Optical fiber sensor system and optical fiber sensor demodulation method

Abstract

To provide an optical fiber sensor system and an optical fiber sensor demodulation method capable of restraining occurrence of asynchronization.SOLUTION: An optical fiber sensor system includes a sensor group 2 that has multiple optical fiber sensors 22 for changing a phase of passing light and periodically transmitting it as return signals on the basis of a detected physical quantity, and passes the return signals from the respective optical fiber sensors 22 in set pulse order; and a demodulation processing part 5 for performing a demodulation process on the basis of the return signals. The demodulation processing part 5 includes: a trigger signal generation part 522 that clears a counted value when a reference trigger signal is sent, counts clock pulses synchronized with the return signals, and outputs a trigger signal when counting pulses corresponding to a set value set to timing when signals that become the leading part of return signals of the optical fiber sensors to be processed are sent to the demodulation processing part 5; and a demodulation circuit part 525 for performing a demodulation process when a trigger signal is sent.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This technology relates to an optical fiber sensor system that uses optical fibers as sensors for detecting physical quantities, and an optical fiber sensor demodulation method, particularly to demodulation when an optical fiber sensor array consisting of optical fiber sensors with multiple channels is used. [Background technology]

[0002] In recent years, there has been remarkable development in technology related to optical fiber sensor systems. Optical fiber sensors are sensors that use optical fiber to measure and detect physical quantities such as sound pressure (sound waves). When the optical fiber that performs sensing expands and contracts depending on the physical quantity, the propagation distance of the light changes, and the phase of the light that passes through it also changes. This makes it possible to detect the physical quantity based on the phase difference between a reference phase and the phase that has changed depending on the physical quantity. In particular, various methods have been proposed for demodulating the amount of phase change from the light that has passed through the optical fiber sensor and returned.

[0003] One of the demodulation methods used in PMDI (Path Matched Differential Interferometry) interferometric optical fiber sensor systems is the PGC (Phase Generated Carrier) demodulation method. In the PGC demodulation method, light from a light source capable of outputting a narrow linewidth and continuous pulse waveform is passed through an optical fiber sensor that expands and contracts in response to a signal. Reflected light from before and after the optical fiber sensor is phase-modulated and interfered with in a downstream compensation coil, and the resulting phase change is demodulated to obtain a phase signal related to sensing. To further reduce the demodulation processing volume in the PGC demodulation method, a PMDI interferometric optical fiber sensor system using a 3 × 3 coupler demodulation method has been proposed (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4844325 Summary of the Invention [Problem to be solved by the invention]

[0005] To obtain a phase signal by performing demodulation processing based on the light obtained after passing through the optical fiber sensor, it is necessary to identify the position (timing of sampling, etc.) of the signal from the optical fiber sensor to be demodulated from the return signal (interfering light or non-interfering light) sent by time-division multiplexing. Therefore, after synchronizing the return signal with a clock that is the basis for the timing of processing in the system, a free-running counter automatically counts pulses in the clock so that the count value circulates in accordance with the period of the return signal. Then, based on a trigger signal output when a certain count value is reached, the demodulation circuit identifies the position of the beginning of the return pulse optical signal to be processed and performs demodulation processing.

[0006] However, if external electrical or electromagnetic noise is introduced, causing the clock to be temporarily interrupted and the number of clock pulses to decrease, a deviation from the actual count value will occur. This causes a shift in the time relationship between signals such as the trigger signal and the position of the return signal (hereinafter referred to as synchronization deviation). If synchronization deviation occurs and the deviation in the count value counted by the counter continues, the return signal will not be obtained at the correct timing in the demodulation process, making it impossible to properly demodulate the phase change amount, which will affect the phasing process in the subsequent stages.

