A Raman optical time domain reflectometer demodulation method and system for optical fiber temperature sensing

Abstract

The invention relates to a Raman optical time domain reflectometer demodulation method and system for optical fiber temperature sensing. The invention measures the real-time temperature of a calibration point and the digital signal ratio of anti-Stokes light to Stokes light at each calibration point, calculates the digital signal ratio of anti-Stokes light to Stokes light at the calibration point at the calibration temperature, then fits the digital signal ratio curve of anti-Stokes light to Stokes light at the calibration temperature, and integrates the digital signal ratio curves of the front end and the calibration optical fiber to form a calibration curve. The method of the invention can well calibrate sensing optical cables at different temperatures, and can also eliminate temperature drift caused by different amplification factors of photoelectric conversion and multi-stage amplification of anti-Stokes light and Stokes light.

Description

Technical Field

[0001] The invention belongs to the technical field of optical fiber sensing systems, and in particular relates to a Raman optical time domain reflectometer demodulation method and system for optical fiber temperature sensing. Background Art

[0002] Raman Optical Time Domain Reflectometer (R-OTDR) is a distributed temperature sensing technology that combines the optical time domain reflectometer (OTDR) technology with the optical fiber Raman scattering effect. When a detection light pulse is injected into the optical fiber, it continuously generates backward Raman scattered light during the transmission along the optical fiber. By detecting the change in the intensity of Raman scattered light along the optical fiber, the temperature field information along the optical fiber can be obtained.

[0003] At present, the temperature demodulation method for the Raman optical time domain reflectometer temperature measurement system is to place the entire sensing optical cable at a certain constant temperature, collect the ratio of the two scattered light intensities of the entire sensing optical cable at this time and save it, and then through real-time detection of the ratio of the two scattered light intensities of the sensing optical cable, the temperature distribution along the sensing optical cable can be demodulated by calculation. The advantage of this demodulation method is that it can eliminate the influence of large loss points such as the fusion point on the optical fiber, but the disadvantage is that the amplification factors of the photoelectric detectors of the two backscattered lights and the multi-stage electric amplifier are inconsistent, and this inconsistency will change with the ambient temperature, thereby introducing a temperature drift to the demodulation temperature of the entire sensing optical cable; in addition, before application, the entire sensing optical cable needs to be placed at a relatively stable ambient temperature to measure the ratio curve and store it, which is no problem for the application scenario of the newly laid sensing optical cable, but it is not applicable to the application scenario where the sensing optical cable has been laid and the ambient temperature of each section of the sensing optical cable is different. To this end, the present invention proposes a Raman optical time domain reflectometer demodulation method and system for optical fiber temperature sensing. Summary of the invention

[0004] The purpose of the present invention is to: in view of the above-mentioned shortcomings, invent a Raman optical time domain reflectometer demodulation method and system for optical fiber temperature sensing.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A Raman optical time domain reflectometer demodulation method for optical fiber temperature sensing, the front end of the sensing optical cable is connected to the calibration optical fiber, and the temperature demodulation formula of each point temperature T on the sensing optical cable is specifically calculated as follows:

[0007]

[0008] Where k is the Boltzmann constant, Δν is the Raman frequency shift, h is the Planck constant, T0 is the calibration temperature, is the temperature of the calibration fiber at the calibration temperature, T 1To calibrate the real-time temperature of the optical fiber, U(T) and U(T0) are the digital signal ratio curves of the anti-Stokes light and Stokes light generated by the sensing optical cable at the real-time temperature and the calibration temperature, respectively. 1 (T) and U 1 (T0) are the digital signal ratio curves of anti-Stokes light and Stokes light generated by the calibration optical fiber at real temperature and calibration temperature, respectively.

[0009] Furthermore, the sensor optical cable is a laid sensor optical cable; the specific calculation method of the digital signal ratio curve U(T0) of the anti-Stokes light and Stokes light generated by the sensor optical cable at the calibration temperature is as follows:

[0010] On the laid sensor optical cable, select n calibration points x1, x2, ..., x n , measure the temperature of each calibration point on the sensing optical cable The digital signal ratio of each calibration point on the sensing optical cable at real-time temperature The calibration temperature T0 of each calibration point of the sensor optical cable and the digital signal ratio of each calibration point under the calibration temperature T0 The digital signal ratio curve U(T0) of anti-Stokes light and Stokes light generated by the sensing optical cable at the calibration temperature T0 is obtained by fitting.

