Distributed optical fiber pipeline high-temperature measurement system and correction method implemented by same

Abstract

The invention discloses a distributed optical fiber pipeline high-temperature measurement system and a correction method implemented by the same, and when a 400-700 DEG C high-temperature pipeline is measured, the measurement error of a traditional measurement system is greatly increased along with the increase of the temperature and the increase of the use time. The mechanism is caused by the increase of optical fiber loss of anti-Stokes light and Stokes light wavebands in the Raman effect; meanwhile, the bending of the optical fiber in the high-temperature pipeline can cause inconsistent loss. Therefore, two pulse weak light lasers with anti-Stokes light and Stokes light wave bands and an optical switch are added, loss changes along the measuring optical fiber can be monitored, and therefore two sets of multi-section anti-slope control signals can be generated to control the control ends of the two variable gain amplifiers respectively. And the output end of the variable gain amplifier reaches an initial set value, so that the measurement error of the high-temperature optical fiber is corrected in multiple sections.

Description

Technical Field

[0001] The invention relates to a distributed optical fiber pipeline high temperature measurement system with segmented correction and a correction method thereof. Background Art

[0002] The current distributed optical fiber temperature measurement system usually uses strong laser pulses to irradiate the temperature measurement optical fiber. According to the Raman effect, the temperature measurement sensing optical fiber generates anti-Stokes signals and Stokes light signals. After filtering out these two signals with filters of different wavelengths, they are converted into electrical signals by photoelectric detectors. The ratio of the two signals is related to the temperature at the location of the optical fiber. After being processed by the signal processing unit, the temperature along the temperature sensing optical fiber can be measured. For calibration, a section of optical fiber is generally placed in a constant temperature box with a known temperature at the beginning of the temperature measurement optical fiber as a reference temperature.

[0003] We replaced the common temperature measuring optical fiber with a 700°C high temperature optical fiber and used the above system to measure the temperature of the steam pipeline. The experiment found that the temperature measurement error of the previously calibrated temperature measurement system had a huge difference of about 100°C from the initial calibrated value as the use time in a high temperature environment (such as 600°C) increased. The slope of the anti-Stokes signal and the Stokes light signal also changed greatly with the distance of the temperature measuring high temperature optical fiber. At the same time, due to the bending of the temperature measuring optical fiber when it is arranged along the pipeline, the error and slope of each section are different. Summary of the invention

[0004] The present invention proposes a distributed optical fiber high temperature measurement system with segmented correction and a correction method thereof, aiming to solve and compensate for the problem that in a high temperature environment (such as 600°C), the anti-Stokes signal and the Stokes light signal generated in the optical fiber change their slopes greatly with the increase of use time and aging, thereby causing a huge error between the temperature measurement value and the initial calibration value, as well as the error and slope inconsistency of each section caused by the bending of the temperature measuring optical fiber.

[0005] Through mechanism analysis and experimental verification, we found that the slope of the anti-Stokes signal and the Stokes optical signal generated in the optical fiber changes greatly with the increase of usage time and aging. The mechanism is due to the increase of optical fiber loss in these two bands. Taking the 1550nm pump laser as an example, the loss coefficient of the anti-Stokes signal 1450nm band and the Stokes optical signal 1640nm band will increase with high temperature aging, especially the former is due to the increase of the 1390nm absorption peak, and the tailing of the peak increases the loss of the 1450nm band; in addition, the loss caused by the bending of the temperature measurement optical fiber causes the inconsistency of the slope of the echo of each section of the optical fiber.

[0006] To solve the above problems, the technical solutions of the present invention are as follows: Distributed optical fiber pipeline high temperature measurement system, including: strong pulse laser, first weak pulse laser, second weak pulse laser, 3*1 optical switch, three-port optical fiber circulator, high temperature sensing optical fiber, 1*2 optical fiber beam splitter, two photoelectric detectors with filters, 2 variable gain amplifiers, and signal processing unit; The strong pulse laser is connected to the first input port of the 3*1 optical switch, the first weak pulse laser is connected to the second input port of the 3*1 optical switch, and the second weak pulse laser is connected to the third input port of the 3*1 optical switch; the output port of the 3*1 optical switch is connected to the first port of the three-port optical fiber circulator, the second port of the three-port optical fiber circulator is connected to the guide multimode optical cable, and the guide multimode optical cable is connected to the high-temperature sensing optical fiber; The third port of the three-port fiber circulator is connected to the two photodetectors with filters having different central wavelengths through the 1*2 fiber splitter, one of the photodetectors is connected to one of the variable gain amplifiers, and the other photodetector is connected to the other variable gain amplifier. The two variable gain amplifiers are respectively input to the signal processing unit; the signal processing unit outputs two control signals corresponding to the control ends of the two variable gain amplifiers.

