JP7735880B2 - Optical fiber sensor system and optical fiber sensor demodulation method - Google Patents

Description

This technology relates to an optical fiber sensor system that uses optical fiber as a sensor to detect physical quantities, and an optical fiber sensor demodulation method. In particular, it relates to demodulation when using an optical fiber sensor array consisting of multiple channel optical fiber sensors.

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 passing through it also changes. As a result, it is possible to detect physical quantities 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 optical fiber sensor systems, which demodulate the amount of phase change from the light that passes through the optical fiber sensor and returns.

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 then 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 3x3 coupler demodulation method has been proposed (see, for example, Patent Document 1).

Patent No. 4844325

To perform demodulation processing based on the light obtained after passing through the optical fiber sensor and obtain a phase signal, it is necessary to identify the position (timing of sampling, etc.) of the beginning 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 forms 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 beginning position, which serves as a marker for the return pulse optical signal to be processed, and performs demodulation processing.

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 discrepancy will occur with the actual count value. This causes a shift in the temporal 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 count value counted by the counter continues to differ, the return signal will not be obtained at the correct timing during the demodulation process, making it impossible to properly demodulate the phase change amount, which will affect the phasing process in the subsequent stages.

Therefore, there was a need to develop an optical fiber sensor system and an optical fiber sensor demodulation method that could reduce the occurrence of synchronization errors.

The disclosed optical fiber sensor system includes a plurality of optical fiber sensors that change the phase of passing light based on the detected physical quantity and periodically transmit the result as a return signal. The system includes an optical fiber sensor array 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. When a reference trigger signal that serves as a reference for defining the beginning of the return signal is input, the demodulation processing unit clears a count value and counts clock pulses synchronized with the return signal. When the demodulation processing unit counts a set number of pulses that correspond to the timing at which the beginning signal of the return signal from the optical fiber sensor being processed is sent to the demodulation processing unit, the system includes a trigger signal generation unit that outputs a trigger signal, and a demodulation circuit unit that performs demodulation processing when a trigger signal is sent.

The disclosed optical fiber sensor demodulation method includes the steps of: passing return signals from multiple 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 that defines 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 that are set for the timing of demodulation processing; and performing demodulation processing when the trigger signal is sent to obtain data on the amount of phase change of the light.

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. As a result, even if signal synchronization deviation occurs due to external noise contamination, the deviation in 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, allowing for highly accurate sensing processing.

1 is a diagram showing a configuration of an optical fiber sensor system 100 according to a first embodiment; 1 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. 10 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. FIG. 10 is a diagram showing the relationship between signals during an initial operation according to the first embodiment. 4 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. 5 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.

The following describes an optical fiber sensor system according to an embodiment, with reference to the drawings. In the following drawings, components with the same reference numerals are the same or equivalent, and this applies throughout the embodiments described below. Furthermore, the dimensional relationships between components in the drawings may differ from those in reality. The forms of components shown throughout the specification are merely examples and are not limited to the forms described in the specification. Not all of the 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.

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 the explanation of the system according to the first embodiment, the physical quantity to be detected is the sound pressure of a sound wave, and an acoustic signal generated from the sound wave will be described as an example of a system that senses the acoustic signal. 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.

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 generator 51 included in the demodulation processor 5, which will be described later. The pulse light signal output by the pulse light source unit 1 passes through the 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, as will be described later.

The sensor group 2 passes a return pulsed optical signal, which includes a pulsed optical signal that has been transmitted through the outgoing transmission fiber 101 and a pulsed optical signal whose phase has changed in response to the sound pressure of the sound waves in the acoustic signal, through the incoming transmission fiber 102 in a set pulse order. Therefore, the return pulsed optical signal has the amount of phase change based on the acoustic signal superimposed as data. The sensor group 2 has multiple outgoing optical couplers 21, multiple optical fiber sensors 22, and multiple incoming optical couplers 23. Here, in the optical fiber sensor system 100 of embodiment 1, the sensor group 2 is described as being configured with six optical fiber sensors 22. However, the number of optical fiber sensors 22 is not limited to six, and any number can be used.