[0007] Therefore, it has been desired to realize an optical fiber sensor system and an optical fiber sensor demodulation method that can suppress the occurrence of synchronization deviation. [Means for solving the problem]

[0008] The disclosed optical fiber sensor system includes an optical fiber sensor array having a plurality of optical fiber sensors that change the phase of passing light based on a detected physical quantity and periodically transmit the changed phase as a return signal, and that passes the return signals from each optical fiber sensor in a set pulse order; and a demodulation processing unit that performs demodulation processing based on the return signals to obtain data on the amount of phase change of the light.The demodulation processing unit is equipped with a trigger signal generation unit that clears a count value when a reference trigger signal that serves as a reference for defining the beginning of the return signal is input, counts clock pulses synchronized with the return signal, and outputs a trigger signal when it counts a set number of pulses that are set at the timing when the signal that is the beginning of the return signal from the optical fiber sensor to be processed is sent to the demodulation processing unit, and a demodulation circuit unit that performs demodulation processing when the trigger signal is sent.

[0009] In addition, the disclosed optical fiber sensor demodulation method includes the steps of: passing return signals from a plurality of optical fiber sensors, which periodically transmit return signals by changing the phase of the passing light based on the detected physical quantity, in a set pulse order; clearing a count value and counting clock pulses synchronized with the return signal when a reference trigger signal serving as a reference for determining the beginning of the return signal is input; outputting a trigger signal when the beginning signal from the optical fiber sensor to be processed counts a set number of pulses set at the timing for performing the demodulation process; and performing demodulation processing when the trigger signal is sent to obtain data on the amount of phase change of the light. [Effects of the Invention]

[0010] According to this disclosure, the trigger signal generation unit of the demodulation processing unit outputs a trigger signal at a timing based on a set value after the reference trigger signal is sent. Therefore, even if signal synchronization deviation occurs due to external noise contamination, the deviation of the trigger signal can be suppressed, and the demodulation circuit unit can demodulate the amount of phase change related to the optical fiber sensor being processed. Therefore, the influence of synchronization deviation in the demodulation processing unit does not extend to the phasing process, and highly accurate sensing processing can be performed. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram showing a configuration of an optical fiber sensor system 100 according to a first embodiment. [Figure 2] 2 is a diagram showing an example of a configuration centered on a circuit related to generation of a trigger signal and the like of a demodulation processing board 52 according to the first embodiment. FIG. [Figure 3] 5 is a diagram showing a processing flow of a demodulation processing unit 5 in an initial operation of the optical fiber sensor system 100 according to the first embodiment. FIG. [Figure 4] FIG. 4 is a diagram showing the relationship between signals during an initial operation according to the first embodiment. [Figure 5] 5 is a diagram showing a processing flow of a demodulation processing unit 5 in a sensing operation of the optical fiber sensor system 100 according to the first embodiment. FIG. [Figure 6] 4 is a diagram showing the relationship between various signals when a synchronization error occurs in the sensing operation of the optical fiber sensor system 100 according to the first embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] An optical fiber sensor system according to an embodiment will be described below with reference to the drawings. In the following drawings, components with the same reference numerals are identical or equivalent and will be common throughout the following embodiments. The size relationships between components in the drawings may differ from those in reality. The configurations of components shown throughout the specification are merely examples and are not limited to the configurations described in the specification. Not all devices described in the specification may be included. In particular, the combinations of components are not limited to the combinations in each embodiment, and components described in other embodiments may be applied to other embodiments. Furthermore, when multiple similar devices are distinguished by subscripts, the reference numerals, subscripts, etc. may be omitted if there is no need to distinguish or identify them.

[0013] Embodiment 1 FIG. 1 is a diagram showing the configuration of an optical fiber sensor system 100 according to a first embodiment. The optical fiber sensor system 100 is a system that performs sensing processing to detect a physical quantity using an optical fiber. In explaining the system according to the first embodiment, the physical quantity to be detected is the sound pressure of a sound wave, and an example of a system that senses an acoustic signal using a sound wave as a signal will be described. The optical fiber sensor system 100 in FIG. 1 includes a pulse light source unit 1, a sensor group 2, a delay compensator 3, a light receiving unit 4, a demodulation processing unit 5, and a phasing processing unit 6.

[0014] The pulse light source unit 1 outputs, for example, a modulated pulse light (laser light) signal in synchronization with a transmission trigger signal sent from a reference signal generating unit 51 of a demodulation processing unit 5 (described later). The pulse light signal output by the pulse light source unit 1 passes through an outgoing transmission fiber 101 and is sent to a sensor group 2 having a plurality of optical fiber sensors 22 that constitute an optical fiber sensor array (described later).