[0011] Furthermore, the specific fitting steps of the digital signal ratio curve U(T0) are as follows:

[0012] First, the state of the calibration fiber is set to remain unchanged, that is, U 1 (T)=U 1 (T0); then the simplified expression of the temperature demodulation formula is as follows:

[0013]

[0014] Where, h is Planck's constant; k is Boltzmann's constant; Δν is the Raman frequency shift; is the real-time temperature of each calibration point on the sensing optical cable; T0 is the calibration temperature; U(T) and U(T0) are the digital signal ratio curves of anti-Stokes light and Stokes light generated by the sensing optical cable at the real-time temperature and the calibration temperature respectively;

[0015] Then, the digital signal ratio corresponding to each calibration point on the sensing optical cable at the calibration temperature is calculated by a simplified temperature demodulation formula. The digital signal ratio The specific calculation formula is as follows:

[0016]

[0017] Where, h is Planck's constant; k is Boltzmann's constant; Δν is the Raman frequency shift; is the real-time temperature of each calibration point on the sensing optical cable; T0 is the calibration temperature; It is the digital signal ratio of anti-Stokes light and Stokes light at each calibration point on the sensing optical cable at real-time temperature;

[0018] Finally, the digital signal ratio of each calibration point on the sensor optical cable at the calculated calibration temperature is Linear fitting is performed to obtain the digital signal ratio curve U(T0) of the anti-Stokes light and Stokes light generated by the sensing optical cable at the calibration temperature T0.

[0019] Furthermore, the number of calibration points n≥2 selected on the laid sensor optical cable, and the selected calibration points include points close to the front end and the rear end of the sensor optical cable.

[0020] Furthermore, the digital signal ratio of the anti-Stokes light and the Stokes light at each calibration point on the sensing optical cable under the real-time temperature is The specific calculation method is as follows:

[0021]

[0022] Among them, α is the amplification factor, k as and k s are the coefficients of anti-Stokes light and Stokes light in the cross section of the fiber scattering end; as and λ s are the wavelengths of anti-Stokes light and Stokes light respectively; α as and α s are the loss coefficients of anti-Stokes and Stokes light in optical fiber respectively; L is the length of the sensing optical cable; h is Planck's constant; k is Boltzmann's constant; Δν represents the Raman frequency shift; It is the real-time temperature of each calibration point on the sensing optical cable.

[0023] Furthermore, the digital signal ratio U(T) of the anti-Stokes light and the Stokes light generated by the sensing optical cable under the real-time temperature can be expressed as:

[0024] U(T)=α·R

[0025] Wherein, α is the amplification factor, and R is the ratio of the anti-Stokes light to the Stokes light signal at the real-time temperature; the specific calculation method of the ratio R of the anti-Stokes light to the Stokes light signal at the real-time temperature is as follows:

[0026]

[0027] Among them, k as and ks are the coefficients of anti-Stokes light and Stokes light in the cross section of the fiber scattering end; as and λ s are the wavelengths of anti-Stokes light and Stokes light respectively; α as and α s are the loss coefficients of anti-Stokes and Stokes light in optical fiber respectively; L is the length of the sensing optical cable; h is Planck's constant; k is the Boltzmann constant; Δν represents the Raman frequency shift.

[0028] Furthermore, the temperature of the calibration optical fiber at the calibration temperature and real-time temperature T 1 It is measured by a temperature sensor.

[0029] The real-time temperature T 1 The digital signal ratio U of the anti-Stokes light and Stokes light generated by the calibration fiber 1 The specific calculation method of (T) is as follows:

[0030]

[0031] The temperature at the calibration temperature The digital signal ratio U of the anti-Stokes light and Stokes light generated by the calibration fiber 1 The specific calculation method of (T0) is as follows:

[0032]

[0033] Among them, α is the amplification factor, k as and k s are the coefficients of anti-Stokes light and Stokes light in the cross section of the fiber scattering end; as and λ s are the wavelengths of anti-Stokes light and Stokes light respectively; α as and α s are the loss coefficients of anti-Stokes and Stokes light in optical fiber respectively; L 1 is the calibration fiber length; h is Planck's constant; k is Boltzmann's constant; Δν represents the Raman frequency shift; is the temperature of the calibrated optical fiber at the calibration temperature, T 1 To calibrate the real-time temperature of the optical fiber.

[0034] A Raman optical time domain reflectometer demodulation system for optical fiber temperature sensing comprises a laser, an erbium-doped optical fiber amplifier, a wavelength division multiplexer, a calibration optical fiber box, an optical switch, a sensing optical cable, a dual-channel APD, a multi-stage amplification circuit, an acquisition card, a processing center and a driving circuit; the laser is sequentially connected to the erbium-doped optical fiber amplifier, the wavelength division multiplexer, the calibration optical fiber box, the optical switch and the sensing optical cable, the wavelength division multiplexer is sequentially connected to the dual-channel APD, the multi-stage amplification circuit, the acquisition card and the processing center, the acquisition card is connected to the driving circuit, the driving circuit is connected to the laser, and the processing center is respectively connected to the calibration optical fiber box and the optical switch.

[0035] Furthermore, it also includes n calibration points and m temperature detectors, where n = m≥2; the calibration points are set on the sensing optical cable and connected to the temperature detectors, and the temperature detectors are connected to the processing center; the calibration point and temperature detector at the leftmost end and the calibration point and temperature detector at the rightmost end are respectively close to the two ends of the sensing optical cable.

[0036] Furthermore, the wavelength division multiplexer comprises a COM port, a 1450 optical port, a 1550 optical port and a 1660 optical port; the COM port is connected to an optical switch, the 1550 optical port is connected to an erbium-doped fiber amplifier, and the 1450 optical port and the 1660 optical port are respectively connected to dual-channel APDs.

