CN204612831U - Distributed optical fiber temperature sensor - Google Patents

Abstract

The utility model discloses a kind of distributed optical fiber temperature sensor, it comprises temperature-measuring optical fiber and (FBG) demodulator, (FBG) demodulator comprises pulsed laser, integrated-type optical fibre wavelength division multiplexer, Stokes ratio opto-electronic conversion amplification module, anti Stokes scattering light opto-electronic conversion amplification module, data collecting card and computing machine, integrated-type optical fibre wavelength division multiplexer is connected with pulsed laser, temperature-measuring optical fiber and two opto-electronic conversion amplification modules simultaneously, and pulsed laser, two opto-electronic conversion amplification modules and computing machine are all connected with data collecting card.The utility model has the advantages that can to solve traditional distributed fibre optic temperature sensor normal temperature temperature measurement accuracy high, and low temperature and the low problem of high-temperature measurement precision, thus the temperature measurement accuracy of superelevation can be obtained within the scope of total temperature.

Description

Distributed optical fiber temperature sensor

Technical field:

The utility model relates to temperature sensor technology field, it is high to be specifically that one can solve traditional distributed fibre optic temperature sensor normal temperature temperature measurement accuracy, and low temperature and the low problem of high-temperature measurement precision, thus obtain the distributed optical fiber temperature sensor of high temperature measurement accuracy within the scope of total temperature.

Background technology:

Southampton University of Southamptons in 1981 take the lead in proposing the concept of distributed optical fiber temperature sensor, and nineteen eighty-three develops concrete experimental provision by people such as Hartog.Within 1985, Britain Dakin has carried out the experiment of distributed optical fiber temperature sensor thermometric in laboratory, and wherein light source is ne ion laser instrument; The same year Hartog and Dakin semiconductor laser as light source, independently develop distributed optical fiber temperature sensor experimental provision.After this, distributed optical fiber temperature sensor develops rapidly, has been widely used in the aspects such as power industry, field, colliery, tunnel, highway and subway at present, has become the important means of industrial on-line monitoring.

Current distributed optical fiber temperature sensor often has high temperature measurement accuracy when normal temperature temperature range is monitored, and temperature measurement accuracy is up to ± 1 DEG C, and current minority high-precision distributed optical fiber temperature sensor temperature measurement accuracy even can reach ± 0.5 DEG C.But at low temperature and high-temperature area, distributed optical fiber temperature sensor temperature measurement accuracy then reduces rapidly, high temperature 300 DEG C of temperature measurement accuracies are low to moderate ± and 5 DEG C.The high-temperature area thermometrics such as heavy crude heat extraction down-hole thermometric, coke drum thermometric, temperatures as high 350 DEG C, current distributed optical fiber temperature sensor can not meet the demand of commercial production to monitoring temperature far away at the temperature measurement accuracy of high-temperature area, be badly in need of exploitation total temperature scope height temperature measurement accuracy distributed optical fiber temperature sensor, to meet engineer applied temperature monitoring demand.

Utility model content:

The technical problems to be solved in the utility model is, there is provided one can solve traditional distributed fibre optic temperature sensor normal temperature temperature measurement accuracy high, and low temperature and the low problem of high-temperature measurement precision, thus obtain the distributed optical fiber temperature sensor of high temperature measurement accuracy within the scope of total temperature.

The utility model relates to a kind of distributed optical fiber temperature sensor, it comprises following structure: it comprises temperature-measuring optical fiber and (FBG) demodulator, (FBG) demodulator comprises pulsed laser, integrated-type optical fibre wavelength division multiplexer, Stokes ratio opto-electronic conversion amplification module, anti Stokes scattering light opto-electronic conversion amplification module, data collecting card and computing machine, two input ports of integrated-type optical fibre wavelength division multiplexer are connected with pulsed laser and temperature-measuring optical fiber respectively, two output ports of integrated-type optical fibre wavelength division multiplexer are connected with Stokes ratio opto-electronic conversion amplification module and anti Stokes scattering light opto-electronic conversion amplification module respectively, pulsed laser, Stokes ratio opto-electronic conversion amplification module, anti Stokes scattering light opto-electronic conversion amplification module and computing machine are all connected with data collecting card.

