrent and the second photocurrent become equal to each other, and the difference between the first photocurrent and the second photocurrent is input to the current-voltage conversion circuit, the DC components of the first photocurrent and the second photocurrent are canceled out, and the AC component is output as a difference, and the measured current flowing through the conductor is converted into an electrical signal and measured, which is called a current measurement device.

[0017] In the current measurement device of this embodiment, it is configured not to include a dividing means.

[0018] According to this configuration, since the DC components in the photocurrents of the two photoelectric conversion elements are made the same and the difference between the photocurrents of the two photoelectric conversion elements is input to the current-voltage conversion circuit, a divider is not required in the signal processing circuit. Further, it is possible to simultaneously achieve the removal of common-mode noise (light source noise that enters the two photoelectric conversion elements simultaneously) and the output from the current measurement device.

[0019] Furthermore, by canceling out the DC components and inputting only the AC component to the current-voltage conversion circuit, it is possible to increase the amplification factor in the current-voltage conversion circuit. Therefore, with the improvement of the amplification factor of the current-voltage conversion circuit, it is also possible to reduce the number of amplifiers and reduce the manufacturing cost by reducing the number of components in the signal processing circuit.

[0020] Furthermore, by not using a divider, the bandwidth limitation of the divider is eliminated, and the bandwidth of the current measurement depends on the performance of the current-voltage conversion circuit. As a result, current measurement in the high-frequency band (several M(Hz) to several hundred M(Hz)) becomes possible.

[0021] Another feature is that the current measurement device has only one current-voltage conversion circuit.

[0022] According to this configuration, since the number of current-voltage conversion circuits is limited to one, the influence of individual differences in the current-voltage conversion circuit is eliminated.

[0023] Hereinafter, referring to FIGS. 1 and 2, a current measurement device according to an embodiment of the present invention will be described. The current measurement device 1 shown in FIG. 1 includes at least each component of a sensor optical fiber 2, a Faraday rotator 3, a polarization beam splitter 4, a light source 5, two optical variable attenuators (6a, 6b), and a signal processing circuit 8. Further, the current measurement device 1 includes optical fibers (11a to 11c, 14a, 14b) that propagate optical signals between the respective components, and an optical circulator 13 that propagates an optical signal to a predetermined optical fiber.

[0024] The signal processing circuit 8 includes photoelectric conversion elements (7a, 7b). From FIG. 1, in order from the signal processing circuit 8, the optical variable attenuators (6a, 6b), the polarization beam splitter 4, the Faraday rotator 3, and the sensor optical fiber 2 are arranged.

[0025] The light source 5 is composed of a semiconductor laser (LD: Laser Diode), a light emitting diode (LED: Light Emitting Diode), a super luminescent diode (SLD: Super Luminescent Diode), an ASE light source, etc., emits an optical signal of a predetermined wavelength λ, and propagates it to the optical circulator 13 via an optical fiber.

[0026] The optical circulator 13 can be either polarization-dependent or polarization-independent, and it directs the optical signal emitted from the light source 5 into the optical fiber 11c. The optical circulator 13 may consist of a birefringent element (not shown), a Faraday rotator with a 45-degree rotation angle, a waveplate, etc. Alternatively, an optical fiber coupler may be used instead of the optical circulator 13.

[0027] The optical signal incident on the optical fiber 11c propagates through the optical connector 12a to the optical fiber 14a and is then incident on the polarization separator 4. The polarization separator 4 consists of a light-transmitting uniaxial single-crystal birefringent element, which can be selected from materials such as rutile (TiO2), calcite (CaCO3), quartz (SiO2), yttrium vanadate (YVO4), alphabarium bodate (αBaB2O4), and lithium niobate (LiNbO3). The birefringent element selected from such materials is processed into a flat plate of a predetermined thickness with opposing optical surfaces for light input and output parallel to each other, thereby constituting the polarization separator 4. One of the parallel optical surfaces faces the Faraday rotor 3, and the other optical surface faces the optical fibers (14a and 14b).

