A distributed optical fiber temperature measurement system and temperature measurement method

Abstract

The present invention discloses a distributed optical fiber temperature measurement system and method, which relates to the field of optical fiber sensing, including an excitation light source, a test light source, a wavelength division multiplexer, a control and signal processing circuit and a temperature measurement optical cable, wherein the control and signal processing circuit is electrically connected to the excitation light source and the test light source; the excitation light source output end is connected to the wavelength division multiplexer, and the wavelength division multiplexer combined end is connected to the temperature measurement optical cable; each test light source output end is connected to an optical attenuator, and the other end of each optical attenuator is connected to the first port of a circulator, each circulator second port is connected to the wavelength division multiplexer, and each circulator third port is correspondingly connected to a photodetector, and the control and signal processing circuit is electrically connected to the output end of each photodetector. The present invention adopts an online measurement method of Raman scattered light propagation loss, realizes the high applicability and flexibility of the distributed optical fiber temperature measurement system to various types of optical cables, and the high-precision measurement of distributed temperature; the structure is simple, the integration is high, and it has engineering practical value.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing, and in particular to a distributed optical fiber temperature measurement system and a temperature measurement method. Background Art

[0002] Distributed fiber optic temperature sensing technology mainly utilizes the correlation between the intensity of Raman scattered light signals and temperature in the optical nonlinear effect. It detects and analyzes the intensity of Raman scattered light signals generated at different positions of the optical fiber to measure the temperature at different positions of the optical fiber. The optical fiber in distributed fiber optic temperature sensing technology is both a sensor and an information transmission medium. This technology has the characteristics of flexible sensor structure, continuous distribution, long monitoring distance, and high operating temperature. Therefore, it has broad application prospects in the fields of fire protection and fire warning, oil well exploration, etc.

[0003] Distributed optical fiber temperature sensing technology is an intensity detection type temperature sensing technology. The transmission loss of temperature measurement Stokes Raman scattered light and anti-Stokes Raman scattered light at each position in the sensing optical fiber is an important factor affecting the accuracy of distributed optical fiber temperature measurement. Therefore, accurately obtaining the propagation loss parameters of temperature measurement Raman scattered light in the sensing optical cable is an important part of distributed optical fiber temperature measurement. When the distributed optical fiber temperature measurement system is applied to the sensing optical cable with unknown propagation loss information, temperature measurement deviation will occur. In addition, the propagation loss coefficient of the sensing optical cable will also change under the influence of the external environment. For example, when the sensing optical cable is subjected to mechanical effects such as squeezing, pressing, pulling, and twisting, the optical fiber structure will deform, which will cause the change of propagation loss when the optical signal passes through the position point. Due to the dispersion effect of optical fiber propagation, the propagation loss of each component of the temperature measurement Raman scattered light will be different when propagating at this location, resulting in a decrease in the accuracy of distributed optical fiber temperature measurement. Therefore, how to quickly and accurately obtain the actual propagation loss parameters of each component of the temperature measurement Raman scattered light in the sensing optical cable, improve the applicability of the temperature measurement system to various optical cables, and achieve high-precision temperature measurement has important significance and application value. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and to provide a distributed optical fiber temperature measurement system and a temperature measurement method, which solves the problem of temperature measurement deviation caused by inaccurate acquisition of Raman scattered light propagation loss parameters in the sensor optical cable, improves the high applicability and flexibility of the distributed optical fiber temperature measurement system for various types of optical cables, and realizes high-precision temperature measurement of the distributed optical fiber temperature measurement system.

[0005] The objective of the present invention is achieved through the following technical solutions: the distributed optical fiber temperature measurement system comprises an excitation light source, at least two test light sources, a wavelength division multiplexer, a control and signal processing circuit and a temperature measurement optical cable, wherein the control and signal processing circuit is electrically connected to the excitation light source and each test light source respectively, and is used to output a pulse modulation signal to generate a pulse excitation light; the working wavelength of the wavelength division multiplexer corresponds to the wavelength of the excitation light source and each test light source, the output end of the excitation light source is connected to the port of the wavelength division multiplexer with the same working wavelength, and the wavelength combining end of the wavelength division multiplexer is connected to the temperature measurement optical cable; the light output end of each test light source is correspondingly connected to an optical attenuator, the other end of each optical attenuator is correspondingly connected to the first port of a circulator, the second port of each circulator is connected to the working port of the wavelength division multiplexer with the same wavelength as the corresponding test light source, the third port of each circulator is correspondingly connected to an optical detector, and the control and signal processing circuit is electrically connected to the output end of each optical detector, so as to synchronously collect the Raman scattered light signal and the Rayleigh scattered light signal output by each optical detector.

