JP2006023230A - Optical fiber ring interference type sensor and method for correcting fluctuations in interference light intensity - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber interference type sensor which allows to calculate a phase difference with high precision by performing correction using a predetermined maximum value and a minimum value even when there are fluctuations in interference light intensity or the output of an amplifier circuit. <P>SOLUTION: The optical fiber interference type sensor comprises an amplification means for amplifying a light signal received by a light receiving element, a level fluctuations amount decision means for monitoring fluctuations in a signal level outputted from the amplification circuit within a predetermined range of time including the initial state, a vibrationless decision means for monitoring whether the fluctuations in the signal level has exceeded a standard level or not, and a correction calculation means for calculating a light level fluctuations correction value by acquiring a voltage level value calculated by a level signal decision means when the signal level is the standard level or less. The phase difference can be thereby calculated, allowing to calculate the phase difference with high precision even when there are fluctuations in the interference light intensity or the output of the amplification circuit. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical fiber ring interference type sensor using an optical fiber and an interference light intensity fluctuation correction method, and more particularly to an optical fiber ring interference type sensor for calculating a phase fluctuation amount and an interference light intensity fluctuation correction method.

  Conventionally, various interference sensors using optical fibers have been reported. For example, there is Patent Document 1 relating to an optical fiber ring interference sensor filed by the applicant of the present application.

  This optical fiber ring interference type sensor includes an optical fiber ring formed in a loop shape, a 3 × 3 optical branch coupling element connected to the end of the optical fiber ring, and the other end of the 3 × 3 optical branch coupling element Is composed of at least three light receiving elements, an amplifier circuit, and a light emitting circuit.

  This optical fiber ring interferometric sensor detects the phase difference generated between clockwise and counterclockwise light propagating in the optical fiber ring due to phase fluctuations caused by disturbances such as vibration applied to the optical fiber ring. The linearity of the interference light intensity and the phase difference is improved by using a 3 × 3 optical branching and coupling element. This configuration diagram is shown in FIG. 4 and will be described in detail.

  According to the optical fiber ring interference sensor 101 disclosed in Patent Document 1, two optical signals output from the light emitting circuit 113 and branched via the 3 × 3 optical branching and coupling element 107 are configured in a loop shape. Are incident on both ends of the optical fiber ring 105, propagated clockwise and counterclockwise in the optical fiber ring (same optical path), respectively, and again 3 × 3 optical branching and coupling as the clockwise propagation light and the counterclockwise propagation light. The light is incident on the element 107, branched into three optical signals by the 3 × 3 optical branching and coupling element 107, and then incident on the first to third light receiving elements 111a to 111b, respectively.

  At this time, interference light having a nonreciprocal phase bias is output from the three ends of the 3 × 3 optical branching and coupling element 107. That is, an optical signal whose phase is shifted by 2π / 3 is output from each end. The interference light intensity P (t) input to each light receiving element that receives these optical signals is given by the following equation (1). From this equation (1), the phase difference Δφ between the clockwise light and the counterclockwise light is calculated. Can be calculated.

Here, the magnitude of the interference light component received by the light receiving element is Pc, the magnitude of the non-interference light component is Pi, the initial phase difference is θ ₀ , and the phase difference between the clockwise light and the counterclockwise light is Δφ (= φ (T−T _CW ) −φ (t−T _CCW ), where CW indicates clockwise light and CCW indicates counterclockwise light.

P (t) = Pi + Pc {cos (θ ₀ + Δφ)} / 2 (1)
According to the above formula (1), vibration of the optical fiber can be detected based on the interference light intensity detected by the light receiving element.

  A specific operation will be described here. First, the signals photoelectrically converted by the light receiving elements 111a to 111c are amplified by the amplifier circuits 115a to 115c. A section in which the light intensity output of the amplified signal is linear in the correlation between the phase difference between the clockwise light and the counterclockwise light is determined in advance. Here, the section that is linear is that each cosine function output from each of the three light receiving elements is shifted by 2π / 3, and a part of these overlaps. Saw-like waveform is obtained by connecting A section between the maximum value and the minimum value of the sawtooth waveform is referred to as a straight section.

  Thus, when the 3 × 3 optical branching and coupling element 107 having a phase shift of 2π / 3 is used, the phase of the signal output from each end is changed from π / 3 + nπ to 2π / 3 + nπ (n = 0, ± 1, By setting the section so as to be between ± 2..., High linearity can be obtained and the entire range of the measurement section can be covered.

