JP3963274B2 - Optical fiber sensor - Google Patents

Description

  The present invention relates to an optical fiber sensor.

  Conventionally, as a technique in such a field, there is one disclosed in Patent Document 1 below.

  According to this, a Mach-Zehnder interferometer is constructed in which laser light propagating from the laser light source in the optical fiber is branched by the optical coupler, passes through the arms of the two interferometers, and then interferes with the optical coupler. The arm of the interferometer has a magnetic signal detector, and a structure in which a magnetostrictive material is bonded to an optical fiber serving as the arm of the interferometer and is arranged in an excitation coil that generates a sinusoidal excitation magnetic field. Further, the output of the interferometer is converted into an electric signal by an O / E converter, the phase of the interference light is demodulated by a phase demodulator such as passive homodyne, and AM demodulation is performed at the frequency of the alternating magnetic field.

Here, when a magnetic field is applied to the magnetic signal detector, the magnetostrictive material is distorted, so that the arm of the interferometer expands and contracts. At this time, the phase of the light transmitted through the arm of the interferometer changes. This phase change appears at the output of the phase demodulator. Further, when a magnetic signal is applied in a state where a sinusoidal excitation magnetic field is applied to the magnetic signal detector, the excitation magnetic field component of the output of the O / E converter is AM-modulated with the magnetic signal. The magnetic signal is demodulated from the excitation magnetic field component, and the magnetic signal input to the magnetic signal detector is detected.
JP 10-339770 A

  However, in the above-described prior art, since the excitation power (electric power that generates the excitation magnetic field) is transmitted by the electric wire, an electric wire is necessary in addition to the optical fiber, that is, a thick and sturdy cable is necessary, and the cost is increased. Noise is generated by electromagnetic interference received by the electric wire. There are also problems such as the need for lightning protection measures depending on the usage environment. Further, in applications where long-term reliability is required for the signal detection unit, there is a problem that the life is short because an electronic circuit using a large number of electronic components is required.

  An object of the present invention is to eliminate the above-described problems and provide a highly reliable optical fiber sensor.

In order to achieve the above object, the present invention provides
[1] In an optical fiber sensor that excites with alternating current and detects a physical quantity, the excitation light intensity-modulated with alternating current at the excitation frequency is transmitted through the excitation light transmission fiber, and the excitation light is converted into electric power by the optical / electrical conversion element. The magnetic signal detection unit includes an excitation coil connected to the optical / electrical conversion element, and an optical fiber that is a part of the interference light transmission fiber and the magnetostrictive material are integrated. An optical fiber interferometer in which an optical fiber that is a part of an interference light transmission fiber forms an arm, has a structure in which the magnetostrictive material is disposed in the excitation coil, and an excitation magnetic field and a signal generated in the excitation coil. It distorts the magnetostrictive material in a magnetic field, characterized by Rukoto changing the output light of the phase of the optical fiber interferometer.

[ 2 ] The optical fiber sensor according to [1], wherein a transformer is connected to an output of the optical / electrical conversion element.

[ 3 ] In the optical fiber sensor according to [ 2 ], the synthesized excitation signal is optically transmitted, and the frequency is separated by a plurality of secondary coils of the transformer and a circuit connected to the secondary coil, and the magnetic signal detection unit A plurality of magnetostrictive materials are excited at different frequencies.

[ 4 ] The optical fiber sensor according to [1], wherein when a plurality of magnetic signal detectors are used, the excitation light is branched and input to the plurality of light / current converters.

  According to the present invention, a highly reliable optical fiber sensor can be provided.

  More specifically, the following effects can be achieved.

  (1) In the first embodiment, since the pumping power is transmitted by the optical fiber, the transmission cable is not required. Accordingly, lightening, cable cost, and lightning protection measures that are not affected by electromagnetic interference become unnecessary. Further, the electronic component required for the light / current conversion unit and the magnetic signal detection unit is one light / electric conversion element, and high reliability is obtained.

  (2) The second embodiment has the same effect as the first embodiment. Further, the first embodiment has a drawback that the AC component also flows in the resistance and the efficiency is lowered, but in this embodiment, an efficiency close to 100% is obtained.

