CN201637666U - A dynamic measuring instrument for solution concentration - Google Patents

Abstract

The utility model relates to a dynamic measuring instrument of solution concentration, which is characterized in that: the output light of a broadband light source enters a long-period fiber grating, and the transmitted light of the long-period fiber grating enters two fiber Bragg gratings through a fiber coupler; a first fiber Bragg grating is used as a signal demodulating element, the reflected light is received by a photodiode, and the transmitted light enters a refractive index matching liquid; a second fiber Bragg grating is used as a signal reference element, the reflected light is blocked by a fiber isolator, and the transmitted light enters a second photodiode; and the long-period fiber grating is used as a sensing element, a bare grating region of the long-period fiber grating is immersed in a solution to be measured, and the concentration of the measured solution can be obtained according to the wavelength shift of the loss peak of the long-period fiber grating. The utility model has the characteristics of high resolution, low cost, rapidness, simplicity and practicality.

Description

A kind of solution concentration dynamic measuring instrument

Technical field

The utility model belongs to the optical fiber grating sensing field of measuring technique, particularly relates to a kind of solution concentration dynamic measuring instrument.

Background technology

Fiber grating is as a kind of optical device, is to set up a kind of space refractive index cycle to distribute in optical fiber, the device that the propagation characteristic of light is therein changed.

After the surrounding layer of long period fiber grating (LPG) peeled off, the structure of remaining inner cladding and fibre core was called as bare fibre, and it not only has the characteristic of general LPG, can absorb the light wave of specific wavelength, occurs several resonance absorbing loss peaks in its transmission spectrum; And, when it is put into any one solution or gas, its refractive index will change along with the variation of ambient concentration, in case refractive index changes, its transmission spectrum also can change so, concrete manifestation is exactly that skew has taken place absorption peak corresponding in the transmission spectrum, and variations in refractive index is big more, is offset big more.Therefore, we can be by the amount of movement Δ λ of its certain peak wavelength _LPTry to achieve the LPG change of refractive, and then try to achieve the concentration of LPG surrounding environment.

The harmonic peak centre wavelength amount of movement of long period fiber grating is as follows with extraneous change of refractive relational expression:

$\frac{\mathrm{\Δ}{\mathrm{\λ}}_{\mathrm{LP}}}{{\mathrm{\λ}}_{\mathrm{LP}}}=[\frac{1}{n_{\mathrm{co}}-n_{\mathrm{cl}}}\frac{d(n_{\mathrm{co}}-n_{\mathrm{cl}})}{{\mathrm{dn}}_{\mathrm{ex}}}+\frac{1}{\mathrm{\Λ}}\frac{\mathrm{d\Λ}}{{\mathrm{dn}}_{\mathrm{ex}}}]\mathrm{\Δ}{n}_{\mathrm{ex}}---\left(1\right)$

λ _LPBe initial resonance wavelength, Δ λ _LPBe the amount of movement of LPG coupling resonance peak center wavelength, Δ n _ExBe extraneous refractive index variable quantity, n _Co, n _ClBe respectively the effective refractive index of basic mode and cladding mode.The solution concentration sensing measurement principle of LPG is exactly that method by simulation calculation and experiment finds refractive index sensitivity coefficient in the bracket, sets up extraneous refractive index change delta n then _ExWith harmonic peak centre wavelength amount of movement Δ λ _LPCorresponding relation, change according to solution concentration again and refractive index variable quantity between relation, can learn the concentration of detected solution.Carry out suitable calibration according to these relations again, can obtain the drift value of harmonic peak centre wavelength and the one-to-one relationship of solution concentration.

In fiber grating sensing technology,, how simply, fast, accurately small wavelength amount of movement demodulation is come out, be the vital problem of optical fiber grating sensing because measured signal is Wavelength-encoding.For head it off, the researchist has developed some Wavelength demodulation technology in succession, mainly contains demodulation techniques, tunable optical source demodulation techniques, tunable filtering demodulation techniques, the matched filtering demodulation technology etc. of interfering.In above-mentioned demodulation method, the measurement range of interference demodulation techniques is subject to the Free Spectral Range of interferometer; Tunable optical source demodulation techniques input is convenient, the resolution height, but light source is difficult to make, and cost is higher; The scan period of tunable filtering demodulation techniques is long, and test speed is slow, and poor repeatability; The demodulation scope of matched filtering demodulation technology is too little.Because the existence of above-mentioned shortcoming makes the Wavelength demodulation technology become one of major obstacle of fiber grating sensing technology application.