[0028] When an optical signal is incident on such a polarization separator 4 from the optical fiber 14a, it is separated into two polarization components: an ordinary ray perpendicular to the crystal axis (not shown) of the birefringent element and an extraordinary ray parallel to it. Only the extraordinary component is shifted to a predetermined separation width corresponding to the thickness of the birefringent element and deviates, so it does not enter the Faraday rotator. Only the linearly polarized ordinary ray is propagated to the Faraday rotator 3.

[0029] The Faraday rotor 3 is a light-transmitting, non-reciprocal polarization plane rotating element with a permanent magnet on its outer circumference. It is formed from bismuth-substituted garnet single crystal, TBIG, GBIG, etc., and has a desired rotation angle (e.g., 22.5 degrees) in the wavelength band used. Note that the permanent magnet is not shown in Figure 1. The Faraday rotor 3 is provided on the first end 2a side, which is the input / output end of the sensor optical fiber 2.

[0030] The outer shape of the Faraday rotor 3 is processed into a flat plate with a predetermined thickness and parallel optical surfaces for light input and output. When the polarization component of the ordinary ray separated by the polarization separator 4 passes through the Faraday rotor 3, the polarization direction is rotated by the Faraday rotation angle (for example, 22.5 degrees). The linearly polarized ordinary ray that has passed through the Faraday rotor 3 is incident on the sensor optical fiber 2 from the first end 2a.

[0031] The sensor optical fiber 2 is installed around the outer circumference of the conductor 9 through which the current to be measured flows, for a desired number of turns. Furthermore, the sensor optical fiber 2 is provided with a first end 2a for receiving linearly polarized light propagated from the Faraday rotor 3, and a second end for reflecting the incident linearly polarized light. A mirror 10 is provided at the second end as a reflective component. In addition to the mirror 10, any other reflective component can be used at the second end. For example, a reflective film made of a metal with low absorption and high reflectivity to light, such as gold (Au), silver (Ag), copper (Cu), chromium (Cr), or aluminum (Al), or a dielectric multilayer film may be used.

[0032] Depending on the magnitude of the current being measured flowing through the conductor 9, the Faraday effect occurs in the optical signal (linearly polarized) propagating through the sensor optical fiber 2, and this Faraday effect rotates the plane of polarization of the optical signal propagating through the sensor optical fiber 2. Furthermore, it is reflected by the mirror 10, and the plane of polarization is rotated in a Faraday fashion along the round-trip propagation path, and then re-entered into the Faraday rotor 3 from the first end 2a.

[0033] As the current propagates back and forth through the sensor optical fiber 2 due to reflection from mirror 10, the linear polarization rotates by α degrees according to the magnitude of the current being measured due to the Faraday effect of the sensor optical fiber 2.

[0034] The type of optical fiber that makes up the sensor optical fiber 2 is not particularly limited, but single-mode optical fibers (SMFs) capable of propagating linearly polarized light, such as lead glass fibers or quartz glass fibers, are optimal. Lead glass fibers are particularly preferred because they have the characteristics of a small photoelastic coefficient and a relatively large Verde constant, which determines the magnitude of the Faraday effect.

[0035] The linearly polarized light that is again incident on the Faraday rotor 3 from the first end 2a is further rotated by the Faraday rotation angle caused by the Faraday rotor 3 as it passes through the Faraday rotor 3. Therefore, the linearly polarized light that was initially transmitted as an ordinary ray when it passed through the Faraday rotor 3 has its plane of polarization rotated by a total of 45 degrees (when the Faraday rotation angle is 22.5 degrees) as it passes through the Faraday rotor 3 back and forth. Next, the linearly polarized light is incident on the polarization separator 4 again.

[0036] When no current is flowing through conductor 9, the total Faraday rotation angle of linearly polarized light transmitted back and forth through the Faraday rotor 3 is 45 degrees. On the other hand, when a current is flowing through conductor 9, the total Faraday rotation angle of linearly polarized light transmitted back and forth through the Faraday rotor 3 is (45 + α) degrees.

[0037] The linearly polarized light that is again incident on the polarization separator 4 is separated into two polarization components: an ordinary ray perpendicular to the crystal axis (not shown) of the birefringent element and an extraordinary ray parallel to it. Only the linearly polarized light of the extraordinary ray parallel to the crystal axis is shifted, and the two linearly polarized lights are incident on the optical fibers 14a or 14b, respectively.