[0006] As a preferred technical solution, there are two test light sources, namely test light source A and test light source B, and the excitation light source is a pulsed laser with a wavelength of 1064nm or 1550nm; according to the light wavelength of the excitation light source, the wavelengths selected by test light source A and test light source B are 850nm and 1300nm or 1450nm and 1660nm respectively, and the working wavelengths selected by the wavelength division multiplexer are 850nm / 1064nm / 1300nm or 1450nm / 1550nm / 1660nm respectively.

[0007] A distributed optical fiber temperature measurement method comprises the following steps:

[0008] 1) Connecting the excitation light source to the port with the same working wavelength in the wavelength division multiplexer; connecting the optical output end of the test light source A to the input end of the optical attenuator A, connecting the output end of the optical attenuator A to the first port of the circulator A, connecting the second port of the circulator A to the port with the same wavelength as the test light source A in the wavelength division multiplexer, and connecting the third port of the circulator A to the optical input end of the photodetector A; connecting the optical output end of the test light source B to the input end of the optical attenuator B, connecting the output end of the optical attenuator B to the first port of the circulator B, connecting the second port of the circulator B to the port with the same wavelength as the test light source B in the wavelength division multiplexer, and connecting the third port of the circulator B to the optical input end of the photodetector B; connecting the combined end of the wavelength division multiplexer to the temperature measurement optical cable; and electrically connecting the output ends of the photodetector A and the photodetector B to the control and signal processing circuit respectively;

[0009] 2) Outputting a pulse modulation signal to the excitation light source through the control and signal processing circuit to generate pulse excitation light, and synchronously collecting the Raman scattered light signals output by the light detector A and the light detector B;

[0010] 3) Outputting pulse modulation signals to the test light source A and the test light source B through the control and signal processing circuit to realize the generation of pulse excitation light, and synchronously collecting the Rayleigh scattered light signals output by the detector A and the light detector B;

[0011] 4) The control and signal processing circuit collects and averages the collected Raman scattered light signals and Rayleigh scattered light signals multiple times to obtain the relative intensity information related to the temperature at different positions of the temperature measuring optical cable;

[0012] 5) The control and signal processing circuit obtains the relative intensity result according to the relative intensity calibration data at different temperatures and completes the temperature calculation by interpolation and fitting.

[0013] As a preferred technical solution, the excitation light source is a high-speed pulse laser with a wavelength of 1064nm or 1550nm; according to the wavelength of the excitation light source, the working wavelengths of the test light source and the wavelength division multiplexer are also selected accordingly; when the wavelength of the excitation light source is 1064nm, the wavelengths of the test light source A and the test light source B are 850nm and 1300nm respectively, and the working wavelengths selected by the wavelength division multiplexer are 850nm / 1064nm / 1300nm; when the wavelength of the excitation light source is 1550nm, the wavelengths of the test light source A and the test light source B are 1450nm and 1660nm respectively, and the working wavelengths selected by the wavelength division multiplexer are 1450nm / 1550nm / 1660nm.

[0014] As a preferred technical solution, the photodetector A and the photodetector B are avalanche diodes.

[0015] As a preferred technical solution, the control and signal processing circuit controls the modulation of the excitation light source, the test light source A and the test light source B and the corresponding signal detection and collection by an alternating rotation operation.

[0016] As a preferred technical solution, in step 4), a processing method is used to perform a square root operation on the Rayleigh scattered light signal after cumulative averaging, compare the Raman scattered light with the Rayleigh scattered light of the corresponding wavelength, and compare the anti-Stokes Raman light signal with the Stokes Raman scattered light signal.

[0017] The beneficial effects of the present invention are:

[0018] 1. The online measurement method of Raman scattered light propagation loss is adopted to realize the high applicability and flexibility of the distributed optical fiber temperature measurement system for various types of optical cables, as well as the high-precision measurement of distributed temperature;

[0019] 2. Simple structure, high integration and practical engineering value. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a structural schematic diagram of the present invention.

