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CN111751020A - Method and system for realizing long-distance calibration-free temperature measurement by utilizing bidirectional Raman scattering signals - Google Patents

Method and system for realizing long-distance calibration-free temperature measurement by utilizing bidirectional Raman scattering signals Download PDF

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CN111751020A
CN111751020A CN202010610882.9A CN202010610882A CN111751020A CN 111751020 A CN111751020 A CN 111751020A CN 202010610882 A CN202010610882 A CN 202010610882A CN 111751020 A CN111751020 A CN 111751020A
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optical fiber
raman
demodulation instrument
fiber raman
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邓屹
李海瑜
马世业
徐进东
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Cpi Electric Power Engineering Co ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
    • G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
    • G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
    • G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
    • G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
    • G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
    • G01D5/35354—Sensor working in reflection
    • G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
    • G01D5/35364—Sensor working in reflection using backscattering to detect the measured quantity using inelastic backscattering to detect the measured quantity, e.g. using Brillouin or Raman backscattering

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Abstract

The invention provides a method for realizing long-distance calibration-free temperature measurement by using a bidirectional Raman scattering signal. The invention also provides a system for realizing long-distance calibration-free temperature measurement by using the bidirectional Raman scattering signal, which is characterized in that an optical fiber Raman demodulation instrument DTS-1 and an optical fiber Raman demodulation instrument DTS-2 are respectively placed at two ends of the optical cable to be measured, and the temperature T of the optical cable to be measured is obtained by solving by using the method. The invention increases the measuring distance. Meanwhile, because the same optical cable has the loss condition completely consistent with the distribution of the temperature field, the measurement of the two instruments is processed by an algorithm, the loss coefficient is eliminated, and the calibration-free temperature measurement is realized.

