JP2013061162A - Measurement method and measurement device using fbg sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measurement method and a measurement device using an FGB sensor, which allows a distortion signal and an AE signal to be measured by a wide-band light source or a laser beam.SOLUTION: A measurement device using an FGB sensor comprises a wide-band light source 13 and an optical fiber amplifier 14 which input a light beam into an FBG sensor 11, a first optical switch 16 which switches the light beam from the FBG sensor 11, an amplifier-side optical coupler 17 which returns one light beam to the optical fiber amplifier 14, a second optical switch 18 which selectively injects the light beam of the first optical switch 16 and the light beam of the amplifier-side optical coupler 17, a measurement-side optical coupler 20 which splits the light beam from the second optical switch 18, Bragg wavelength measurement means 21 which measures one optical beam split by the measurement-side optical couple 20, and a photoelectric transducer 22 for AE measurement which measures another optical beam split by the measurement-side optical coupler 20. The wide-band light source 13 and a fiber ring laser of the optical fiber amplifier 14 can be selected.

Description

  The present invention relates to an FBG sensor measuring method and measuring apparatus.

  In recent years, there is a means for measuring the strain to be inspected by using an FBG (Fiber Bragg Grating) sensor (see, for example, Patent Document 1), and the FBG sensor is a Bragg that is an optical signal having a specific wavelength. Since it reflects the wavelength, the strain change and temperature change are measured by using the Bragg wavelength.

  Specifically, as shown in FIG. 3, the FBG sensor measuring device includes an FBG sensor 1 arranged in a structure to be inspected (not shown) and an FBG sensor 1 as shown in FIG. A broadband light source 3 that outputs light through an optical fiber 2, an optical circulator 4 that separates reflected light generated at the Bragg wavelength of the FBG sensor 1, and a WDM (Wavelength Division Multiplexing wavelength) that makes the reflected light from the optical circulator 4 incident Some include a division multiplexing filter 5, a photoelectric conversion unit 6 that receives transmitted light and reflected light from the WDM filter 5, and a processing unit 7 that processes a voltage signal from the photoelectric conversion unit 6.

  Such a measuring device of the FBG sensor 1 divides the reflected light from the optical circulator 4 into transmitted light and reflected light by the WDM filter 5, and further converts the transmitted light and reflected light into respective voltages by the photoelectric conversion unit 6. The processing means 7 calculates the strain.

  Other means of measurement using FBG sensors include a broadband light source, fiber Fabry-Perot filter (FFP), photoelectric converter, etc., and elastic wave emission (AE: acoustic emission) due to the occurrence of defects. ) Has been considered (for example, see Patent Document 2).

JP 2007-114072 A JP 2008-46036 A

  As described above, when the strain signal or AE signal is measured by the FBG sensor 1, it is common to use the broadband light source 3 or the wavelength tunable laser light source. When detecting the AE signal, there is a problem that the S / N ratio becomes small.

  Also, when measuring strain signals using a wavelength tunable laser light source, there is a problem that the phase between sensors is shifted in a multi-point FBG sensor array due to the sweep time of the wavelength tunable laser, and strain signal measurement is performed at high speed. It was difficult. In addition, in order to measure ultrasonic waves with a wavelength tunable laser, it is necessary to follow a change in the Bragg wavelength of the FBG sensor with a laser beam having a very narrow line width, which is difficult to apply to structures with large strain changes. there were. Furthermore, it is impossible to simultaneously measure the distortion signal and the AE signal with the wavelength tunable laser because of the characteristics of the wavelength tunable laser.

  In view of such circumstances, the present invention intends to provide an FBG sensor measuring method and measuring apparatus capable of measuring a strain signal and an AE signal with a broadband light source or laser light.

The FBG sensor measurement method of the present invention selects a broadband light source and an optical fiber amplifier, inputs light to the FBG sensor,
When the broadband light source is selected, the light from the FBG sensor is divided by the measurement-side optical coupler via the first optical switch and the second optical switch, and further divided by the measurement-side optical coupler. Is measured as a strain signal by Bragg wavelength measuring means,
When the optical fiber amplifier is selected, the light from the FBG sensor is returned to the optical fiber amplifier via the first optical switch and the optical coupler on the amplifier side, and becomes a fiber ring laser by self-excitation accompanying the circulation of the light. The light emitted from the optical coupler on the amplifier side is divided by the optical coupler on the measurement side via the second optical switch, and one of the lights divided by the optical coupler on the measurement side is further divided by the Bragg wavelength measuring means. While measuring as a distortion signal, the other light divided by the optical coupler on the measurement side is measured as an AE signal by a photoelectric converter for AE measurement.