[0015] The sensor group 2 passes a return pulsed optical signal, which includes a pulsed optical signal having a phase shift corresponding to the sound pressure of the sound wave in the acoustic signal, through the return transmission fiber 102 in a set pulse order in addition to the pulsed optical signal that has passed through the outgoing transmission fiber 101. Therefore, the amount of phase shift based on the acoustic signal is superimposed as data on the return pulsed optical signal. The sensor group 2 includes a plurality of outgoing optical couplers 21, a plurality of optical fiber sensors 22, and a plurality of return optical couplers 23. Here, the optical fiber sensor system 100 of the first embodiment will be described assuming that the sensor group 2 includes six optical fiber sensors 22. However, the number of optical fiber sensors 22 is not limited to six, and any number of optical fiber sensors 22 may be used.

[0016] The outgoing path optical couplers 21 (outgoing path optical couplers 21-1 to 21-6) branch the pulsed optical signal sent from the pulse light source unit 1 and passed through the outgoing path transmission fiber 101. The light that has passed through each outgoing path optical coupler 21 is sent to a plurality of optical fiber sensors 22. Here, although the outgoing path optical coupler 21-6 is installed in FIG. 1, the optical fiber sensor 22-6 that is located at the farthest distance from the pulse light source unit 1 in terms of the transmission of the pulsed optical signal does not necessarily need to be provided with the outgoing path optical coupler 21-6.

[0017] The optical fiber sensors 22 (optical fiber sensors 22-1 to 22-6) serve as sensing channels and output return pulsed optical signals, which are return signals including pulsed optical signals whose phases are changed based on acoustic signals. In the optical fiber sensor 22, the optical fiber that performs sensing is wound around, for example, an elastic cylinder. When sound pressure causes distortion in the elastic cylinder, the optical fiber also expands and contracts according to the magnitude of the acoustic signal. At this time, the path length (propagation distance) of the light passing through the optical fiber changes, causing a change in the phase of the light, and an acoustic signal corresponding to the phase change can be detected. Therefore, the amount of phase change in the pulsed optical signal based on the acoustic signal is superimposed as data.

[0018] The return pulse optical couplers 23 (return pulse optical couplers 23-1 to 23-6) combine the return pulse optical signals from the corresponding optical fiber sensors 22 with other return pulse optical signals. The combined return pulse optical signal passes through the return transmission fiber 102 and is sent to the delay compensator 3. The combined return pulse optical signal from the optical fiber sensors 22 is a signal obtained by time division multiplexing (TDM) the return pulse optical signals from the optical fiber sensors 22. Therefore, the return pulse optical signals from the optical fiber sensors 22 do not overlap in time. Here, although the return pulse optical coupler 23-6 is provided in FIG. 1, it is not necessary to provide it.

[0019] The delay compensator 3 of the first embodiment acquires interference light from the return pulse light signals (non-interfering light) from the optical fiber sensors 22 by using the same delay time difference as each of the optical fiber sensors 22. Then, the delay compensator 3 outputs two paths of return signal pulse light with the phases of the pulse light shifted by +1 / 3π and −1 / 3π through a 3×3 coupler.

[0020] The light receiving unit 4 adjusts the intensity of the interference light and non-interference light in the return signal pulse light sent from the delay compensator 3. Furthermore, the light receiving unit 4 functions as an O / E converter that converts the optical signal into an analog electrical signal and outputs it to the demodulation processing unit 5.

[0021] The demodulation processing unit 5 converts the analog electrical signal from the light receiving unit 4 into a digital electrical signal. The demodulation processing unit 5 also generates a reference trigger signal and a reference clock. The demodulation processing unit 5 further detects, from the digital electrical signal, the leading position (reference timing for sampling) of the return pulse optical signal in the optical fiber sensor 22 to be processed (hereinafter referred to as the target). The demodulation processing unit 5 then performs demodulation processing to acquire the amount of phase change from the data value in the signal sampled based on the leading position. The demodulation processing unit 5 also outputs a phase signal containing the amount of phase change as data to the phasing processing unit 6, which will be described later. As shown in FIG. 1, the demodulation processing unit 5 has a reference signal generating unit 51, a demodulation processing board 52, and an external interface unit 53.