[0038] When a measurement current flows through the conductor 9, the total Faraday rotation angle generated in the linearly polarized light transmitted back and forth through the Faraday rotator 3 is (45 + α) degrees, so a bias occurs in the intensity ratio when separating between the ordinary ray and the extraordinary ray.

[0039] The light signal emitted from the light source 5 is reflected by the mirror 10 at the second end of the sensor optical fiber 2, thereby setting up a round-trip optical path that travels back and forth between the polarization separator 4, the Faraday rotor 3, and the sensor optical fiber 2.

[0040] Linearly polarized light incident on optical fiber 14a or 14b propagates further through optical fiber 11c or 11b via optical connector 12a or 12b. The optical signal propagating through optical fiber 11c is propagated from optical fiber 11c to optical fiber 11a by optical circulator 13.

[0041] Furthermore, for the optical fibers (11a, 11b, 11c, 14a, 14b) and the optical fibers installed between the light source 5 and the optical circulator 13, SMF or polarization-maintaining fiber (so-called PMF) may be used.

[0042] The optical signals propagating through the optical fiber 11a or 11b are incident on the optical variable attenuator 6a or 6b, respectively. The optical variable attenuator 6a or 6b is an optical variable attenuator driven by an electrical signal and is optically connected to the optical fiber 11a or 11b, respectively.

[0043] Furthermore, the output light from the variable optical attenuator 6a or 6b is incident on two photoelectric conversion elements 7a or 7b provided in the signal processing circuit 8. The two photoelectric conversion elements 7a or 7b convert the incident optical signal into a first photocurrent and a second photocurrent, respectively.

[0044] Depending on the magnitude of the optical signal incident from the variable optical attenuator 6a or 6b, the two photoelectric conversion elements 7a or 7b convert the optical signal into a first photocurrent and a second photocurrent, respectively. These first and second photocurrents are then fed back to the variable optical attenuator 6a or 6b, respectively, to adjust the amount of light in the optical signal incident on the two photoelectric conversion elements 7a or 7b.

[0045] When no feedback signal is input, the optical variable attenuator 6a or 6b directs the input optical signal directly into the photoelectric conversion element 7a or 7b. If the amount of light in the optical signal incident on the photoelectric conversion element 7a or 7b is insufficient, the attenuation of the optical variable attenuator 6a or 6b becomes 0 (zero), and the DC component of the photocurrent output from the photoelectric conversion element 7a or 7b falls below the set value.

[0046] As shown in Figure 1 or Figure 2, the signal processing circuit 8 comprises two photoelectric conversion elements 7a or 7b, amplifiers (15a, 15b, 17), and a current-voltage conversion circuit 16. Figure 2 shows the configuration of the signal processing circuit 8 and the details of the connections of each element. As shown in Figure 2, the two photoelectric conversion elements 7a and 7b are connected in series. Furthermore, amplifiers 15a or 15b are connected to the respective output sides of the photoelectric conversion elements 7a or 7b via resistors 18a or 18b. In addition, the current-voltage conversion circuit 16 and amplifier 17 are connected in series to the output sides of the photoelectric conversion elements 7a and 7b.

[0047] Therefore, the signal processing circuit 8 provided in the current measuring device 1 according to the present invention does not use a divider.

[0048] The optical signal incident on the two photoelectric conversion elements 7a or 7b is converted into a first electrical signal (photocurrent) and a second electrical signal (photocurrent), respectively. More specifically, when an optical signal is incident on the two photoelectric conversion elements 7a or 7b, a photocurrent in which a DC (Direct Current) component and an AC (Alternating Current) component are superimposed is output from the photoelectric conversion elements 7a or 7b, respectively, depending on the magnitude of the incident optical signal.

[0049] In the signal processing circuit 8, a voltage proportional to each photocurrent is generated across the resistors 18a or 18b connected to each photoelectric conversion element 7a or 7b, and these voltages are amplified and output by amplifiers 15a or 15b, respectively.

