CN102607737A - Device for monitoring temperature of oil tank by FBG (Fiber Bragg Grating) - Google Patents

Abstract

The invention relates to a device for monitoring the temperature of an oil tank by FBGs (Fiber Bragg Grating) and belongs to the technical field of FBG detection. The device comprises an ABE (Amplified Spontaneous Emission) light source, a spectrum demodulation instrument, a computer and the like and is characterized in that the ASE light source is connected with the input end of a 3db coupler by an optical fiber; one output end of the 3db coupler is connected onto an optical switch by an optical fiber; the output end of the optical switch is connected with a splitter by an optical cable; the output end of the splitter is connected with a plurality of FBGs by optical cables; the other output end of the 3db coupler is connected onto the spectrum demodulation instrument by an optical fiber; the spectrum demodulation instrument is connected with the computer; and the computer is connected with an alarm. According to the device disclosed by the invention, the temperature calibration is firstly carried out and then the temperature of the oil tank is timely monitored; and the device has the advantages of rapidness, accuracy, sensitivity, safety and stability for measuring and capability of simultaneously measuring the oil temperature and the oil gas temperature by the computer and can replace an original complex measurement instrument easy to influence by external factors, so that the cost is reduced.

Description

Carry out device for monitoring with optical fiber grating pair oil tank temperature

Technical field

The present invention relates to a kind ofly carry out device for monitoring, belong to fiber grating detection technique field with optical fiber grating pair oil tank temperature.

Background technology

Can reflect this critical nature of light of specific wavelength according to fiber grating; Fiber grating can reflect the light of different wave length under conditions such as different temperature, medium, utilize this character of fiber grating fiber grating as the sensor-based systems such as temperature of sensor be widely used with productive life in numerous areas.Petroleum products is between the storage life, because oil plant has thermal expansivity, along with the rising of temperature; Oil plant volume in the oil tank is with expanded by heating, and crude oil must have certain storage time in the storage tank of oil depot, deposit the growth of time along with jar; Crude oil temperature will descend gradually, and its temperature never allows to be lower than certain numerical value (being generally 29 ℃), otherwise will cause serious accidents such as coagulating jar; Crude oil accumulating work can't normally be carried out, and its consequence will be very serious.So guarantee oil tank operation not only safety but also economy, must the correct oil storage temperature of confirming oil tank.(necessity of air themperature in the test oil tank)

Therefore it is significant to seek quick, accurate, sensitive, safe measurement oil tank method of temperature.The system that is applied to Measurement of Oil-tank Temperature at present relies on platinum resistance sensor to measure the oil temperature more, complex equipments, and sensitivity is lower; It is bigger influenced by extraneous factor; Like the patent No. is 200920251207.0, and the utility model name is called the patent of " oil tank thermometer ", promptly is this kind situation.

Summary of the invention

In order to overcome the shortcomings and deficiencies that prior art exists, the present invention proposes and a kind ofly carry out device for monitoring with optical fiber grating pair oil tank temperature, be intended to make things convenient for, measurement accurately, replace original surveying instrument, thereby reduce cost.

Technical scheme of the present invention is following:

A kind ofly carry out device for monitoring with optical fiber grating pair oil tank temperature; Comprise ASE light source, 3db coupling mechanism, photoswitch, spectrum (FBG) demodulator, computing machine, shunt, optical cable, fiber grating; It is characterized in that the ASE light source is connected through the input end of optical fiber with the 3db coupling mechanism; The output terminal of 3db coupling mechanism is connected on the photoswitch by optical fiber, and the output terminal of photoswitch is connected with shunt through optical cable, and the shunt output terminal is connected with the multi-channel optical fibre grating through optical cable; Another output terminal of 3db coupling mechanism is connected on the spectrum (FBG) demodulator by optical fiber, and the spectrum (FBG) demodulator is connected with computing machine; Computing machine is connected with alarm.

Described fiber grating is a 0.4nm bandwidth Fiber Bragg Grating FBG (FBG), and the way of fiber grating is the 8-64 road, and each oil tank is provided with fiber grating monitoring point, 2-4 road.Monitor the temperature of each tested oil tank simultaneously by the switching of the photoswitch in the device.