The utility model has the advantages that: the utility model distributed optical fiber temperature sensor can according to Raman ratio and temperature in the different principle of different temperatures scope curve feature, at low temperature, normal temperature and high temperature three temperature sections, different temperature demodulation algorithms is set, thus within the scope of total temperature, obtain the temperature measurement accuracy of superelevation, thoroughly solve the problem that normal temperature section temperature measurement accuracy high and low temperature and high temperature section temperature measurement accuracy reduce rapidly.

Accompanying drawing illustrates:

Fig. 1 is the structural representation of the utility model distributed optical fiber temperature sensor;

Fig. 2 is the graph of a relation of Raman ratio and temperature.

Embodiment:

Below in conjunction with the drawings and specific embodiments, the utility model distributed optical fiber temperature sensor is described further:

As shown in Figure 1, the utility model distributed optical fiber temperature sensor is made up of temperature-measuring optical fiber 6 and (FBG) demodulator, (FBG) demodulator comprises pulsed laser 1, integrated-type optical fibre wavelength division multiplexer 2, Stokes ratio opto-electronic conversion amplification module 3, anti Stokes scattering light opto-electronic conversion amplification module 4, data collecting card 5 and computing machine 7, two input ports of integrated-type optical fibre wavelength division multiplexer 2 are connected with pulsed laser 1 and temperature-measuring optical fiber 6 respectively, two output ports of integrated-type optical fibre wavelength division multiplexer 2 are connected with Stokes ratio opto-electronic conversion amplification module 3 and anti Stokes scattering light opto-electronic conversion amplification module 4 respectively, pulsed laser 1, Stokes ratio opto-electronic conversion amplification module 3, anti Stokes scattering light opto-electronic conversion amplification module 4 and computing machine 7 are all connected with data collecting card 5.Wherein high-rate laser pulse launched by pulsed laser 1, integrated-type optical fibre wavelength division multiplexer 2 is responsible for light splitting and filtering, temperature-measuring optical fiber 6 perception and transmission temperature information, Stokes ratio opto-electronic conversion amplification module 3 and anti Stokes scattering light opto-electronic conversion amplification module 4 carry out opto-electronic conversion and signal amplifies, high-speed data acquisition card 5 carries out signals collecting in real time and adds up, and computing machine 7 carries out three demodulating algorithm solutions mediation displays temperatures.

Pulsed laser 1 in the present invention is high stability LASER Light Source, centre wavelength is 1550nm, pulse width is 10ns, peak power is 30.2W, core devices adopts the laser instrument of high stability, adopt unique APC (automated power control) and ATC (automatic temperature-adjusting control) circuit, make output power and wavelength stability high; Adopt high stable and high-precision MPU (microprocessor) system, easy to adjust, reliable.

The type of the integrated-type optical fibre wavelength division multiplexer 2 in the present invention is 1 × 3 Raman WDM1550nm/1663nm/1450nm, and fibre-optical splice is FC/APC, insertion loss 0.6dB, return loss 60dB, isolation 32dB.Integrated-type optical fibre wavelength division multiplexer 2 has four ports, 1550nm interface (the first port) is connected with pulsed laser 1, com port (the second port) is connected with temperature-measuring optical fiber 6,1663nm port (the 3rd port) is connected with the input end of Stokes ratio opto-electronic conversion amplification module 3, and 1450nm port (the 4th port) is connected with the input end of anti Stokes scattering light opto-electronic conversion amplification module 4.

The signal gain 2000 times of the Stokes ratio opto-electronic conversion amplification module 3 in the present invention and anti Stokes scattering light opto-electronic conversion amplification module 4,3db bandwidth 100MHz, the positive and negative 2.5v of output voltage amplitude, photoelectricity amplification module contains high stability APD constant temperature control circuit.

The sample frequency of high speed data collecting card 5 of the present invention is 150M, A/D resolution is 12bit, and port number has 2.

Temperature-measuring optical fiber 6 available standards optical communication in the present invention G.652 single-mode fiber, G.651 multimode optical fiber or 62.5/125 multimode optical fiber, temperature-measuring optical fiber length is 300m ~ 50km.Temperature-measuring optical fiber sense temperature can transmit temperature information again, possesses electromagnetism interference, corrosion resistance characteristic.Temperature-measuring optical fiber surface application polyimide, for a long time can be high temperature resistant 300 DEG C, short-term 350 DEG C.If measuring tempeature is higher than 350 DEG C, surface gold-plating optical fiber can be selected, but price is more expensive.