  Subsequently, when the light intensity detected by the light receiving element reaches the light intensity corresponding to the section, the phase difference of the signal output from the light receiving element 111a is calculated. On the other hand, when the upper limit value or the lower limit value set in the above section is exceeded, the phase difference of the signal output from the next light receiving element 111b is calculated to calculate a wide range of phase difference with good linearity. Can do.

  That is, the interference light intensity detected by the optical fiber ring interference sensor is folded back to the maximum level when the phase difference between the clockwise light and the counterclockwise light is 2nπ (n = 0, ± 1, ± 2...). When the phase difference becomes (2n + 1) π (n = 0, ± 1, ± 2...), The signal is folded back at the minimum level.

When the phase difference is calculated in this way, the maximum level of the output levels of the first to third amplifier circuits 115a to 115c (the level of adding the clockwise light and the counterclockwise light: phase difference 2nπ) and the minimum level. It is necessary to make (cancellation level: phase difference (2n + 1) π) known in advance and normalize the interference light intensity based on the value. In order to know this value, as shown in FIG. 5, a vibration that causes phase modulation such that the intensity of the interference light reaches the upper and lower folding levels is applied to the optical fiber ring 105 and is then output from the amplifier circuit. This can be realized by measuring in advance the maximum and minimum values of the voltage.
JP 2003-139540 A JP 2003-344147 A Takeshi Tokura, 3 others, “Identification of vibration position by optical fiber ring interference type vibration sensor”, Fujikura Technical Report, Fujikura Co., Ltd., October 2002, No. 103, p. 18-21

  By the way, the above-described optical fiber ring interference type sensor operates normally under a certain condition, but its output fluctuates due to the following situation change.

(1) Light output fluctuations due to temperature fluctuations and temporal changes of the light emitting circuit.

(2) Loss fluctuations at connection points of optical fiber rings, optical branching coupling elements, and other optical fibers.

(3) Light reception sensitivity fluctuations due to temperature fluctuations and changes with time of the light receiving element.

  Here, the phenomenon caused by these problems will be described with reference to FIG. FIG. 6 (a) shows the interference light intensity during normal operation under a certain condition, and FIG. 6 (b) shows the temperature fluctuation of the environment after a lapse of a certain time from that point. It shows the interference light intensity when there is.

  As shown in FIG. 6, due to fluctuations caused by the above (1) to (3) from the normal operation, the interference light intensity at each output terminal of the optical branching coupling element or the amplification circuit as shown in FIG. 6 (b) Output fluctuates (hereinafter referred to as interference light level fluctuation). When such interference light level fluctuations occur, an error occurs when the phase difference is obtained by standardizing the interference light intensity from the preset maximum value and minimum value shown in FIG. It cannot be calculated with high accuracy.

  The present invention has been made in view of the above problems, and its purpose is to perform correction using the preset maximum and minimum values even when fluctuations in interference light intensity or fluctuations occur in the output of the amplifier circuit. Another object of the present invention is to provide an optical fiber ring interference sensor capable of calculating a phase difference with high accuracy, and an interference light intensity fluctuation correction method.

  In order to solve the above object, according to the present invention, the light source, the light receiving element, and both ends of the open portion of the loop optical fiber are connected to the branch coupling element, and the light emitted from the light source is branched and coupled. Branched by the element and made incident on the looped optical fiber from both ends of the open part, propagated in the looped optical fiber clockwise and counterclockwise, and branched clockwise and counterclockwise propagating light Coupled by a coupling element, the coupled clockwise and counterclockwise propagating light is incident on the light receiving element, and the intensity difference of the interference light is changed by the phase difference between the clockwise and counterclockwise propagating light. The intensity of the interference light due to the phase difference between the clockwise and counterclockwise propagated light caused by a physical change locally applied to an arbitrary place of the loop optical fiber by outputting the signal shown from the light receiving element Strange An optical fiber ring interference type sensor that outputs a signal indicating light from the light receiving element, amplifying means for amplifying the optical signal received by the light receiving element, and within a predetermined time range from the initial state of the signal level output from the amplifier circuit A level variation determining means for monitoring the amount of fluctuation, a no-vibration determining means for monitoring whether the fluctuation of the signal level exceeds the reference level, and a level signal determining means when the signal level is equal to or lower than the reference level. The gist of the present invention is to provide correction calculation means for acquiring the calculated voltage level value and calculating the light level fluctuation correction value.