[0050] The output of amplifier 15a or 15b is compared with a reference voltage (not shown), and the optical attenuation is adjusted by controlling each optical variable attenuator 6a or 6b with a drive circuit (not shown) so that the output of amplifier 15a or 15b outputs the same voltage as the reference voltage. As a result, the DC component of the photocurrent of each photoelectric conversion element 7a or 7b is controlled to be constant. By keeping the DC component of each photoelectric conversion element 7a or 7b constant, fluctuations in the optical power of the light source 5 and differences in optical loss in each optical path after the polarization separator 4 are compensated for.

[0051] Furthermore, the midpoint between the photoelectric conversion elements 7a and 7b is connected to the current-voltage conversion circuit 16, and the difference between the first photocurrent and the second photocurrent is input to the current-voltage conversion circuit 16. The current-voltage conversion circuit 16 converts the difference between the first photocurrent and the second photocurrent into a voltage signal. This voltage signal is then output to the amplifier 17, which acts as a buffer, to obtain a voltage signal corresponding to the current being measured flowing through the conductor 9.

[0052] As described above, by feeding back each photocurrent to the variable optical attenuator 6a or 6b, the amount of light in the optical signal incident on the photoelectric conversion element 7a or 7b is adjusted by the variable optical attenuator 6a or 6b when the optical signal is next incident on the variable optical attenuator 6a or 6b. The amount of attenuation by the variable optical attenuator 6a or 6b due to the feedback signals of each photocurrent is controlled so that the DC components of the first photocurrent and the second photocurrent output from the amplifier 15a or 15b are equal and constant.

[0053] As the DC component becomes constant, the DC components of the first and second photocurrents cancel each other out in the difference input to the current-voltage conversion circuit 16. The AC component, on the other hand, is in opposite phase. Since the difference is taken in opposite phase, and the output of photoelectric conversion element 7a is on the negative side and the output of photoelectric conversion element 7b is on the positive side, the AC component is output as the difference in the output value of the current measuring device 1.

[0054] As described above, with the current measuring device 1 according to the present invention, the DC component in the photocurrent of each photoelectric conversion element 7a or 7b is made the same, and the difference between the first photocurrent and the second photocurrent is input to the current-voltage conversion circuit 16, thus eliminating the need for a divider in the signal processing circuit 8. Furthermore, it becomes possible to simultaneously eliminate common-mode noise (light source noise that enters both photoelectric conversion elements 7a and 7b simultaneously) and achieve output from the current measuring device 1.

[0055] Furthermore, by canceling out the DC component and inputting only the difference in the AC component to the current-voltage conversion circuit 16, it becomes possible to increase the amplification factor in the current-voltage conversion circuit 16. Consequently, as the amplification factor of the current-voltage conversion circuit 16 improves, the number of amplifiers can be reduced, and manufacturing costs can be reduced by reducing the number of components in the signal processing circuit 8. In this embodiment, the number of amplifiers connected to the current-voltage conversion circuit 16 is reduced to one amplifier 17 that constitutes the buffer circuit.

[0056] Furthermore, by eliminating the use of a divider, the bandwidth limitation imposed by the divider is removed, and the current measurement bandwidth becomes dependent on the performance of the current-voltage conversion circuit 16. This makes it possible to measure currents in the high-frequency range (several MHz to several hundred MHz).

[0057] Furthermore, it becomes possible to measure the current of devices operating at higher switching frequencies.

[0058] Furthermore, since the number of current-voltage conversion circuits 16 is reduced to one, the influence of individual differences in the current-voltage conversion circuits is eliminated.

[0059] Examples of the present invention are described below, but the present invention is not limited to the following examples. [Examples]

[0060] The configuration of the current measuring device 1 according to this embodiment is as shown in Figures 1 and 2. Accordingly, the same reference numbers are used for components that overlap with the above embodiment, and redundant explanations are omitted or simplified.

[0061] The light source 5 of the current measuring device 1 in this embodiment is either an ASE light source or an SLD (both with an oscillation wavelength of 1550 nm). The photoelectric conversion elements (7a, 7b) are InGaAs photodiodes.

[0062] The Verde constant of the optical fiber 2 for the sensor is 3.75 × 10 -6 The value is {rad / (A·turn)}, the number of turns of the sensor optical fiber 2 around the outer circumference of conductor 9 is 10 (turns), and the current to be measured is 1 (A).