PC in the present invention is standard industrial control machine general on market.

The know-why of the utility model distributed optical fiber temperature sensor is: the laser pulse that high speed pulsed laser 1 sends high power, high injects temperature-measuring optical fiber 6, and laser pulse, in temperature-measuring optical fiber 6, spontaneous Raman scattering occurs.Laser pulse will produce anti-Stokes Raman scattered light than incident pulse laser wave length and the Stokes Raman scattered light longer than incident pulse optical maser wavelength because of spontaneous Raman scattering, wherein anti-Stokes Raman scattered light contains temperature information, and Stokes Raman scattered light is to temperature-insensitive, as reference light during demodulation temperature curve.Two bundle Raman diffused lights enter in Stokes ratio opto-electronic conversion amplification module 3 and anti Stokes scattering light opto-electronic conversion amplification module 4 respectively after integrated-type optical fibre wavelength division multiplexer 2 light splitting, carry out opto-electronic conversion and circuit amplification, gather through high-speed data acquisition card 5 again, the two paths of signals gathered after adding up utilizes three demodulating algorithms to carry out temperature demodulation, finally obtains the temperature information in region to be measured.

The know-why of temperature three demodulating algorithm that the utility model distributed optical fiber temperature sensor relates to is:

First need making one to calibrate optical fiber, calibration optical fiber used is bare fibre, can be multimode optical fiber also can be single-mode fiber.Calibration fiber lengths 500m, calibration optical fiber one end makes a standard FC/APC wire jumper head, to match with the FC/APC optical fiber output interface of high-speed pulse light source, calibration optical fiber coiling diameter is the fiber turns of 15-30cm, carries out three demodulating algorithm demarcation to facilitate to be placed in constant temperature oven.Calibration optical fiber adopts polyimide coating high-temperature resistant optical fiber, and polyimide coating high-temperature resistant optical fiber for a long time can be high temperature resistant 300 DEG C, and short-term can reach 350 DEG C, and calibration optical fiber also can be gold-plated or other high-temperature resistant optical fiber, to demarcate and thermometric within the scope of total temperature.

After calibration optical fiber is ready, by FC/APC wire jumper head access pulsed laser 1 output port of calibration optical fiber, calibration optical fiber is placed in constant temperature oven.Low temperature range-40 DEG C ~ 0 DEG C (can expand low temperature range as required), arranges a calibration point every 5 DEG C, carries out the demarcation of Cubic Curve Fitting formula; Normal temperature scope 0 DEG C ~ 120 DEG C, arranges a calibration point every 10 DEG C, carries out a curve formula and demarcates; High temperature range 120 DEG C ~ 350 DEG C (can expand high temperature range as required), arranges a calibration point every 20 DEG C, carries out the demarcation of conic fitting formula.Demarcate temperature interval to arrange according to temperature measurement accuracy demand, demarcation is counted more, and fitting formula is more accurate, but the time of corresponding demarcation cost is also more.In general, a calibration point is set every 10 DEG C and just can obtains very high temperature measurement accuracy.The Cubic Curve Fitting formula used in fitting coefficient calibration process, a curve formula and conic fitting formula are all derive by following temperature three demodulating algorithm that will elaborate, in other words, we first will draw distributed optical fiber temperature sensor demodulation formula by temperature three demodulating algorithm, then in the constant temperature oven of known temperature value, calculate corresponding scale-up factor according to these demodulation formula, recycle demodulation formula after obtaining scale-up factor and carry out temperature demodulation.Calibration optical fiber is placed in constant temperature oven to be used to carry out curve formula fitting, because use constant temperature oven, temperature so in constant temperature oven we can know, this is that we set ourselves, such as calorstat temperature is set to 20 DEG C, at this moment we run whole system, anti Stokes scattering light and Stokes ratio become electric signal by opto-electronic conversion, gather with data collecting card again, computing machine processes the two path signal that data collecting card collects, obtain the ratio of two paths of signals, we just can obtain (20 DEG C, anti-Stokes/Stokes) this point, in like manner, we can obtain (30 DEG C, anti-Stokes/Stokes), (40 DEG C, anti-Stokes/Stokes) ... a series of point of .. etc., we just can be carried out curve fitting formulae discovery by least square method like this, obtain curve equation (as once, secondary, three times) in coefficient.In low temperature range, the temperature that constant temperature oven is arranged is in low temperature range; Normal temperature scope, the temperature arranged in constant temperature oven is in normal temperature scope; High temperature range, the temperature arranged in constant temperature oven is at high temperature range.The said temperature of timing signal is exactly the temperature in constant temperature oven.The effect of constant temperature oven is used to determine the scale-up factor in formula, and after having calculated scale-up factor, the task of constant temperature oven just completes.The effect of constant temperature oven occurs in the process of sensor production.