Every road fiber grating is inequality with the foveal reflex wavelength of other fiber grating in the described multi-channel optical fibre grating.

Above-mentioned ASE light source is meant C-band amplified spontaneous emission light source.Light source body partly is gain media Er-doped fiber and high performance pump laser.

Above-mentioned FBG is the abbreviation of Fiber Bragg Grating, i.e. Fiber Bragg Grating FBG.

The light that the ASE light source sends in apparatus of the present invention arrives fiber grating through the transmission of 3db coupling mechanism, photoswitch and optical cable, earlier fiber grating vertically is fixed in the tested oil tank.The catoptrical optical wavelength of FBG satisfies: λ _g=2n _EffΛ, wherein n _EffThe effective refractive index of expression FBG, Λ representes the natural period of FBG.Multichannel FBG should select to have different parameters, intersects so that on reflectance spectrum, evenly distribute not have, and is easy to read.Reflected light is back to Wavelength demodulation system through same paths, obtains catoptrical luminous power spectrum on computers.Because when fiber grating was in the different medium, the spectrum summit in the reflectance spectrum was split into two adjacent peaks, wherein bimodal middle corresponding short wavelength's peak value one is designated as P ₁, long wavelength's peak value two is designated as P ₂, corresponding wavelength is for Wei not λ ₁With λ ₂Wavelength X ₁Luminous power P ₁, wavelength X ₂Luminous power P ₂Draw by the wavelength demodulation device demodulation, and be input to computing machine and read by in fact the time.

The wavelength coverage broad of ASE light source in apparatus of the present invention; Spectral shape, power are comparatively stable; And the light of reflected back has less spectrum width when FBG is in the different medium; So can utilize a plurality of FBG distribution measuring in same oil tank, thereby the reliability, the diversity that increase data are utilized data in the different oil tanks of photoswitch handover measurement, increase the capacity of monitoring.

The principle that apparatus of the present invention are monitored the oil tank temperature is following: when temperature variation, can make the effective refractive index of fiber grating and the variation of pitch, thereby cause the drift to the fiber grating bragg wavelength.By the fiber grating bragg wavelengths _gExpression formula λ _g=2n _EfffΛ knows, λ _gFormula with temperature T changes is following:

: $\frac{\∂{\mathrm{\λ}}_g}{\∂T}=2[\frac{\∂n_{\mathrm{Efff}}}{\∂T}\mathrm{\Λ}+n_{\mathrm{Efff}}\frac{\∂\mathrm{\Λ}}{\∂T}]$

That is: $d{\mathrm{\λ}}_g=2[\mathrm{\Λ}\frac{\∂n_{\mathrm{Efff}}}{\∂T}\mathrm{DT}+n_{\mathrm{Efff}}\frac{\∂\mathrm{\Λ}}{\∂T}\mathrm{DT}]$

So have: Δ λ _g=2 (Λ Δ n _Efff+ n _EfffΔ Λ) (1)

Wherein, Δ n _EfffBe the variation that the fiber grating effective refractive index produces with variation of temperature, Δ Λ is the variation that the change of fiber grating pitch Yin Wendu produces, and

Δ n _Efff=ζ Δ Tn _Efff(ζ is a thermo-optical coeffecient)

Δ Λ=α Δ T Λ (α is a thermal expansivity)

Two formulas are brought in above-mentioned (1) formula:

Δλ _g＝2(ΛζΔTn _efff+n _efffαΔTΛ)＝2n _efffΛ(ζ+α)ΔT (2)

The α because α much smaller than ζ, can neglect is by λ _g=2n _EfffΛ and (2) formula can obtain Δ λ _g=λ _gζ Δ T,

Change Δ T during by the visible temperature change of following formula and can cause bragg reflection wavelength λ _gDrift be Δ λ _g, the drift delta λ of variation of temperature value Δ T and bragg reflection wavelength _gBe directly proportional, promptly temperature raises, and the reflected light wavelength is elongated.