  According to the second aspect of the present invention, the light emitted from the light source is branched by the branch coupling element and is incident from both ends of the open portion of the loop-shaped optical fiber, and the loop-shaped optical fiber is counterclockwise. The clockwise and counterclockwise propagated light propagated in the clockwise direction and coupled in the loop optical fiber are combined by the branch coupling element and made incident on the light receiving element, and counteract with the clockwise propagated light output from the light receiving element. An interference light intensity fluctuation correction method for detecting a physical change locally applied to an arbitrary place of a loop-shaped optical fiber based on a signal indicating an intensity change of the interference light due to a phase difference with the clockwise propagation light, Measuring the interference light intensity within a certain time, determining whether the fluctuation amount of the interference light intensity within the certain time is less than or equal to a preset amplitude, and the fluctuation amount being less than or equal to this amplitude When it is determined that there is no vibration, the step of comparing the interference light intensity average value during the period determined as no vibration with a preset initial value, and the comparison result shows that the ratio of the interference light intensity average value and the initial value is And a step of calculating a phase difference by performing fluctuation correction value calculation of the interference light intensity.

  The present invention described in claim 3 is the interference light intensity fluctuation correction method according to claim 2, wherein the average interference light intensity value fluctuates more than a preset deviation compared to the initial value. The gist is to perform fluctuation correction value calculation.

  According to the present invention, the interference light intensity within a certain time is measured, it is determined whether or not the fluctuation amount of the interference light intensity within this certain time is equal to or less than a preset amplitude, and this fluctuation amount is When the amplitude is equal to or less than the amplitude, the average value of the interference light intensity during the period determined as no vibration is compared with the preset initial value. As a result of this comparison, the fluctuation of the interference light intensity is corrected from the ratio of the average interference light intensity value to the initial value. Since the phase difference can be calculated by performing the value calculation, the phase difference can be calculated with high accuracy even when the interference light intensity varies or the output of the amplifier circuit varies.

  As a result, even if the output fluctuates due to temperature change or secular change, the maximum value and the minimum value can be corrected at any time according to the fluctuation. For example, position identification by this optical fiber ring interference sensor is performed. In this case, the phase difference can be accurately detected in a wide range of sensitivity from the vicinity of the middle point of the low-sensitivity optical fiber ring to the vicinity of the end of the high-sensitivity optical fiber ring.

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

  FIG. 1 is a schematic configuration diagram of an optical fiber ring interference type sensor 1 according to an embodiment of the present invention.

  This optical fiber ring interference type sensor 1 is characterized in that the conventional optical fiber ring interference type sensor 101 is provided with a correction function for setting the maximum value and the minimum value according to the output fluctuation of the interference light intensity. Accordingly, the same members as those in the conventional configuration are denoted by the same reference numerals.

  As described in the conventional configuration, the configuration of this sensor includes an optical fiber ring 105 configured in a loop shape, a 3 × 3 optical branching and coupling element 107 connected to the open end of the optical fiber ring 105, A first light receiving element 111a connected to the × 3 optical branching and coupling element 107, a second light receiving element 111b and a light emitting circuit connected via the optical branching and coupling element 109, a third light receiving element 111c, At least first to third amplifier circuits 115a to 115c connected to the third light receiving elements 111a to 111c are provided.

  Further, as a correction function, the first to third vibrationless determination circuits 3a to 3c connected to the first to third amplifier circuits 115a to 115c and the first to third vibrationless determination circuits 3a to 3c are connected in parallel. First to third level fluctuation amount determination circuits 5a to 5c, and the first to third no-vibration determination circuits 3a to 3c and the first to third level fluctuation amount determination circuits 5a to 5c. To third correction calculation circuits 7a to 7c, and first to third amplification circuits 115a to 115c and a phase difference calculation circuit 9 connected to the first to third correction calculation circuits 7a to 7c.

  Here, the first to third no-vibration determination circuits 3a to 3c acquire the respective interference light intensities output from the first to third amplification circuits 115a to 115b, perform the no-vibration determination, and then perform the determination. It is a function part which outputs a result to the 1st-3rd correction | amendment calculation circuits 7a-7c, respectively.

  Specifically, the outputs of the first to third amplifier circuits 115a to 115c are set to a preset amplitude (= no vibration determination amplitude: Anv (referred to as a reference value Anv in this embodiment) during the measurement time T. ) A circuit that determines “no vibration” when it is detected that the frequency is less than or equal to a predetermined amplitude and detects “vibration”. This no-vibration determination amplitude Anv is an amplitude that is determined based on the vibration environment in which this sensor is installed and the magnitude of electrical noise.