  (3) The third embodiment has an effect of suppressing noise other than the frequency band of the excitation magnetic field output from the optical / electrical conversion element in addition to the effect of the second embodiment. Therefore, it is suitable for an application for detecting a smaller signal magnetic field.

  (4) In the fourth embodiment, in addition to the effect of the first embodiment, there is an effect of canceling the noise magnetic field generated in the excitation coil. Suitable for applications that detect smaller signal fields.

  (5) In the fifth embodiment, in addition to the effects of the third embodiment, a plurality of signal magnetic fields are detected by one pump light transmission fiber and one optical / electrical conversion element in order to perform frequency multiplexing transmission of pump power. be able to.

  (6) In the sixth embodiment, in addition to the effects of the first to fifth embodiments, both the pumping light transmission fiber and the interference light transmission fiber can be shared by transmission from a plurality of magnetic signal detectors. Can be

The optical fiber sensor of the present invention is an optical fiber sensor that excites with alternating current and detects other physical quantities, transmits the excitation light intensity-modulated with alternating current of the excitation frequency through the excitation light transmission fiber, and transmits the excitation light to the light / The electric signal is converted into electric power by an electric conversion element and sent to a magnetic signal detection unit. The magnetic signal detection unit includes an excitation coil connected to the optical / electrical conversion element, and an optical fiber that is a part of an interference light transmission fiber. An optical fiber interferometer in which a magnetostrictive material is integrated and an optical fiber that is a part of the interference light transmission fiber forms an arm, and the magnetostrictive material is arranged in the excitation coil , and the excitation coil The magnetostrictive material is distorted by the excitation magnetic field and the signal magnetic field generated in step 1, and the phase of the output light of the optical fiber interferometer is changed.

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

  FIG. 1 is a block diagram of an optical fiber sensor showing a first embodiment of the present invention.

  As shown in this figure, the output of the excitation light source 2 whose intensity changes with a sine wave of the excitation magnetic field frequency from the excitation signal generator 1 is transmitted through the excitation light transmission fiber 3 to the light / current converter 7. It is configured to input to the electrical conversion element 4. As the photoelectric conversion element 4, an element called a photovoltaic element or a solar cell having high sensitivity at the wavelength of the excitation light source 2 is used. When the pumping light transmission fiber 3 is long, a configuration using an infrared (1.3, 1.55 band) light source with a small optical fiber transmission loss and an infrared photodiode such as InGaAs, InGaAsP, or Ge is suitable. .

  The light / current conversion unit 7 is configured such that the parallel resistor 5 and the series capacitor 6 are combined to release the bias current (DC component), and only the AC current flows through the excitation coil 9A of the magnetic signal detection unit 10. Here, it is desirable to set the impedance of the excitation coil 9A and the series capacitor 6 to be minimum at the excitation magnetic field frequency so that the sinusoidal alternating current flowing through the excitation coil 9A is maximized.

  The photoelectric conversion element 4 has an inherent load called an optimum load that maximizes output power. It is desirable to set the circuit constants so that the combined impedance of the excitation coil 9A, the series capacitor 6 and the parallel resistor 5 serving as the load of the photoelectric conversion element 4 substantially matches the optimum load.

  The magnetic signal detection unit 10 integrates the optical fiber 13A and the magnetostrictive material 8A by means such as adhesion, constitutes an optical fiber interferometer in which the optical fiber 13A serves as an arm, and the magnetostrictive material 8A is disposed in the excitation coil 9A. Structure. The output of the interferometer light source 14 passes through the optical coupler 15 and reciprocates between the interference light transmission fiber 16 and the interferometer of the magnetic signal detector 10, so that the interferometer light source 14, the optical coupler 15, the interference light transmission fiber 16, An O / E converter 17 that constitutes an interferometer of the magnetic signal detector 10 and converts the light returned to the optical coupler 15 into an electric signal, an optical phase demodulator 18 that detects the phase of the interference waveform, and demodulates the magnetic signal. The AM demodulator 19 is connected in order. 11A and 11B are mirrors, 12 is an optical coupler, and 13B is the other optical fiber.

  The operation of this optical fiber sensor will be described below.