Summary of the invention

Technical problem to be solved in the utility model provide a kind of can be in real time, the fiber-optic grating sensor of kinetic measurement solution concentration, can realize the high-precision measurement of parameters such as solution concentration, and realize the signal dynamics demodulation techniques of lower cost.

The technical scheme that its technical matters that solves the utility model adopts is: a kind of solution concentration dynamic measuring instrument is provided, comprises wideband light source, optical signal transmission optical fiber, long period fiber grating, 2 * 2 coupling mechanism, first Bragg fiber grating, second Bragg fiber grating, optoisolator, first photodetector, second photodetector, index-matching fluid, signal amplifier, oscillograph, data collecting card, computing machine.The output light of described wideband light source enters long period fiber grating through Transmission Fibers, the transmitted light of long period fiber grating enters coupling mechanism through first end arm of coupling mechanism, then wherein a part of light enters first Fiber Bragg Grating through second of coupling mechanism end arm, and another part light enters in optoisolator and second Fiber Bragg Grating through the 3rd end arm of photo-coupler; The transmitted light of first Fiber Bragg Grating enters in the index-matching fluid, and its reflected light enters in first photodetector through the 4th end arm of coupling mechanism, and the transmitted light of second Fiber Bragg Grating enters in second photodetector; In the output signal entering signal amplifier of first photodetector and second photodetector, the output signal of amplifier enters oscillograph and data collecting card simultaneously, enters in the computing machine after the data collecting card analog-to-digital conversion, by Computer Processing and demonstration in real time.

Described sensing measurement instrument is when measuring solution concentration, and long period fiber grating is a sensing element, and its naked grating region is dipped in the solution to be measured.

Described first Fiber Bragg Grating is common Fiber Bragg Grating, is used as the signal restitution element.

Described second Fiber Bragg Grating is the Fiber Bragg Grating through the temperature compensation encapsulation.

Described first Fiber Bragg Grating also can be used as other certain performance parameter of solution (for example: sensing element temperature), and utilize long period fiber grating to make the signal restitution element, realize the measurement of other certain parameter of solution.

The sensing element of system and signal restitution element are fiber optic component, can realize real-time, the kinetic measurement of solution concentration (or other certain parameter).

The present invention proposes to utilize the resonance wavelength restitution element of Bragg fiber grating as long period fiber grating.In the transmission spectrum of long-period gratings, its light intensity is reduce (or the increase) of linear (the linear fit error is in the 10-4 magnitude) in a certain wavelength coverage that the strength degradation limit (or rising edge) of particular resonance loss peak is comprised, utilize this point can realize the modulation of long-period gratings to wideband light source, produce one in certain wavelength coverage intensity be the light source of linear change (descend or rise).Selection has the Bragg grating of suitable wavelength, and its central wavelength lambda B is in the linear zone scope of long-period gratings transmission spectrum, and the centre position of close linear zone, as shown in Figure 2.When the wavelength of long period fiber grating is modulated by transducing signal, the reflection peak of Bragg fiber grating changes at the relative position of transmission spectrum linear zone, but its spectral pattern does not change with measured signal, then the absolute light power of Bragg fiber grating reflection is with linear change, therefore the photocurrent of photodetector is linear change, but the wavelength variations of demodulating long period optical fiber optical grating like this.This principle is similar to linear filter, but Bragg fiber grating has 2 obvious advantages with respect to linear filter: speed is fast and cost is little.

Beneficial effect

(1) the solution concentration dynamic sensitive measuring instrument of the utility model realization only needs three fiber gratings just can realize dynamic, real-time, the on-line measurement of solution concentration (or other certain parameter of solution), and do not need special wavelength checkout equipment, only need just can calculate the loss peak wavelength shift of sensing element-long period fiber grating accurately, thereby learn the concentration of detected solution according to the output valve of photodetector.

(2) the utility model utilizes the monolateral realization linear filtering of long period fiber grating master loss peak function, and the demodulation speed that therefore has a linear filtering demodulation is fast, no diadic problem etc.; And adopt part signal light as reference light, eliminated because the influence that the light source output power fluctuation causes Wavelength demodulation.