Description

Method and system for realizing long-distance calibration-free temperature measurement by utilizing bidirectional Raman scattering signals
Technical Field
The invention relates to the field of optical fiber sensing, in particular to a method for realizing long-distance temperature measurement by using an optical fiber Raman scattering signal and a system adopting the method.
Background
The distributed optical fiber Raman temperature sensing system is used for measuring temperature by utilizing a Raman scattering phenomenon in optical fiber, specifically, incident light pulses can generate 1450nm anti-Stokes Raman scattered light and 1660nm Stokes Raman scattered light, and the anti-Stokes light is sensitive to ambient temperature change and can be used for detecting ambient temperature change.
In recent years, the application range of the distributed fiber raman sensing system is wider and wider, but some problems are exposed along with the application range. Including the detection distance is difficult further to increase, because the stimulated raman scattering needs to be avoided in the raman temperature measurement, consequently can't prolong the measurement distance through the mode that promotes optical power. In addition, the raman temperature measurement is performed by comparing the intensity changes of the anti-stokes scattered light and the stokes raman scattered light, and different optical cables, even the same optical cable, have different loss characteristics under different arrangement conditions, so the distributed optical fiber raman sensing system needs to perform loss measurement and temperature calibration on the optical cable to be measured before measurement.
The distributed optical fiber raman sensing system cannot use the common raman online amplification technology for communication, and simultaneously, the stimulated raman scattering can be caused by the excessively high optical power, even if the technologies such as coding pulses are adopted, for example: patent CN201310177011.2 and CN201510626442.1, etc., currently the maximum measurement distance is commonly determined to be 30 km. The coded pulses can make the light source control and demodulation more difficult.
In order to realize calibration-free distributed fiber raman sensing systems, a dual light source method (as shown in fig. 1) or a measurement method of a loop circuit (as shown in fig. 2) is generally adopted. The former requires a separation of the wavelengths of the two lasers equal to the raman stokes wavelength (i.e., 100 nm). The latter connects the two ends of the optical cable to be measured to two channels of the same optical fiber Raman demodulation instrument, so that the measurement distance is reduced by half.
The methods only aim at partial problems and cannot solve both long distance and calibration-free.
Disclosure of Invention
The purpose of the invention is: and the optical fiber Raman scattering signal is utilized to realize the calibration-free temperature measurement of the optical cable in a long distance.
In order to achieve the above object, the technical solution of the present invention is to provide a method for realizing long-distance calibration-free temperature measurement by using a bidirectional raman scattering signal, which is characterized by comprising the following steps:
step 1, respectively placing an optical fiber Raman demodulation instrument at each of two ends of an optical cable to be detected, wherein the optical fiber Raman demodulation instruments are respectively an optical fiber Raman demodulation instrument DTS-1 and an optical fiber Raman demodulation instrument DTS-2, and the optical fiber Raman demodulation instruments comprise: the optical fiber Raman demodulation instrument DTS-1 receives a backward Raman scattering signal of a self-transmitted pulse and also receives a forward Raman scattering signal of a transmitted pulse of the optical fiber Raman demodulation instrument DTS-2; the optical fiber Raman demodulation instrument DTS-2 receives a backward Raman scattering signal of a self-transmitted pulse and also receives a forward Raman scattering signal of a transmitted pulse of the optical fiber Raman demodulation instrument DTS-1;
for the fiber Raman demodulation instrument DTS-1, there are:
Figure BDA0002562078690000021
Figure BDA0002562078690000022
for the fiber raman demodulation instrument DTS-2, there are:
Figure BDA0002562078690000023
Figure BDA0002562078690000024
the temperature conversion formula of the fiber Raman demodulation instrument is as follows:
Figure BDA0002562078690000025
in formulae (1) to (5), CTCoefficient of temperature sensitivity α0、αsAnd αasLoss coefficients for incident light, stokes and anti-stokes light, respectively; kasAnd KsBoltzmann factors of anti-stokes and stokes scattered light, respectively, related to the number of arrangements of molecular energy levels ηasAnd ηsRespectively, anti-stokesAnd a scattering cross-sectional coefficient of stokes scattered light; the temperature T is the solution quantity to be solved;
Figure BDA0002562078690000026
respectively the Stokes light intensity signals from the optical fiber Raman demodulation instrument DTS-1 and the optical fiber Raman demodulation instrument DTS-2;
Figure BDA0002562078690000027
respectively are anti-stokes light intensity signals from an optical fiber Raman demodulation instrument DTS-1 and an optical fiber Raman demodulation instrument DTS-2;
Figure BDA0002562078690000028
respectively the initial light intensity signals from the optical fiber Raman demodulation instrument DTS-1 and the optical fiber Raman demodulation instrument DTS-2; z is the distance between the position with the temperature measuring point and the DTS-1, and L is the total length of the optical cable to be measured;
and 2, demodulating the temperature according to the formula (5) to obtain:
Figure BDA0002562078690000029
in the formula (6), the reaction mixture is,
Figure BDA00025620786900000210
Figure BDA0002562078690000031
Figure BDA0002562078690000032
then there are:
Figure BDA0002562078690000033
and 4, solving by using a formula (9) to obtain the temperature T.
The invention provides a system for realizing long-distance calibration-free temperature measurement by utilizing a bidirectional Raman scattering signal, which is characterized by comprising an optical fiber Raman demodulation instrument DTS-1 and an optical fiber Raman demodulation instrument DTS-2, wherein the optical fiber Raman demodulation instrument DTS-1 and the optical fiber Raman demodulation instrument DTS-2 are respectively placed at two ends of an optical cable to be measured, and the optical fiber Raman demodulation instrument DTS-1 receives a forward Raman scattering signal of a pulse transmitted by the optical fiber Raman demodulation instrument DTS-2 while receiving a backward Raman scattering signal of the pulse transmitted by the optical fiber Raman demodulation instrument DTS-1; the optical fiber Raman demodulation instrument DTS-2 receives backward Raman scattering signals of self-transmitted pulses and also receives forward Raman scattering signals of the transmitted pulses of the optical fiber Raman demodulation instrument DTS-1, and the temperature T of the optical cable to be measured is obtained by solving through the method.