[0021] Explanation of the reference numerals: excitation light source 1, test light source A2, test light source B3, photodetector A4, photodetector B5, optical attenuator A6, optical attenuator B7, circulator A8, circulator B9, wavelength division multiplexer 10, control and signal processing circuit 11, temperature measurement optical cable 12. DETAILED DESCRIPTION

[0022] The present invention will be described in detail below with reference to the accompanying drawings:

[0023] Example: As attached Figure 1 As shown, taking two test light sources as an example, a distributed optical fiber temperature measurement system includes an excitation light source 1, a test light source A2, a test light source B3, a light detector A4, a light detector B5, an optical attenuator A6, an optical attenuator B7, a circulator A8, a circulator B9, a wavelength division multiplexer 10, a control and signal processing circuit 11 and a temperature measurement optical cable 12. Among them, the control and signal processing circuit 11 is electrically connected to the excitation light source 1, the test light source A2, and the test light source B3, respectively, and is used to output a pulse modulation signal to generate a pulse excitation light. The working wavelength of the wavelength division multiplexer 10 corresponds to the wavelength of the excitation light source 1, the test light source A2, and the test light source B3. The output end of the excitation light source 1 is connected to the port of the same working wavelength of the wavelength division multiplexer 10, and the combined end of the wavelength division multiplexer 10 is connected to the temperature measurement optical cable 12. The light output end of the test light source A2 is connected to the optical attenuator A6, and the light output end of the test light source B3 is connected to the optical attenuator B7; the other end of the optical attenuator A6 is connected to the first port of the circulator A8, and the other end of the optical attenuator B7 is connected to the first port of the circulator B9; the second port of the circulator A8 is connected to the working port with the same wavelength as the test light source A2 on the wavelength division multiplexer 10, and the second port of the circulator B9 is connected to the working port with the same wavelength as the test light source B3 on the wavelength division multiplexer 10; the third port of the circulator A8 is connected to the optical detector A4, and the third port of the circulator B9 is connected to the optical detector B5. The control and signal processing circuit 11 is electrically connected to the output ends of the optical detectors A4 and B5, so as to synchronously collect the Raman scattered light signals and Rayleigh scattered light signals output by the optical detectors A4 and B5.

[0024] Preferably, the excitation light source 1 is a pulsed laser with a wavelength of 1064nm or 1550nm; the wavelengths selected by the test light source A2 and the test light source B3 are 850nm and 1300nm or 1450nm and 1660nm respectively; accordingly, the working wavelengths selected by the wavelength division multiplexer 10 are 850nm / 1064nm / 1300nm or 1450nm / 1550nm / 1660nm respectively.

[0025] A distributed optical fiber temperature measurement method comprises the following steps:

[0026] 1) Connecting the excitation light source 1 to the port with the same working wavelength in the wavelength division multiplexer 10; connecting the optical output end of the test light source A2 to the input end of the optical attenuator A6, connecting the output end of the optical attenuator A6 to the first port of the circulator A8, connecting the second port of the circulator A8 to the port with the same wavelength as the test light source A2 in the wavelength division multiplexer 10, and connecting the third port of the circulator A8 to the optical input end of the photodetector A4; connecting the optical output end of the test light source B3 to the input end of the optical attenuator B7, connecting the output end of the optical attenuator B7 to the first port of the circulator B9, connecting the second port of the circulator B9 to the port with the same wavelength as the test light source B3 in the wavelength division multiplexer 10, and connecting the third port of the circulator B9 to the optical input end of the photodetector B5; connecting the combined end of the wavelength division multiplexer 10 to the temperature measuring optical cable 12; and electrically connecting the output ends of the photodetectors A4 and B5 to the control and signal processing circuit 11 respectively;

[0027] 2) Outputting a pulse modulation signal to the excitation light source 1 through the control and signal processing circuit 11 to realize the generation of pulse excitation light, and synchronously collecting the Raman scattered light signals output by the light detector A4 and the light detector B5;

[0028] 3) Outputting pulse modulation signals to the test light source A2 and the test light source B3 through the control and signal processing circuit 11 to generate pulse excitation light, and synchronously collecting the Rayleigh scattered light signals output by the detector A4 and the light detector B5;

[0029] 4) The control and signal processing circuit 11 collects and averages the collected Raman scattered light signals and Rayleigh scattered light signals for multiple times, performs square root operation on the Rayleigh scattered light signals after the accumulation and average, compares the Raman scattered light with the Rayleigh scattered light of the corresponding wavelength, and compares the anti-Stokes Raman light signal with the Stokes Raman scattered light signal, thereby obtaining the relative intensity information related to the temperature at different positions of the temperature measuring optical cable 12;

[0030] 5) The control and signal processing circuit 11 obtains the relative intensity results according to the relative intensity calibration data at different temperatures and completes the temperature calculation by interpolation and fitting.

