Real-time correction distributed optical fiber high-temperature measurement system and real-time correction method thereof

Abstract

The invention discloses a real-time correction distributed optical fiber high-temperature measurement system and a real-time correction method thereof, and when the high temperature of 400-700 DEG C is measured, the measurement error of a traditional measurement system is greatly increased along with the increase of the use time. Therefore, the high-temperature-resistant optical fiber introduced into the high-temperature hearth is folded with the initial nearby high-temperature optical fiber after being subjected to a section of ten-meter-magnitude optical fiber rotation, and then continuously extends to a required temperature measurement area, and the length is dozens of meters to several kilometers; a high-temperature-resistant point thermometer is arranged at the position of the closed optical fiber, the numerical value of the point thermometer reflects the temperature values of the two closed optical fiber sections, and the data can correct the temperature of the anti-Stokes light and the Stokes light in the closed optical fiber sections and also can measure the slopes of the anti-Stokes light and the Stokes light along with the distance of the measured optical fiber, so that two groups of sawtooth signals with the anti-slopes can be generated; and the control ends of the two variable gain amplifiers are respectively controlled, so that the output ends of the variable gain amplifiers reach initial set values, and the high-temperature measurement error is corrected in real time.

Description

Technical Field

[0001] The invention relates to a real-time corrected distributed optical fiber high temperature measurement system and a real-time 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 ordinary temperature measuring optical fiber with a high-temperature optical fiber that can withstand 700°C, and used the above system to measure the temperature of the steam pipe. The experiment found that the temperature measurement error of the originally 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 from the temperature measuring high-temperature optical fiber. Summary of the invention

[0004] The present invention proposes a distributed optical fiber high temperature measurement system with real-time correction, which aims 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 usage time and aging, thereby causing a huge error between the measured temperature value and the initial calibration value.

[0005] To solve the above problems, the technical solutions of the present invention are as follows: A real-time corrected distributed optical fiber high temperature measurement system comprises: an intense pulse laser, a three-port optical fiber circulator, a guide multimode optical cable, a high temperature sensing optical fiber in a loop of ten meters, a spot thermometer, an optical fiber beam splitter, two photoelectric detectors with filters, two variable gain amplifiers, and a signal processing unit; the intense pulse laser 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, the guide multimode optical cable is connected to the looped high temperature sensing optical fiber, the looped high temperature sensing optical fiber has a close-together portion, the close-together portion of the optical fiber length is in the order of meters, the close-together portion of the optical fiber is provided with the spot thermometer as a reference, the looped high temperature sensing optical fiber continues to be connected to a long section of high temperature sensing optical fiber with a length of tens of meters to several kilometers to a required temperature measurement area after the looped high temperature sensing optical fiber is looped; the third port of the three-port optical fiber circulator is connected to the two photoelectric detectors with filters and the photoelectric detector with different central wavelengths via the optical fiber beam 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 temperature value of the point thermometer is input to the signal processing unit, and the signal processing unit outputs two control signals corresponding to the control ends of the two variable gain amplifiers.

[0006] Furthermore, the looped high-temperature sensing optical fiber, the point thermometer, and the long section of high-temperature sensing optical fiber are all inside the high-temperature furnace.

[0007] Furthermore, among the two photodetectors with filters, the front end of one of the photodetectors is covered with an anti-Stokes filter of the 1450nm band, and the front end of the other photodetector is covered with a Stokes filter of the 1650nm band.

[0008] Furthermore, the point thermometer measures the temperature of the close-together parts in the high-temperature optical fiber optical path in real time, the close-together parts are the front and rear positions of the looped optical fiber, and they have the same temperature value. Then the point thermometer inputs the temperature value to the signal processing unit to obtain reference values ​​for correcting the size and slope of the anti-Stokes signal and the Stokes signal respectively. By controlling the control ends of the two variable gain amplifiers, the original correction value when the distributed optical fiber high-temperature measurement system is enabled is restored, thereby correcting the changes in the performance of the entire high-temperature sensing optical fiber with temperature and usage time in real time.

[0009] Furthermore, the looped high-temperature sensing optical fiber and the long section of high-temperature sensing optical fiber both adopt copper alloy-plated protective layer multimode optical fiber.

[0010] Furthermore, the point thermometer is a thermocouple thermometer.