The invention has the following beneficial effects: the long-distance calibration-free distributed optical fiber temperature measurement system is formed by respectively placing an optical fiber Raman demodulation instrument at each of two ends of the optical cable to be measured, and the measurement distance is increased by utilizing two scattered lights, namely a forward scattered light and a backward scattered light. Meanwhile, because the same optical cable has the loss condition completely consistent with the distribution of the temperature field, the measurement of the two instruments is processed by an algorithm, the loss coefficient is eliminated, and the calibration-free temperature measurement is realized.
Drawings
FIG. 1 is a schematic diagram of a dual-light source fiber grating sensor monitoring network, in which λ isPIs the incident pulse wavelength, λ, of the first light sourceasIs the anti-Stokes wavelength, λ, of the first light sourceP2Is the incident pulse wavelength, λ, of the second light sources2The stokes wavelength of the second light source.
FIG. 2 is a schematic diagram of a measurement method for a loop circuit;
fig. 3 is a long-distance calibration-free distributed optical fiber temperature measurement system, namely, an optical fiber raman demodulation instrument is respectively arranged at two ends of an optical cable to be measured.
Detailed Description
The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Further, it should be understood that various changes or modifications of the present invention may be made by those skilled in the art after reading the teaching of the present invention, and such equivalents may fall within the scope of the present invention as defined in the appended claims.
As shown in fig. 3, the method for realizing long-distance calibration-free temperature measurement by using a bidirectional raman scattering signal provided by the present invention comprises the following steps:
step 1, respectively placing an optical fiber Raman demodulation instrument at each of two ends of an optical cable to be detected, wherein the optical fiber Raman demodulation instruments are respectively an optical fiber Raman demodulation instrument DTS-1 and an optical fiber Raman demodulation instrument DTS-2, and the optical fiber Raman demodulation instruments comprise: the optical fiber Raman demodulation instrument DTS-1 receives a backward Raman scattering signal of a self-transmitted pulse and also receives a forward Raman scattering signal of a transmitted pulse of the optical fiber Raman demodulation instrument DTS-2; the optical fiber Raman demodulation instrument DTS-2 receives the backward Raman scattering signal of the self-transmitted pulse and also receives the forward Raman scattering signal of the transmitted pulse of the optical fiber Raman demodulation instrument DTS-1.
For the fiber Raman demodulation instrument DTS-1, there are:
Figure BDA0002562078690000041
Figure BDA0002562078690000042
for the fiber raman demodulation instrument DTS-2, there are:
Figure BDA0002562078690000043
Figure BDA0002562078690000044
the temperature conversion formula of the fiber Raman demodulation instrument is as follows:
Figure BDA0002562078690000045
in formulae (1) to (5), CTCoefficient of temperature sensitivity α0、αsAnd αasLoss coefficients for incident light, stokes and anti-stokes light, respectively; kasAnd KsBoltzmann factors of anti-stokes and stokes scattered light, respectively, related to the number of arrangements of molecular energy levels ηasAnd ηsScattering cross-sectional coefficients for anti-stokes and stokes scattered light, respectively; the temperature T is the solution quantity to be solved;
Figure BDA0002562078690000046
respectively the Stokes light intensity signals from the optical fiber Raman demodulation instrument DTS-1 and the optical fiber Raman demodulation instrument DTS-2;
Figure BDA0002562078690000047
respectively are anti-stokes light intensity signals from an optical fiber Raman demodulation instrument DTS-1 and an optical fiber Raman demodulation instrument DTS-2;
Figure BDA0002562078690000048
respectively the initial light intensity signals from the optical fiber Raman demodulation instrument DTS-1 and the optical fiber Raman demodulation instrument DTS-2; z is the distance between the position with the temperature measuring point and the DTS-1, and L is the total length of the optical cable to be measured;
for the traditional single distributed optical fiber temperature measurement method, taking only the optical fiber Raman demodulation instrument DTS-1 as an example, the method can be obtained by the following formula (5):
Figure BDA0002562078690000051
taking the logarithm of both sides of equation (6) can solve for temperature T, but it can be seen that α thereinsAnd αasThe value of (a) is related to the cable and even has an influence on different laying conditions in the same cable. So field loss calibration of the cable must be performed. In addition, only the backscatter signal is utilized in equation (6).
In the invention, two distributed optical fiber thermometers are placed at two ends of the same optical cable to be measured, and the following steps are adopted:
step 2, temperature demodulation is carried out according to the formula (5) to obtain:
Figure BDA0002562078690000052
in the formula (7), the reaction mixture is,
Figure BDA0002562078690000053
Figure BDA0002562078690000054
the merging of the pair formula (8) is simplified
Figure BDA0002562078690000055
The same can be obtained:
Figure BDA0002562078690000056
then there are:
Figure BDA0002562078690000057
comparing equation (6) and equation (11), it can be seen that the loss coefficients in equation (11) are offset by the coefficient ratio, and the forward scattered light intensity is increased in the signal. The invention can measure farther distance without need of field calibration of optical cable.
And 3, solving by using a formula (11) to obtain the temperature T.
Compared with the traditional mode that only backward Raman scattering signals are utilized, the method makes full use of the forward Raman scattering signals and the backward Raman scattering signals, and can effectively improve the measurement distance. In addition, according to the comparison between the formula (6) and the formula (11), the temperature demodulation of the conventional optical fiber temperature measurement system is related to the stokes attenuation and the anti-stokes attenuation, so that different optical cables, even different laying conditions in the same optical cable, have influence on the loss, which is a direct reason that the field loss calibration of the optical cable needs to be performed by the conventional method. The invention provides a method for uniformly processing the results of two optical fiber Raman demodulation instruments, as shown in formula (11), the loss factor of the optical cable can be eliminated, and therefore, the field calibration is not needed. Thereby realizing the dual purposes of long-distance measurement and calibration-free.