The FBG sensor measuring device of the present invention inputs a light to the FBG sensor and is selectively connected to a broadband light source and an optical fiber amplifier,
A first optical switch that enables switching of light from the FBG sensor in a plurality of directions;
An optical coupler on the amplifier side that splits one light switched by the first optical switch and returns it to the optical fiber amplifier;
A second optical switch that selectively enters the other light switched by the first optical switch and the other light divided by the optical coupler on the amplifier side;
An optical coupler on the measurement side that splits the light from the second optical switch;
Bragg wavelength measuring means for measuring one light divided by the optical coupler on the measurement side;
With a photoelectric converter for AE measurement that measures the other light divided by the optical coupler on the measurement side,
When the optical fiber amplifier is selected, light is circulated and amplified by a first optical switch, and a fiber ring laser is formed by self-excitation.

  In the FBG sensor measuring apparatus of the present invention, the optical fiber amplifier is preferably an erbium-doped optical fiber amplifier or a semiconductor optical amplifier so as to emit a fiber ring laser.

  In the FBG sensor measuring apparatus of the present invention, it is preferable that the broadband light source and the optical fiber amplifier can be selected by switching an optical switch for switching or by inputting one of the power supplies.

  In the FBG sensor measuring apparatus according to the present invention, it is preferable that the FBG sensor measuring apparatus includes a signal adjusting unit that adjusts a signal by processing an output voltage from the photoelectric converter for AE measurement.

  According to the FBG sensor measurement method and measurement apparatus of the present invention, when a broadband light source or an optical fiber amplifier is selected and light is input to the FBG sensor, a strain signal is measured with broadband light when the broadband light source is selected. When an optical fiber amplifier is selected, it is possible to circulate and amplify the light, use a fiber ring laser by self-excitation, and measure strain signals and AE signals with the fiber ring laser. Accordingly, it is possible to obtain an excellent effect that a wideband light and a fiber ring laser can be selected and a distortion signal and an AE signal can be measured.

It is a block diagram which shows the example of embodiment of this invention. It is a flow which processes the embodiment of this invention. It is a block diagram which shows a prior art example.

  Hereinafter, an exemplary embodiment for carrying out the measuring method and measuring apparatus of the FBG sensor of the present invention will be described with reference to FIGS.

  An FBG sensor measurement method and measurement apparatus according to an embodiment includes an FBG sensor 11 arranged in a measurement target structure (not shown), and inputs and selects light through the optical fiber 12 to the FBG sensor 11. A broadband light source 13 and an optical fiber amplifier 14 that can be connected, an optical circulator 15 that separates reflected light generated by the FBG sensor 11, and a first optical switch 16 that switches light from the optical circulator 15 in a plurality of directions. An amplifier-side optical coupler 17 connected to one of the first optical switches 16, and a second optical switch connected to the other of the first optical switch 16 and the amplifier-side optical coupler 17 and switching to one of them. 18, a wavelength divider 19 connected to the second optical switch 18 for dividing the wavelength, a measurement-side optical coupler 20 connected to the wavelength divider 19 for dividing the light, and each measurement side A Bragg wavelength measuring means 21 connected to one of the optical couplers 20 for processing light, an AE measuring photoelectric converter 22 connected to the other of the optical couplers 20 on each measurement side for processing light, and each Bragg wavelength A signal adjusting unit 22 a connected to the measuring unit 21 and the photoelectric converter 22 for AE measurement, a measuring unit 23, and a data recording unit 24 are provided.

  The FBG sensor 11 arranged in a structure to be inspected (not shown) has diffraction gratings formed at regular intervals along the optical axis direction in the core portion of the optical fiber 12, and the distortion and temperature of the object to be inspected. The reflection wavelength is changed by the change, and the strain change and temperature change of the structure are detected.