[0007] Furthermore, the high-temperature sensing optical fiber is arranged along the high-temperature pipeline and is bent in multiple sections, and the measuring temperature range is 400-700°C.

[0008] Furthermore, the high temperature sensing optical fiber has a length of several tens of meters to several kilometers and adopts a multimode optical fiber with a copper alloy protective layer.

[0009] Furthermore, the intense pulse laser generates 1550nm laser, and among the two photodetectors with filters, the front end of one photodetector is covered with an anti-Stokes filter of 1450nm band, and the front end of the other photodetector is covered with a Stokes filter of 1650nm band.

[0010] Furthermore, the first weak pulse laser generates a 1450 nm band laser having the same wavelength as the anti-Stokes light.

[0011] Furthermore, the second weak pulse laser generates a 1650 nm band laser having the same wavelength as the Stokes light.

[0012] Furthermore, the two variable gain amplifiers are high-speed variable gain analog amplifiers.

[0013] Furthermore, the signal processing unit includes AD sampling, digital filtering, distributed temperature algorithm calculation, generation of multi-segment control signals for two variable gain amplifiers, transmission of temperature values ​​to a host computer and alarm functions.

[0014] The present invention also proposes a correction method implemented by the above-mentioned distributed optical fiber high temperature measurement system with segmented correction, comprising: a pulsed strong laser light source generates anti-Stokes light and Stokes light of Raman effect in the looped high temperature sensing optical fiber, two beams of light return to the three-port optical fiber circulator and are output from the third port, the anti-Stokes light and the Stokes light are filtered out by the two filters respectively, and then are converted into two groups of electrical signals by two photoelectric detectors respectively, and the two groups of electrical signals are respectively connected to the two variable gain amplifiers; the first weak pulse laser and the second weak pulse laser used as reference measure the Rayleigh loss in the anti-Stokes light band and the Stokes light band in a time-sharing operation mode through a 3*1 optical switch, thereby the signal processing unit generates two groups of multi-segment sawtooth signals with reverse slopes, respectively controlling the control ends of the two variable gain amplifiers, so that the output ends of the variable gain amplifiers reach the original set value, thereby correcting the performance of the high temperature sensing optical fiber that changes with temperature and use time.

[0015] Beneficial Effects In the present invention, the high-temperature sensing optical fiber adopts a high-temperature optical fiber that can measure temperatures above 500°C, such as a copper-coated or gold-coated optical fiber on the side. At the same time, due to the change in the performance of the high-temperature sensing optical fiber in a high-temperature environment, two weak pulse lasers are used to generate Rayleigh backscattering, and the anti-Stokes signal and the multi-segment slope of the Stokes signal along the length direction of the high-temperature sensing optical fiber can be directly measured, and the control ends of the two variable gain amplifiers provide gain compensation opposite to the multi-segment slope, thereby achieving temperature measurement that does not change with the use time of the sensing optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a distributed optical fiber high temperature measurement system that can be corrected in real time. Reference numerals: Strong pulse laser: 1; first weak pulse laser: 2; second weak pulse laser: 3; 3*1 optical switch: 4; three-port fiber circulator: 5; high-temperature sensing fiber arranged along the high-temperature pipeline: 6; 1*2 fiber beam splitter: 7; photodetector with anti-Stokes filter: 8; photodetector with Stokes filter: 9; anti-Stokes signal variable gain amplifier: 10, its control end: 10-1; Stokes signal variable gain amplifier: 11, its control end: 11-1; signal processing unit: 12. DETAILED DESCRIPTION

[0017] In order to make the description of the purpose, technical solution, advantages, etc. of the present invention clearer and more accurate, the embodiments of the present invention are described in detail below, and examples of the embodiments are given in the form of drawings. It is particularly noted that the exemplary embodiments of the present invention and their descriptions are only used to explain the present invention, but are not intended to limit the design of the present invention.