Utilize said apparatus to carry out the method for temperature monitoring, step is following:

1, the Temperature Scaling of fiber grating

Device is connected, thermometric is placed in the thermostat with fiber grating, change the temperature in the thermostat, by the temperature characteristics T of fiber grating ₀-λ ₀Measurement is also determined the centre wavelength of fiber grating and the one-to-one relationship between the temperature, is got off by computer recording; According to the oily temperature numerical value of the safety of oil tank, confirm the range of drift of the centre wavelength of fiber grating, setting safety oil temperature is T _Min-T _Max, the centre wavelength of corresponding fiber grating is λ _Min-λ _MaxEvery thermometric is repeated above-mentioned calibration process with fiber grating, accomplished the Temperature Scaling of whole device thermometric with fiber grating;

2, monitoring device is to the temperature monitoring of oil tank

Fiber grating after the calibration is contained on the inwall of tested oil tank; Connect monitoring device; The ASE light source arrives fiber grating through the transmission of coupling mechanism, photoswitch, shunt and optical cable, and the light of fiber grating reflected back shows the form of reflectance spectrum with two-dimensional coordinate through same paths reflected back wavelength (FBG) demodulator; Draw out every thermometric after fetching data by computer-readable with the two-dimentional oscillogram of the centre wavelength-time of fiber grating, demonstrate corresponding temperature value through fitting formula;

3, the overload alarm of monitor temperature

The temperature that monitoring device detects tested oil tank is lower than T _MinPerhaps be higher than T _MaxThe time, report to the police through the alarm that is connected with computing machine, pointing out a certain oil tank temperature over-range, thereby get rid of potential safety hazard.

Apparatus of the present invention have measure fast, accurately, sensitive, safety, stable, and can measure the advantage of oily temperature and oil gas temperature simultaneously, can replace original complicacy, be subject to the surveying instrument of extraneous factor influence, thereby reduced cost.

Description of drawings

Fig. 1 is the structural representation of apparatus of the present invention:

Wherein: 1-ASE light source, 2-3db coupling mechanism, 3-photoswitch, 4-spectrum (FBG) demodulator, 5-computing machine, 6-shunt, 7-optical cable, 8-fiber grating (each fiber grating has different centre wavelength), 9-optical cable, 10-alarm.

Embodiment

Below in conjunction with accompanying drawing and embodiment the present invention is described further, but is not limited thereto.

Embodiment 1:

The embodiment of the invention 1 is as shown in Figure 1; A kind ofly carry out device for monitoring with optical fiber grating pair oil tank temperature; Comprise ASE light source 1,3db coupling mechanism 2, photoswitch 3, spectrum (FBG) demodulator 4, computing machine 5, shunt 6, fiber grating 8; It is characterized in that ASE light source 1 is connected through the input end of optical fiber with 3db coupling mechanism 2; The output terminal of 3db coupling mechanism 2 is connected on the photoswitch 3 by optical fiber, and the output terminal of photoswitch 3 is connected with shunt 6 through optical cable, and shunt 6 output terminals are connected with multi-channel optical fibre grating 8 through optical cable 7; Another output terminal of 3db coupling mechanism 2 is connected on the spectrum (FBG) demodulator 4 by optical fiber, and spectrum (FBG) demodulator 4 is connected with computing machine 5; Computing machine 5 is connected with alarm 10.

Described fiber grating 8 is 0.4nm bandwidth Fiber Bragg Grating FBGs (FBG), and the way of fiber grating is 16 the tunnel, and each oil tank is provided with 2 road fiber grating monitoring points, monitors the temperature of 8 tested oil tanks simultaneously by the switching of the photoswitch 3 in the device.

Every road fiber grating 8 is inequality with the foveal reflex wavelength of other fiber grating in the described multi-channel optical fibre grating.

Embodiment 2:

Identical with embodiment 1, just the way of fiber grating is 64 the tunnel, and each oil tank is provided with 4 road fiber grating monitoring points, monitors 16 oil tanks simultaneously by the switching of photoswitch 3.