[0037] Furthermore, the calibration optical fiber box comprises a calibration optical fiber and a temperature sensor; the calibration optical fiber is connected to a wavelength division multiplexer and an optical switch respectively; the temperature sensor is arranged on the calibration optical fiber and connected to a processing center.

[0038] Furthermore, the acquisition card includes a data acquisition card and an AD conversion circuit; the AD conversion circuit is respectively connected to the data acquisition card and the multi-stage amplification circuit, and the data acquisition card is respectively connected to the processing center and the driving circuit.

[0039] Furthermore, the acquisition card drives the laser through a driving circuit to generate a laser pulse signal. After being amplified by an erbium-doped fiber amplifier, the laser pulse signal passes through a wavelength division multiplexer, a calibration fiber box and an optical switch in sequence, and is incident on a sensing optical cable to generate backward Raman scattered light. The backward Raman scattered light passes through a sensing optical cable, an optical switch and a calibration fiber box in sequence, and is incident on a wavelength division multiplexer to filter and separate anti-Stokes light and Stokes light. After the anti-Stokes light and Stokes light are subjected to photoelectric conversion and multi-stage amplification by a dual-channel APD and a multi-stage amplification circuit, they are transmitted to the acquisition card for analog-to-digital conversion, average noise reduction and data acquisition. The acquisition card sends the collected digital signals of the anti-Stokes light and Stokes light to a processing center for calculation. The processing center is also responsible for controlling the optical switch to perform channel switching to realize multi-channel sensing.

[0040] Beneficial effects of the present invention:

[0041] 1. It can effectively improve the problem of large temperature deviation of the loss point on the sensing optical cable or large temperature deviation of the remote demodulation of the sensing optical cable in the existing technology;

[0042] 2. It can calibrate the sensor optical cables at different temperatures, and can effectively eliminate the overall temperature drift problem caused by the inconsistency of the anti-Stokes light and Stokes light gain coefficients;

[0043] 3. Further reduce the hardware cost of the system and improve long-term stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a system structure diagram of a Raman optical time domain reflectometer demodulation method and system for optical fiber temperature sensing of the present invention; in the figure: 1-laser, 2-erbium-doped optical fiber amplifier, 3-wavelength division multiplexer, 4-calibration optical fiber box, 41-temperature sensor, 5-optical switch, 6-sensing optical cable, 7-dual-channel APD, 8-multi-stage amplification circuit, 9-acquisition card, 10-processing center, 11-driving circuit;

[0045] Figure 2 A flow chart of a temperature demodulation method of a Raman optical time domain reflectometer demodulation method and system for optical fiber temperature sensing according to the present invention;

[0046] Figure 3 A Raman optical time domain reflectometer demodulation method and system for optical fiber temperature sensing of the present invention measures temperature at a calibration point, and at the calibration temperature, obtains a schematic diagram of a digital signal ratio curve of anti-Stokes light and Stokes light by fitting;

[0047] Figure 4 The present invention is a schematic diagram of a temperature curve finally demodulated by a Raman optical time domain reflectometer demodulation method and system for optical fiber temperature sensing. DETAILED DESCRIPTION

[0048] Example 1

[0049] A Raman optical time domain reflectometer demodulation system for optical fiber temperature sensing, comprising a laser 1, an erbium-doped optical fiber amplifier 2, a wavelength division multiplexer 3, a calibration optical fiber box 4, an optical switch 5, a sensing optical cable 6, a dual-channel APD 7, a multi-stage amplification circuit 8, an acquisition card 9, a processing center 10, a drive circuit 11, n calibration points and m temperature detectors; the wavelength division multiplexer 3 comprises a COM port, a 1450 optical port, a 1550 optical port and a 1660 optical port; the calibration optical fiber box 4 comprises a calibration optical fiber and a temperature sensor 41, and the acquisition card 9 comprises a data acquisition card and an AD conversion circuit;

[0050] The data acquisition card 9 drives the laser 1 through the driving circuit 11 to output a laser pulse signal with a wavelength of 1550.12nm, which is incident on the 1550nm optical port of the wavelength division multiplexer 3, and then incident on the calibration optical fiber from the COM port of the wavelength division multiplexer 3, wherein the calibration optical fiber is provided with a temperature sensor 41 for measuring the temperature of the calibration optical fiber in real time, and transmitting the temperature of the calibration optical fiber to the processing center 10;

[0051] After the laser pulse signal passes through the calibration optical fiber and the optical switch 5 in sequence, it is incident on the sensing optical cable 6 to generate backward Raman scattered light, wherein the sensing optical cable 6 is a laid sensing optical cable 6, on which n calibration points and m temperature detectors are set, wherein n=m≥2, and the calibration point and temperature detector at the leftmost end and the calibration point and temperature detector at the rightmost end are respectively close to the two ends of the sensing optical cable 6, and the temperature detector is used to detect the temperature of the sensing optical cable 6 where the calibration point is located, and transmit the temperature of the sensing optical cable 6 to the processing center 10 by wireless means;