[0018] like Figure 1 As shown, the distributed optical fiber pipeline high temperature measurement system of the present invention comprises a strong pulse laser 1, a first weak pulse laser 2, a second weak pulse laser 3, a 3*1 optical switch 4, a three-port optical fiber circulator 5, a high temperature sensing optical fiber 6 arranged along the high temperature pipeline, a 1*2 optical fiber beam splitter 7, a photoelectric detector with an anti-Stokes filter 8, a photoelectric detector with a Stokes filter 9, an anti-Stokes signal variable gain amplifier 10, whose control end is 10-1, a Stokes signal variable gain amplifier 11, whose control end is 11-1, and a signal processing unit: 12; The strong pulse laser 1 is connected to the first input port of the 3*1 optical switch 4, the first weak pulse laser 2 is connected to the second input port of the optical switch 4, and the second weak pulse laser 3 is connected to the third input port of the optical switch 4; the output port of the 3*1 optical switch 4 is connected to the first port of the three-port optical fiber circulator 5, and the second port of the optical fiber ring 5 is connected to the multi-section curved high-temperature sensing optical fiber 6 arranged along the high-temperature pipeline through a section of guiding multi-mode optical cable; the third port of the three-port optical fiber circulator 5 is connected to the two photodetectors 8 and the photodetector 9 with different central wavelengths through a 1*2 optical fiber splitter 7, one of the photodetectors 8 is connected to one of the variable gain amplifiers 10, and the other photodetector 9 is connected to another variable gain amplifier 11, and the two variable gain amplifiers are respectively input to the signal processing unit 12; the signal processing unit 12 outputs two control signals 10-1 and 11-1 corresponding to the control ends of the two variable gain amplifiers respectively.

[0019] Among them, the laser wavelength emitted by the first weak pulse laser 2 is consistent with the anti-Stokes wavelength during normal temperature measurement, and the laser wavelength emitted by the second weak pulse laser 3 is consistent with the Stokes wavelength during normal temperature measurement. The strong pulse laser 1 is used for normal temperature measurement to generate anti-Stokes light and Stokes light; and the first weak pulse laser 2 and the second weak pulse laser 3 are connected to the optical path of the high-temperature optical fiber through the optical switch 4 at appropriate time intervals to generate Rayleigh backscattering, that is, OTDR signals. Since its wavelength just selects the wavelength band of the anti-Stokes light and Stokes light during normal measurement, the loss of the high-temperature optical fiber in these two wavelength bands can be correctly monitored. The two OTDR signals obtained by the first weak pulse laser 2 and the second weak pulse laser 3 can be used by the signal processing unit 12 to generate the control signal 10-1 of the variable gain amplifier 10 and the control signal 11-1 of the variable gain amplifier 11, so that the two variable gain amplifiers 10 and 11 output the factory setting values.

[0020] The correction method implemented by the above distributed optical fiber high temperature measurement system of the present invention comprises: a pulsed strong laser light source generates anti-Stokes light and Stokes light of Raman effect in a looped high temperature sensing optical fiber, two beams of light return to the three-port optical fiber circulator 5 and are output from the third port, and the anti-Stokes light and Stokes light are filtered out by two filters respectively, and then converted into two groups of electrical signals by two photoelectric detectors 8 and 9 respectively, and the two groups of electrical signals are respectively connected to two variable gain amplifiers 10 and 11; the first weak pulse laser 2 and the second weak pulse laser 3 as references measure the Rayleigh loss in the anti-Stokes light band and the Stokes light band in a time-sharing operation mode through the 3*1 optical switch 3, thereby the signal processing unit 12 generates two groups of multi-segment sawtooth signals with reverse slopes, respectively controlling the control ends 10-1 and 11-1 of the two variable gain amplifiers, so that the output end of the variable gain amplifier reaches the original set value, thereby correcting the performance of the high temperature sensing optical fiber that changes with temperature and use time.

[0021] Example Figure 1 This is a structural diagram of a distributed optical fiber pipeline high temperature measurement system with segmented correction. Specifically, first, the laser 1 uses a 1550nm pulse laser with a pulse width of 1ns, the first weak pulse laser 2 uses a 1460nm laser, the second weak pulse laser 3 uses a 1650nm laser, the 3*1 optical switch 4 uses an electrically controllable optical switch, the three-port circulator 5 uses an ordinary multimode optical fiber circulator, and the high-temperature sensing optical fiber 6 uses a copper-clad multimode optical fiber with a length of 500 meters and a maximum temperature resistance of 700°C. It is arranged along the high-temperature pipeline. The third end of the three-port circulator 2 is connected to the photodetector 8 and the photodetector 9 respectively through the optical fiber beam splitter 7. The front end of the photodetector 8 is covered with an anti-Stokes filter in the 1450nm band; the front end of the photodetector 9 is covered with a Stokes filter in the 1650nm band. Both the photodetector 8 and the photodetector 9 use APD avalanche diodes. The photodetector 8 and the photodetector 9 are respectively connected to a high-speed variable gain amplifier 10 and a high-speed variable gain amplifier 11. The signal processing unit 12 includes two-way AD adoption, digital signal processing, control signal output of the control end 10-1 of the variable gain amplifier 10 and the control end 11-1 of the variable gain amplifier 11, distributed temperature signal display and alarm, and an RS485 interface to the host computer.