[0011] Furthermore, the two variable gain amplifiers are high-speed analog variable gain amplifiers.

[0012] Furthermore, the signal processing unit includes AD sampling, digital filtering, distributed temperature algorithm calculation, signal transmission to the host computer and alarm functions.

[0013] The present invention also proposes a real-time correction method implemented by the above-mentioned distributed optical fiber high temperature measurement system with real-time 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 electrical signal of the point thermometer used as a reference is input to the signal processing unit to obtain the temperature of the anti-Stokes light and the Stokes light in the adjacent optical fiber section and their slopes with the measured distance, thereby the signal processing unit generates two groups of sawtooth signals with reverse slopes, and respectively controls 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 real-time correction of the performance of the high temperature sensing optical fiber that changes with temperature and use time.

[0014] 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, a high-temperature resistant point thermometer is placed at a cross-joint position, which can be used as a temperature measurement correction for the two ends of the looped high-temperature sensing optical fiber. At the same time, the slope of the anti-Stokes signal and the Stokes signal along the high-temperature sensing optical fiber is corrected, and the control ends of the two variable gain amplifiers provide gain compensation opposite to the slope, thereby achieving temperature measurement that does not change with the use time of the sensing optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a distributed optical fiber high temperature measurement system that can be corrected in real time. Reference numerals: Laser: 1; three-port optical fiber circulator: 2; guided multimode optical cable: 3; looped high-temperature sensing optical fiber: 4; closed part: 5; a small section of high-temperature sensing optical fiber: 6; optical 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: 13; point thermometer: 12. DETAILED DESCRIPTION

[0016] 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.

[0017] like Figure 1 As shown, a distributed optical fiber high temperature measurement system with real-time correction of the present invention comprises an intense pulse laser 1, a three-port optical fiber circulator 2, a section of guided multimode optical cable 3, a looped high temperature sensing optical fiber 4, a high temperature resistant point thermometer 12, a long section of high temperature sensing optical fiber 6, an optical fiber beam splitter 7, two photoelectric detectors 8 and 9 with filters, two variable gain amplifiers 10 and 11, and a signal processing unit 13; Among them, the intense pulse laser 1 is connected to the first port of the three-port fiber circulator 2, the second port of the three-port fiber circulator 2 is connected to a section of guiding multimode optical cable 3, the other end of the guiding multimode optical cable 3 is connected to a short section of high-temperature sensing optical fiber 4 in a loop, the high-temperature sensing optical fiber 4 is looped into a closed part 5, and the high-temperature sensing optical fiber 4 is connected to a long section of high-temperature sensing optical fiber 6 after passing through the closed part 5; a high-temperature resistant point thermometer is closely attached to the closed part 5.

[0018] Among them, the third port of the three-port fiber circulator 2 is connected to two photodetectors 8 and photodetectors 9 with filters having different central wavelengths through the fiber beam splitter 7, wherein 8 is a photodetector with an anti-Stokes filter, and 9 is a photodetector with a Stokes filter, and an anti-Stokes signal and a Stokes signal are obtained respectively. The photodetector 8 is connected to the variable gain amplifier 10, and the photodetector 9 is connected to the variable gain amplifier 11, and the variable gain amplifier 10 and the variable gain amplifier 11 are respectively input to the signal processing unit 13; the temperature value of the aforementioned point thermometer 12 is input to the signal processing unit 13, and the processing unit 13 outputs two control signals to the control end 10-1 of the variable gain amplifier 10 and the control end 11-1 of the variable gain amplifier 11 respectively. The signal processing unit 13 includes functions such as AD sampling, digital filtering, distributed temperature algorithm calculation, signal transmission to the host computer and alarm.

[0019] As mentioned above, a short section of high temperature sensing optical fiber 4 in a loop, the closed portion 5, a long section of high temperature sensing optical fiber 6, and a high temperature point thermometer 12 are all placed in the high temperature environment to be measured, and other components are placed outside the high temperature environment.