The outbound optical couplers 21 (outbound optical couplers 21-1 to 21-6) branch the pulsed optical signal sent from the pulse light source unit 1 and passed through the outbound transmission fiber 101. The light that passes through each outbound optical coupler 21 is sent to multiple optical fiber sensors 22. While the outbound optical coupler 21-6 is installed in Figure 1, the optical fiber sensor 22-6, which 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 equipped with the outbound optical coupler 21-6.

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 shifted based on the acoustic signal. In the optical fiber sensors 22, the optical fiber used for 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 in accordance with the magnitude of the acoustic signal. At this time, the path length (propagation distance) of the light passing through the optical fiber changes, changing the phase of the light, allowing the detection of an acoustic signal corresponding to the shifted phase. Therefore, the amount of phase change in the pulsed optical signal based on the acoustic signal is superimposed as data.

The return pulse optical couplers 23 (return pulse optical couplers 23-1 to 23-6) combine the return pulse optical signal from the corresponding optical fiber sensor 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 sensor 22 is a signal in which the return pulse optical signals from each optical fiber sensor 22 are time division multiplexed (TDM). Therefore, the return pulse optical signals from each optical fiber sensor 22 do not overlap in time. Here, although return pulse optical coupler 23-6 is installed in Figure 1, it is not necessary.

The delay compensator 3 of embodiment 1 obtains interference light from the return pulse light signals (non-interfering light) from each optical fiber sensor 22 by using the same delay time difference as each optical fiber sensor 22. The delay compensator 3 then outputs two return signal pulse light paths, with the phases of the pulse light shifted by +1/3π and -1/3π, via a 3x3 coupler.

The light receiving unit 4 adjusts the intensity of the coherent and non-coherent 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.

The demodulation processing unit 5 converts the analog electrical signal from the light receiving unit 4 into a digital electrical signal. It also generates a reference trigger signal and a reference clock. From the digital electrical signal, the demodulation processing unit 5 detects the leading edge (the reference timing for sampling) of the return pulse optical signal from the optical fiber sensor 22 to be processed (hereinafter referred to as the target). The demodulation processing unit 5 then performs demodulation processing to obtain the amount of phase change from the data value in the sampled signal based on the leading edge. The demodulation processing unit 5 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 generation unit 51, a demodulation processing board 52, and an external interface unit 53.

The reference signal generation 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.

The demodulation processing board 52 is a board equipped with circuits and other devices, and performs demodulation processing. Here, the demodulation processing board 52 can achieve demodulation processing using specialized software for digital signal processing, such as a DSP (Digital Signal Processor), or hardware using programmable logic circuits, such as an FPGA (Field-Programmable Gate Array).

The external interface unit 53 is a device that acts as an interface for inputting and outputting data with external devices. 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 to the demodulation processing unit 5 from the outside. 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, which is used to check the positional relationship of the return pulse optical signal indicated by the trigger signal, clock, and digital electrical signal, which will be described later. The output interface unit 532 is an interface that connects to an external control device 703, which is capable of communicating signals with the demodulation processing unit 5.

The phasing processor 6 performs phasing processing to emphasize the sound from the desired direction of arrival based on the phase signal from the demodulator 5, and detects the direction of arrival of the sound, etc.

Figure 2 shows an example of the configuration of the demodulation processing board 52 according to embodiment 1, focusing on circuits related to the generation of trigger signals and the like. The demodulation processing board 52 has a phase synchronization unit 521, a trigger signal generation unit 522, a trigger signal monitoring unit 523, a setting value storage unit 524, and a demodulation circuit unit 525.

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 multiplying the reference clock to generate a clock, the phase synchronization unit 521 can accurately detect the center of the pulse width, which is on the order of tens of nanoseconds, in the return pulse optical signal.

The set value memory unit 524 stores the set value data entered by the system user via the input device 701 and the input interface unit 531. The set value is data that defines the leading position of the return pulsed light 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 account the propagation delay time of the pulses in the pulsed light signal that has passed through the transmission path from the pulsed light source unit 1 to the demodulation processing unit 5.

