Optical fiber distributed temperature measurement device and method with phase correction sampling accumulation

Abstract

The invention relates to an optical fiber distributed temperature measurement device and method for phase correction sampling accumulation, comprising a laser, wherein the laser is connected to an optical pulse modulator, the optical pulse modulator can convert continuous light generated by the laser into pulse light, the optical pulse modulator is connected to an optical coupler, the optical coupler is respectively connected to a sensing optical fiber and an optical splitter, the pulse light generated by the optical pulse modulator can enter the sensing optical fiber through the optical coupler, the backward Raman scattered light in the sensing optical fiber can enter the optical splitter through the optical coupler, the optical splitter can divide the Raman scattered light into Stokes light and anti-Stokes light, the optical splitter is respectively connected to two photoelectric detectors, the two photoelectric detectors are connected to a data acquisition card, the data acquisition card is connected to a signal generator and a processor, the reference signal generated by the signal generator can be transmitted to the processor through the data acquisition card, the phase of the Stokes light and the anti-Stokes light is corrected, and the measurement result of the measurement device of the invention is accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber distributed temperature measurement devices, and in particular to an optical fiber distributed temperature measurement device and method for phase correction sampling accumulation. Background Art

[0002] The fiber optic distributed temperature measurement system is a sensor system used to measure the distribution of spatial temperature field in real time. It uses the same optical fiber as the sensing and transmission medium of temperature information, uses the temperature effect of the fiber Raman backscattering spectrum to measure the temperature field information where the fiber is located, and uses the optical time domain reflection technology of the optical fiber to locate the measurement point. Because the system has the advantages of intrinsic safety, corrosion resistance, high pressure resistance, electromagnetic interference resistance, and the ability to quickly measure and locate multiple points, it has a wide range of applications. It has been used for temperature monitoring in fields such as petroleum engineering, power stations, mines, tunnels, and dams.

[0003] In the fiber-optic distributed temperature measurement system, the laser outputs pulsed light, which is injected from the beginning of the fiber. Most of the energy of the pulsed light is transmitted to the end of the fiber and disappears, and a small part of the backscattered light wave is reflected back along the fiber. According to the temperature effect of Raman scattering spectrum and optical time domain reflection technology, the optical power returned to the incident end is a function of both the fiber position and the ambient temperature. Using this principle, the temperature of the entire fiber link can be measured, and the measurement point can be accurately located.

[0004] Since the Raman scattering signal is very weak and completely submerged in the noise, the fiber-optic distributed temperature measurement system needs to use weak signal detection technology to extract the signal to be measured from the noise. Since the main component of the noise in the fiber-optic distributed temperature measurement system has the statistical characteristic of zero mean, the statistical characteristic of the noise can be used to achieve the purpose of noise reduction. Therefore, in order to improve the signal-to-noise ratio, the signal processing part uses the sampling accumulation and averaging method for noise reduction, that is, the N-point data of a measurement is stored in the memory unit in sequence, the N-point data of the next measurement is added to the data of the corresponding unit of the memory, and then put back to the original memory unit, and cycle M times in sequence, and then average each unit.

[0005] The inventors found that the existing fiber-optic distributed temperature measurement system uses a digital trigger signal as a reference when performing sampling accumulation, and accumulates and averages the M sampling data sequences point by point, without considering the sampling errors caused by the trigger signal phase noise and sampling clock jitter. Therefore, the sampling points at a certain position or time in multiple samplings are not precisely aligned. This sampling error will cause the sampling accumulation results to be incompletely correct, affecting the accuracy of ambient temperature measurement. Summary of the invention