The distributed optical fiber temperature sensor demarcated is connected with temperature-measuring optical fiber, temperature-measuring optical fiber is arranged into the region needing thermometric, uses temperature three demodulating algorithm just can carry out distributed temperature measuring.

In actual thermometric process, when the principle of temperature three demodulating algorithm is:

Laser pulse incides after in optical fiber, interacts, nonlinear scattering can occur, comprise Brillouin scattering and Raman scattering in the process propagated with optical fiber.According to quantum-mechanical viewpoint, when Raman scattering can be regarded as incident light and medium molecule interaction, photonic absorption or a transmitting phonon.The Raman Phonon frequency Δ ν=1.32 × 1023Hz of optical fiber.The photon produced is Stokes Raman scattered photon and anti-Stokes Raman scattered photon:

hν _s＝h(ν _p-Δν) 11

hν _a＝h(ν _p+Δν) 12

ν in formula 11 and formula 12 _p, ν _s, ν _abe respectively the light frequency of incident light, Stokes ratio and anti Stokes scattering light, h is Planck's constant, h=6.62606876.52x10 ^-34j.s, Δ ν are the Raman Phonon frequency of optical fiber, Δ ν=13.2THz;

When laser pulse is propagated in a fiber, get back to the top of optical fiber, the luminous flux of the Stokes Raman back-scattering light that each laser pulse produces is:

${\mathrm{\φ}}_s=K_s\·S\·{\mathrm{\ν}}_s^4\·{\mathrm{\φ}}_e\·R_s\left(T\right)\·\exp \[-({\mathrm{\α}}_0+{\mathrm{\α}}_s)\·L\]---13$

The luminous flux of anti-Stokes Raman back-scattering light:

${\mathrm{\φ}}_a=K_a\·S\·{\mathrm{\ν}}_a^4\·{\mathrm{\φ}}_e\·R_a\left(T\right)\·\exp \[-({\mathrm{\α}}_0+{\mathrm{\α}}_s)\·L\]---14$

In formula 13 and formula 14, φ _efor inciding the luminous flux of the laser pulse of optical fiber, φ _s, φ _αbe respectively stokes light luminous flux and anti-Stokes light luminous flux, K _sand K _αbe respectively the coefficient relevant with the stokes scattering of optical fiber and anti Stokes scattering cross section, S is the optical fiber backscattering factor, v _s, v _αbe respectively the frequency of stokes light and the frequency of anti-Stokes light, L is the distance that laser is propagated in a fiber, α ₀, α _s, α _αbe respectively the average transmission loss in a fiber of incident light, stokes light, anti-Stokes light, R _s(T), R _α(T) being respectively the coefficient relevant with the i on population on optical fiber molecule low-lying level and high level, is the temperature modulation function of Stokes Raman back-scattering light and anti-Stokes Raman back-scattering light.

R _S(T)＝[1-exp(-hΔv/kT)] ^-115

R _a(T)＝[exp(hΔv/kT)-1] ^-116

In formula 15 and formula 16, h is Planck (Planck) constant, h=6.62606876.52x10 ^-34j.s, Δ ν are the Raman Phonon frequency of optical fiber, and Δ ν=13.2THz, k are Boltzmann constants, k=1.380650324x10 ^-23jK-1, T are Kai Erwen absolute temperature.