  The output of the excitation light source 2 whose intensity is changed by a sine wave of the excitation magnetic field frequency is input to the optical / electrical conversion element 4 of the light / current conversion unit 7 via the excitation light transmission fiber 3. An alternating current and a bias current are output. Since the bias current is cut off by the series capacitor 6, only an alternating current having an excitation magnetic field frequency flows through the excitation coil 9A. The parallel resistor 5 connected in parallel with the excitation coil 9A has a function of preventing a phenomenon in which the output current of the photoelectric conversion element 4 is saturated when a load with respect to the bias current is large.

  The magnetostrictive material 8A is distorted by the excitation magnetic field and the signal magnetic field generated by the excitation coil 9A, and the optical fiber 13A serving as the arm of the interferometer expands and contracts, so that the phase of the interferometer output light changes. The interferometer output light propagates through the interference light transmission fiber 16, is converted into an electrical signal by the O / E converter 17, is phase demodulated by the optical phase demodulator 18, and is AM demodulated by the AM demodulator 19 at the excitation magnetic field frequency. Thus, a magnetic signal is detected.

  FIG. 2 is a block diagram of an optical fiber sensor showing a second embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the same component as 1st Example, and those description is abbreviate | omitted.

  In this embodiment, the parallel resistor 5 of the first embodiment is replaced with a parallel coil 20. Here, the inductance of the parallel coil 20 is set so that most of the alternating current of the excitation frequency flows to the excitation coil 9 </ b> A side, and the current flows only through the parallel coil 20 by bias.

  The operation of this optical fiber sensor will be described below.

  The operation other than the light / current converter 7 is the same as in the first embodiment. An alternating current having an excitation magnetic field frequency output from the optical / electrical conversion element 4 of the optical / current conversion unit 7 flows through the parallel coil 20 to generate an excitation magnetic field. The parallel coil 20 functions to release a bias current and prevent saturation of the output current of the photoelectric conversion element 4.

  FIG. 3 is a block diagram of an optical fiber sensor showing a third embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the same component as 1st Example, and those description is abbreviate | omitted.

  In this embodiment, the configuration other than the light / current converter 7 is the same as that of the first embodiment.

  The output of the optical / electrical conversion element 4 of the optical / current conversion unit 7 is connected to the primary side of the transformer 21. A series capacitor 6 and an excitation coil 9 </ b> A are connected to the secondary side of the transformer 21. Here, the resonance frequency determined by the capacitance of the series capacitor 6 and the inductance of the excitation coil 9A substantially matches the excitation magnetic field frequency, and the transformer 21, the series capacitor 6 and the excitation coil at the excitation magnetic field frequency viewed from the primary side of the transformer 21. It is desirable to set the winding ratio of the transformer 21, the capacitance of the series capacitor 6, and the inductance of the excitation coil 9 </ b> A so that the impedance of 9 </ b> A substantially matches the optimum load of the optical / electrical conversion element 4.

  The operation of this optical fiber sensor will be described below.

  The operation other than the light / current converter 7 is the same as in the first embodiment. An alternating current having an excitation magnetic field frequency and a bias current output from the optical / electrical conversion element 4 of the optical / current conversion unit 7 flow to the primary side of the transformer 21. Since the transformer 21 has a characteristic of interrupting a direct current, only an alternating current having an excitation magnetic field frequency flows on the secondary side of the transformer 21, and an excitation magnetic field is generated from the excitation coil 9A. Since the combined impedance of the transformer 21 and the optical / electrical conversion element 4 seen from the secondary side is low, the circuit formed by the secondary side winding, the series capacitor 6 and the excitation coil 9A of the transformer 21 has the characteristics of a band pass filter. have. Therefore, noise other than the frequency band of the excitation magnetic field included in the photoelectric conversion element 4 is suppressed.

  FIG. 4 is a block diagram of an optical fiber sensor showing a fourth embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the same component as 1st Example, and those description is abbreviate | omitted.

  Magnetostrictive materials 8A and 8B are bonded to the two optical fibers 13A and 13B which are arms of the interferometer of the magnetic signal detector 10, respectively, and the two magnetostrictive materials 8A and 8B are individually placed in the excitation coils 9A and 9B in parallel. Deploy. The output of the light / current converter 7 is connected to the excitation coils 9A and 9B so that opposite magnetic fields are generated from the two excitation coils 9A and 9B. The configuration other than the magnetic signal detector 10 is the same as that of the first embodiment.