  Next, the first to third level fluctuation amount determination circuits 5a to 5c obtain the interference light intensity output from the first to third amplification circuits 115a to 115b, and the maximum value and the minimum value of the interference light intensity. The function unit compares the value with preset maximum and minimum values and outputs the comparison result to the first to third correction calculation circuits 7a to 7c.

  Specifically, the maximum value and the minimum value of each interference light intensity during normal operation output from the first to third amplifier circuits 115a to 115c, which are measured in advance before the start of observation, are stored. This is a storage means for reading from the first correction calculation circuits 7a to 7c when the third no-vibration determination circuits 3a to 3c determine “no vibration”.

  Obtaining the maximum and minimum values of the interference light intensity of the clockwise light and the counterclockwise light propagating in the optical fiber ring 105 during the measurement time T, and comparing the maximum value and the minimum value stored in advance; The fluctuation amount is calculated and output to the first to third correction calculation circuits.

  On the other hand, the first to third correction calculation circuits 7a to 7c obtain the determination result of “no vibration” or “vibration” from the first to third level variation determination circuits 5a to 5c, and A function unit that obtains the maximum value and the minimum value during normal operation from the three-level fluctuation amount determination circuits 5a to 5c, calculates the maximum value and the minimum value of the interference light intensity in real time based on these information, and outputs them. is there.

  The phase difference calculation circuit 9 is the maximum of the interference light intensity output from the first to third amplification circuits 115a to 115c and the interference light intensity output from the first to third correction calculation circuits 7a to 7c. It is a functional unit that acquires a value and a minimum value, calculates a phase difference based on the information, and outputs the phase difference to an externally connected notification device.

  In the present embodiment, the first to third amplifier circuits 115a to 115b, the first to third no-vibration determination circuits 3a to 3c, the first to third level fluctuation amount determination circuits 5a to 5c, and the first to first levels. The three correction calculation circuits 7a to 7c and the phase difference calculation circuit 9 are analog circuits configured by electronic components such as operational amplifiers and transistors.

  However, the circuit configuration is not limited to an analog circuit, and an analog / digital conversion circuit may be inserted after the first to third amplifier circuits 115a to 115c, and the subsequent processing may be digitally processed.

  In this case, determination functions of the first to third no-vibration determination circuits 3a to 3c, the first to third level fluctuation amount determination circuits 5a to 5c, the first to third correction calculation circuits 7a to 7c, and the phase difference calculation circuit 9 The calculation function is replaced with a logic circuit, and the calculation function is stored in a nonvolatile memory or the like as an auxiliary storage device. The phase difference can be calculated by controlling these functional units by a CPU (Central Processing Unit) or an FPGA (Field Programmable Gate Array).

  Next, with reference to FIG. 2, the setting procedure before the measurement start of the optical fiber ring interference sensor 1 of the present invention will be described.

  First, after propagating light is output from the light emitting circuit 113 of the optical fiber ring interference sensor 1, the propagating light is branched into two signal lights via the optical branching coupling element 109 and the 3 × 3 optical branching coupling element 107. The clockwise light and the counterclockwise light are propagated in the optical fiber ring 105.

  Here, as step S11, a certain part of the optical fiber ring 105 is vibrated.

  In step S13, the phase difference between the clockwise light and the counterclockwise light generated by the vibration is received by the first to third light receiving elements 111a to 111c, respectively, and further, the first to third amplifier circuits 115a to 115c. Amplify the signal. Next, the amplified signals are voltage monitored by the first to third level fluctuation amount determination circuits 5a to 5c, and the highest interference high intensity and the lowest interference light intensity are extracted from the measured voltage levels.

  In step S15, the first to third correction calculation circuits 7a to 7c store the highest interference high intensity as the “reference maximum value” and the lowest interference light intensity as the “reference minimum value”. Then, the vibration of the optical fiber ring is finished.

  Next, a procedure for measuring the voltage level within a predetermined time and calculating the average level will be described.

  First, in step S17, the measurement of a preset measurement time is started using a timer counter (not shown). Here, the measurement time is T and the voltage is V. Further, the time at the start of timing is set to T = 0, and initial setting is performed so that the voltage V = 0.

  Subsequently, in step S19, the first to third level variation determination circuits 5a to 5c acquire the output voltage levels of the first to third amplifier circuits 115a to 115c at regular intervals and temporarily store them in the storage circuit. The value is held and the voltage V is added to the previous measurement result.