Embodiment 3:

Utilize said apparatus to carry out the method for temperature monitoring, step is following:

1, the Temperature Scaling of fiber grating

Device is connected, thermometric is placed in the thermostat with fiber grating, change the temperature in the thermostat, by the temperature characteristics T of fiber grating ₀-λ ₀Measurement is also determined the centre wavelength of fiber grating and the one-to-one relationship between the temperature, is got off by computer recording; According to the oily temperature numerical value of the safety of oil tank, confirm the range of drift of the centre wavelength of fiber grating, setting safety oil temperature is T _Min-T _Max, the centre wavelength of corresponding fiber grating is λ _Min-λ _MaxEvery thermometric is repeated above-mentioned calibration process with fiber grating, accomplished the Temperature Scaling of whole device thermometric with fiber grating;

2, monitoring device is to the temperature monitoring of oil tank

Fiber grating after the calibration is contained on the inwall of tested oil tank; Connect monitoring device; The ASE light source arrives fiber grating through the transmission of coupling mechanism, photoswitch, shunt and optical cable, and the light of fiber grating reflected back shows the form of reflectance spectrum with two-dimensional coordinate through same paths reflected back wavelength (FBG) demodulator; Draw out every thermometric after fetching data by computer-readable with the two-dimentional oscillogram of the centre wavelength-time of fiber grating, demonstrate corresponding temperature value through fitting formula;

3, the overload alarm of monitor temperature

The temperature that monitoring device detects tested oil tank is lower than T _MinPerhaps be higher than T _MaxThe time, report to the police through the alarm that is connected with computing machine, pointing out a certain oil tank temperature over-range, thereby get rid of potential safety hazard.

Claims (4)

1. one kind is carried out device for monitoring with optical fiber grating pair oil tank temperature; Comprise ASE light source, 3db coupling mechanism, photoswitch, spectrum (FBG) demodulator, computing machine, shunt, optical cable, fiber grating; It is characterized in that the ASE light source is connected through the input end of optical fiber with the 3db coupling mechanism; The output terminal of 3db coupling mechanism is connected on the photoswitch by optical fiber, and the output terminal of photoswitch is connected with shunt through optical cable, and the shunt output terminal is connected with the multi-channel optical fibre grating through optical cable; Another output terminal of 3db coupling mechanism is connected on the spectrum (FBG) demodulator by optical fiber, and the spectrum (FBG) demodulator is connected with computing machine; Computing machine is connected with alarm.

2. as claimed in claim 1ly a kind ofly carry out device for monitoring with optical fiber grating pair oil tank temperature; It is characterized in that described fiber grating is a 0.4nm bandwidth Fiber Bragg Grating FBG; The way of fiber grating is the 8-64 road, and each oil tank is provided with fiber grating monitoring point, 2-4 road.

3. as claimed in claim 1ly a kind ofly carry out device for monitoring, it is characterized in that every road fiber grating in the described multi-channel optical fibre grating is inequality with the foveal reflex wavelength of other fiber grating with optical fiber grating pair oil tank temperature.

4. a device as claimed in claim 1 carries out the method for temperature monitoring, and step is following:

1) Temperature Scaling of fiber grating

Device is connected, thermometric is placed in the thermostat with fiber grating, change the temperature in the thermostat, by the temperature characteristics T of fiber grating ₀-λ ₀Measurement is also determined the centre wavelength of fiber grating and the one-to-one relationship between the temperature, is got off by computer recording; According to the oily temperature numerical value of the safety of oil tank, confirm the range of drift of the centre wavelength of fiber grating, setting safety oil temperature is T _Min-T _Max, the centre wavelength of corresponding fiber grating is λ _Min-λ _MaxEvery thermometric is repeated above-mentioned calibration process with fiber grating, accomplished the Temperature Scaling of whole device thermometric with fiber grating;

2) monitoring device is to the temperature monitoring of oil tank

Fiber grating after the calibration is contained on the inwall of tested oil tank; Connect monitoring device; The ASE light source arrives fiber grating through the transmission of coupling mechanism, photoswitch, shunt and optical cable, and the light of fiber grating reflected back shows the form of reflectance spectrum with two-dimensional coordinate through same paths reflected back wavelength (FBG) demodulator; Draw out every thermometric after fetching data by computer-readable with the two-dimentional oscillogram of the centre wavelength-time of fiber grating, demonstrate corresponding temperature value through fitting formula;

3) overload alarm of monitor temperature

The temperature that monitoring device detects tested oil tank is lower than T _MinPerhaps be higher than T _MaxThe time, report to the police through the alarm that is connected with computing machine, pointing out a certain oil tank temperature over-range, thereby get rid of potential safety hazard.

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