  The broadband light source 13 continuously outputs broadband light to the FBG sensor 11 via the optical circulator 15. On the other hand, the optical fiber amplifier 14 is an erbium-doped fiber amplifier (EDFA) or a semiconductor optical amplifier (SOA). FBG is transmitted through the optical circulator 15 through the FBG. A continuous output is made to the sensor 11. The optical fiber amplifier 14 circulates light by the first optical switch 16 and the optical coupler 17 on the amplifier side and is self-excited to emit a fiber ring laser (laser light). Here, since the fiber ring laser using the optical fiber amplifier 14 emits laser light having a single wavelength, there is a problem that it cannot be handled when the FBG sensors 11 having a plurality of wavelengths are connected. Therefore, in such a case, a plurality of amplification media such as erbium-doped optical fibers (EDF) are arranged in parallel corresponding to the FBG sensors 11 of a plurality of wavelengths, and a solid-state laser (Pump LD) that excites the amplification media. It is preferable to further include a wavelength demultiplexer that performs demultiplexing and multiplexing in the wavelength band of each FBG sensor 11. A plurality of optical fiber amplifiers 14 may be arranged in parallel.

  Between the broadband light source 13 and the optical fiber amplifier 14 and the optical circulator 15, a switching optical switch 25 that can select the broadband light source 13 and the optical fiber amplifier 14 is provided. Furthermore, instead of the optical switch 25 for switching, either the broadband light source 13 or the optical fiber amplifier 14 may be input to select the broadband light source 13 and the optical fiber amplifier 14 as appropriate.

  The optical circulator 15 is configured to control the direction of light guide by light. Specifically, the optical circulator 15 guides the light from the broadband light source 13 or the optical fiber amplifier 14 to the FBG sensor 11, and at the same time, the FBG sensor 11. The reflected light from the light is guided to the first optical switch 16. Here, an auxiliary optical coupler 26 for dividing the light from the optical circulator 15 is provided between the optical circulator 15 and the first optical switch 16 (FIG. 1 shows a 90:10 division), and further auxiliary. An optical spectrum analyzer 27 may be connected to the optical coupler 26 for monitoring the light spectrum of the light source.

  The first optical switch 16 is connected to one side corresponding to the optical coupler 17 on the amplifier side so that the light from the optical circulator 15 can be switched in a plurality of directions (two directions in FIG. 1). (One side) and a two-channel side (the other side) connected corresponding to the second optical switch 18 side. When the broadband light source 13 is selected, the two-channel side (the other side) is selected. When the light from the optical circulator 15 is output to the second optical switch 18 and the optical fiber amplifier 14 is selected, the light from the optical circulator 15 is selected as one channel side (one side). Output to the optical coupler 17.

  The amplifier-side optical coupler 17 is configured to divide the light from the first optical switch 16 by 99: 1, and returns 99% (one) of light to the optical fiber amplifier 14 and 1% (the other). ) Is output to the second optical switch 18. Here, the ratio of the light split by the optical coupler 17 on the amplifier side is not limited to 99: 1. If a large proportion of the light is returned to the optical fiber amplifier 14 to be a fiber ring laser by self-pumping. It is not limited to a specific numerical value. The amplifier-side optical coupler 17 may be other means as long as it divides light.

  The second optical switch 18 is configured so that the two-channel light switched by the first optical switch 16 and the 1% light divided by the optical coupler 17 on the amplifier side are selectively incident. 1 channel side (one side) connected corresponding to the optical coupler 17 side and two channel side (other side) connected corresponding to the first optical switch 16 side are provided, and the broadband light source 13 is selected. When selecting the two-channel side, the light from the first optical switch 16 is made incident, and when selecting the optical fiber amplifier 14, the one-channel side is selected and the optical coupler 17 on the amplifier side is selected. Light is incident.

  The wavelength divider 19 divides the wavelength from the light from the second optical switch 18 into a plurality of (four in FIG. 1) so as to cope with the change in wavelength, and according to the divided wavelengths. The light is output to a plurality of measurement-side optical couplers 20 (four in FIG. 1). Here, the wavelength divider 19 divides the wavelength into four in the embodiment, but it may be divided into other numbers.

  The optical couplers 20 on the measurement side are each configured to divide the light from the wavelength divider 19 into 50:50, and output 50% (one) of light to the Bragg wavelength measuring means 21 and 50 % (The other) light is output to the photoelectric converter 22 for AE measurement.