[0022] The reference signal generating unit 51 generates a transmission trigger signal, a reference trigger signal, and a reference clock. The transmission trigger signal is sent to the pulse light source unit 1 as described above. The reference clock is a signal with a frequency of, for example, about 10 MHz. The reference trigger signal is a signal sent in synchronization with the transmission trigger signal. The reference trigger signal is a signal used by the demodulation circuit unit 525 (described later) to detect the leading position of the return signal pulse light associated with the return pulse light signal that has passed through the sensor group 2 from the converted digital electrical signal.

[0023] The demodulation processing board 52 is a board on which devices such as circuits are mounted, and performs demodulation processing. Here, the demodulation processing board 52 can realize demodulation processing using software specialized for digital signal processing, such as a DSP (Digital Signal Processor), or hardware using a programmable logic circuit, such as an FPGA (Field-Programmable Gate Array).

[0024] The external interface unit 53 is a device that serves as an interface for inputting and outputting data and the like with an external device. The external interface unit 53 has an input interface unit 531 and an output interface unit 532. The input interface unit 531 is an interface through which signals are input from the outside to the demodulation processing unit 5. The input interface unit 531 is an interface that connects to an input device 701 through which a system user inputs signals related to data such as setting values, which will be described later. The output interface unit 532 is an interface that outputs signals from the demodulation processing unit 5 to the outside. The output interface unit 532 is an interface that connects to a display device such as an oscilloscope 702 for checking the positional relationship of a return pulse optical signal indicated by a trigger signal, a clock, and a digital electrical signal, which will be described later. The output interface unit 532 is an interface that connects to an external control device 703 that can communicate signals with the demodulation processing unit 5.

[0025] The phasing processor 6 performs phasing processing to enhance the sound from a desired arrival direction based on the phase signal from the demodulation processor 5, and detects the arrival direction of the sound.

[0026] 2 is a diagram showing an example of a configuration centered on circuits related to generation of trigger signals, etc., of the demodulation processing board 52 according to embodiment 1. The demodulation processing board 52 has a phase synchronization unit 521, a trigger signal generation unit 522, a trigger signal monitoring unit 523, a set value storage unit 524, and a demodulation circuit unit 525.

[0027] The phase synchronization unit 521 has a PLL circuit and performs processing to generate a clock signal by multiplying the reference clock generated by the reference signal generation unit 51. By the phase synchronization unit 521 multiplying the reference clock to generate a clock, it is possible to accurately detect the center of the pulse width of the return pulse optical signal, which is on the order of several tens of nanoseconds.

[0028] The set value storage unit 524 stores data of set values ​​input by the system user via the input device 701 and the input interface unit 531. The set value is data that specifies the leading position of the return pulsed optical signal that has passed through the sensor group 2. The set value is set based on the waveform displayed on the oscilloscope 702, etc., taking into consideration the propagation delay time of the pulse in the pulsed optical signal that has passed through the transmission path from the pulsed light source unit 1 to the demodulation processing unit 5.

[0029] The trigger signal generation unit 522 performs processing to generate a trigger signal that identifies the leading position of the return pulse optical signal of the optical fiber sensor 22 that is the target of demodulation. The trigger signal generation unit 522 has a reference trigger synchronization counter 522A and a trigger signal comparison circuit 522B. The reference trigger synchronization counter 522A counts (counts up) the clock and outputs the count value for trigger. The reference trigger synchronization counter 522A cycles through count values ​​from 0 to n. The value of n is set to, for example, the count number of the clock corresponding to the period of the pulse optical signal sent out by the pulse light source unit 1 (the time of the time-division multiplexed return pulse optical signal from the sensor group 2, which also becomes the sensing period of each optical fiber sensor 22). Therefore, the period of the reference trigger signal generated by the reference signal generation unit 51 and the count value from 0 to n of the reference trigger synchronization counter 522A are synchronized. Therefore, basically, after the reference trigger synchronous counter 522A counts up to the count value n, the reference trigger signal from the reference signal generating unit 51 and the clock from the phase synchronization unit 521 are input in synchronization with each other, and the counting in the next cycle starts from the initial count value "0". However, when the reference trigger synchronous counter 522A in the first embodiment receives the reference trigger signal, it clears the count value, returns it to the initial count value "0", and resumes counting. Therefore, the reference trigger synchronous counter 522A in the first embodiment uses the reference trigger signal as a signal to clear the count value and return it to the initial value. In addition, the trigger signal comparison circuit 522B outputs a trigger signal when the count value output from the reference trigger synchronous counter 522A becomes the same as the set value stored in the set value storage unit 524. Here, the initial count value is set to "0", but it may be any count value.