[0022] When the distributed optical fiber temperature sensor (the sensing optical fiber uses copper-coated optical fiber instead of ordinary temperature measurement optical fiber) of the traditional control scheme is used to measure 600°C, the error of the front end of the sensing optical fiber 6 is 30°C after the calibrated system is used for 24 hours, and the difference of the rear end of the sensing optical fiber 6 is 120°C. The control scheme of the above case of the present invention is started, the first weak pulse laser 2 and the second weak pulse laser 3 are connected to the main optical path every 10 minutes to obtain the correction signal, and the variable gain amplifier is controlled by multi-segment broken line approximation, which can be calibrated to within plus or minus 1°C.

[0023] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A distributed optical fiber pipeline high temperature measurement system, characterized in that: include: Strong pulse laser, first weak pulse laser, second weak pulse laser, 3*1 optical switch, three-port fiber circulator, high-temperature sensing fiber, 1*2 fiber beam splitter, two photodetectors with filters, 2 variable gain amplifiers, signal processing unit; The strong pulse laser is connected to the first input port of the 3*1 optical switch, the first weak pulse laser is connected to the second input port of the 3*1 optical switch, and the second weak pulse laser is connected to the third input port of the 3*1 optical switch; the output port of the 3*1 optical switch is connected to the first port of the three-port optical fiber circulator, the second port of the three-port optical fiber circulator is connected to the guide multimode optical cable, and the guide multimode optical cable is connected to the high-temperature sensing optical fiber; The third port of the three-port fiber circulator is connected to the two photodetectors with filters having different central wavelengths through the 1*2 fiber splitter, one of the photodetectors is connected to one of the variable gain amplifiers, and the other photodetector is connected to the other variable gain amplifier. The two variable gain amplifiers are respectively input to the signal processing unit; the signal processing unit outputs two control signals corresponding to the control ends of the two variable gain amplifiers.

2. The distributed optical fiber pipeline high temperature measurement system according to claim 1, characterized in that: The high-temperature sensing optical fiber is arranged along the high-temperature pipeline and is bent in multiple sections, and the measuring temperature range is 400-700°C.

3. The distributed optical fiber pipeline high temperature measurement system according to claim 1, characterized in that: The high temperature sensing optical fiber has a length of several tens of meters to several kilometers and adopts a multi-mode optical fiber with a copper alloy protective layer.

4. The distributed optical fiber pipeline high temperature measurement system according to claim 1, characterized in that: The intense pulse laser generates 1550nm laser. Among the two photoelectric detectors with filters, the front end of one photoelectric detector is covered with an anti-Stokes filter of 1450nm band, and the front end of the other photoelectric detector is covered with a Stokes filter of 1650nm band.

5. The distributed optical fiber pipeline high temperature measurement system according to claim 4, characterized in that: The first weak pulse laser generates a 1450nm band laser having the same wavelength as the anti-Stokes light.

6. The distributed optical fiber pipeline high temperature measurement system according to claim 4, characterized in that: The second weak pulse laser generates laser light in the 1650nm band which has the same wavelength as the Stokes light.

7. The distributed optical fiber pipeline high temperature measurement system according to claim 1, characterized in that: The two variable gain amplifiers are high-speed variable gain analog amplifiers.

8. The distributed optical fiber pipeline high temperature measurement system according to claim 1, characterized in that: The signal processing unit includes AD sampling, digital filtering, distributed temperature algorithm calculation, generation of multi-segment control signals for two variable gain amplifiers, transmission of temperature values ​​to a host computer and alarm functions.

9. The calibration method implemented by the distributed optical fiber pipeline high temperature measurement system according to claim 4, characterized in that: include: A pulsed strong laser light source generates anti-Stokes light and Stokes light of Raman effect in the high-temperature sensing optical fiber. The two beams of light return to the three-port optical fiber circulator and are output from the third port. The anti-Stokes light and the Stokes light are filtered out by the two filters respectively, and then converted into two groups of electrical signals by two photoelectric detectors respectively. The two groups of electrical signals are connected to the two variable gain amplifiers respectively. The first weak pulse laser and the second weak pulse laser used as reference measure the loss of the high-temperature optical fiber along the measuring distance in the anti-Stokes optical band and the Stokes optical band in a time-sharing manner through a 3*1 optical switch, thereby obtaining two groups of multi-segment data, and the data signal processing unit generates two groups of multi-segment control signals with reverse slopes, which respectively control the control ends of the two variable gain amplifiers, so that the output end of the variable gain amplifier reaches the original set value, thereby correcting the error of the high-temperature sensing optical fiber measurement value that changes with temperature and usage time.

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