The present invention Stokes Raman (Stokes ratio) signalling channel makes reference, temperature regulating is separated with Anti-Stokes (anti Stokes scattering light) and the ratio of Stokes Raman, obtain the distribution of space temperature field, derive as follows: being divided by by formula 14 and formula 13 obtains:

$\frac{{\mathrm{\φ}}_a\left(T\right)}{{\mathrm{\φ}}_s\left(T\right)}=\frac{K_a}{K_s}\·{\left(\frac{{\mathrm{\ν}}_a}{{\mathrm{\ν}}_s}\right)}^4\·\frac{R_a\left(T\right)}{R_s\left(T\right)}\·\exp \[-({\mathrm{\α}}_a-{\mathrm{\α}}_s)\·L\]---17$

According to the relation of the Raman ratio in formula 17 and temperature, the graph of a relation of Raman ratio as shown in Figure 2 and temperature can be drawn out, as can be seen from Figure 2, within the scope of 0 ~ 120 DEG C, Raman ratio is approximately a straight-line equation, this straight-line equation normal temperature section that is 0 ~ 120 DEG C of scope time, distributed optical fiber temperature sensor demodulation formula is:

$T=m\frac{I_a}{I_s}+a---9$

In formula 9, m is scale-up factor, and a is constant, I _afor the light intensity of anti-Stokes light, I _sfor the light intensity of stokes light.

I in Fig. 2 _awith I _sthe curve of ratio draws like this: temperature-measuring optical fiber is placed in constant temperature oven by we, supposes that arranging calorstat temperature is 20 DEG C, our operational outfit, obtains the light intensity I of anti-Stokes light _anumerical value and the light intensity I of stokes light _snumerical value (certainly actual obtain be electric signal), we just can obtain both ratio like this, so we just obtain (20 DEG C, anti-Stokes/Stokes), in like manner we also can obtain (21 DEG C, anti-Stokes/Stokes), we repeat such process in whole temperature range, just can draw out I in Fig. 2 _awith I _sthe curve of ratio, namely horizontal ordinate is ratio, and ordinate is temperature.I _awith I _sthe formula of ratio be theoretical formula, it is infeasible for carrying out that actual temperature calculates with this, because a lot of parameter of this formula cannot obtain.So during actual computation temperature, we are the methods adopting curve, I _awith I _sthe effect of curve of ratio be to illustrate that what kind of curve Raman ratio and temperature are under actual conditions, if matched curve and this coincide, just illustrating that matched curve is feasible, is right.

Single demodulating algorithm is exactly that laser pulse injects from one end of optical fiber, then a long way off end injection, the two paths of signals ratio that scattering is returned only carrys out demodulation with formula 9.But in temperature lower than 0 DEG C with higher than 120 DEG C of these two low temperature and high-temperature areas, the pass of Raman ratio and temperature is non-linear, obviously can find out that a curve-fitting results and actual temperature have very large deviation, if at this moment also only separate temperature regulating with a curve formula, demodulation temperature value is out compared with actual temperature value must larger deviation.As can be seen from Figure 2, when temperature is lower than 0 DEG C, the relation object of Raman ratio and temperature is similar to a cubic curve, and when temperature is higher than 120 DEG C, the relation object of Raman ratio and temperature is similar to a para-curve.

Three demodulating algorithm distributed optical fiber temperature sensors are exactly that arranging demodulating algorithm at low temperature, normal temperature and high temperature is respectively the demodulation of Cubic Curve Fitting formula, the demodulation of a curve Formula Solution mediation conic fitting formula according to Raman ratio and temperature in the different principle of different temperatures interval curve feature.

When low-temperature zone and temperature are lower than 0 DEG C of scope, distributed optical fiber temperature sensor demodulation formula is:

$T=k_1{\left(\frac{I_a}{I_s}\right)}^3+k_2{\left(\frac{I_a}{I_s}\right)}^2+k_3\frac{I_a}{I_s}+k_0---8$

In formula 8, k ₁for cubic term scale-up factor, k ₂for quadratic term scale-up factor, k ₃for once item scale-up factor, k _ofor constant, I _afor the light intensity of anti-Stokes light, I _sfor the light intensity of stokes light;

When high temperature section and temperature are higher than 120 DEG C of scopes, distributed optical fiber temperature sensor demodulation formula is:

$T=n_2{\left(\frac{I_a}{I_s}\right)}^2+n_1\frac{I_a}{I_s}+n_0---10$

In formula 10, n ₂for quadratic term scale-up factor, n ₁for once item scale-up factor, n ₀for constant, I _afor the light intensity of anti-Stokes light, I _sfor the light intensity of stokes light.