(3) the utility model possesses the advantage that the convertible function of sensing element and signal restitution element is used, the sensing element when promptly its signal restitution element--Fiber Bragg Grating--can be used as other parameter measurements such as solution temperature; And the sensing element of solution concentration--long period fiber grating--can be used as the signal restitution element of other parameter sensings such as solution temperature; Therefore this solution concentration dynamic sensitive measuring instrument not only can be used for the kinetic measurement of solution concentration, also can be used for the measurement of other parameters of solution, can realize the fibre-optical multiparameter sensor of high performance-price ratio.

(4) the utility model all is made of optical fiber and fiber optic passive device, and is stable and reliable for performance.The technological level of all components and parts is all very ripe, easy to make feasible, is convenient to promote the industrialization process of fiber grating sensing technology, can be widely used in various fields.

Description of drawings

Fig. 1 is the utility model sensor-based system synoptic diagram;

Fig. 2 is long period fiber grating transmission spectrum and Fiber Bragg Grating reflectance spectrum synoptic diagram.

Embodiment

Below in conjunction with specific embodiment, further set forth the utility model.Should be understood that these embodiment only to be used to the utility model is described and be not used in the restriction scope of the present utility model.Should be understood that in addition those skilled in the art can make various changes or modifications the utility model after the content of having read the utility model instruction, these equivalent form of values fall within the application's appended claims institute restricted portion equally.

As shown in Figure 1, the sensing measurement instrument that can measure solution concentration dynamically, in real time that the utility model is realized, its feature formation is: the output light of a wideband light source 1 enters long period fiber grating 3 through connecting optical fiber 2.The transmitted light of long period fiber grating 3 enters coupling mechanism 4 through first end arm 5 of the coupling mechanism 4 of optical fiber 2 and 2 * 2: then wherein a part of light enters first Fiber Bragg Grating 7 through second of coupling mechanism 4 end arm 6, and another part light enters in optoisolator 9 and second Fiber Bragg Grating 10 through the 3rd end arm 8 of photo-coupler 4.The transmitted light of Fiber Bragg Grating 7 enters in the index-matching fluid 11, and the 4th end arm 12 of its reflected light optical branching device 4 enters in first photodetector 13, and the transmitted light of Fiber Bragg Grating 10 enters in second photodetector 14.In the output signal entering signal amplifier 15 of two photodetectors 13,14, the output signal of amplifier 15 is divided two-way, and one the tunnel is transfused in the computing machine 17 through analog-to-digital conversion device 16, and another road signal enters in the oscillograph 18.And sensing element long period fiber grating 3 is dipped in the solution 19 to be measured.

When measuring solution concentration, long period fiber grating 3 is made sensing element, and first Fiber Bragg Grating 7 is common Fiber Bragg Grating as restitution element; Second Fiber Bragg Grating 10 is the Fiber Bragg Grating through the temperature compensation encapsulation, and its centre wavelength is not drifted about with variation of temperature.Also can long period fiber grating be used for the signal restitution element, realize the measurement of other parameters such as solution temperature with first Fiber Bragg Grating as sensing element.

The sensing measurement instrument that can measure solution concentration dynamically, in real time that the utility model is realized, when measuring solution concentration, long period fiber grating is dipped in the solution 19 to be measured, and the position in total system device synoptic diagram is as shown in fig. 1;

The sensing measurement instrument that can measure solution concentration dynamically, in real time that the utility model is realized, the Fiber Bragg Grating 10 of described Bragg grating 7 and temperature compensation encapsulation, the former is a signal demodulation grating, and the latter is that signal is with reference to grating, parameters such as both cloth loudspeaker lattice centre wavelength, bandwidth, reflectivity should be mated, and that both cloth loudspeaker lattice centre wavelength should be with long period fiber grating master loss peak is Wavelength matched.

What the utility model was realized can be dynamic, measure the sensing measurement instrument of solution concentration in real time, no matter be to measure any parameters such as solution concentration or solution temperature, the transmission course of signal is such: the output light of wideband light source is after long period fiber grating 3 modulation, a part enters Fiber Bragg Grating 7 behind 2 * 2 coupling mechanism, and wherein another part enters second Fiber Bragg Grating 10 through isolator, the transmitted light of the reflected light of Fiber Bragg Grating 7 and Fiber Bragg Grating 10 enters first photodetector 13 and second photodetector 14 respectively, equal then entering signal amplifier carries out the processing and the demonstration of data at last.