[0052] The back Raman scattered light is incident on the COM port of the wavelength division multiplexer 3 through the sensing optical cable 6, the optical switch 5 and the calibration optical fiber in sequence. After being filtered by the wavelength division multiplexer 3, the back Raman scattered light is output from the 1660 optical port and the 1450 optical port of the wavelength division multiplexer as Stokes light and anti-Stokes light to the dual-channel APD 7 respectively. The dual-channel APD 7 performs photoelectric conversion on the Stokes light and the anti-Stokes light, and then outputs them to the multi-stage amplifier circuit 8 for multi-stage amplification. Then, the analog-to-digital conversion is performed through the AD conversion circuit and then output to the data acquisition card for average noise reduction and data acquisition. The data acquisition card transmits the collected digital signals of the anti-Stokes light and the Stokes light to the processing center 10, and uses the temperature demodulation algorithm to demodulate the temperature T of each point along the sensing optical cable 6. The processing center 10 is also responsible for controlling the optical switch 5 to perform channel switching to realize multi-channel sensing.

[0053] A Raman optical time domain reflectometer demodulation method for optical fiber temperature sensing, comprising:

[0054] On the already laid sensor optical cable, select n calibration points x1, x2, ..., x n , wherein the number of calibration points n≥2, and the selected leftmost calibration point and the rightmost calibration point are respectively close to the two ends of the sensing optical cable; the real-time temperature of each calibration point on the sensing optical cable 6 is detected by a temperature detector The real-time temperature of each calibration point on the sensing optical cable is obtained Output to the processing center; use the temperature sensor 41 to measure the temperature of the calibration optical fiber at the calibration temperature And real-time temperature T 1, and the temperature at the calibration fiber calibration temperature And real-time temperature T 1 Transmit to the processing center 10;

[0055] A laser pulse signal propagating in the sensing optical cable will generate a backward anti-Stokes light P as With Stokes light P s , according to the real-time temperature T, the incident light P0 of the optical cable, the coefficient k of the anti-Stokes light and the Stokes light of the optical cable scattering end cross section as and k s , the wavelengths λ of anti-Stokes light and Stokes light as and λ s , the loss coefficient α of anti-Stokes and Stokes light in optical fiber as and α s , sensing optical cable length L, Planck constant h, Boltzmann constant k, Raman frequency shift Δv = 1.32×10 13 Hz, and the anti-Stokes light power P of the sensing optical cable at real-time temperature is obtained. as (T) and the optical power P of Stokes light s (T); the optical power P of the anti-Stokes light of the sensing optical cable at the real-time temperature as The specific calculation method of (T) is as follows:

[0056]

[0057] The optical power P of the Stokes light of the sensing optical cable at the real-time temperature as The specific calculation method of (T) is as follows:

[0058]

[0059] Thus, the optical power ratio R of the anti-Stokes light and the Stokes light of the sensing optical cable at the real-time temperature T is obtained; the specific calculation method of the optical power ratio R of the anti-Stokes light and the Stokes light of the sensing optical cable at the real-time temperature is as follows:

[0060]

[0061] Further, the specific calculation method of the optical power ratio R(T) of the anti-Stokes light and the Stokes light of the sensing optical cable at the real-time temperature is as follows:

[0062]

[0063] Similarly, according to the real-time temperature T of the calibration optical fiber 1 And the temperature at the calibration temperature The correlation coefficient k between the anti-Stokes light and the Stokes light at the scattering end of the optical cableas and k s , the wavelengths λ of anti-Stokes light and Stokes light as and λ s , the loss coefficient α of anti-Stokes and Stokes light in optical fiber as and α s , calibration fiber length L 1 , Planck constant h, Boltzmann constant k, Raman frequency shift Δv = 1.32×10 13 Hz, and the optical power ratio R of the anti-Stokes light and the Stokes light generated by the calibration fiber at the real-time temperature and the calibration temperature is obtained. 1 (T) and R 1 (T0);

[0064] The optical power ratio R of the anti-Stokes light and the Stokes light of the calibration optical fiber at the real-time temperature 1 The specific calculation method of (T) is as follows:

[0065]

[0066] The optical power ratio R of the anti-Stokes light and the Stokes light of the calibration optical fiber at the calibration temperature 1 The specific calculation method of (T) is as follows:

[0067]

[0068] The optical signals of the anti-Stokes light and the Stokes light are subjected to photoelectric conversion by the dual-channel APD 7, amplified by the multi-stage amplifier circuit 8, and then subjected to analog-to-digital conversion, average noise reduction and data acquisition by the acquisition card 9 to obtain digital signals of the anti-Stokes light and the Stokes light; because the dual-channel APD 7, the multi-stage amplifier circuit 8 and the data acquisition cannot be completely consistent, using the ratio of the digital signal instead of the optical power for the calculation formula will introduce an amplification factor, wherein the amplification factor α is affected by the temperature, so the amplification factor at different times is also different;

[0069] According to the amplification factor α and the optical power R of the anti-Stokes light and the Stokes light of the sensing optical cable at the real-time temperature, the digital signal ratio U of the anti-Stokes light and the Stokes light of the sensing optical cable is obtained. The specific calculation method of the digital signal ratio U of the anti-Stokes light and the Stokes light of the sensing optical cable is as follows:

