CN112729605A

CN112729605A - Optical fiber temperature measurement system based on spectrum absorption principle

Info

Publication number: CN112729605A
Application number: CN202110213381.1A
Authority: CN
Inventors: 王世有
Original assignee: Individual
Current assignee: Dalian Shiyou Electric Power Technology Co ltd
Priority date: 2021-02-26
Filing date: 2021-02-26
Publication date: 2021-04-30
Anticipated expiration: 2041-02-26
Also published as: CN112729605B

Abstract

The invention discloses an optical fiber temperature measurement system based on a spectral absorption principle, which measures the broadening range of a spectral absorption line by utilizing the Doppler broadening effect of gas spectral absorption during pressure change so as to realize temperature measurement. The structure is simple, the price is low, the temperature measuring range is only limited by the working temperature range of the optical fiber and can reach 700 ℃; the optical fiber type is single mode optical fiber, the distance between the temperature measuring probe and the host can reach more than 50km, and the problem of short transmission distance of the existing fluorescence temperature measuring optical fiber is solved. The temperature measuring probe is of a full-sealing structure, so that heated impurities of the probe are prevented from being mixed into a measured medium during high-temperature measurement, the internal gas pressure is not influenced by external pressure, and the temperature measuring result is accurate; the filled pure gas can not generate decomposition products, thereby ensuring the insulating property of the tested environment (such as transformer oil). The transmission medium and the probe are made of non-metallic materials, and can be used in occasions with severe electromagnetic environments or insulation requirements, such as power transformers, switch cabinet interiors or heating furnaces and the like.

Description

Optical fiber temperature measurement system based on spectrum absorption principle

Technical Field

The invention relates to the technical field of optical fiber temperature measurement, in particular to an optical fiber temperature measurement system based on a spectrum absorption principle.

Background

Currently, the known optical fiber temperature measurement basically takes two forms: one is to measure the temperature based on the fluorescence characteristics of the temperature-sensitive fluorescent material, such as afterglow fluorescence temperature measurement; the other is measurement using a Fiber Bragg Grating (FBG) system. The fluorescence temperature measurement of the afterglow is realized by connecting an optical fiber with a fluorescent probe internally provided with fluorescent powder, when the fluorescent powder is excited by light with a certain wavelength, the fluorescent energy is excited and radiated, when the excitation is cancelled, the persistence (time) of the fluorescence afterglow is related to the ambient temperature, and the purpose of temperature measurement is further achieved by measuring the time of the fluorescence afterglow; the used fluorescence temperature measurement has the problems of high price of fluorescent powder (such as ruby and the like), large hardness, difficulty in powder preparation, narrow detection range, short transmission distance of fluorescent optical fiber and the like. The Fiber Bragg Grating (FBG) system obtains sensing information by modulating the fiber Bragg wavelength by the external temperature, the demodulating device is complex and expensive, especially, the pressure of a heat conducting agent filled in the fiber Bragg grating temperature measuring probe is increased during high-temperature measurement, and the temperature and stress cross sensitivity of the sensor can influence the temperature measuring precision. In addition, the fluorescent powder or the heat conducting agent in the existing optical fiber temperature measuring probe can generate decomposition products when the temperature is too high, and the insulation performance of the measured environment (such as transformer oil) is directly influenced.

Disclosure of Invention

The invention aims to solve the technical problems in the prior art and provides an optical fiber temperature measurement system based on a spectral absorption principle.

The technical solution of the invention is as follows: an optical fiber temperature measurement system based on a spectrum absorption principle comprises a single chip microcomputer, wherein the single chip microcomputer is connected with a constant temperature base through a temperature controller, the single chip microcomputer is connected with a laser through a current driver, the laser is arranged on the constant temperature base, the laser is connected with the input end of an optical circulator, the common end of the optical circulator is connected with a temperature measurement probe through an optical fiber, the output end of the optical circulator is connected with a photoelectric detector, the output end of the photoelectric detector is connected with the single chip microcomputer through an A/D converter, the temperature measurement probe is provided with a quartz sleeve, one end of the quartz sleeve is tightly sleeved on a self-focusing collimating lens connected with the optical fiber, the other end of the quartz sleeve is hermetically connected with a plane reflector vertical to an axis, and pure gas with a strong absorption spectrum to the laser is filled in the quartz sleeve; the singlechip controls the laser to emit laser with periodically changed wavelength, and the central wavelength is the wavelength of the strongest absorption spectral line of the pure gas; the method comprises the steps that a single chip microcomputer collects an output current change curve of a photoelectric detector in each laser scanning period to obtain the half-peak width D of a spectrum absorption line, D = t2-t1, t1 and t2 are moments when the output current of the photoelectric detector in each laser scanning period reaches PH twice, PH = (Pmax + Pmin)/2, Pmax is the maximum value of the output current of the photoelectric detector, and Pmin is the minimum value of the output current of the photoelectric detector; temperature T = f (d) of the thermometric probe.