Claims (2)

1. A method for realizing long-distance calibration-free temperature measurement by using a bidirectional Raman scattering signal is characterized by comprising the following steps:
step 1, respectively placing an optical fiber Raman demodulation instrument at each of two ends of an optical cable to be detected, wherein the optical fiber Raman demodulation instruments are respectively an optical fiber Raman demodulation instrument DTS-1 and an optical fiber Raman demodulation instrument DTS-2, and the optical fiber Raman demodulation instruments comprise: the optical fiber Raman demodulation instrument DTS-1 receives a backward Raman scattering signal of a self-transmitted pulse and also receives a forward Raman scattering signal of a transmitted pulse of the optical fiber Raman demodulation instrument DTS-2; the optical fiber Raman demodulation instrument DTS-2 receives a backward Raman scattering signal of a self-transmitted pulse and also receives a forward Raman scattering signal of a transmitted pulse of the optical fiber Raman demodulation instrument DTS-1;
for the fiber Raman demodulation instrument DTS-1, there are:
Figure FDA0002562078680000011
Figure FDA0002562078680000012
for the fiber raman demodulation instrument DTS-2, there are:
Figure FDA0002562078680000013
Figure FDA0002562078680000014
the temperature conversion formula of the fiber Raman demodulation instrument is as follows:
Figure FDA0002562078680000015
in formulae (1) to (5), CTCoefficient of temperature sensitivity α0、αsAnd αasLoss coefficients for incident light, stokes and anti-stokes light, respectively; kasAnd KsBoltzmann factors of anti-stokes and stokes scattered light, respectively, related to the number of arrangements of molecular energy levels ηasAnd ηasScattering cross-sectional coefficients for anti-stokes and stokes scattered light, respectively; the temperature T is the solution quantity to be solved;
Figure FDA0002562078680000016
respectively the Stokes light intensity signals from the optical fiber Raman demodulation instrument DTS-1 and the optical fiber Raman demodulation instrument DTS-2;
Figure FDA0002562078680000017
respectively are anti-stokes light intensity signals from an optical fiber Raman demodulation instrument DTS-1 and an optical fiber Raman demodulation instrument DTS-2;
Figure FDA0002562078680000018
respectively the initial light intensity signals from the optical fiber Raman demodulation instrument DTS-1 and the optical fiber Raman demodulation instrument DTS-2; z is the distance between the position with the temperature measuring point and the DTS-1, and L is the total length of the optical cable to be measured;
and 2, demodulating the temperature according to the formula (5) to obtain:
Figure FDA0002562078680000021
in the formula (6), the reaction mixture is,
Figure FDA0002562078680000022
Figure FDA0002562078680000023
Figure FDA0002562078680000024
then there are:
Figure FDA0002562078680000025
and 4, solving by using a formula (9) to obtain the temperature T.
2. A system for realizing long-distance calibration-free temperature measurement by utilizing a bidirectional Raman scattering signal is characterized by comprising an optical fiber Raman demodulation instrument DTS-1 and an optical fiber Raman demodulation instrument DTS-2, wherein the optical fiber Raman demodulation instrument DTS-1 and the optical fiber Raman demodulation instrument DTS-2 are respectively placed at two ends of an optical cable to be measured, and the optical fiber Raman demodulation instrument DTS-1 receives a backward Raman scattering signal of a pulse transmitted by the optical fiber Raman demodulation instrument DTS-2 and also receives a forward Raman scattering signal of the pulse transmitted by the optical fiber Raman demodulation instrument DTS-2; the optical fiber Raman demodulation instrument DTS-2 receives a backward Raman scattering signal of a self-emission pulse and also receives a forward Raman scattering signal of an emission pulse of the optical fiber Raman demodulation instrument DTS-1, and the temperature T of the optical cable to be measured is obtained by solving according to the method in claim 1.
CN202010610882.9A 2020-06-30 2020-06-30 Method and system for realizing long-distance calibration-free temperature measurement by utilizing bidirectional Raman scattering signals Pending CN111751020A (en)

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