The trigger signal generation unit 522 generates a trigger signal that identifies the leading edge of the return pulse light signal from the optical fiber sensor 22 targeted for 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 up the clock and outputs the count value for the trigger. The reference trigger synchronization counter 522A cycles through count values from 0 to n. The value of n is set, for example, to the clock count corresponding to the period of the pulse light signal sent by the pulse light source unit 1 (the time of the time-division multiplexed return pulse light signal from the sensor group 2, which is also 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 is synchronized with the count value from 0 to n of the reference trigger synchronization counter 522A. Therefore, 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, and the counting in the next cycle begins with the initial count value of "0." However, when the reference trigger synchronous counter 522A in embodiment 1 receives the reference trigger signal, it clears the count value, returns it to the initial count value of "0," and resumes counting. Therefore, the reference trigger synchronous counter 522A in embodiment 1 uses the reference trigger signal as a signal to clear the count value and return it to the initial value. Furthermore, 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.

The trigger signal monitoring unit 523 monitors the trigger signal and determines 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. Like the reference trigger synchronous counter 522A, the trigger signal monitoring self-running counter 523A counts clocks from 0 to n. The trigger signal monitoring self-running counter 523A then outputs the count value as a monitoring count value. However, the trigger signal monitoring self-running counter 523A of embodiment 1 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 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 memory unit 524. The trigger signal deviation detection circuit 523C has an XOR circuit and outputs a deviation detection signal when there is a deviation between the trigger signal and the monitoring signal. In the first embodiment, the demodulation processing board 52 is described as having a trigger signal monitoring unit 523, but the trigger signal monitoring unit 523 is not essential.

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 through the demodulation processing.

Figure 3 shows the processing flow of the demodulation processing unit 5 during initial operation of the optical fiber sensor system 100 according to embodiment 1. Here, initial operation refers not only to the time of system installation, but also to cases where reconfiguration is required following changes to the system equipment, such as the addition of an optical fiber sensor 22. It is also assumed here that the input device 701 and oscilloscope 702 are connected to the external interface unit 53 of the demodulation processing unit 5.

For example, when a system user activates the optical fiber sensor system 100, the reference signal generator 51 of the demodulation processor 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 generator 51, the optical fiber sensor system 100 begins operation.

When the optical fiber sensor system 100 is initially operating, the demodulation processing unit 5 sends a display signal to the oscilloscope 702 via the output interface unit 532, causing the oscilloscope 702 to display the clock, trigger signal, and return pulse light 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 into the input device 701. The signal containing 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). The optical fiber sensor system 100 then terminates its initial operation.

Figure 4 shows the relationship between signals during initial operation in embodiment 1. 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. Here, 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 return pulsed optical signal. This allows the leading edge of the return 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 then passes through each optical fiber sensor 22 of the sensor group 2 and is input to the delay compensator 3 as a return pulsed optical signal. The delay compensator 3 and the light receiver 4 then process the return pulsed optical signal, resulting in an analog electrical signal that is sent to the demodulation processor 5. Here, we explain the return pulsed optical signal associated with the digital electrical signal shown in Figure 4. For example, of the return pulse light signals from optical fiber sensor 22-1, the reference light (non-interfering light) from the reference fiber is designated p11, the detection light (non-interfering light) from the sensing fiber is designated p12, and the interference light obtained by delay compensator 3 is designated I1. The return pulse light signals from the other optical fiber sensors 22-2 to 22-6 are also indicated in a similar manner.

In the demodulation processing unit 5, as described above, the reference signal generation unit 51 generates a reference trigger signal and a reference clock along with the 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.

The system user determines the number of clock pulses required to confirm the leading position of the return pulse optical signal from the target optical fiber sensor 22 after the reference trigger signal is input and the reference trigger synchronization counter 522A resets its count to 0 and restarts counting. Here, assume that the digital electrical signal corresponding to the return pulse optical signal from optical fiber sensor 22-1 is the target of the demodulation process. As shown in FIG. 4, when the reference trigger synchronization counter 522A has a count of "6," the digital electrical signal of reference light p11, which is the leading return pulse optical signal from optical fiber sensor 22-1, is input. Therefore, the system user inputs a setting value of "6" into 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."

Figure 5 shows the processing flow of the demodulation processing unit 5 during sensing operation of the optical fiber sensor system 100 according to embodiment 1. For example, when a system user starts up the optical fiber sensor system 100, the reference signal generation 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 generation unit 51, the optical fiber sensor system 100 starts operating.

The trigger signal generation 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 generation 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 comparison 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 memory unit 524.