[0030] The trigger signal monitoring unit 523 monitors the trigger signal and performs processing to determine whether a deviation has occurred in the trigger signal. The trigger signal monitoring unit 523 includes a trigger signal monitoring self-running counter 523A, a monitoring comparison circuit 523B, and a trigger signal deviation detection circuit 523C. The trigger signal monitoring self-running counter 523A counts clocks from 0 to n, similar to the reference trigger synchronous counter 522A. The trigger signal monitoring self-running counter 523A outputs the count value as a monitoring count value. However, the trigger signal monitoring self-running counter 523A of the first embodiment differs from the reference trigger synchronous counter 522A in that, except in the initial state, even if a reference trigger signal is input, the count value does not get cleared to 0 but continues to count up to the count value n. Furthermore, the monitoring comparison circuit 523B outputs a monitoring signal when the monitoring count value from the trigger signal monitoring self-running counter 523A becomes the same as the set value stored in the set value storage unit 524. The trigger signal deviation detection circuit 523C has an XOR circuit, and outputs a deviation detection signal when a deviation occurs between the trigger signal and the monitoring signal. Here, in the first embodiment, the demodulation processing board 52 is described as having the trigger signal monitoring unit 523, but the trigger signal monitoring unit 523 is not essential.

[0031] The demodulation circuit unit 525 detects the leading position of the return pulse optical signal contained in the digital electrical signal based on the trigger signal, and obtains a digital electrical signal corresponding to the return pulse optical signal from the target optical fiber sensor 22. The demodulation circuit unit 525 also performs demodulation processing based on the digital electrical signal corresponding to the return pulse optical signal from the target optical fiber sensor 22. The demodulation circuit unit 525 then outputs a phase signal containing, as data, the amount of phase change in the detected light due to sensing in the target optical fiber sensor 22, obtained by the demodulation processing.

[0032] 3 is a diagram showing a processing flow of the demodulation processing unit 5 in the initial operation of the optical fiber sensor system 100 according to the first embodiment. Here, the initial operation includes not only the operation at the time of system installation but also the case where reconfiguration is performed after a change in the system equipment, such as the addition of the optical fiber sensor 22. In addition, it is assumed here that the input device 701 and the oscilloscope 702 are connected to the external interface unit 53 of the demodulation processing unit 5.

[0033] For example, when a system user activates the optical fiber sensor system 100, the reference signal generating unit 51 of the demodulation processing unit 5 generates a transmission trigger signal, a reference trigger signal, and a reference clock (step S1). Based on the signals generated by the reference signal generating unit 51, the optical fiber sensor system 100 starts operating.

[0034] During the initial operation of the optical fiber sensor system 100, the demodulation processing unit 5 sends a display-related signal to the oscilloscope 702 via the output interface unit 532, causing the oscilloscope 702 to display the clock, trigger signal, and return pulse optical signal (step S2). The system user sets the timing at which the trigger signal generation unit 522 outputs a trigger signal based on the relationship between the signals displayed on the oscilloscope 702, and inputs the setting value to the input device 701. The signal including the setting value is input to the demodulation processing unit 5 via the input interface unit 531. The setting value storage unit 524 of the demodulation processing unit 5 stores the input setting value as data (step S3). Then, the initial operation of the optical fiber sensor system 100 ends.