[0020] Figure 1The structure diagram of a distributed optical fiber high temperature measurement system with real-time correction is shown. Specifically, first, the laser 1 uses a 1550nm pulse laser with a pulse width of 1ns. The three-port circulator 2 uses an ordinary multimode optical fiber circulator to guide the multimode optical cable 3 to sample the ordinary multimode optical fiber cable. A short section of high-temperature sensing optical fiber 4 uses a copper-clad multimode optical fiber with a length of 20 meters and a maximum temperature resistance of 700°C. The high-temperature sensing optical fiber 4 is looped and intersected head to tail to form a close section 5 with a length of 1 meter. The high-temperature sensing optical fiber 6 uses the same high-temperature resistant side surface copper-clad multimode optical fiber as 4 and a length of 1 kilometer. A high-temperature resistant thermocouple is closely attached to the close section 5 as a point thermometer 12. The third end of the three-port circulator 2 is connected to the photodetector 8 and the photodetector 9 through the optical fiber beam splitter 7. The front end of the photodetector 8 is covered with an anti-Stokes filter of the 1450nm band; the front end of the photodetector 9 is covered with a Stokes filter of 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 13 includes two-way AD sampling, digital signal processing, 12 signal input 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, RS485 interface to the host computer, etc.

[0021] When using the distributed optical fiber temperature sensor (the sensing optical fiber uses copper-coated optical fiber instead of ordinary temperature measurement optical fiber) with the traditional control scheme 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 back end of the sensing optical fiber 6 is 120°C. Starting the control scheme of the above case of the present invention, the error can be calibrated to within 1.5°C.

[0022] 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 high temperature measurement system with real-time correction, characterized in that: include: Intense pulse laser, three-port fiber circulator, guided multimode optical cable, a ten-meter loop of high-temperature sensing fiber, spot thermometer, fiber beam splitter, two photodetectors with filters, two variable gain amplifiers, and a signal processing unit; The intense pulse laser is connected to the first port of a three-port optical fiber circulator, the second port of the three-port optical fiber circulator is connected to a guide multimode optical cable, the guide multimode optical cable is connected to a looped high-temperature sensing optical fiber, the looped high-temperature sensing optical fiber has a close-together portion, the optical fiber length of the close-together portion is in the order of meters, the close-together portion of the optical fiber is provided with the point thermometer as a reference, and the looped high-temperature sensing optical fiber continues to be connected to a long section of high-temperature sensing optical fiber with a length of tens of meters to several kilometers to the required temperature measurement area after the looped high-temperature sensing optical fiber is looped; The third port of the three-port fiber circulator is connected to the two photodetectors with filters and photodetectors with different central wavelengths via a fiber optic 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, and the two variable gain amplifiers are respectively input to a signal processing unit; the temperature value of the spot thermometer is input to the signal processing unit, and the signal processing unit outputs two control signals corresponding to the control ends of the two variable gain amplifiers.

2. A distributed optical fiber high temperature measurement system with real-time correction according to claim 1, characterized in that: The looped high-temperature sensing optical fiber, the point thermometer, and a long section of high-temperature sensing optical fiber are all inside the high-temperature furnace, and the temperature range is 400-700°C.

3. A distributed optical fiber high temperature measurement system with real-time correction according to claim 1 or 2, characterized in that: 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.

4. A distributed optical fiber high temperature measurement system with real-time correction according to claim 1, characterized in that: The looped high-temperature sensing optical fiber and a long section of high-temperature sensing optical fiber with a length of tens of meters to several kilometers both adopt copper alloy-plated protective layer multimode optical fiber.

5. A distributed optical fiber high temperature measurement system with real-time correction according to claim 1, characterized in that: The point thermometer adopts a thermocouple thermometer.

6. A distributed optical fiber high temperature measurement system with real-time correction according to claim 1, characterized in that: The two variable gain amplifiers are high-speed analog variable gain amplifiers.

7. A distributed optical fiber high temperature measurement system with real-time correction according to claim 1, characterized in that: The signal processing unit includes AD sampling, digital filtering, distributed temperature algorithm calculation, signal transmission to the host computer and alarm functions.

8. The real-time correction method implemented by the distributed optical fiber high temperature measurement system with real-time correction according to claim 3 is characterized in that: include: A pulsed strong laser light source generates anti-Stokes light and Stokes light of the Raman effect in the looped 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 electrical signal of the reference point thermometer is input to the signal processing unit to obtain the temperature of the anti-Stokes light and the Stokes light in the adjacent optical fiber segments and their slopes with the measured distance. The signal processing unit generates two sets of anti-slope sawtooth signals to control the control ends of the two variable gain amplifiers respectively, 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 in real time.

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