[0006] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an optical fiber distributed temperature measurement device with phase correction sampling accumulation, which can accurately measure the ambient temperature.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] The optical fiber distributed temperature measuring device with phase correction sampling accumulation comprises a laser, wherein the laser is connected to an optical pulse modulator, the optical pulse modulator can convert the continuous light generated by the laser into pulse light, the optical pulse modulator is connected to an optical coupler, the optical coupler is respectively connected to a sensing optical fiber and an optical splitter, the pulse light generated by the optical pulse modulator can enter the sensing optical fiber through the optical coupler, the backward Raman scattered light in the sensing optical fiber can enter the optical splitter through the optical coupler, the optical splitter can divide the Raman scattered light into Stokes light and anti-Stokes light, the optical splitter is respectively connected to two photoelectric detectors, the two photoelectric detectors can respectively convert the Stokes light signal and the anti-Stokes light signal into electrical signals and transmit them to a data acquisition card, the data acquisition card is connected to a signal generator and a processor, the signal generated by the signal generator can be transmitted to the processor through the data acquisition card, and the processor is used to analyze the phase information of a reference signal and perform phase correction on the Stokes light signal and the anti-Stokes light signal.

[0009] Furthermore, the optical pulse modulator is connected to a processor, and the processor can control the optical pulse modulator to generate a set pulse light.

[0010] Furthermore, the signal generator is connected to a processor, and the processor can control the signal generator to generate a set reference signal.

[0011] Furthermore, an optical filter is arranged between the two photodetectors and the spectrometer.

[0012] A working method of a phase-corrected sampling and accumulation optical fiber distributed temperature measurement device comprises the following steps:

[0013] Step 1: The signal generator generates a set reference signal and transmits it to the processor through the data acquisition card. The processor obtains the phase information of the reference signal of multiple working cycles. Based on the phase information of the reference signal of multiple working cycles, the first working cycle of the Stokes optical signal and the anti-Stokes optical signal is used as a reference to perform phase correction on other working cycles of the Stokes optical signal and the anti-Stokes optical signal to obtain sampling data after the sampling moments of multiple working cycles of the Stokes optical signal and the anti-Stokes optical signal are aligned.

[0014] Step 2: Calculate the temperature data based on the sampled data obtained in step 1.

[0015] Furthermore, in step 1, the specific method of phase correction is: according to the phase information of the sampling moments of multiple working cycles of the reference signal, the phase difference between the first working cycle and other working cycles of the reference signal is obtained, and then the sampling moment deviation is determined, and according to the sampling moment deviation, the sampling moment data after the multiple working cycles of the Stokes optical signal and the anti-Stokes optical signal are aligned with the sampling moment of the first working cycle is obtained by using the interpolation method.

[0016] Furthermore, the method for obtaining the phase information of the reference signal is as follows: the processor performs Hilbert transform on the reference signal to obtain an imaginary signal of the reference signal, and performs an inverse tangent calculation on the real signal of the reference signal to obtain the phase information of the reference signal.

[0017] Furthermore, the specific steps of step 2 are: accumulating and averaging the data of the phase-corrected Stokes light signal and the anti-Stokes light signal at the corresponding sampling moments to obtain the denoised Stokes light signal and the anti-Stokes light signal data, and the processor performs subtraction calculation on the data of the denoised Stokes light and anti-Stokes light digital signals at the corresponding sampling moments to obtain temperature data.

[0018] Furthermore, the reference signal is a single-frequency sinusoidal analog signal.

[0019] Furthermore, in step 1, the Raman scattered light transmitted backward by the sensing optical fiber enters the optical splitter through the optical coupler, and the optical splitter splits the Raman scattered light into Stokes light signal and anti-Stokes light.

[0020] Beneficial effects of the present invention:

[0021] The optical fiber distributed temperature measurement device with phase correction sampling accumulation of the present invention has a signal generator connected to a data acquisition card, the signal generator can send a set reference signal, a processor can obtain phase information of the reference signal, and can perform phase correction on Stokes optical signals and anti-Stokes optical signals according to phase differences at sampling moments of reference signals of multiple working cycles, and can obtain sampling data when the sampling moment of each working cycle is aligned with the sampling moment of the first working cycle, thereby compensating for sampling errors caused by clock jitter during sampling, performing accurate sampling moment alignment on data of multiple working cycles, and improving the temperature measurement accuracy of the sensing optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings in the specification, which constitute a part of the present application, are used to provide a further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute a limitation on the present application.