[0035] FIG. 4 illustrates the relationship between signals during initial operation according to the first embodiment. Here, we explain how the system user determines the setting values. As described above, during operation of the optical fiber sensor system 100, the pulse light source unit 1 emits a pulsed optical signal based on a transmission trigger signal sent from the reference signal generator 51 of the demodulation processor 5. During initial startup, the pulse light source unit 1 provides a period during which it does not emit a pulsed optical signal, widening the interval between transmitted pulses. This creates a period of time during which there is no returning pulsed optical signal. This allows the leading edge of the returning pulsed optical signal from the sensor group 2 to be clearly identified in the digital electrical signal. The pulsed optical signal sent from the pulse light source unit 1 passes through each optical fiber sensor 22 of the sensor group 2 and is input to the delay compensator 3 as a returning pulsed optical signal. The delay compensator 3 and the light receiver 4 then process the returning pulsed optical signal to obtain an analog electrical signal, which is then sent to the demodulation processor 5. Here, we explain the returning pulsed optical signal associated with the digital electrical signal shown in FIG. 4. For example, among the return pulse optical signals from the optical fiber sensor 22-1, the reference light (non-interfering light) from the reference fiber is designated as p11, the detection light (non-interfering light) from the sensing fiber is designated as p12, and the interference light obtained by the delay compensator 3 is designated as I1. Return pulse optical signals from the other optical fiber sensors 22-2 to 22-6 are also indicated in a similar manner.

[0036] As described above, in the demodulation processing unit 5, the reference signal generating unit 51 generates a reference trigger signal and a reference clock together with a transmission trigger signal. The demodulation processing board 52 generates a trigger signal and a clock based on the reference trigger signal and the reference clock. Here, the clock is generated so that the pulse rises at a timing near the center of the pulse width of the pulse in the return pulse optical signal. Furthermore, the trigger signal is generated so that the falling edge and rising edge of the clock are synchronized.

[0037] The system user determines the number of clock pulses until the leading position of the return pulse optical signal of the target optical fiber sensor 22 is confirmed after the reference trigger signal is input and the reference trigger synchronization counter 522A resets its count value to 0 and restarts counting. Here, assume that the digital electrical signal corresponding to the return pulse optical signal of the optical fiber sensor 22-1 is the target of the demodulation process. At this time, as shown in FIG. 4, when the reference trigger synchronization counter 522A has a count value of "6," the digital electrical signal of the reference light p11, which is the leading return pulse optical signal of the optical fiber sensor 22-1, is input. Therefore, the system user inputs a setting value of "6" to the input device 701, and the setting value storage unit 524 of the demodulation processing unit 5 stores the setting value "6" as data. This sets the setting value to "6."

[0038] 5 is a diagram showing the flow of processing by the demodulation processing unit 5 in the sensing operation of the optical fiber sensor system 100 according to the first embodiment. For example, when a system user starts up the optical fiber sensor system 100, the reference signal generating unit 51 of the demodulation processing unit 5 generates a transmission trigger signal, a reference trigger signal, and a reference clock for the demodulation processing board 52 (step S11). Based on the signals generated by the reference signal generating unit 51, the optical fiber sensor system 100 starts operating.

[0039] The trigger signal generating unit 522 outputs a trigger signal based on the count value obtained by counting the clock obtained by multiplying the reference clock by the phase synchronization unit 521 (step S12). As described above, the reference trigger synchronization counter 522A of the trigger signal generating unit 522 counts the clock. The reference trigger synchronization counter 522A uses the reference trigger signal as a clear signal, and when the reference trigger signal is input, it clears the count value to "0" and resumes counting. Then, the trigger signal comparing circuit 522B outputs a trigger signal when the count value counted by the reference trigger synchronization counter 522A becomes the same as the set value stored in the set value storage unit 524.

[0040] The trigger signal monitoring unit 523 also determines whether a synchronization deviation has occurred in the signal (step S13). If the trigger signal monitoring unit 523 determines that a synchronization deviation has occurred, it outputs a deviation detection signal (step S14). The trigger signal monitoring free-running counter 523A of the trigger signal monitoring unit 523 counts clocks while circulating the count value from "0" to "n". The monitoring comparison circuit 523B outputs a monitoring signal when the count value counted by the trigger signal monitoring free-running counter 523A becomes the same as the set value stored in the set value storage unit 524. Then, the trigger signal deviation detection circuit 523C outputs a deviation detection signal when a deviation has occurred between the trigger signal and the monitoring signal.