The self-focusing collimating lens is of a cylindrical solid structure and is bonded with the quartz sleeve, and the length of the bonding area is 50-60% of that of the self-focusing collimating lens.

The length of the self-focusing collimating lens is 18mm, and the filling length of the pure gas is at least 10 mm.

The purified gas is acetylene or methane.

The invention relates to an optical fiber temperature measurement system based on a spectral absorption principle, which measures the broadening range of a spectral absorption line by utilizing the Doppler broadening effect of gas spectral absorption during pressure change so as to realize temperature measurement. The structure is simple, the price is low, the temperature measuring range is only limited by the working temperature range of the optical fiber and can reach 700 ℃ (the high-temperature coating optical fiber); the optical fiber type is single mode optical fiber, the transmission distance between the temperature measuring probe and the host can reach more than 50km, and the problem of short transmission distance of the existing fluorescence temperature measuring optical fiber is solved. The temperature measuring probe is of a full-sealing structure, so that heated impurities of the probe are prevented from being mixed into a measured medium during high-temperature measurement, the internal gas pressure is not influenced by external pressure, and the temperature measuring result is accurate; the filled pure gas can not generate decomposition products, thereby ensuring the insulating property of the tested environment (such as transformer oil). The transmission medium and the probe are made of non-metallic materials, and can be used in occasions with severe electromagnetic environments or insulation requirements, such as power transformers, switch cabinet interiors or heating furnaces and the like.

Drawings

FIG. 1 is a schematic diagram of an embodiment of the present invention.

FIG. 2 is a schematic structural diagram of a temperature probe according to an embodiment of the present invention.

FIG. 3 is a graph showing the variation of the output current of the photo-detector during the laser scanning period according to the embodiment of the present invention.

Detailed Description

The optical fiber temperature measuring system based on the spectrum absorption principle is shown in figure 1, and comprises a singlechip 1, the singlechip 1 is connected with a constant temperature base 3 through a temperature controller 2, the singlechip 1 is connected with a laser 5 through a current driver 4, the laser 5 is arranged on the constant temperature base 3, the laser 5 is connected with the input end of the optical circulator 6, the common end of the optical circulator 6 is connected with the temperature measuring probe 8 through the optical fiber 7 (single mode fiber), the output end of the optical circulator 6 is connected with the photoelectric detector 9, the output end of the photoelectric detector 9 is connected with the singlechip 1 through an A/D converter 10, the single chip microcomputer 1, the temperature controller 2, the constant temperature base 3, the current driver 4, the laser 5, the optical circulator 6, the optical fiber 7, the photoelectric detector 9 and the A/D converter 10 are all in the prior art, and the laser 5 can adopt a DFB laser or a VCSEL laser. The temperature measuring probe 8 is provided with a quartz sleeve 8-1 as shown in figure 2, the quartz sleeve 8-1 is a plane back cover with an opening at one end and a vertical axis at the other end, the opening end of the quartz sleeve 8-1 is tightly sleeved on a self-focusing collimating lens 8-2 connected with the optical fiber 7, pure gas 8-4 with the concentration of 100 percent and strong absorption spectrum to laser is filled in the quartz sleeve 8-1, such as acetylene, methane, etc., the pure gas 8-4 can be filled in the quartz sleeve 8-1 by adopting the existing gas filling technology, then the bonding technology is adopted to lead the quartz sleeve 8-1 and the cylindrical solid structured self-focusing collimating lens 8-2 made of quartz material to form an integrated structure, and then a layer of reflecting medium film is plated outside the other end sealing bottom of the quartz sleeve 8-1 to form the plane reflector 8-3. The length of the self-focusing collimating lens 8-2 can be 18mm, then the bonding zone length is 50% (9 mm) of the length of the self-focusing collimating lens 8-2, and the filling length of the pure gas 8-4 is at least 10 mm.

The single chip microcomputer 1 sends out a laser signal at a certain temperature through the control of the temperature controller 2 and the current driver 4 and the laser 5, the laser signal enters the input end of the optical circulator 6, is coupled to the self-focusing collimating lens 8-2 from the common end of the optical circulator 6 through the optical fiber 7, and then passes through the pure gas 8-4 to the plane reflector 8-3; the reflected light signal of the plane mirror 8-3 returns to the common end of the optical circulator 6 along the original path, reaches the photoelectric detector 9 from the output end of the optical circulator 6, and then reaches the singlechip 1 through the A/D converter 10.