[0023] Figure 1 This is a schematic diagram of the overall structure of Embodiment 1 of the present invention;

[0024] Figure 2 This is a schematic diagram of the working principle of Embodiment 2 of the present invention;

[0025] Among them, 1. laser, 2. optical pulse modulator, 3. optical coupler, 4. spectrometer, 5. first optical filter, 6. second optical filter, 7. first photodetector, 8. second photodetector, 9. data acquisition card, 10. processor, 11. signal generator. DETAILED DESCRIPTION

[0026] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0027] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0028] For the convenience of description, if the words "up", "down", "left" and "right" appear in the present invention, they only indicate that they are consistent with the up, down, left and right directions of the drawings themselves, and do not limit the structure. They are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0029] As introduced in the background technology, when the existing fiber-optic distributed temperature measurement system performs cumulative sampling, sampling errors are caused by phase noise and sampling clock jitter, which affects the temperature measurement accuracy. To address the above problems, this application proposes a fiber-optic distributed temperature measurement device with phase-corrected sampling and accumulation.

[0030] In a typical implementation example 1 of the present application, Figure 1 As shown, a phase-corrected sampling and accumulation optical fiber distributed temperature measurement device includes a laser 1, which is connected to an optical pulse modulator 2 via an optical fiber. The laser can output a continuous light signal with a wavelength of 1550nm or 1310nm suitable for optical fiber transmission, and transmit it to the optical pulse modulator via the optical fiber. The optical pulse modulator can convert the continuous light into pulse light.

[0031] The optical pulse modulator is connected to the optical coupler 3 through an optical fiber, and the optical coupler is respectively connected to the sensing optical fiber and the optical splitter 4 through optical fibers. The pulse light generated by the optical pulse modulator is transmitted to the sensing optical fiber through the optical coupler. During the transmission of the pulse light in the sensing optical fiber, the backward Raman scattered light signal of the sensing optical fiber returns along the original transmission optical path and enters the optical splitter through the optical coupler. The optical splitter can separate the Stokes light and anti-Stokes light of different frequencies in the Raman scattered light.

[0032] The optical splitter is connected to the first optical filter 5 and the second optical filter 6 respectively through optical fibers. The Stokes light and anti-Stokes light output by the optical splitter can enter the first optical filter and the second optical filter respectively. The first optical filter and the second optical filter filter out other scattered light and interference light in the Stokes light and the anti-Stokes light, and only allow the Stokes light and the anti-Stokes light with temperature information to pass through.

[0033] The first optical filter is connected to the first photodetector 7 through an optical fiber, and the second optical filter is connected to the second photodetector 8 through an optical fiber. Both the first photodetector and the second photodetector are APD detectors.

[0034] The first photodetector and the second photodetector are connected to the data acquisition card 9 via a signal line, and can respectively amplify the Stokes light and the anti-Stokes light, and convert them into electrical signals and output them to the data acquisition card.

[0035] The data acquisition card is connected to the processor 10 and can transmit the electrical signals of the Stokes light and the anti-Stokes light to the processor.

[0036] The data acquisition card is also connected to the signal generator 11 through a signal line. The signal generator is a single-frequency signal generator that can generate a set reference signal. In this embodiment, the reference signal is a single-frequency sinusoidal analog signal.

[0037] The single-frequency sinusoidal analog signal generated by the single-frequency signal generator can be transmitted to the data acquisition card, and the data acquisition card converts the single-frequency sinusoidal analog signal into a digital signal and transmits it to the processor.

[0038] The optical pulse modulator and the single-frequency signal generator are also connected to the processor via a signal line. The processor can control the optical pulse modulator to generate a set pulse light, and the processor can control the single-frequency signal generator to generate a set single-frequency sinusoidal analog signal.

