CN104089682A - Liquid level measurement device and method - Google Patents

Abstract

The invention discloses a liquid level measurement device and method and relates to liquid level measurement. The device is provided with a light source, a three-port circulator, a spectrograph, a liquid container to be measured and a liquid level sensor. The sensor is inserted into the liquid container to be measured, the other end of the sensor is connected with a first output port of the circulator, the light source is connected with the input end of the circulator, and a second output port of the circulator is connected with the spectrograph; signal light enters the circulator and then is output through the first output port of the circulator; after the signal light reaches the sensor, interference occurs at the position of a fiber bragg grating through reflection of a silver film; reflected light re-enters the circulator through the first output port of the circulator and then is output to the spectrograph through the second output port of the circulator, and the spectrum of the output light can be obtained by measuring the spectrum of the reflected light; the relation between the height of the outside liquid level and the wavelength of interference fringes can be obtained by measuring the drifting of the wavelength of the interference fringes through the spectrograph, and liquid level height can be measured through spectrum analysis. By the adoption of the liquid level measurement device and method, continuous liquid level measurement is realized, measurement accuracy is high, and safety performance is high.

Description

A kind of liquid level detection device and detection method thereof

Technical field

The present invention relates to liquid level and detect, especially relate to a kind of liquid level detection device and detection method thereof.

Background technology

Level gauging technology has application very widely at engineering field.In modern enterprise production process, require the object of measuring to want wide, it is high that the precision of measurement is wanted, and has good reliability and practicality, and will be applicable to the measurement in particular surroundings, such as fluid to be measured has corrosivity and inflammable and explosive property.This just has higher requirement to level gauging technology.Optical fiber sensing technology have volume little, lightweight, highly sensitive, can remote measurement and corrosion-resistant, be applicable to the advantage of inflammable and explosive measurement occasion, therefore develop based on optical fiber sensing technology on a large scale continuously level measuring method tool be of great significance.

Chinese patent CN203688041U discloses a kind of Full-optical optical fiber oil tank level pick-up unit.Rotating disk is equipped with at top at oil tank, one side of the first rotating disk arranges float, opposite side arranges weight, the disk center that rotates in the first rotating disk is evenly equipped with multiple optical filters, a pair of coupled lens is arranged on the both sides of the first rotating disk, the light that light source sends arrives spectroanalysis instrument successively after a coupled lens, a tablet filter, another coupled lens, and described spectroanalysis instrument is connected with Computer signal; Described float changes up and down with liquid level, and weight drives the first turntable rotation, and the information of liquid level converts the angle information of the first rotating disk to, detects the first dial rotation angle and can calculate oil tank level variation.

Chinese patent CN202119506U discloses a kind of liquid level detection device for liquid storage liquid compensating cylinder, comprise the glass tube being communicated with liquid storage liquid compensating cylinder and be relative shape and be arranged at the launching fiber of glass tube both sides and receive optical fiber, receive optical fiber and be used for receiving the light signal of launching fiber transmitting and sending a photoelectric commutator to, photoelectric commutator is used for light signal to be converted to electric signal output.

Summary of the invention

The object of the invention is to, poor stability poor for existing level measuring method measuring accuracy, be easily subject to the problems such as measurement environment impact, the continuous coverage that can realize liquid level is provided, and measuring accuracy is high, security is good, a kind of liquid level detection device and the detection method thereof that can in severe measurement environment, play a role.

Described liquid level detection device is provided with light source, three port circulators, spectrometer, testing liquid container and liquid level sensor; Described light source is connected with the input port of three port circulators, the 1st output port of three port circulators is connected with liquid level sensor by optical fiber, liquid level sensor inserts in the testing liquid of testing liquid container, and the 2nd output port of three port circulators is connected with the detection signal input end of spectrometer;

Described liquid level sensor is provided with sandwich layer, covering, and sandwich layer is located in covering, is provided with fiber grating in sandwich layer, is coated with silverskin at the end face of sandwich layer.

Described fiber grating can adopt long period fiber grating.