Calibration optical fiber is connected with pulsed laser 1 by three demodulating algorithm timing signals, is then placed in constant temperature oven by calibration optical fiber, wherein, when low temperature range-40 DEG C ~ 0 DEG C, arranges a calibration point, utilize formula every 5 DEG C

$T=k_1{\left(\frac{I_a}{I_s}\right)}^3+k_2{\left(\frac{I_a}{I_s}\right)}^2+k_3\frac{I_a}{I_s}+k_0---8$

Carry out the demarcation of Cubic Curve Fitting formula, calculate cubic term scale-up factor k ₁, quadratic term scale-up factor k ₂, once item scale-up factor k ₃and constant k ₀;

When normal temperature scope 0 DEG C ~ 120 DEG C, a calibration point is set every 10 DEG C, utilizes formula

$T=m\frac{I_a}{I_s}+a---9$

Carry out a curve formula to demarcate, calculate scale-up factor m, constant a;

When high temperature range 120 DEG C ~ 350 DEG C, a calibration point is set every 20 DEG C, utilizes formula

$T=n_2{\left(\frac{I_a}{I_s}\right)}^2+n_1\frac{I_a}{I_s}+n_0---10$

Carry out the demarcation of conic fitting formula, calculate quadratic term scale-up factor n ₂, once item scale-up factor n ₁, constant n ₀.

During actual thermometric, the data after data collecting card 5 collection is cumulative are first by a curve formula

$T=m\frac{I_a}{I_s}+a---9$

Pointwise calculates one by one,

If the temperature value 1. obtained is between 0 ~ 120 DEG C, then the temperature value of this point directly shows on the graphical interfaces of computing machine 17, and as final end value;

If certain the some temperature value 2. obtained is lower than 0 DEG C, then this collection corresponding to point add up after raw data again transfer to Cubic Curve Fitting formula

$T=k_1{\left(\frac{I_a}{I_s}\right)}^3+k_2{\left(\frac{I_a}{I_s}\right)}^2+k_3\frac{I_a}{I_s}+k_0---8$

Calculate, the temperature value after calculating directly shows on the graphical interfaces of computing machine 17, and as final end value;

If the temperature value 3. obtained is higher than 120 DEG C, then this collection corresponding to point add up after raw data again transfer to conic fitting formula

$T=n_2{\left(\frac{I_a}{I_s}\right)}^2+n_1\frac{I_a}{I_s}+n_0---10$

Calculate, the temperature value after calculating directly shows on the graphical interfaces of computing machine 17, and as final end value;

Value a little all calculate complete and graphical interfaces display after, whole temperature demodulation process terminates.

Above-described embodiment is only be described preferred implementation of the present utility model; not scope of the present utility model is limited; under the prerequisite not departing from the utility model design spirit; the various distortion that those of ordinary skill in the art make the technical solution of the utility model and improvement, all should fall in protection domain that the utility model claims determine.

Claims (1)

1. a distributed optical fiber temperature sensor, it comprises temperature-measuring optical fiber (6) and (FBG) demodulator, (FBG) demodulator comprises pulsed laser (1), integrated-type optical fibre wavelength division multiplexer (2), Stokes ratio opto-electronic conversion amplification module (3), anti Stokes scattering light opto-electronic conversion amplification module (4), data collecting card (5) and computing machine (7), two input ports of described integrated-type optical fibre wavelength division multiplexer (2) are connected with pulsed laser (1) and temperature-measuring optical fiber (6) respectively, two output ports of described integrated-type optical fibre wavelength division multiplexer (2) are connected with Stokes ratio opto-electronic conversion amplification module (3) and anti Stokes scattering light opto-electronic conversion amplification module (4) respectively, described pulsed laser (1), Stokes ratio opto-electronic conversion amplification module (3), anti Stokes scattering light opto-electronic conversion amplification module (4) and computing machine (7) are all connected with data collecting card (5).