[0070] U=α·R

[0071] The specific calculation method of the digital signal ratio U(T) of the anti-Stokes light and the Stokes light of the sensing optical cable at the real-time temperature is as follows:

[0072]

[0073] According to the amplification factor α, the coefficient k of the anti-Stokes light and Stokes light in the fiber scattering end cross section is as and k s , the wavelengths λ of anti-Stokes light and Stokes light as and λ s , the loss coefficient α of anti-Stokes and Stokes light in optical fiber as and α s , sensing optical cable length L; Planck constant h, Boltzmann constant k, Raman frequency shift Δv, real-time temperature of each calibration point on the sensing optical cable Obtain the digital signal ratio of each calibration point on the sensing optical cable at real-time temperature The digital signal ratio of anti-Stokes light and Stokes light at each calibration point on the sensing optical cable at the real-time temperature The specific calculation method is as follows:

[0074]

[0075] Set the state of the calibration fiber to remain unchanged, that is, U 1 (T)=U 1 (T0); based on Planck constant h; Boltzmann constant k; Raman frequency shift Δν; real-time temperature of each calibration point on the sensing optical cable Calibration temperature T0; digital signal ratios U(T) and U(T0) of anti-Stokes light and Stokes light generated by the sensing optical cable at real-time temperature and calibration temperature, and a simplified temperature demodulation formula is obtained: The simplified temperature demodulation formula is specifically expressed as follows:

[0076]

[0077] According to the measured temperature of each calibration point on the sensing optical cable The digital signal ratio of each calibration point on the sensing optical cable at real-time temperature Planck constant h, Boltzmann constant k, Raman frequency shift Δv, simplified temperature demodulation formula, and the digital signal ratio of anti-Stokes light and Stokes light at each calibration point on the sensing optical cable at the calibration temperature are obtained. The digital signal ratio of the anti-Stokes light and the Stokes light at each calibration point at the calibration temperature of each calibration point on the sensing optical cable The specific calculation method is as follows:

[0078]

[0079] The digital signal ratio of each calibration point on the sensing optical cable to the calibration temperature T0 and the calibration temperature T0 The digital signal ratio curve U(T0) of anti-Stokes light and Stokes light generated by the sensing optical cable at the calibration temperature T0 is obtained by linear fitting;

[0080] According to the amplification factor α, the optical power ratio R of the anti-Stokes light and the Stokes light of the temperature calibration fiber at the real-time temperature and the calibration temperature 1 (T) and R 1 (T0), the digital signal ratio U of the anti-Stokes light and the Stokes light generated by the calibration fiber at the real-time temperature and the calibration temperature is obtained. 1 (T) and U 1 (T0);

[0081] The digital signal ratio U of the anti-Stokes light and the Stokes light generated by the real-time temperature calibration optical fiber 1 The specific calculation method of (T) is as follows:

[0082]

[0083] The digital signal ratio U of the anti-Stokes light and the Stokes light generated by the calibration optical fiber at the calibration temperature 1 The specific calculation method of (T0) is as follows:

[0084]

[0085] The processing center will calibrate the fiber real-time temperature T 1 and the temperature at the calibration temperature The digital signal ratio U of the anti-Stokes light and Stokes light generated by the calibration fiber at real-time temperature and calibration temperature 1 (T) and U 1 (T0), the digital signal ratio curve U(T) of the anti-Stokes light and Stokes light generated by the real-time temperature sensing optical cable, the digital signal ratio curve U(T0) of the anti-Stokes light and Stokes light generated by the sensing optical cable at the calibration temperature obtained by linear fitting, Planck constant h, Boltzmann constant k, and Raman frequency shift Δv, where Δv = 1.32×10 13 Hz, and then the temperature demodulation formula of each point temperature T on the sensing optical cable is brought into the temperature demodulation formula to obtain the temperature T of each point along the sensing optical cable. The specific calculation method of the temperature demodulation formula of each point temperature T on the sensing optical cable is as follows:

[0086]

[0087] Example 2

[0088] A Raman optical time domain reflectometer demodulation system for optical fiber temperature sensing, comprising a laser 1, an erbium-doped fiber amplifier 2, a wavelength division multiplexer 3, a calibration fiber box 4, an optical switch 5, a sensing optical cable 6, a dual-channel APD 7, a multi-stage amplifier circuit 8, an acquisition card 9, a processing center 10 and a drive circuit 11; the wavelength division multiplexer 3 comprises a COM port, a 1450 optical port, a 1550 optical port and a 1660 optical port; the calibration fiber box 4 comprises a calibration optical fiber and a temperature sensor 41, and the acquisition card 9 comprises a data acquisition card and an AD conversion circuit;

[0089] The data acquisition card 9 drives the laser 1 through the driving circuit 11 to output a laser pulse signal with a wavelength of 1550.12nm, which is incident on the 1550nm optical port of the wavelength division multiplexer 3, and then incident on the calibration optical fiber from the COM port of the wavelength division multiplexer 3, wherein the calibration optical fiber is provided with a temperature sensor 41 for real-time measurement of the temperature of the calibration optical fiber, and the temperature of the calibration optical fiber is transmitted to the processing center 10;