  The operation of this optical fiber sensor will be described below.

  The excitation light source 2, the excitation light transmission fiber 3, and the light / current converter 7 operate in the same manner as in the first embodiment to generate excitation magnetic fields from the excitation coils 9A and 9B. In this embodiment, two magnetostrictive members 8A and 8B bonded to the two optical fibers 13A and 13B serving as the arms of the interferometer are subjected to a push-pull operation by applying opposite excitation magnetic fields. Interferometer output light that does not include noise components of the output of the light / current converter 7 can be obtained by the principle described later. The interferometer output light propagates through the interference light transmission fiber 16, is converted into an electrical signal by the O / E converter 17, is phase demodulated by the optical phase demodulator 18, and is AM demodulated by the AM demodulator 19 at the excitation magnetic field frequency. Thus, a magnetic signal is detected.

  The magnetic field H applied to the magnetostrictive material in the prior art or the present invention and the phase φ of the interference light are expressed by the following equations.

H = H _S + H _d + H _N (1)
φ = k · H ² = k · (2 · H _S · H _d + 2 · H _d · H _N + 2H _N · H _S + H _S ² + H _d ² + H _N ² ) ≒ k · (2 · H _S · H _{d +2 · H d · H N +} H S 2 + H d 2) <H d »H N>
... (2)
Here, H _S , H _d , and H _N are signal magnetic fields, excitation magnetic fields, and noise magnetic fields due to noise components flowing in the excitation coils, and k is a constant representing sensitivity. The phase φ of the interference light is demodulated at the output of the optical phase demodulator 18, and the AM demodulator 19 detects the signal magnetic field component H _S of the first term of the above equation (2), but at the same time the noise magnetic field of the second term. Since the component H _N also appears, the minimum detection limit of the signal magnetic field is limited. In the fourth embodiment, the magnetic fields H _A and H _B applied to the two magnetostrictive materials and the phase φ of the interference light are H _A = H _S + H _d + H _N (3A)
H _B = H _S -H _d -H _N (3B)
φ = k (H _A ² −H _B ² ) ≈4H _S · H _d <H _d >> H _N > (4)
And a noise component corresponding to the second term of the equation (2) does not appear.

  FIG. 5 is a block diagram of an optical fiber sensor showing a fifth embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the same component as 1st Example, and those description is abbreviate | omitted.

In this example, 3-frequency excitation field frequency f _x, f _y, f _z output of the excitation light source 2 intensity waveform obtained by adding the sine wave changes via a pump light transmission fiber 3 light / current conversion of the It is configured to input to the optical / electrical conversion element 4 of the unit 7. The output of the photoelectric conversion element 4 is connected to the primary side of the transformer 31. Three windings 32, 33, and 34 are attached to the secondary side of the transformer 31, and excitation coils 40, 39, and 38 and capacitors 35, 36, and 37 are connected to the respective windings. Here, the excitation magnetic field frequency f _x of the resonant frequency is 3 frequency determined by the capacitance of the inductance and the capacitor 35, 36, 37 of the excitation coil 38, 39, 40, f _y, the respective circuit constants so as to correspond to f _z Set.

  In the magnetic signal detection unit 10, magnetostrictive materials 41, 42, and 43 are placed in three excitation coils 38, 39, and 40, respectively, and arranged in three orthogonal directions. The optical fiber 13A and the three magnetostrictive members 41, 42, and 43 are integrated by means such as adhesion, and the optical fiber 13A forms an optical fiber interferometer. The interferometer light source 14, the optical coupler 15, the interferometer, the O / E converter 17, and the optical phase demodulator 18 are configured in the same manner as in the first embodiment.

Configured to detect the three AM demodulators 19A to the output of the optical phase demodulator 18, 19B, 19C and connected excitation field frequency f _x, f _y, the 3-direction magnetic signals orthogonal included in f _z individually To do.

  The operation of this optical fiber sensor will be described below.