  The Bragg wavelength measuring means 21 is a reflection from the WDM (Wavelength Division Multiplexing) filters 28a, 28b, 28c, and 28d and the WDM filters 28a, 28b, 28c, and 28d on which light from the optical coupler 20 on the measurement side is incident. A first photoelectric converter 29 that receives light and a second photoelectric converter 30 that receives light transmitted from the WDM filters 28a, 28b, 28c, and 28d, and receives light from the optical coupler 20 on the measurement side. The reflected light or transmitted light is converted into an electrical strain signal and sent to the measuring instrument 23 and the data recorder 24. The Bragg wavelength measuring means 21 is not limited to the WDM filters 28a, 28b, 28c, 28d, the first photoelectric converter 29, and the second photoelectric converter 30, and an optical spectrum analyzer (not shown) is used. It may be used, and other measurement methods and apparatuses may be used. Here, the WDM filters 28a, 28b, 28c, and 28d provided in each Bragg wavelength measuring means 21 correspond to the band of optical fiber communication. In FIG. 1, the WDM filter 28a is 1531 nm. 28b is 1551 nm, WDM filter 28c is 1571 nm, and WDM filter 28d is 1591 nm. The number of Bragg wavelength measuring means 21 is not limited to four, but may be other numbers.

  The photoelectric converter 22 for AE measurement receives light from the optical coupler 20 on the measurement side, converts it into an electrical AE signal, and sends it to the measuring instrument 23 and the data recorder 24. Here, between the second optical switch 18 and the photoelectric converter 22 for AE measurement, the fiber Fabry-Perot required for measuring the AE signal by the method and apparatus described in Patent Document 2. The filter (FFP) is unnecessary. Further, the number of photoelectric converters 22 for AE measurement is not limited to four, and may be other numbers.

  The signal adjusting unit 22a, the measuring device 23, and the data recording unit 24 process the strain signal measured by the Bragg wavelength measuring unit 21 or the AE signal measured by the photoelectric converter 22 for AE measurement as necessary. It has become. In the case of the strain signal measured by the Bragg wavelength measuring means 21, the measuring device 23 and the data recording device 24 process and record the strain signal in the structure of the inspection object or the temperature change strain signal. . On the other hand, in the case of an AE signal measured by the photoelectric converter 22 for AE measurement, a DC bias is applied to the output voltage from the photoelectric converter 22 for AE measurement by the signal adjusting means 22a, and a bandpass filter and an amplification are applied. The signal is adjusted via a circuit or the like, and the measuring instrument 23 and the data recorder 24 process and record the elastic wave emission signal in the structure of the inspection object. Here, the signal adjustment means 22a includes a bias circuit (not shown) that takes a DC bias with respect to the output voltage from the photoelectric converter 22 for AE measurement, and a bandpass filter (not shown) that forms an appropriate bandpass. And an amplifier circuit (not shown) for amplifying the signal. Further, the signal adjusting means 22a, the measuring instrument 23, and the data recorder 24 may be configured separately or may be configured as one.

  The operation of the embodiment for carrying out the present invention will be described below.

  When inspecting the structure of the object to be inspected, it is first determined whether to acquire the strain signal or the strain signal and the AE signal (step S1). When acquiring the strain signal, the broadband light source 13 is selected. When selecting and acquiring the distortion signal and the AE signal, the optical fiber amplifier 14 is selected (steps S2 and S3). Here, when the broadband light source 13 or the optical fiber amplifier 14 is selected, it may be switched to one using the switching optical switch 25 or may be selected by inputting one of the power supplies.

  When the broadband light source 13 is selected, the first optical switch 16 and the second optical switch 18 are switched, and the light is switched from the FBG sensor 11 to the optical circulator 15, the auxiliary optical coupler 26, the first optical switch 16, A circuit that outputs to the wavelength divider 19 via the second optical switch 18 is configured (step S4). Then, the light from the FBG sensor 11 accompanying the emission of the broadband light source 13 is output to the wavelength divider 19 via the optical circulator 15, auxiliary optical coupler 26, first optical switch 16, and second optical switch 18. Further, the light from the wavelength divider 19 and the optical coupler 20 on each measurement side is measured as a distortion signal by the Bragg wavelength measuring means 21 (step S5), and the distortion signal is acquired by the measuring instrument 23 and the data recorder 24, and recorded. (Step S6). Here, the Bragg wavelength measuring means 21 converts the reflected light or transmitted light into an electrical distortion signal by the WDM filters 28a, 28b, 28c, 28d, the first photoelectric converter 29, and the second photoelectric converter 30, In the measuring instrument 23 and the data collector 24, the Bragg wavelength accompanying the distortion or temperature change in the structure of the inspection object is acquired as a distortion signal. When the broadband light source 13 is selected, the AE signal can be simultaneously measured by the photoelectric converter 22 for AE measurement, but the S / N ratio may be small and is not suitable for practical use.