[0041] Then, the demodulation circuit unit 525 samples the value of the digital electric signal corresponding to the target optical fiber sensor 22 based on the trigger signal, and outputs a phase signal including the amount of phase change obtained by the demodulation process as data (step S15). The process is continued until it is determined that the sensing operation of the optical fiber sensor system 100 is completed (step S16).

[0042] 6 is a diagram showing the relationship between various signals when a synchronization error occurs in the sensing operation of the optical fiber sensor system 100 according to the embodiment 1. Here, as described above, it is assumed that the target of the demodulation process is a digital electrical signal corresponding to the return pulse optical signal of the optical fiber sensor 22-1, and that the set value storage unit 524 stores data of a set value of "6."

[0043] If no synchronization error occurs in the sensing operation, a reference trigger signal is input, and when the reference trigger synchronization counter 522A reaches a count value of "6", the trigger signal generation unit 522 outputs a trigger signal.

[0044] Here, as shown in Figure 6, external noise is superimposed on the clock, causing two pulses that should be counted as count values ​​"10" and "11" to be missing, resulting in those pulses not being counted. As a result, as shown in Figure 4 above, the count value corresponding to the input of interference light I1 should actually be count value "12," but in Figure 6 it is count value "10," resulting in a discrepancy.

[0045] However, as shown in FIG. 6, in the optical fiber sensor system 100 of the first embodiment, when the reference trigger synchronous counter 522A receives an input of a reference trigger signal, it clears the count to "0" and restarts counting, even if the count is "n-2." Therefore, the count corresponding to the reference light p11 in the next period will be "6." Therefore, the influence of the deviation between the clock (count) and the trigger signal in a certain period will not extend to the next period. Also, although not shown in FIG. 6, if a clock pulse is missing while the reference trigger synchronous counter 522A is counting from the count "0" to the count "6," an output deviation will occur in the trigger signal in that period, but this will not extend to the next period. Therefore, the output timing of the trigger signal will be corrected in a maximum of one period.

[0046] On the other hand, the trigger signal monitoring free-running counter 523A of the trigger signal monitoring unit 523 is free-running, and does not clear its count at the count value "n-2." After counting up to the count value "n," it returns to the count value "0" and starts counting again. Therefore, in the next period, the monitoring signal output when the trigger signal monitoring free-running counter 523A counts up to the count value "6" is output later than the trigger signal. This causes a deviation between the trigger signal and the monitoring signal, and a deviation detection signal is output. The deviation detection signal is sent to the external control device 703 via the output interface unit 532. For example, the external control device 703 issues an alarm indicating that a deviation has occurred.

[0047] As described above, according to the optical fiber sensor system 100 of the first embodiment, the demodulation processing board 52 of the demodulation processing unit 5 includes the trigger signal generating unit 522. The trigger signal generating unit 522 outputs a trigger signal at a timing based on a setting value set during the initial system operation after the reference trigger signal is sent. Therefore, even if signal synchronization is lost due to external noise, the trigger signal and the return pulse optical signal are shifted by at most one period. Then, in the next period, the trigger signal generating unit 522 outputs the trigger signal at the same timing after the reference trigger signal is input to the trigger signal generating unit 522, thereby synchronizing the trigger signal and the return pulse optical signal. The demodulation circuit unit 525 of the demodulation processing unit 5 can demodulate the phase change amount associated with the target optical fiber sensor 22. Therefore, the optical fiber sensor system 100 of the first embodiment can limit the shift in the trigger signal to a maximum of one period and resynchronize in the next period, thereby preventing the influence of synchronization loss in the demodulation processing unit 5 from affecting the phasing processing unit 6 and enabling highly accurate sensing.