3 frequency excitation field frequency f _x, f _y, f _z sine wave for excitation light / current converting section 7 outputs through the excitation optical transmission fiber 3 of the light source 2 which adds the intensity waveform changes light / excitation field frequency f _x of the 3-frequency by inputting the electromechanical transducer 4, f _y, alternating current and the bias current waveform obtained by adding a sine wave of f _z is outputted, injected into the primary side winding of the transformer 31 Is done. Only one frequency alternating current corresponding to each resonance frequency flows through the three sets of excitation coils 38, 39, 40 and capacitors 35, 36, 37 connected to the secondary side of the transformer 31. Therefore, the excitation magnetic fields generated by the three excitation coils 38, 39, and 40 are sine waves having different frequencies. Since the magnetostrictive members 41, 42, 43 are distorted by the excitation magnetic field generated by the excitation coils 38, 39, 40 and the signal magnetic field in the same direction as the excitation magnetic field, the optical fiber 13A that becomes the arm of the interferometer expands and contracts. The phase of the output light changes. Here, the interferometer output light of the phase, the excitation magnetic field frequency f _x to 3 direction of the signal magnetic field perpendicular to correspond to the respective, f _y, has an AM modulated wave frequency multiplexed by f _z. Interferometer output light propagates interference light transmission fiber 16 is converted into an electric signal by the O / E converter 17, is phase-demodulated by the optical phase demodulator 18, 3-frequency excitation field frequency f _x, f _y, f _{At z} , magnetic signals in three orthogonal directions are detected by performing AM demodulation individually by the AM demodulator 19.

  FIG. 6 is a block diagram of an optical fiber sensor showing a sixth embodiment of the present invention. In addition, the same code | symbol is attached | subjected about the same component as 1st Example, and those description is abbreviate | omitted.

  In this embodiment, the excitation signal generator 1, the excitation light source 2, and the excitation light transmission fiber 3 are configured in the same manner as in any of the first to fifth embodiments. Are divided by optical couplers 51, 52,... And connected to a plurality of light / current converters 61, 62,. The outputs of the light / current converters 61, 62,... Are connected to a plurality of magnetic signal detectors 71-1, 71-2,. Here, the magnetic signal detection unit connected to one light / current conversion unit is a range that is not affected by electromagnetic interference or the like with an electric wire connecting the magnetic signal detection unit. .. And the magnetic signal detectors 71-1, 71-2,..., 72-1,... Are configured in the same manner as any of the first to fifth embodiments.

  The output of the interferometer light source 14 that repeatedly generates pulsed light is branched by optical couplers 81-1, 81-2,..., 82-1,. , 71-2,..., 72-1,..., And is sent back to the O / E converter 17 as a pulse train. Here, the fiber length and the pulse width of the pulsed light are set between the magnetic signal detectors 71-1, 71-2,..., 72-1,. A demultiplexer (DMUX) 83 that separates the pulse trains returned from the magnetic signal detectors 71-1, 71-2, ..., 72-1, ... to the O / E converter 17 and detects the phase of the interference waveform. The optical phase demodulators 84-1, 84-2,... And the AM demodulators 85-1, 85-2,.

  The operation of this optical fiber sensor will be described below.

  The output of the excitation light source 2 is branched by optical couplers 51, 52,..., Converted into alternating current by a plurality of light / current converters 61, 62,..., And a plurality of magnetic signal detectors 71-1, 71-2. ,..., 72-1,... Are converted into excitation magnetic fields. The optical pulse output from the interferometer light source 14 is transmitted through the interference light transmission fiber 16 and branched by the optical couplers 81-1, 81-2,..., 82-1,. .., 72-1,. Similar to the first to fifth embodiments, the light passing through the interferometer of the magnetic signal detector is phase-modulated with the magnetic signal. The optical pulse returned from each magnetic signal detector becomes a pulse train, is transmitted by time division multiplexing, and is converted into an electric signal by the O / E converter 17. The output of the O / E converter 17 is channel-separated by the DMUX 83, and the magnetic signals are demodulated by the optical phase demodulators 84-1, 84-2,... And the AM demodulators 85-1, 85-2,. Is done.

  Furthermore, this invention has the following utilization forms.

  In the fourth embodiment, an example in which the same light / current converter as in the first embodiment is used has been described. However, a light / current converter may be used as in the second or third embodiment.