  After acquiring the distortion signal, the distortion signal may be acquired again, or the distortion signal and the AE signal may be acquired by switching from the broadband light source 13 to the fiber ring laser of the optical fiber amplifier 14.

  When the optical fiber amplifier 14 is selected, the first optical switch 16 and the second optical switch 18 are switched, and the light is switched from the FBG sensor 11 to the optical circulator 15, the auxiliary optical coupler 26, and the first optical switch 16. The circuit is configured to return to the optical fiber amplifier 14 via the amplifier-side optical coupler 17. Then, the light from the FBG sensor 11 accompanying the output of the optical fiber amplifier 14 is circulated and amplified via the optical circulator 15, the auxiliary optical coupler 26, the first optical switch 16, and the optical coupler 17 on the amplifier side, It emits as a fiber ring laser (laser light) by self-excitation (step S7). Here, the fiber ring laser has confirmed by a preliminary test that the laser transmission wavelength changes due to the strain loaded on the FBG sensor 11, and the strain loaded on the FBG sensor 11 and the laser transmission of the fiber ring laser. It has been confirmed that it has linearity with respect to the wavelength. Furthermore, the principle of measuring the AE signal using a fiber ring laser is to use the wavelength dependence of the amplification factor of the optical fiber amplifier 14. Furthermore, in the fiber ring laser, the FBG sensor 11 functions as a cavity mirror of the fiber ring laser.

  The optical coupler 17 on the amplifier side emits a fiber ring laser, outputs it to the wavelength divider 19 via the second optical switch 18, and further Braggs the light from the wavelength divider 19 and the optical coupler 20 on each measurement side. The wavelength measurement means 21 measures the distortion signal (step S5), and the measurement instrument 23 and the data recorder 24 acquire and record the distortion signal (step S6). At the same time, the other light divided by the optical coupler 20 on the measurement side is measured as an AE signal by the photoelectric converter 22 for AE measurement (step S8), and is measured by the measuring instrument 23 and the data recorder 24 via the signal adjusting means 22a. An AE signal is acquired and recorded (step S9). Here, in the Bragg wavelength measuring means 21, as in the case of the broadband light source 13, the WDM filters 28 a, 28 b, 28 c and 28 d, the first photoelectric converter 29, and the second photoelectric converter 30 receive reflected light and transmitted light. By converting into an electrical strain signal, the measuring instrument 23 and the data collector 24 acquire the Bragg wavelength accompanying the strain or temperature change in the structure of the inspection object as the strain signal. In the photoelectric converter 22 on the AE measurement side, the signal adjustment unit 22a, the measurement unit 23, and the data recording unit 24, a DC bias is applied to the output voltage from the photoelectric converter 22 for AE measurement by the bias circuit of the signal adjustment unit 22a. The signal is adjusted via a bandpass filter and an amplifier circuit, and the signal accompanying acoustic wave emission (AE: acoustic emission) in the structure of the object to be inspected is measured by the measuring instrument 23 and the data recorder 24. Obtained as a signal.

  After acquiring the distortion signal and the AE signal, the distortion signal and the AE signal may be acquired again, or the distortion signal may be acquired by switching from the fiber ring laser of the optical fiber amplifier 14 to the broadband light source 13. .