[0063] Therefore, the Faraday rotation angle in the sensor optical fiber 2 is calculated as follows, using 2 as a constant since it is a round-trip optical path due to the mirror 10: 2 × Verde constant {rad / (A·turn)} × number of turns (turn) × current being measured (A) = 2 × 3.75 × 10 -6 ×10×1=7.5×10 -5 (rad)

[0064] Furthermore, the power of the optical signal input to each photodiode is set to 0.526 m(W), the response of the photodiode to 0.95 (A / W), the DC current of the photodiode to 0.5 m(A), and the transimpedance of the monitor output of the photodiode to 10 kV (V / A).

[0065] Therefore, the DC component in the photocurrent of the two photodiodes is equal to the power of the optical signal (W) × the responsiveness of the photodiode (A / W) × the transimpedance (V / A), and is constant at 0.526m(W) × 0.95(A / W) × 10k(V / A) ≈ 5(V).

[0066] On the other hand, the AC component in the photocurrent of each photodiode is given by: Power of the input optical signal (W) × Responsiveness of the photodiode (A / W) × sin{2 × Faraday rotation angle in the sensor optical fiber 2 (rad)} = 0.526m × 0.95 × sin(2 × 7.5 × 10 -5 ) = 0.074 μA.

[0067] From the above, the AC component (V) output from the current-voltage conversion circuit 16 is calculated to be 2 × 0.074 μA × {transimpedance of the current-voltage conversion circuit 30 kV / A} = 4.44 mV.

[0068] In actual measurements, an output of 4.6 mV was obtained for a voltage of 1 A. Figure 3 shows the waveform of the output results of this embodiment as measured with an oscilloscope. Ch1 and Ch2 are the monitor voltage signals, Ch3 is the signal from the current measuring device, and Ch4 is the current value (reference) measured by the current probe.

[0069] Furthermore, it has been confirmed that the current measuring device according to this embodiment has the same effects as the current measuring device 1 of the above embodiment. [Explanation of Symbols]

[0070] 1 Current measuring device 2 Optical fibers for sensors 2a First end of optical fiber for sensor 3 Faraday rotor 4 Polarization separator 5 light source 6a, 6b Optical variable attenuator 7a, 7b Photoelectric conversion element 8. Signal Processing Circuit 9 Conductors 10 Mirror 11a, 11b, 11c, 14a, 14b optical fibers 12a, 12b optical connectors 13. Light Circulator 15a, 15b, 17 Amplifier 16 Current-Voltage Conversion Circuit 18a, 18b resistance

Claims

1. The current measuring device includes at least a sensor optical fiber, a light source, two optical variable attenuators, and a signal processing circuit comprising two photoelectric conversion elements. The optical fiber for the sensor is installed around the outer circumference of the conductor through which the current to be measured is flowing. The optical signal emitted from the light source is propagated through the sensor optical fiber, and the Faraday effect occurring in the optical signal propagating through the sensor optical fiber rotates the plane of polarization of the optical signal, thereby measuring the current being measured flowing through the conductor. Furthermore, the signal processing circuit comprises at least two photoelectric conversion elements, multiple amplifiers, and a current-to-voltage conversion circuit. The two photoelectric conversion elements are connected in series. An optical signal is injected into a variable optical attenuator, then injected into two photoelectric conversion elements, and converted into a first photocurrent and a second photocurrent. The first or second photocurrent is fed back to each variable photoattenuator, adjusting the amount of light incident on the two photoelectric conversion elements, so that the DC components of the first and second photocurrents become equal. The difference between the first and second photocurrents is input to a current-voltage conversion circuit, where the DC components of the first and second photocurrents cancel each other out, and the AC component is output as a difference. The current flowing through the conductor is then converted into an electrical signal and measured. A current measuring device in which two amplifiers are connected to each output side of a photoelectric conversion element via resistors, and a current-to-voltage conversion circuit and a third amplifier are connected in series to the output side of the photoelectric conversion element.

2. The current measuring device according to claim 1, wherein there is one current-to-voltage conversion circuit.

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