  In the fifth embodiment, the signal magnetic field in one direction is detected by one magnetostrictive material and the excitation coil as in the first to third magnetic signal detectors and the embodiment. Two magnetostrictive members may be arranged in parallel to apply a reverse excitation magnetic field.

  In the fifth embodiment, an example in which signal magnetic fields in three orthogonal directions are detected is shown. However, the number of AM demodulators is changed from the magnetostrictive material and the secondary winding of the transformer to the excitation coil, so that two directions or four directions or more can be obtained. It can also be detected at an arbitrary angle.

  In all the embodiments, an example in which a magnetic signal is detected has been shown. However, an electric field can also be detected by replacing the magnetostrictive material with an electrostrictive material and replacing the excitation coil with an electrode.

  In the sixth embodiment, an example is shown in which a plurality of excitation coils are connected to each of a plurality of light / current converters. However, all the excitation coils are connected to one light / current converter, or a plurality of light / currents are connected. It is good also as a structure which connects each one excitation coil to a converter.

  In all the embodiments, an example in which one excitation light transmission fiber and one interference light transmission fiber are used has been described, but two or more may be used. It is also possible to transmit both excitation light and interference light to one transmission fiber using wavelength division multiplexing.

  Although all examples have shown examples using Michelson interferometers, other interferometers such as a Mach-Zehnder interferometer may be used.

  In addition, this invention is not limited to the said Example, Based on the meaning of this invention, a various deformation | transformation is possible and these are not excluded from the scope of the present invention.

  The present invention is suitable for a highly reliable optical fiber sensor.

It is a block diagram of the optical fiber sensor which shows 1st Example of this invention. It is a block diagram of the optical fiber sensor which shows 2nd Example of this invention. It is a block diagram of the optical fiber sensor which shows 3rd Example of this invention. It is a block diagram of the optical fiber sensor which shows 4th Example of this invention. It is a block diagram of the optical fiber sensor which shows 5th Example of this invention. It is a block diagram of the optical fiber sensor which shows 6th Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Excitation signal generator 2 Excitation light source 3 Excitation light transmission fiber 4 Optical / electrical conversion element 5 Resistance 6,35,36,37 Capacitor 7,61,62, ... Optical / current conversion part 8A, 8B, 41, 42, 43 Magnetostrictive material 9A, 9B, 38, 39, 40 Excitation coil 10, 71-1, 71-2, ..., 72-1, ... Magnetic signal detector 11A, 11B Mirror 12, 15, 51, 52, ..., 81 -1, 81-2, ..., 82-1, ... Optical couplers 13A, 13B Optical fiber 14 Interferometer light source 16 Interference light transmission fiber 17 O / E converter 18, 84-1, 84-2, ... Optical phase Demodulator 19, 19A, 19B, 19C, 85-1, 85-2, ... AM demodulator 20 Parallel coil 21, 31 Transformer 32, 33, 34 Winding 83 Demultiplexer (DMUX)

Claims (4)

In an optical fiber sensor that excites with an alternating current and detects a physical quantity,
The excitation light intensity modulated by the AC excitation frequency is transmitted by the excitation light transmission fiber, feed the magnetic signal detection unit converts the excitation light power in the optical / electrical conversion element, the magnetic signal detection unit the optical / An optical fiber interference having an excitation coil connected to an electrical conversion element, an optical fiber that is part of an interference light transmission fiber, and a magnetostrictive material, and an optical fiber that is part of the interference light transmission fiber serving as an arm The magnetostrictive material is arranged in the excitation coil, the magnetostrictive material is distorted by an excitation magnetic field and a signal magnetic field generated by the excitation coil, and the phase of the output light of the optical fiber interferometer optical fiber sensor according to claim Rukoto changing the.   2. The optical fiber sensor according to claim 1, wherein a transformer is connected to an output of the optical / electrical conversion element. 3. The optical fiber sensor according to claim 2, wherein the synthesized excitation signal is optically transmitted and frequency-separated by a plurality of secondary coils of the transformer and a circuit connected to the secondary coil, and the plurality of magnetostrictive members of the magnetic signal detection unit. An optical fiber sensor that excites at different frequencies.   2. The optical fiber sensor according to claim 1, wherein when a plurality of magnetic signal detectors are used, the excitation light is branched and input to the plurality of light / current converters.

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