[0031] Preferably, the excitation light source 1 uses a high-speed pulse laser with a wavelength of 1064nm or 1550nm; according to the wavelength of the excitation light source 1, the working wavelengths of the test light source and the wavelength division multiplexer 10 are also selected accordingly; when the wavelength of the excitation light source 1 is 1064nm, the wavelengths of the test light source A2 and the test light source B3 are 850nm and 1300nm respectively, and the working wavelengths selected by the wavelength division multiplexer 10 are 850nm / 1064nm / 1300nm; when the wavelength of the excitation light source 1 is 1550nm, the wavelengths of the test light source A2 and the test light source B3 are 1450nm and 1660nm respectively, and the working wavelengths selected by the wavelength division multiplexer 10 are 1450nm / 1550nm / 1660nm. The photodetectors A4 and B5 use high-bandwidth avalanche diodes; the control and signal processing circuit 11 uses an alternating rotation mode to control the modulation of the excitation light source 1, the test light source A2 and the test light source B3 and the corresponding signal detection and collection.

[0032] The working process of the present invention is as follows: a test light source generates a pulsed laser under the drive of a control and signal processing circuit, which is used for exciting the Rayleigh scattered light of a temperature measuring optical cable; two optical attenuators are used for adjusting the optical power input from the test light source to the temperature measuring optical cable, so that the Rayleigh scattered light power returned by the temperature measuring optical cable meets the input requirement of an optical detector; a circulator and a wavelength division multiplexer guide optical signals of different wavelengths emitted by an excitation light source and a test light source to the temperature measuring optical cable, and distinguish different wavelength components in the optical signal returned by the temperature measuring optical cable and introduce them into the optical detector respectively; the optical detector converts the Raman scattered light signal generated by the excitation light source and the Rayleigh scattered light signal generated by the test light source into an electrical signal; and the control and signal processing circuit is used for the generation of control signals, the collection of detection signals, and the processing and calculation of data.

[0033] It is understandable that, for those skilled in the art, any equivalent replacement or change to the technical solution and inventive concept of the present invention should fall within the protection scope of the claims attached to the present invention.

Claims

1. A distributed optical fiber temperature measurement system, characterized in that: The invention comprises an excitation light source (1), at least two test light sources, a wavelength division multiplexer (10), a control and signal processing circuit (11) and a temperature measuring optical cable (12); the control and signal processing circuit (11) is electrically connected to the excitation light source (1) and each test light source, respectively, and is used to output a pulse modulation signal to generate pulse excitation light; the working wavelength of the wavelength division multiplexer (10) corresponds to the wavelength of the excitation light source (1) and each test light source; the output end of the excitation light source (1) is connected to a port of the wavelength division multiplexer (10) with the same working wavelength; The combined end of the device (10) is connected to the temperature measuring optical cable (12); the light output end of each test light source is correspondingly connected to an optical attenuator, the other end of each optical attenuator is correspondingly connected to the first port of a circulator, the second port of each circulator is connected to the working port of the wavelength division multiplexer (10) with the same wavelength as the corresponding test light source, the third port of each circulator is correspondingly connected to a light detector, and the control and signal processing circuit (11) is electrically connected to the output end of each light detector, so as to synchronously collect the Raman scattered light signal and the Rayleigh scattered light signal output by each light detector; There are two test light sources, namely test light source A (2) and test light source B (3); the excitation light source (1) is a pulsed laser with a wavelength of 1064nm or 1550nm; according to the wavelength of the excitation light source (1), the wavelengths selected by the test light source A (2) and the test light source B (3) are 850nm and 1300nm or 1450nm and 1660nm respectively, and the working wavelengths selected by the wavelength division multiplexer (10) are 850nm / 1064nm / 1300nm or 1450nm / 1550nm / 1660nm respectively; The photodetector A (4) and the photodetector B (5) are avalanche diodes; The control and signal processing circuit (11) controls the modulation of the excitation light source (1), the test light source A (2) and the test light source B (3) and the detection and collection of corresponding signals in an alternating manner; The circulator and wavelength division multiplexer guide the different wavelength optical signals emitted by the excitation light source and the test light source to the temperature measuring optical cable, and distinguish the different wavelength components in the optical signal returned by the temperature measuring optical cable and introduce them into the optical detector respectively; the optical detector converts the Raman scattered light signal generated by the excitation light source and the Rayleigh scattered light signal generated by the test light source into electrical signals.