  Thus, according to the embodiment, when the broadband light source 13 or the optical fiber amplifier 14 is selected and light is input to the FBG sensor 11 and the broadband light source 13 is selected, the broadband light is distorted. When the optical fiber amplifier 14 is selected, the light is circulated and amplified, and the fiber ring laser (laser light) is obtained by self-excitation, and the strain signal and the AE signal are generated by the fiber ring laser. It becomes possible to measure, and it is possible to select a broadband light and a fiber ring laser as necessary, and measure a distortion signal and an AE signal. Further, since the fiber ring laser is used, it is possible to prevent the S / N ratio from becoming small even when ultrasonic measurement, particularly when detecting an AE signal as a transient signal. Furthermore, when measuring a strain signal with a fiber ring laser, it is possible to suppress a phase shift between the multipoint FBG sensors 11 due to the sweep time, and to measure the strain signal at a high speed. Furthermore, when measuring ultrasonic waves with a fiber ring laser, it is possible to follow a change in the Bragg wavelength of an FBG sensor with a laser beam with a very narrow line width, which can be applied to structures with large strain changes. Can be easily. In addition, strain signals and AE signals can be measured simultaneously with a fiber ring laser.

  In the embodiment, when the optical fiber amplifier 14 is an erbium-doped optical fiber amplifier or a semiconductor optical amplifier so as to emit the fiber ring laser, the fiber ring laser easily emits the distortion signal and the fiber ring laser. The AE signal can be suitably measured.

  In the embodiment, when the broadband light source 13 and the optical fiber amplifier 14 can be selected by switching an optical switch for switching or by inputting one of the power supplies, the fiber ring laser of the broadband light source 13 or the optical fiber amplifier 14 is used. Therefore, the distortion signal and the AE signal can be suitably measured as necessary.

  In the embodiment, when the signal adjustment means 22a for processing the output voltage from the photoelectric converter 22 for AE measurement and adjusting the signal is provided, the output voltage from the photoelectric converter 22 for AE measurement is appropriately processed. Therefore, the AE signal can be suitably measured.

  The FBG sensor measuring method and measuring apparatus according to the present invention are not limited to the illustrated examples described above, and various changes can be made without departing from the scope of the present invention.

11 FBG sensor 13 Broadband light source 14 Optical fiber amplifier 16 First optical switch 17 Amplifier-side optical coupler 18 Second optical switch 20 Measurement-side optical coupler 21 Bragg wavelength measurement means 22 AE measurement-side photoelectric converter 22a Signal adjustment Means 25 Optical switch for switching

Claims (5)

Select a broadband light source and an optical fiber amplifier to input light to the FBG sensor,
When the broadband light source is selected, the light from the FBG sensor is divided by the measurement-side optical coupler via the first optical switch and the second optical switch, and further divided by the measurement-side optical coupler. Is measured as a strain signal by Bragg wavelength measuring means,
When the optical fiber amplifier is selected, the light from the FBG sensor is returned to the optical fiber amplifier via the first optical switch and the optical coupler on the amplifier side, and becomes a fiber ring laser by self-excitation accompanying the circulation of the light. The light emitted from the optical coupler on the amplifier side is divided by the optical coupler on the measurement side via the second optical switch, and one of the lights divided by the optical coupler on the measurement side is further divided by the Bragg wavelength measuring means. While measuring as a strain signal, measure the other light divided by the optical coupler on the measurement side as an AE signal by a photoelectric converter for AE measurement,
FBG sensor measurement method characterized by this. A broadband light source and an optical fiber amplifier that inputs light to the FBG sensor and is selectively connected;
A first optical switch that enables switching of light from the FBG sensor in a plurality of directions;
An optical coupler on the amplifier side that splits one light switched by the first optical switch and returns it to the optical fiber amplifier;
A second optical switch that selectively enters the other light switched by the first optical switch and the other light divided by the optical coupler on the amplifier side;
An optical coupler on the measurement side that splits the light from the second optical switch;
Bragg wavelength measuring means for measuring one light divided by the optical coupler on the measurement side;
With a photoelectric converter for AE measurement that measures the other light divided by the optical coupler on the measurement side,
When the optical fiber amplifier is selected, the FBG sensor measuring apparatus is configured so that light is circulated and amplified by a first optical switch to become a fiber ring laser by self-excitation.   3. The FBG sensor measuring apparatus according to claim 2, wherein the optical fiber amplifier is an erbium-doped optical fiber amplifier or a semiconductor optical amplifier so as to emit a fiber ring laser.   4. The FBG sensor measuring apparatus according to claim 2, wherein the broadband light source and the optical fiber amplifier can be selected by switching an optical switch for switching or by inputting one of the power supplies.   5. The FBG sensor measuring apparatus according to claim 2, further comprising: a signal adjustment unit that processes an output voltage from the photoelectric converter for AE measurement to adjust a signal. 6.

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