[0039] Embodiment 2:

[0040] This embodiment discloses a working method of a phase-corrected sampling and accumulation optical fiber distributed temperature measurement device: Figure 2As shown, the laser outputs continuous light with a wavelength of 1550nm or 1330nm, and is converted into pulsed light under the action of an optical pulse modulator, and enters the sensing optical fiber through an optical coupler. During the transmission of the pulsed light, the backward Raman scattered light signal of the sensing optical fiber returns to the optical coupler along the original transmission optical path, and enters the optical splitter through the optical coupler. The optical splitter separates the Stokes light and anti-Stokes light of different frequencies in the Raman radiated light, and converts them into digital signals after passing through the first optical filter, the second optical filter, the first photodetector, the second photodetector, and the data acquisition card, and transmits them to the processor.

[0041] Under the control of the processor, the single-frequency signal generator generates a single-frequency sinusoidal analog signal in the form of a pulse synchronized with the pulse light, which is converted into a digital signal by the data acquisition card and then transmitted to the processor. The processor synchronously receives the single-frequency sinusoidal digital signal, Stokes light and anti-Stokes light digital signal of multiple working cycles. The processor obtains temperature data using the data of the Stokes light signal and the anti-Stokes light signal, which specifically includes the following steps:

[0042] Step 1: The single-frequency signal generator generates a set single-frequency sinusoidal analog signal and transmits it to the processor through the data acquisition card. The processor obtains the phase information of the single-frequency sinusoidal analog signal of multiple working cycles. The processor takes the first working cycle of the single-frequency sinusoidal signal as a reference, compares the phase information of multiple sampling moments of the first working cycle with the phase information of the sampling moments of other working cycles, and obtains the phase difference between the sampling moments corresponding to different working cycles and the first working cycle.

[0043] For example, the phase information of the single-frequency sinusoidal signal at sampling times t1, t2, t3, etc. in the first working cycle is obtained, and the t1 corresponding to the second working cycle is obtained. ’ , t2 ’ , t3 ’ ...the phase information of the sampling time, and then obtain t1 and t1 ’ The phase difference between the sampling times, t2 and t2 ’ The phase difference between sampling times, t3 and t3 ’ The phase difference at the sampling time..., through the phase difference, t1 and t1 are obtained ’ , t2 and t2 ’ , t3 and t3 ’ …, and the sampling time deviations of other working cycles and the first working cycle are obtained by the same method.

[0044] Taking the first working cycle of the Stokes optical signal and the anti-Stokes optical signal as a reference, phase correction is performed on other working cycles of the Stokes optical signal and the anti-Stokes optical signal. The specific method of the phase correction is: according to the obtained sampling time deviations of multiple working cycles of the single-frequency sinusoidal signal and the first working cycle, an interpolation algorithm is used to obtain sampling time data after the sampling times of multiple working cycles of the Stokes optical signal and the anti-Stokes optical signal are aligned.

[0045] For example, the sampling time of the first working cycle of the Stokes optical signal and the anti-Stokes optical signal is k1, k2, k3..., and the sampling time of the second working cycle is k1 ‘ , k2 ’ 、k3 ’ …, using the obtained sampling time deviation of the single-frequency sinusoidal signal and the interpolation algorithm, the data values ​​of the Stokes optical signal and the anti-Stokes optical signal at the sampling times k1, k2, k3… in the second working cycle are obtained, and the same method is used to obtain the data values ​​of the sampling times k1, k2, k3… in other working cycles.

[0046] The interpolation algorithm is an existing algorithm and will not be described in detail.

[0047] Step 2: Calculate the temperature data based on the data obtained at the corresponding sampling time after the phases of the Stokes optical signal and the anti-Stokes optical signal are aligned.

[0048] The data of the phase-corrected Stokes light signal and the anti-Stokes light signal at the corresponding sampling time are accumulated and averaged to obtain the denoised Stokes light signal and the anti-Stokes light signal. The processor performs subtraction calculation on the data of the denoised Stokes light and the anti-Stokes light digital signals at the corresponding sampling time to obtain the temperature data.

[0049] The optical fiber distributed temperature measurement device of this embodiment can realize phase correction of Stokes optical signal and anti-Stokes optical signal by setting a single-frequency signal generator, so that the sampling moments of multiple working cycles of Stokes optical signal and anti-Stokes optical signal are aligned, so that the obtained sampling data is the data after the sampling moments of multiple working cycles are aligned, the sampling error caused by the sampling clock jitter is compensated, and the temperature measurement accuracy of the sensing optical fiber is improved.