2. A distributed optical fiber temperature measurement method, characterized in that: The following steps are involved: 1) connecting the excitation light source (1) to a port with the same working wavelength in a wavelength division multiplexer (10); connecting the optical output end of the test light source A (2) to the input end of the optical attenuator A (6); connecting the output end of the optical attenuator A (6) to the first port of the circulator A (8); connecting the second port of the circulator A (8) to the port with the same wavelength as the test light source A (2) in the wavelength division multiplexer (10); connecting the third port of the circulator A (8) to the optical input end of the optical detector A (4); connecting the optical output end of the test light source B (3) to the input end of the optical attenuator A (6); connecting the second port of the circulator A (8) to the second port of the circulator A (8); connecting the third port of the circulator A (8) to the optical input end of the optical detector A (4); connecting the optical output end of the test light source B (3) to the input end of the optical attenuator A (6); connecting the optical output end of the test light source B (3) to the input end of the optical attenuator A (6); connecting the optical output end of the test light source B (3) to the input end of the optical attenuator A (6); connecting the optical output end of the optical attenuator A (6) to the first port of the circulator A (8 ... The input end of the attenuator B (7) is connected, the output end of the optical attenuator B (7) is connected to the first port of the circulator B (9), the second port of the circulator B (9) is connected to the port with the same wavelength as the test light source B (3) in the wavelength division multiplexer (10), and the third port of the circulator B (9) is connected to the optical input end of the optical detector B (5); the wavelength combining end of the wavelength division multiplexer (10) is connected to the temperature measuring optical cable (12); the output ends of the optical detector A (4) and the optical detector B (5) are respectively electrically connected to the control and signal processing circuit (11); 2) outputting a pulse modulation signal to the excitation light source (1) through the control and signal processing circuit (11) to generate pulse excitation light, and synchronously collecting Raman scattered light signals output by the light detector A (4) and the light detector B (5); 3) outputting a pulse modulation signal to the test light source A (2) and the test light source B (3) through the control and signal processing circuit (11) to generate pulse excitation light, and synchronously collecting the Rayleigh scattered light signals output by the detector A (4) and the light detector B (5); 4) The control and signal processing circuit (11) collects the collected Raman scattered light signals and Rayleigh scattered light signals multiple times and accumulates and averages them to obtain relative intensity information related to temperature at different positions of the temperature measuring optical cable (12); 5) The control and signal processing circuit (11) obtains the relative intensity result by interpolation and fitting according to the relative intensity calibration data at different temperatures to complete the temperature solution; The excitation light source (1) is a high-speed pulse laser with a wavelength of 1064nm or 1550nm; according to the wavelength of the excitation light source (1), the working wavelengths of the test light source and the wavelength division multiplexer (10) are also selected accordingly; when the wavelength of the excitation light source (1) is 1064nm, the wavelengths of the test light source A (2) and the test light source B (3) are 850nm and 1300nm respectively, and the working wavelength of the wavelength division multiplexer (10) is 850nm / 1064nm / 1300nm; when the wavelength of the excitation light source (1) is 1550nm, the wavelengths of the test light source A (2) and the test light source B (3) are 1450nm and 1660nm respectively, and the working wavelength of the wavelength division multiplexer (10) is 1450nm / 1550nm / 1660nm; The photodetector A (4) and the photodetector B (5) are avalanche diodes; The control and signal processing circuit (11) controls the modulation of the excitation light source (1), the test light source A (2) and the test light source B (3) and the detection and collection of corresponding signals in an alternating manner; The circulator and wavelength division multiplexer guide the different wavelength optical signals emitted by the excitation light source and the test light source to the temperature measuring optical cable, and distinguish the different wavelength components in the optical signal returned by the temperature measuring optical cable and introduce them into the optical detector respectively; the optical detector converts the Raman scattered light signal generated by the excitation light source and the Rayleigh scattered light signal generated by the test light source into electrical signals.

3. The distributed optical fiber temperature measurement method according to claim 2, characterized in that: In step 4), a square root operation is performed on the Rayleigh scattered light signal after cumulative average, the Raman scattered light is compared with the Rayleigh scattered light of the corresponding wavelength, and the anti-Stokes Raman light signal is compared with the Stokes Raman scattered light signal.

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