[0090] The laser pulse signal passes through the calibration optical fiber and the optical switch 5 in sequence, and then enters the sensing optical cable 6 to generate backward Raman scattered light, wherein a temperature detector is arranged at the front end of the sensing optical cable 6, and the temperature detector is used to detect the temperature of the sensing optical cable 6, and transmit the temperature of the sensing optical cable 6 to the processing center 10 by wireless means;

[0091] The back Raman scattered light is incident on the COM port of the wavelength division multiplexer 3 through the sensing optical cable 6, the optical switch 5 and the calibration optical fiber in sequence. After being filtered by the wavelength division multiplexer 3, the back Raman scattered light is output from the 1660 optical port and the 1450 optical port of the wavelength division multiplexer as Stokes light and anti-Stokes light to the dual-channel APD 7 respectively. The dual-channel APD 7 performs photoelectric conversion on the Stokes light and anti-Stokes light, and then outputs them to the multi-stage amplifier circuit 8 for multi-stage amplification. Then, the AD conversion circuit performs analog-to-digital conversion and outputs them to the data acquisition card for average noise reduction and data acquisition. The data acquisition card transmits the collected digital signals of the anti-Stokes light and the Stokes light to the processing center 10, and uses the temperature demodulation algorithm to demodulate the temperature T of each point along the sensing optical cable 6. The processing center 10 is also responsible for controlling the optical switch 5 to perform channel switching to realize multi-channel sensing.

[0092] A Raman optical time domain reflectometer demodulation method for sensing optical cables, comprising:

[0093] The sensing optical cable 6 is placed in a stable environment, and the calibration temperature T0 and the real-time temperature T of the sensing optical cable 6 are detected by a temperature detector, and the calibration temperature T0 and the real-time temperature T of the sensing optical cable 6 are transmitted to the processing center 10; the temperature sensor 41 is used to measure the temperature of the calibration optical fiber at the calibration temperature And real-time temperature T 1 , and the temperature at the calibration fiber calibration temperature And real-time temperature T 1 Transmit to the processing center 10;

[0094] A laser pulse signal propagating in the sensing optical cable will generate a backward anti-Stokes light P as With Stokes light P s According to the calibration temperature T0 and real-time temperature T of the sensing optical cable, the incident light P0 of the optical cable, the coefficient k of the anti-Stokes light and the Stokes light of the optical cable scattering end section as and k s , the wavelengths λ of anti-Stokes light and Stokes light as and λ s , the loss coefficient α of anti-Stokes and Stokes light in optical fiber as and α s , sensing optical cable length L, Planck constant h, Boltzmann constant k, Raman frequency shift Δv, where Δv = 1.32×10 13 Hz, and the optical power P of the anti-Stokes light at the real-time temperature of the sensing optical cable is obtained. as (T) and the optical power P of Stokes light s (T); the optical power P of the anti-Stokes light of the sensing optical cable at the real-time temperature as The specific calculation method of (T) is as follows:

[0095]

[0096] The optical power P of the Stokes light of the sensing optical cable at the real-time temperature is as The specific calculation method of (T) is as follows:

[0097]

[0098] Thus, the optical power ratio R of the anti-Stokes light and the Stokes light of the sensing optical cable at the real-time temperature and the calibration temperature is obtained. The specific calculation method of the optical power ratio R of the anti-Stokes light and the Stokes light of the sensing optical cable at the real-time temperature is as follows:

[0099]

[0100] Further, the specific calculation method of the optical power ratio R(T) of the anti-Stokes light and the Stokes light of the sensing optical cable at the real-time temperature is as follows:

[0101]

[0102] The specific calculation method of the optical power ratio R(T0) of the anti-Stokes light and the Stokes light generated by the sensing optical cable at the calibration temperature is as follows:

[0103]

[0104] Similarly, according to the real-time temperature T of the calibration optical fiber 1 and the temperature at the calibration temperature The correlation coefficient k between the anti-Stokes light and the Stokes light at the scattering end of the optical cable as and k s , the wavelengths λ of anti-Stokes light and Stokes light as and λ s , the loss coefficient α of anti-Stokes and Stokes light in optical fiber as and α s , calibration fiber length L 1 , Planck constant h, Boltzmann constant k, Raman frequency shift Δv, where Δv = 1.32×10 13 Hz, and the optical power ratio R of the anti-Stokes light and the Stokes light of the calibration fiber at the real-time temperature and the calibration temperature is obtained. 1 (T) and R 1 (T0);

[0105] The optical power ratio R of the anti-Stokes light and the Stokes light of the calibration optical fiber at the real-time temperature 1 The specific calculation method of (T) is as follows:

[0106]

[0107] The optical power ratio R of the anti-Stokes light and the Stokes light of the calibration optical fiber at the calibration temperature 1 The specific calculation method of (T) is as follows:

[0108]