[0048] Furthermore, in the optical fiber sensor system 100 of the first embodiment, the demodulation processing board 52 of the demodulation processing unit 5 has a trigger signal monitoring unit 523. When the trigger signal monitoring unit 523 determines that a synchronization error has occurred between signals, it outputs a deviation detection signal, making it possible to monitor the state of the system. This makes it possible to take measures such as reducing external noise based on the monitoring, thereby improving the accuracy of the optical fiber sensor system 100.

[0049] Embodiment 2 In the optical fiber sensor system 100 according to the first embodiment, the deviation detection signal output by the trigger signal monitoring unit 523 is output to the external control device 703, but this is not limitative. For example, a notification device that notifies of a synchronization deviation by sound, display, or the like may be connected to the external interface unit 53.

[0050] In the first embodiment, the optical fiber sensor system 100 employs PMDI interferometry, but the present invention is not limited to this. For example, the present invention can be applied to any interferometric optical fiber sensor system that is synchronous and has a TDM output structure. [Explanation of symbols]

[0051] 1 Pulse light source 2 Sensor group 3 Delay Compensator 4 Light receiving section 5 Demodulation processing section 6. Phase adjustment section 21, 21-1 to 21-6 Outgoing optical coupler 22, 22-1 to 22-6 Optical fiber sensors 23, 23-1 to 23-6 Return optical coupler 51 Reference signal generation section 52 Demodulation processing board 53 External interface section 100 Optical Fiber Sensor System 101 Outgoing transmission fiber 102 Return transmission fiber 521 Phase synchronization section 522 Trigger signal generator 522A Reference Trigger Synchronous Counter 522B Trigger signal comparison circuit 523 Trigger signal monitoring unit 523A Free-Running Counter for Monitoring Trigger Signals 523B Monitoring Comparison Circuit 523C Trigger signal deviation detection circuit 524 Setting value memory section 525 Demodulation Circuit Section 531 Input interface section 532 Output interface section 701 Input Device 702 oscilloscope 703 External Control Device

Claims

1. an optical fiber sensor array having a plurality of optical fiber sensors that change the phase of passing light based on a detected physical quantity and periodically transmit the changed light as a return signal, and that passes the return signals from the optical fiber sensors in a set pulse order; a demodulation processing unit that performs demodulation processing based on the return signal to obtain data on the amount of phase change of the light, The demodulation processing unit a trigger signal generating unit that, when a reference trigger signal that is a reference for defining the beginning of the return signal is input, clears a count value, counts clock pulses synchronized with the return signal, and outputs a trigger signal when a set value of the counted pulses that is set at the timing when the beginning signal of the return signal from the optical fiber sensor to be processed is sent to the demodulation processing unit; a demodulation circuit section that performs the demodulation process when the trigger signal is sent; An optical fiber sensor system comprising:

2. The trigger signal generation unit a reference trigger synchronous counter that, when the reference trigger signal is input, clears the count value to return it to an initial value and counts pulses of the clock; a trigger signal comparison circuit that compares the count value of the reference trigger synchronous counter with the set value, and outputs the trigger signal when the count value and the set value become the same; 10. The optical fiber sensor system of claim 1, comprising:

3. The demodulation processing unit 3. The optical fiber sensor system according to claim 1, further comprising a trigger signal monitoring unit that outputs a deviation detection signal when it is determined that a deviation occurs between the signals.

4. The demodulation processing unit The optical fiber sensor system according to any one of claims 1 to 3, further comprising a setting value storage unit that stores the setting value that is set based on the timing of the clock, the reference trigger signal, and the return signal in an initial operation.

5. a step of passing return signals from a plurality of optical fiber sensors, the return signals being periodically transmitted by changing the phase of the light passing through the optical fiber sensors based on the detected physical quantity, in a set pulse order; a step of clearing a count value and counting clock pulses synchronized with the return signal when a reference trigger signal that defines the beginning of the return signal is input; a step of outputting a trigger signal when a set value of pulses set at a timing for performing demodulation processing on a leading signal of the return signals of the optical fiber sensor to be processed is counted; a step of performing the demodulation process when the trigger signal is sent to obtain data on the amount of phase change of the light; A method for demodulating an optical fiber sensor comprising:

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