  Subsequently, in step S21, the first to third no-vibration determination circuits 3a to 3c are temporarily stored and held in step S19 and the reference set in advance to the first to third no-vibration determination circuits. The value Anv is compared, and it is compared whether or not the acquired voltage level exceeds the reference value Anv. If it is detected that the voltage level is not exceeded, the process proceeds to step S25. If it is detected that the voltage level is exceeded, the process proceeds to step S23. As the process proceeds, 1 is added to the counter X that counts up the number of times that the number of times has been exceeded and stored in X.

  Next, in step S25, the control unit (not shown) monitors the time of the timer counter to determine whether or not the preset measurement time T has been reached. When the measurement time T has been reached, the process proceeds to step S27, where the measurement time T is reached. If not, the process returns to step S19, and the processes of steps S19 to S25 are repeated again.

  When the measurement time T ends, in step S25, the first to third no-vibration determination circuits 3a to 3c acquire the count number of the counter X, and a voltage level exceeding the reference value Anv is detected even once. In the case (ie, when X> 0), it is determined as “vibration”, the process returns to step S17, and the processes of steps S17 to S25 are repeated again.

  On the other hand, if a voltage level exceeding the reference value Anv is not detected, the voltage level integrated in step S19 is divided by the measurement time T to obtain an average value of the voltage level, which is set as the static average level La as the first to first values. The data is stored in the three-level variation determination circuits 5a to 5c.

  By the above processing, the maximum and minimum voltage levels at the start of use of the present optical fiber ring interference type sensor are set. The processing of FIG. 3 shown below is performed at the time of measurement based on the reference values (maximum value and minimum value) set in FIG. 2 corresponding to the secular change caused by actually using the sensor and the environmental temperature change. The maximum and minimum values are corrected in real time, and the phase difference is calculated from the maximum and minimum values.

  Next, with reference to FIG. 3, the correction method of the maximum value and the minimum value of the voltage level after the start of use of the optical fiber ring interference sensor 1 of the present invention and the phase difference calculation method following this correction will be described.

  In the measurement procedure shown in FIG. 3, steps S31 to S41 correspond to steps S19 to S27 of the setting procedure shown in FIG.

  In the present embodiment, in parallel with the phase difference calculation, the first to third level fluctuation amount determination circuits 5a to 5c periodically output from the first to third amplifier circuits 115a to 115c during the measurement time T. The average value of the output voltage level is calculated.

  Therefore, the description starts from step S43. If the first to third no-vibration determination circuits 3a to 3b determine “no vibration” in step S43, the first to third level fluctuation amount determination circuits 5a to 5c determine the voltage level integrated in step S33. The average value of the voltage level is obtained by dividing by the measurement time T, and this is stored as the current static average level Lac.

  In step S45, the first to third level fluctuation amount determination circuits 5a to 5c compare the current static average level Lac and the static average level La, set a preset correction execution deviation as ΔL, and set ABS ( Lac = La when Lac−La)> ΔL, the current static average level Lac is updated to the static average level La, and the process proceeds to step S47. If ABS (Lac−La) <ΔL, the process proceeds to step S31. Return and start measuring the next current static average level Lac.

  Next, in step S47, the first to third correction calculation circuits 7a to 7c perform correction calculation of the maximum value and the minimum value. Here, the correction value is obtained by multiplying a preset reference maximum value and reference minimum value by a ratio of the current static average level Lac and the static average level La. That is, the maximum value at the current measurement point is calculated from the reference maximum value × (Lac / La), and the minimum value at the current measurement is calculated from the reference minimum value × (Lac / La).

  Next, in step S49, the first to third correction calculation circuits 7a to 7c update the current static average level Lac to the static average level La. When the maximum value and the minimum value are updated, the first to third correction calculation circuits 7a to 7c output the update result to the phase difference calculation circuit 9, and the phase difference calculation circuit 9 based on the update result. The phase difference is calculated.

  Thus, by calculating the phase difference based on the maximum value and the minimum value of the interference light intensity that varies depending on the environmental factors at the time of measurement, if P (t) is obtained using the above equation (1), The vibration of the optical fiber ring 105 can be detected based on the interference light intensity detected by the third light receiving elements 111a to 111c.

  In this measurement method, correction is performed only when ABS (Lac−La)> ΔL in step S45. However, when measurement is performed at a certain interval and it is determined that there is no vibration, You may make it correct | amend.

  If “vibration” is detected in step S41 in this measurement method, the process returns to step S31 to start measurement of the next current static average level Lac. In step S51, if the measurement in the entire range is not completed, the process returns to step S31, and measurement of the next current static average level Lac is started.