[0109] The optical signals of the anti-Stokes light and the Stokes light are subjected to photoelectric conversion by the dual-channel APD 7, amplified by the multi-stage amplifier circuit 8, and then subjected to analog-to-digital conversion, average noise reduction and data acquisition by the acquisition card 9 to obtain the digital signals of the anti-Stokes light and the Stokes light; because the dual-channel APD 7 and the multi-stage amplifier circuit 8 and the data acquisition cannot be completely consistent, using the ratio of the digital signal instead of the optical power for calculation will introduce an amplification factor, wherein the amplification factor α is affected by the temperature, so the amplification factor at different times is also different; according to the amplification factor α, the optical power R of the anti-Stokes light and the Stokes light of the sensing optical cable at the real-time temperature, the digital signal ratio U of the anti-Stokes light and the Stokes light of the sensing optical cable is obtained, and the specific calculation method of the digital signal ratio U of the anti-Stokes light and the Stokes light of the sensing optical cable is as follows:

[0110] U=α·R

[0111] The specific calculation method of the digital signal ratio U(T) of the anti-Stokes light and the Stokes light of the sensing optical cable at the real-time temperature is as follows:

[0112]

[0113] The specific calculation method of the digital signal ratio U(T0) of the anti-Stokes light and the Stokes light of the sensing optical cable at the calibration temperature is as follows:

[0114]

[0115] Calibrate the optical power ratio R of the anti-Stokes light and the Stokes light of the optical fiber according to the amplification factor α, the real-time temperature and the calibration temperature. 1 (T) and R 1 (T0), the digital signal ratio U of the anti-Stokes light and Stokes light generated by the calibration fiber at the real temperature and the calibration temperature is obtained 1 (T) and U 1 (T0); the real-time temperature of the calibration optical fiber T 1 The digital signal ratio U of the generated anti-Stokes light and Stokes light 1 The specific calculation method of (T) is as follows:

[0116]

[0117] The digital signal ratio U of the anti-Stokes light and the Stokes light generated by the calibration optical fiber at the calibration temperature 1 The specific calculation method of (T0) is as follows:

[0118]

[0119] The processing center 10 obtains the real-time temperature T of the calibration optical fiber. 1 and the temperature at the calibration temperature The real-time temperature T and calibration temperature T0 of the sensing optical cable, the digital signal ratio U of the anti-Stokes light and Stokes light generated by the calibration optical fiber at the real-time temperature and calibration temperature 1 (T) and U 1 (T0), the digital signal ratios of anti-Stokes light and Stokes light generated by the sensing optical cable at real-time temperature and calibration temperature, U(T) and U(T0), Planck constant h, Boltzmann constant k, Raman frequency shift Δv = 1.32×10 13 Hz is substituted into the temperature demodulation formula of the temperature T of each point on the sensing optical cable to obtain the temperature T of each point along the sensing optical cable; the specific calculation method of the temperature demodulation formula of the temperature T of each point on the sensing optical cable is as follows:

[0120]

[0121] The specific models of hardware involved in the above embodiment are as follows:

[0122] The laser uses a DFB laser with a wavelength of 1550.12nm, a bandwidth of 2.5GHz, and a peak power of 10dBm;

[0123] The erbium-doped fiber amplifier adopts a self-developed erbium-doped fiber amplifier;

[0124] The wavelength division multiplexer adopts a 4-port multimode wavelength division multiplexer;

[0125] The calibration optical fiber box is a self-developed calibration optical fiber box;

[0126] The optical switch adopts a multi-mode 1X4 optical switch;

[0127] The sensor optical cable adopts 62.5 / 125 multi-mode optical cable;

[0128] The temperature detector adopts a thin film platinum thermistor;

[0129] The dual-channel APD adopts a self-developed dual-channel APD module;

[0130] The data acquisition card adopts a self-developed dual-channel 100MHz data acquisition card;

[0131] The processing center uses Advantech industrial computers.

[0132] The present invention has many specific application paths. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements can be made without departing from the principle of the present invention. These improvements should also be regarded as the protection scope of the present invention.

Claims

1. A Raman optical time domain reflectometer demodulation method for optical fiber temperature sensing, wherein the front end of the sensing optical cable is connected to a calibration optical fiber, characterized in that: The specific expression of the temperature demodulation formula of each point temperature T on the sensing optical cable is as follows: Where k is the Boltzmann constant, Δν is the Raman frequency shift, h is the Planck constant, T0 is the calibration temperature, is the temperature of the calibration fiber at the calibration temperature, T 1 To calibrate the real-time temperature of the optical fiber, U(T) and U(T0) are the digital signal ratio curves of the anti-Stokes light and Stokes light generated by the sensing optical cable at the real-time temperature and the calibration temperature, respectively. 1 (T) and U 1 (T0) is the digital signal ratio of anti-Stokes light and Stokes light generated by the calibration optical fiber at the real-time temperature and calibration temperature respectively.

2. According to the Raman optical time domain reflectometer demodulation method for optical fiber temperature sensing in claim 1, the front end of the sensing optical cable is connected to the calibration optical fiber, characterized in that: The sensor optical cable is a laid sensor optical cable; the specific calculation method of the digital signal ratio curve U(T0) of anti-Stokes light and Stokes light generated by the sensor optical cable at the calibration temperature is as follows: On the laid sensor optical cable, select n calibration points x1, x2, ..., x n , measure the temperature of each calibration point on the sensing optical cable The digital signal ratio of each calibration point on the sensing optical cable at real-time temperature The digital signal ratio of each calibration point on the sensing optical cable to the calibration temperature T0 and the calibration temperature T0 The digital signal ratio curve U(T0) of anti-Stokes light and Stokes light generated by the sensing optical cable at the calibration temperature T0 is obtained by fitting.