The signal demodulation principle that can measure the sensing measurement instrument of solution concentration dynamically, in real time that the utility model is realized: about long-period gratings transmission spectrum and Bragg grating reflectance spectrum, as shown in Figure 2, dotted line is the reflectance spectrum of Bragg fiber grating 7, and solid line is the main loss peak in the LPG transmitted spectrum.(the linear fit error is 10 for linearity for its light intensity in the wavelength coverage that the strength degradation limit (or rising edge) of main loss peak is comprised ^-4Reducing magnitude) (or increase), utilize this point can realize the modulation of long-period gratings to wideband light source, produce one in particular range of wavelengths intensity be the light source (can change) of linear change (descend or rise) referring to the monolateral light intensity at the maximum loss peak among Fig. 2.The spectrum of light in the wavelength coverage of being utilized after the long-period gratings modulation is linear.

Make Fiber Bragg Grating 7 have suitable wavelengths, make its central wavelength lambda _BBe in the main loss peak linear zone scope of long period fiber grating transmission spectrum, and the centre position of close linear zone, as shown in Figure 2.When measuring solution concentration, long period fiber grating 3 is dipped in the detected solution, when solution concentration changes and its refractive index is linear thereupon when changing, when the loss peak wavelength of long period fiber grating 3 is modulated, its peak wavelength will drift about, be that the spectrum linear zone will translation, but its spectral shape does not change with measured signal; And the centre wavelength of Fiber Bragg Grating 7 is constant, the relative difference of itself and long period fiber grating 3 loss peak wavelength changes, be that the Bragg fiber grating reflection peak changes at the relative position of spectrum linear zone, then Fan She absolute light power is with linear change, therefore the photocurrent of photodetector is linear change, but the peak wavelength of demodulating long period optical fiber optical grating variation like this.This principle is similar to linear filter, but the optical fiber restitution element has 2 obvious advantages with respect to linear filter, and promptly speed is fast and cost is little.

When other parameters such as measurement solution temperature, Bragg fiber grating 7 will be as sensing element, when temperature variation, the central wavelength lambda B of Bragg fiber grating changes linearity, the relative distance of Bragg grating centre wavelength and main loss peak wavelength changes, be that its reflection peak changes in the position of linear zone, then Fan She absolute light power is with linear change.

Claims (5)

1. A solution concentration dynamic measuring instrument, comprising a broadband light source (1), an optical signal transmission fiber (2), a long-period fiber grating (3), a 2×2 coupler (4), the first Bragg fiber grating (7), second Bragg fiber grating (10), optical isolator (9), first photodetector (13), second photodetector (14), refractive index matching liquid (11), signal amplifier (15), oscilloscope (16), data acquisition card (17), computer (18), it is characterized in that: the output light of described broadband light source (1) enters long-period fiber grating (3) through transmission fiber (2), The transmitted light of the long-period fiber grating (3) enters the coupler (4) through the first end arm (5) of the coupler (4), and then part of the light passes through the second end arm (6) of the coupler (4). ) enters the first fiber Bragg grating (7), while another part of the light enters the optical isolator (9) and the second fiber Bragg grating through the third end arm (8) of the optical coupler (4) (10); the transmitted light of the first fiber Bragg grating (7) enters the refractive index matching liquid (11), and its reflected light enters the fourth end arm (12) of the coupler (4) into the first In one photodetector (13), the transmitted light of the second fiber Bragg grating (10) enters in the second photodetector (14); the first photodetector (13) and the second photodetector The output signal of the device (14) enters the signal amplifier (15), and the output signal of the amplifier (15) enters the oscilloscope (16) and enters the computer (18) through the analog-to-digital converter (17) at the same time, and is processed and displayed in real time by the computer . 2. a kind of solution concentration dynamic measuring instrument according to claim 1, is characterized in that, described first fiber Bragg grating (7) is common fiber Bragg grating, is used as signal demodulation element . 3. A solution concentration dynamic measuring instrument according to claim 1, characterized in that, the second fiber Bragg grating (10) is a fiber Bragg grating packaged with temperature compensation. 4. A kind of solution concentration dynamic measuring instrument according to claim 1, is characterized in that: use described first optical fiber Bragg grating (7) as the sensing element that solution performance parameter comprises temperature parameter, and utilize long The periodic fiber grating (3) is used as a signal demodulation element. 5. A solution concentration dynamic measuring instrument according to claim 1, characterized in that the sensing elements and signal demodulation elements of the system are all optical fiber elements.

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