[0050] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A working method of a phase-corrected sampling and accumulation optical fiber distributed temperature measurement device, characterized in that: The phase-corrected sampling and accumulation optical fiber distributed temperature measurement device comprises a laser, the laser is connected to an optical pulse modulator, the optical pulse modulator can convert the continuous light generated by the laser into pulse light, the optical pulse modulator is connected to an optical coupler, the optical coupler is respectively connected to a sensing optical fiber and an optical splitter, the pulse light generated by the optical pulse modulator can enter the sensing optical fiber through the optical coupler, the backward Raman scattered light in the sensing optical fiber can enter the optical splitter through the optical coupler, the optical splitter can divide the Raman scattered light into Stokes light and anti-Stokes light, the optical splitter is respectively connected to two photodetectors, the two photodetectors are connected to a data acquisition card, and can convert the Stokes light signal and the anti-Stokes light signal into electrical signals and transmit them to the data acquisition card, the data acquisition card is connected to a signal generator and a processor, and the signal generated by the signal generator can be transmitted to the processor through the data acquisition card; The working method includes the following steps: Step 1: The signal generator generates a set reference signal and transmits it to the processor through the data acquisition card. The processor obtains phase information of the reference signal of multiple working cycles. Based on the phase information of the reference signal of multiple working cycles, the first working cycle of the Stokes optical signal and the anti-Stokes optical signal is used as a reference to perform phase correction on other working cycles of the Stokes optical signal and the anti-Stokes optical signal, so as to obtain sampling data after the sampling moments of multiple working cycles of the Stokes optical signal and the anti-Stokes optical signal are aligned; In step 1, the specific method of phase correction is: according to the phase information of the sampling moments of multiple working cycles of the reference signal, the phase difference between the first working cycle and other working cycles of the reference signal is obtained, and then the sampling moment deviation is determined, and according to the sampling moment deviation, the sampling moment data after the multiple working cycles of the Stokes optical signal and the anti-Stokes optical signal are aligned with the sampling moment of the first working cycle is obtained by using the interpolation method; The method for obtaining the phase information of the reference signal is as follows: the processor performs Hilbert transform on the reference signal to obtain the imaginary signal of the reference signal, and performs inverse tangent calculation on the real signal of the reference signal to obtain the phase information of the reference signal; Step 2: Calculate temperature data based on the sampled data obtained in step 1; The specific steps of step 2 are: accumulating and averaging the data of the phase-corrected Stokes light signal and the anti-Stokes light signal at the corresponding sampling time to obtain the denoised Stokes light signal and the anti-Stokes light signal data, and performing subtraction calculation on the data of the denoised Stokes light and anti-Stokes light digital signals at the corresponding sampling time to obtain the temperature data by the processor.

2. The working method of the optical fiber distributed temperature measurement device with phase correction sampling accumulation as claimed in claim 1, characterized in that: The optical pulse modulator is connected to a processor, and the processor can control the optical pulse modulator to generate a set pulse light.

3. The working method of the optical fiber distributed temperature measurement device with phase correction sampling and accumulation as claimed in claim 1, characterized in that: The signal generator is connected to the processor, and the processor can control the signal generator to generate a set reference signal.

4. The working method of the optical fiber distributed temperature measurement device with phase correction sampling and accumulation as claimed in claim 1, characterized in that: An optical filter is arranged between the two photoelectric detectors and the spectrometer.

5. The working method of the optical fiber distributed temperature measurement device with phase correction sampling and accumulation as claimed in claim 1, characterized in that: The reference signal is a single-frequency sinusoidal analog signal.

6. The working method of the optical fiber distributed temperature measurement device with phase correction sampling and accumulation as claimed in claim 1, characterized in that: In the step 1, the Raman scattered light transmitted backward by the sensing optical fiber enters the optical splitter through the optical coupler, and the optical splitter splits the Raman scattered light into a Stokes light signal and an anti-Stokes light.

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