3. According to the Raman optical time domain reflectometer demodulation method for optical fiber temperature sensing in claim 2, the front end of the sensing optical cable is connected to the calibration optical fiber, characterized in that: The number of calibration points n selected on the laid sensor optical cable is ≥ 2, and the selected calibration points include points close to the front end and the rear end of the sensor optical cable.

4. According to the Raman optical time domain reflectometer demodulation method for optical fiber temperature sensing in claim 2, the front end of the sensing optical cable is connected to the calibration optical fiber, characterized in that: The specific fitting steps of the digital signal ratio curve U(T0) are as follows: First, the state of the calibration fiber is set to remain unchanged, that is, U 1 (T)=U 1 (T0); then the simplified expression of the temperature demodulation formula is as follows: Where, h is Planck's constant; k is Boltzmann's constant; Δν is the Raman frequency shift; is the real-time temperature of each calibration point on the sensing optical cable; T0 is the calibration temperature; U(T) and U(T0) are the digital signal ratio curves of anti-Stokes light and Stokes light generated by the sensing optical cable at the real-time temperature and the calibration temperature respectively; Then, the digital signal ratio corresponding to each calibration point on the sensing optical cable at the calibration temperature is calculated by a simplified temperature demodulation formula. The digital signal ratio The specific calculation formula is as follows: Where, h is Planck's constant; k is Boltzmann's constant; Δν is the Raman frequency shift; is the real-time temperature of each calibration point on the sensing optical cable; T0 is the calibration temperature; It is the digital signal ratio of anti-Stokes light and Stokes light at each calibration point on the sensing optical cable at real-time temperature; Finally, the digital signal ratio of each calibration point on the sensor optical cable at the calculated calibration temperature is Linear fitting is performed to obtain the digital signal ratio curve U(T0) of the anti-Stokes light and Stokes light generated by the sensing optical cable at the calibration temperature T0.

5. According to the Raman optical time domain reflectometer demodulation method for optical fiber temperature sensing in claim 4, the front end of the sensing optical cable is connected to the calibration optical fiber, characterized in that: The digital signal ratio of anti-Stokes light and Stokes light at each calibration point on the sensing optical cable at the real-time temperature The specific calculation method is as follows: Among them, α is the amplification factor, k as and k s are the coefficients of anti-Stokes light and Stokes light in the cross section of the fiber scattering end; as and λ s are the wavelengths of anti-Stokes light and Stokes light respectively; α as and α s are the loss coefficients of anti-Stokes and Stokes light in optical fiber respectively; L is the length of the sensing optical cable; h is Planck's constant; k is Boltzmann's constant; Δν is the Raman frequency shift; It is the real-time temperature of each calibration point on the sensing optical cable.

6. According to the Raman optical time domain reflectometer demodulation method for optical fiber temperature sensing in claim 1, the front end of the sensing optical cable is connected to the calibration optical fiber, characterized in that: The digital signal ratio U(T) of the anti-Stokes light and the Stokes light generated by the sensing optical cable under the real-time temperature can be expressed as: U(T)=α·R Wherein, α is the amplification factor, and R is the ratio of the anti-Stokes light to the Stokes light signal at the real-time temperature; the specific calculation method of the ratio R of the anti-Stokes light to the Stokes light signal at the real-time temperature is as follows: Among them, k as and k s are the coefficients of anti-Stokes light and Stokes light in the cross section of the fiber scattering end; as and λ s are the wavelengths of anti-Stokes light and Stokes light respectively; α as and α s are the loss coefficients of anti-Stokes and Stokes light in the optical fiber respectively; L is the length of the sensing optical cable; h is the Planck constant; k is the Boltzmann constant; Δν is the Raman frequency shift; and T is the real-time temperature.

7. According to the Raman optical time domain reflectometer demodulation method for optical fiber temperature sensing in claim 1, the front end of the sensing optical cable is connected to the calibration optical fiber, characterized in that: The temperature of the calibration optical fiber at the calibration temperature and real-time temperature T 1 It is measured by a temperature sensor. The real-time temperature T 1 The digital signal ratio U of the anti-Stokes light and Stokes light generated by the calibration fiber 1 The specific calculation method of (T) is as follows: The temperature at the calibration temperature The digital signal ratio U of the anti-Stokes light and Stokes light generated by the calibration fiber 1 The specific calculation method of (T0) is as follows: Among them, α is the amplification factor, k as and k s are the coefficients of anti-Stokes light and Stokes light in the cross section of the fiber scattering end; as and λ s are the wavelengths of anti-Stokes light and Stokes light respectively; α as and α s are the loss coefficients of anti-Stokes and Stokes light in optical fiber respectively; L 1 is the calibration fiber length; h is Planck's constant; k is Boltzmann's constant; Δν is the Raman frequency shift; is the temperature of the calibration fiber at the calibration temperature, t 1 To calibrate the real-time temperature of the optical fiber.

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