The trigger signal monitoring unit 523 also determines whether a synchronization error has occurred in the signal (step S13). If the trigger signal monitoring unit 523 determines that a synchronization error 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 cycling through count values "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 memory unit 524. The trigger signal deviation detection circuit 523C then outputs a deviation detection signal if a deviation has occurred between the trigger signal and the monitoring signal.

The demodulation circuit unit 525 then samples the value of the digital electrical signal corresponding to the target optical fiber sensor 22 based on the trigger signal, and outputs a phase signal containing the phase change amount obtained by performing the demodulation process (step S15). This processing continues until it is determined that the sensing operation of the optical fiber sensor system 100 has ended (step S16).

Figure 6 shows the relationship between various signals when a synchronization error occurs during the sensing operation of the optical fiber sensor system 100 according to the first embodiment. Here, as mentioned above, 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 the set value memory unit 524 stores data for a set value of "6."

If no synchronization error occurs during sensing operation, a reference trigger signal is input, and when the reference trigger synchronization counter 522A reaches the count value "6", a trigger signal is output from the trigger signal generation unit 522.

Here, as shown in Figure 6, external noise is superimposed on the clock, causing two pulses that would normally be counted as count values "10" and "11" to be missing, resulting in those pulses not being counted. Therefore, 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.

However, as shown in FIG. 6, in the optical fiber sensor system 100 of embodiment 1, when the reference trigger synchronization counter 522A receives 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 cycle will be "6." Therefore, the impact of a discrepancy between the clock (count) and the trigger signal in a certain cycle does not extend to the next cycle. Also, although not shown in FIG. 6, if a clock pulse is missing while the reference trigger synchronization counter 522A counts from "0" to "6," an output discrepancy will occur in the trigger signal in that cycle, but this will not extend to the next cycle. Therefore, the output timing of the trigger signal is corrected for a maximum of one cycle.

Meanwhile, 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 cycle, when the trigger signal monitoring free-running counter 523A counts up to the count value "6," the monitoring signal is output later than the trigger signal. This causes a discrepancy between the trigger signal and the monitoring signal, and a discrepancy detection signal is output. The discrepancy 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 discrepancy has occurred.

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 a trigger signal generation unit 522. The trigger signal generation 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 error occurs due to external noise interference, the trigger signal and the return pulse optical signal are shifted by at most one period. Then, in the next period, the timing at which the trigger signal generation unit 522 outputs the trigger signal after the reference trigger signal is input to the trigger signal generation unit 522 is synchronized, 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, preventing the effects of synchronization error in the demodulation processing unit 5 from affecting the phasing processing unit 6, enabling highly accurate sensing.

Furthermore, in the optical fiber sensor system 100 of embodiment 1, 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, allowing the system status to be monitored. This allows measures such as external noise reduction to be taken based on the monitoring, thereby improving the accuracy of the optical fiber sensor system 100.

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.

Furthermore, in the above-mentioned first embodiment, the optical fiber sensor system 100 using the PMDI interferometry method has been described, 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.

REFERENCE SIGNS LIST 1 pulse light source unit 2 sensor group 3 delay compensator 4 light receiving unit 5 demodulation processing unit 6 phasing processing unit 21, 21-1 to 21-6 outgoing path side optical coupler 22, 22-1 to 22-6 optical fiber sensor 23, 23-1 to 23-6 return path side optical coupler 51 reference signal generating unit 52 demodulation processing board 53 external interface unit 100 optical fiber sensor system 101 outgoing path side transmission fiber 102 return path side transmission fiber 521 phase synchronization unit 522 trigger signal generating unit 522A reference trigger synchronization counter 522B trigger signal comparison circuit 523 trigger signal monitoring unit 523A trigger signal monitoring free-running counter 523B monitoring comparison circuit 523C trigger signal deviation detection circuit 524 set value storage unit 525 demodulation circuit unit 531 input interface unit 532 Output interface unit 701 Input device 702 Oscilloscope 703 External control device

Claims (5)

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. 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;
2. The optical fiber sensor system according to claim 1, further comprising a trigger signal comparison circuit that compares the count value of the reference trigger synchronization counter with the set value and outputs the trigger signal when the count value and the set value become the same. 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. 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. 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;
and performing the demodulation process when the trigger signal is sent to obtain data on the amount of phase change of the light.