Described liquid-level detecting method, adopts described liquid level detection device, comprises the following steps:

1) liquid level sensor is inserted in the testing liquid of testing liquid container, the other end of liquid level sensor is connected with the 1st output port of three port circulators;

2) light source is connected with the input port of three port circulators;

3) the 2nd output port of three port circulators is connected with the detection signal input end of spectrometer;

4) open light source, flashlight can enter three port circulators from the input port of three port circulators, then exports from the 1st output port of three port circulators, when flashlight arrives after liquid level sensor, through silverskin reflection, can interfere at long period fiber grating place;

5) reflected light can reenter three port circulators through the 1st output port of three port circulators, then outputs to spectrometer from the 2nd output port of three port circulators, at this moment measures catoptrical spectrum, if the spectrum of input light is S _i(λ) spectrum that, can obtain exporting light is:

S _o(λ)＝S _i(λ)R(λ)

6) in the time that the height of testing liquid changes, for liquid level sensor, refractive index outside its covering can change, the variation of the refractive index of external environment can affect the effective refractive index of covering, the specific refractivity Δ n of fibre cladding and sandwich layer also will change, thereby affects the phase differential of interferometer and cause the drift of resonance wavelength;

7) by the drift of spectrometer measurement interference fringe wavelength, can obtain the relation of height and the interference fringe wavelength of extraneous liquid level, analyze spectrum, can record liquid level.

The present invention adopts the long period fiber grating of end face silvered mirror to form liquid level sensor, its beneficial effect is, the reflection-type long period fiber grating Mach-Zehnder interferometer that utilizes long period fiber grating end face silvered mirror to form, realize the continuous coverage of liquid level, and measuring accuracy is high, good stability, uses in the rugged surroundings such as can be more inflammable and explosive.

Brief description of the drawings

Fig. 1 is the structure composition schematic diagram of liquid level detection device embodiment of the present invention.

Fig. 2 is the liquid level sensor structure composition schematic diagram of liquid level detection device embodiment of the present invention.

Fig. 3 is catoptrical spectrogram.Curve a express liquid height 10mm, curve b express liquid height 20mm, curve c express liquid height 30mm, curve d express liquid height 40mm, curve e express liquid height 50mm.

Embodiment

The present invention is further illustrated in connection with accompanying drawing for following examples.

Referring to Fig. 1 and 2, described liquid level detection device embodiment is provided with light source 1, three port circulators 2, spectrometer 3, testing liquid container 4 and liquid level sensor 5; Described light source 1 is connected with the input port 21 of three port circulators 2, the 1st output port 22 of three port circulators 2 is connected with liquid level sensor 5 by optical fiber, liquid level sensor 5 inserts in the testing liquid of testing liquid container 4, and the 2nd output port 23 of three port circulators 2 is connected with the detection signal input end of spectrometer 3.

Described liquid level sensor is provided with sandwich layer 51, covering 52, and sandwich layer 51 is located in covering 52, is provided with fiber grating 53 in sandwich layer 51, is coated with silverskin 54 at the end face of sandwich layer 51.Described fiber grating adopts long period fiber grating.

The action principle of described liquid level sensor is as follows:

The silver-plated long period fiber grating of end face has formed a kind of Mach-Zehnder interferometer of self-interference, and long period fiber grating has played the effect of beam splitter in interferometer.Flashlight can be coupled at long period fiber grating place, can be coupled to cladding mode in the pattern of sandwich layer transmission, and taking the long period fiber grating of 3dB as example, 50% light can be coupled to covering to be propagated, and remaining light continues to propagate at sandwich layer.

In the time that two-beam arrives the end face of optical fiber, can reflect at silverskin place.From light path principle of reversibility, the cladding mode reflecting is coupled to again sandwich layer pattern at fiber grating place, and interferes with sandwich layer transmission mode, produces interference fringe.The reflectivity R of this liquid level sensor and the relation of wavelength X are as follows:

$R\left(\mathrm{\λ}\right)=(T_{\mathrm{co}}^2\left(\mathrm{\λ}\right)+T_{\mathrm{cl}}^2\left(\mathrm{\λ}\right))\×(1+\frac{{2T}_{\mathrm{co}}\left(\mathrm{\λ}\right)T_{\mathrm{cl}}\left(\mathrm{\λ}\right)}{T_{\mathrm{co}}^2\left(\mathrm{\λ}\right)+T_{\mathrm{cl}}^2\left(\mathrm{\λ}\right)}\cos (\frac{4\mathrm{\π\Δn}{L}_{\mathrm{cav}}}{\mathrm{\λ}}+2\mathrm{\θ}))---\left(1\right)$

If do not consider loss, this expression formula can be reduced to:

$R\left(\mathrm{\λ}\right)=1-4T_{\mathrm{co}}\left(\mathrm{\λ}\right)T_{\mathrm{cl}}\left(\mathrm{\λ}\right){\sin }^2(\frac{2\mathrm{\π\Δn}{L}_{\mathrm{cav}}}{\mathrm{\λ}}+\mathrm{\θ})---\left(2\right)$

Wherein T _co(λ) be the transmissivity of fiber core layer, T _cl(λ) be the transmissivity of fiber core layer to covering, Δ n is the difference of sandwich layer and cladding-effective-index, and θ is the phase shift that cross-couplings causes, L _cavthe chamber that is interferometer is long.This reflectance spectrum is pectination interference fringe.