  In this embodiment, the case where the 3 × 3 optical branching and coupling element is applied has been described. However, the present invention is not limited to the 3 × 3 optical branching and coupling element, and the initial phase difference between the clockwise light and the counterclockwise light is nπ. This is also effective when calculating the phase difference using an N × N optical branching and coupling element having at least two light intensity outputs other than (n = 0, 1, 2,...).

  Further, when the correction result of the maximum value and the minimum value exceeds the dynamic range of the analog / digital conversion circuit or becomes a value that is not so large as to have sufficient resolution, the first to third amplifier circuits 115a to 115c. It is possible to cope with large light level fluctuations by changing the amplification factor of 1 by a preset value.

It is a schematic block diagram of the optical fiber ring interference type sensor which concerns on embodiment of this invention. It is a flowchart for measuring the maximum value and minimum value which are preset in the optical fiber ring interference type sensor of the present invention. It is a flowchart for showing the measurement procedure and correction | amendment procedure of the optical fiber ring interference type sensor of this invention. It is a schematic block diagram of the conventional optical fiber ring interference type sensor. It is a figure which shows the structure (a) of an optical fiber ring interference type sensor, and the output waveform (b) output from the amplifier circuit 115a. It is a figure which shows the output waveform (a) at the time of normal, and the output waveform (b) fluctuate | varied by the external factor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Optical fiber ring interference type | mold sensor 3a-3c ... 1st-3rd non-vibration determination circuit 5a-5b ... 1st-3rd level variation | change_quantity determination circuit 7a-7c ... 1st-3rd correction | amendment calculation circuit 9 ... rank Phase difference calculation circuit 101 ... Optical fiber ring interference type sensor 105 ... Optical fiber ring 107 ... 3x3 optical branch coupling element 109 ... Optical branch coupling element 111a ... First to third light receiving elements 113 ... Light emitting circuit 115a ... First to first 3 amplifier circuit

Claims (3)

A light source, a light receiving element, and both ends of the open portion of the loop optical fiber are connected to the branch coupling element, and the light emitted from the light source is branched by the branch coupling element, and the loop optical fiber has Incident from both ends, propagating clockwise and counterclockwise in the loop-shaped optical fiber, and coupling the clockwise and counterclockwise propagating light with the branch coupling element, the coupled clockwise rotation By propagating propagating light and counterclockwise propagating light to the light receiving element, and outputting a signal indicating the intensity change of interference light from the light receiving element due to the phase difference between the clockwise propagating light and the counterclockwise propagating light. A signal indicating a change in intensity of the interference light due to a phase difference between the clockwise propagation light and the counterclockwise propagation light caused by a physical change locally applied to an arbitrary place of the loop optical fiber is transmitted from the light receiving element. An optical fiber ring interferometer type sensor outputs,
Amplifying means for amplifying an optical signal received by the light receiving element; level fluctuation amount judging means for monitoring a fluctuation amount within a predetermined time range from an initial state of a signal level output from the amplifier circuit; Non-vibration determination means for monitoring whether or not the fluctuation exceeds a reference level, and when the signal level is equal to or lower than the reference level, the voltage level value calculated by the level signal determination means is acquired to obtain a light level fluctuation correction value. And an optical fiber ring interference sensor. The light emitted from the light source is branched by the branch coupling element, and is incident from both ends of the open portion of the loop-shaped optical fiber, and propagates in the loop-shaped optical fiber in the clockwise and counterclockwise directions. The clockwise propagation light and the counterclockwise propagation light propagated in the optical fiber are combined by the branch coupling element and incident on the light receiving element, and the clockwise propagation light and the counterclockwise propagation light output from the light receiving element are An interference light intensity fluctuation correction method for detecting a physical change locally applied to an arbitrary place of the loop optical fiber based on a signal indicating an intensity change of the interference light due to a phase difference of
Measuring the interference light intensity within a fixed time; determining whether the fluctuation amount of the interference light intensity within the fixed time is less than or equal to a preset amplitude; and When determining that there is no vibration, the step of comparing the interference light intensity average value of the period determined as no vibration with a preset initial value, and as a result of the comparison, the interference light intensity average value and the initial value And a step of calculating a phase difference by calculating a fluctuation correction value of the interference light intensity from the ratio.   3. The interference light intensity fluctuation correction method according to claim 2, wherein the fluctuation correction value calculation is performed when the interference light intensity average value fluctuates more than a preset deviation compared to the initial value. .

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