The detection principle of the invention is as follows: the quartz sleeve 8-1 is a full-sealing structure, and when the external temperature rises, the pressure p of constant gas in the quartz sleeve 8-1 is in direct proportion to the absolute temperature T. The absorption spectrum of the gas is subject to Doppler broadening effect as the internal gas pressure becomes higherInfluence, Doppler spread factor

Can be expressed as:

wherein P is the gas pressure,

k is a temperature coefficient constant. As the temperature increases, the pressure increases and the Doppler broadening coefficient increases

The linearity increases. Gas absorption line intensity of

，

Is the difference between the output wavelength of the laser 5 and the center wavelength; the gas absorption line intensity S is characterized by

Centrosymmetric parabola with downward opening

Is increased.

Typically measured as the half-peak width, i.e., the difference between the two wavelengths at which the intensity of the gas absorption line is 50% of the maximum. According to the Labobel law, the total energy of the gas spectrum absorption is in direct proportion to the intensity of the gas absorption line.

The temperature detection method of the invention comprises the following steps: the singlechip 1 controls the laser 5 to emit laser with periodically changing wavelength, the wavelength changing range is determined by the current changing amplitude, and the changing size is based on a single absorption spectral line covering the filled pure gas 8-4. The operation is that the singlechip 1 controls the periodic output range of the current driver 4 to be 20mA-80mA, namely sawtooth wave current which continuously changes, and the correlation of 0.01 nm/mA exists between the output wavelength of the laser 5 and the working current, so that the output wavelength of the laser 5 also periodically changes along with the correlation, and the wavelength adjusting amplitude is 60 mA/0.01 nm =0.6 nm. The laser center wavelength of the laser 5 is the wavelength of the strongest absorption spectral line of the pure gas 8-4, if the pure gas 8-4 is acetylene, the center wavelength is 1530.3nm, and if the pure gas 8-4 is methane, the center wavelength is 1653.7 nm; the single chip microcomputer 1 acquires an output current change curve (shown in fig. 3) of the photodetector 9 in each laser scanning period to obtain a half-peak width D of a spectral absorption line, where D = t2-t1, and t1 and t2 are moments when the output current of the photodetector 6 in each laser scanning period reaches PH twice in sequence, where PH = (Pmax + Pmin)/2, Pmax is a maximum value of the output current of the photodetector 6, and Pmin is a minimum value of the output current of the photodetector 6; temperature T = f (d) of the thermometric probe 8. Firstly, establishing a model of the temperature T = f (D) according to the detection method, and then carrying out corresponding temperature detection.

Claims

1. An optical fiber temperature measurement system based on spectral absorption principle is characterized in that: the temperature measurement device is provided with a singlechip (1), the singlechip (1) is connected with a constant temperature base (3) through a temperature controller (2), the singlechip (1) is connected with a laser (5) through a current driver (4), the laser (5) is arranged on the constant temperature base (3), the laser (5) is connected with the input end of an optical circulator (6), the common end of the optical circulator (6) is connected with a temperature measurement probe (8) through an optical fiber (7), the output end of the optical circulator (6) is connected with a photoelectric detector (9), the output end of the photoelectric detector (9) is connected with the singlechip (1) through an A/D converter (10), the temperature measurement probe (8) is provided with a quartz sleeve (8-1), one end of the quartz sleeve (8-1) is tightly sleeved on a self-focusing collimating lens (8-2) connected with the optical fiber (7), the other end of the quartz sleeve (8-1) is connected with a plane reflector (8-3) vertical to the axis in a sealing way, and pure gas (8-4) with strong absorption spectrum to laser is filled in the quartz sleeve (8-1); the singlechip (1) controls the laser (5) to emit laser with periodically changing wavelength, and the central wavelength is the wavelength of the strongest absorption spectral line of the pure gas (8-4); the method comprises the steps that a single chip microcomputer (1) collects an output current change curve of a photoelectric detector (9) in each laser scanning period to obtain a half-peak width D of a spectral absorption line, D = t2-t1, t1 and t2 are moments when the output current of the photoelectric detector (6) in each laser scanning period reaches PH twice, PH = (Pmax + Pmin)/2, Pmax is the maximum value of the output current of the photoelectric detector (6), and Pmin is the minimum value of the output current of the photoelectric detector (6); the temperature T = f (D) of the temperature probe (8).

2. The optical fiber temperature measurement system based on the spectral absorption principle according to claim 1, wherein: the self-focusing collimating lens (8-2) is of a cylindrical solid structure and is bonded with the quartz sleeve (8-1), and the length of a bonding area is 50-60% of that of the self-focusing collimating lens (8-2).

3. The optical fiber temperature measurement system based on the spectral absorption principle according to claim 2, wherein: the length of the self-focusing collimating lens (8-2) is 18mm, and the filling length of the pure gas (8-4) is at least 10 mm.

4. The optical fiber temperature measurement system based on the spectral absorption principle according to claim 1, 2 or 3, wherein: the purified gas (8-4) is acetylene or methane.