In the time that the liquid level of extraneous testing liquid changes, the reflectivity R of sensor also can change thereupon, thereby plays the effect of level sensing.

Described liquid-level detecting method, adopts described liquid level detection device, comprises the following steps:

1) liquid level sensor 5 is inserted in the testing liquid of testing liquid container 4, the other end of liquid level sensor 5 is connected with the 1st output port 22 of three port circulators 2;

2) light source 1 is connected with the input port 21 of three port circulators 2;

3) the 2nd output port 23 of three port circulators 2 is connected with the detection signal input end of spectrometer 3;

4) open light source 1, flashlight can enter three port circulators 2 from the input port of three port circulators 2 21, then exports from the 1st output port 22 of three port circulators 2, when flashlight arrives after liquid level sensor 5, reflect through silverskin 54, can interfere at long period fiber grating 53 places;

5) reflected light can reenter three port circulators 2 through the 1st output port 22 of three port circulators 2, then outputs to spectrometer 3 from the 2nd output port 23 of three port circulators 2, at this moment measures catoptrical spectrum, if the spectrum of input light is S _i(λ) spectrum that, can obtain exporting light is:

S _o(λ)＝S _i(λ)R(λ) ⑶

6) in the time that the height of testing liquid changes, for liquid level sensor 5, refractive index outside its covering 52 can change, the variation of the refractive index of external environment can affect the effective refractive index of covering 52, the specific refractivity Δ n of fibre cladding 52 and sandwich layer 51 also will change, thereby affects the phase differential of interferometer and cause the drift of resonance wavelength;

7) measure the drift of interference fringe wavelength by spectrometer 3, can obtain the relation of height and the interference fringe wavelength of extraneous liquid level, analyze spectrum, can record liquid level.

Fig. 3 is that liquid height is respectively 10mm, 20mm, and 30mm, 40mm, when 50mm, catoptrical spectrum.

Described light source can adopt wideband light source.

Claims (3)

1. a liquid level detection device, is characterized in that being provided with light source, three port circulators, spectrometer, testing liquid container and liquid level sensor; Described light source is connected with the input port of three port circulators, the 1st output port of three port circulators is connected with liquid level sensor by optical fiber, liquid level sensor inserts in the testing liquid of testing liquid container, and the 2nd output port of three port circulators is connected with the detection signal input end of spectrometer;

Described liquid level sensor is provided with sandwich layer, covering, and sandwich layer is located in covering, is provided with fiber grating in sandwich layer, is coated with silverskin at the end face of sandwich layer.

2. a kind of liquid level detection device as claimed in claim 1, is characterized in that described fiber grating adopts long period fiber grating.

3. a liquid-level detecting method, is characterized in that adopting liquid level detection device as claimed in claim 1, comprises the following steps:

1) liquid level sensor is inserted in the testing liquid of testing liquid container, the other end of liquid level sensor is connected with the 1st output port of three port circulators;

2) light source is connected with the input port of three port circulators;

3) the 2nd output port of three port circulators is connected with the detection signal input end of spectrometer;

4) open light source, flashlight can enter three port circulators from the input port of three port circulators, then exports from the 1st output port of three port circulators, when flashlight arrives after liquid level sensor, through silverskin reflection, can interfere at long period fiber grating place;

5) reflected light can reenter three port circulators through the 1st output port of three port circulators, then outputs to spectrometer from the 2nd output port of three port circulators, at this moment measures catoptrical spectrum, if the spectrum of input light is S _i(λ) spectrum that, obtains exporting light is:

S _o(λ)＝S _i(λ)R(λ)

6) in the time that the height of testing liquid changes, for liquid level sensor, refractive index outside its covering can change, the variation of the refractive index of external environment can affect the effective refractive index of covering, the specific refractivity Δ n of fibre cladding and sandwich layer also will change, thereby affects the phase differential of interferometer and cause the drift of resonance wavelength;

7) by the drift of spectrometer measurement interference fringe wavelength, obtain the relation of height and the interference fringe wavelength of extraneous liquid level, analyze spectrum, record liquid level.