CN107515033A - Point type liquid level sensor device and its measuring method based on optical frequency domain reflection technology - Google Patents
Point type liquid level sensor device and its measuring method based on optical frequency domain reflection technology Download PDFInfo
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- CN107515033A CN107515033A CN201710673698.7A CN201710673698A CN107515033A CN 107515033 A CN107515033 A CN 107515033A CN 201710673698 A CN201710673698 A CN 201710673698A CN 107515033 A CN107515033 A CN 107515033A
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- 239000000835 fiber Substances 0.000 claims abstract description 192
- 239000013307 optical fiber Substances 0.000 claims abstract description 41
- 230000035559 beat frequency Effects 0.000 claims abstract description 40
- 238000010408 sweeping Methods 0.000 claims abstract description 5
- 238000012360 testing method Methods 0.000 claims description 24
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- 238000005259 measurement Methods 0.000 description 12
- 238000012544 monitoring process Methods 0.000 description 11
- 238000002168 optical frequency-domain reflectometry Methods 0.000 description 7
- 238000001514 detection method Methods 0.000 description 6
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
- G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
- G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
- G01F23/28—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
- G01F23/284—Electromagnetic waves
- G01F23/292—Light, e.g. infrared or ultraviolet
Abstract
The invention discloses a kind of point type liquid level sensor device and its measuring method based on optical frequency domain reflection technology, wherein sensor device includes linear frequency sweep laser, fiber optic splitter, optical fiber circulator, sensing module, fiber coupler, photodetector, data collecting card, computer and warning circuit；Wherein：Sweeping laser is divided into flashlight and reference light by fiber optic splitter；Flashlight returns along road in Fresnel reflection signal caused by the tail end end of each sensor fibre and through being coupled into single-mode fiber at fiber optic splitter, and the backreflected signals light in single-mode fiber produces beat frequency interference signal with reference light at fiber coupler；Beat frequency interference signal in data collecting card collection electric signal；Computer controls the linear frequency sweep laser and the data collecting card.The present invention measures liquid level using the Fresnel reflection characteristic of sensor fibre tail end, and single-point or multiple spot liquid level are monitored and alerted.
Description
Technical field
The present invention relates to technical field of optical fiber sensing, more specifically, is related to a kind of point type level sensing based on OFDR
Device and measuring method.
Background technology
It is extensive that level monitoring is related to field, and fibre optic liquid level sensor has burn-proof and explosion prevention, precision height, high sensitivity, anti-dry
The features such as ability is strong is disturbed, especially suitable for the level monitoring in the industrial productions such as petrochemical industry.Fibre optic liquid level sensor has at present
Many deficiencies, such as based on full optical fiber interferometer liquid level sensor, it is necessary to be carried out using special optical fiber structure or to optical fiber
Special processing, repeatability is not high, and measurement range is limited；Liquid level sensor based on FBG, it is necessary to plus respective external component, drop
Low Measurement reliability；Liquid level sensor based on OTDR, spatial resolution is other in centimetre rank even meter level, surveys its liquid level
It is big to measure blind area, sensing head also needs to use special optical fiber fabrication, and fixed form is also more complicated.
Existing fiber liquid level sensor measurement range can not be compatible with measurement accuracy at present, and there is an urgent need to a kind of big measurement model
Enclose, high-precision fibre optic liquid level sensor, while must assure that the accuracy and stability of measurement.
The content of the invention
For the disadvantages described above or Improvement requirement of prior art, the invention provides a kind of point type liquid level biography based on OFDR
Sensor and measuring method.The present invention uses OFDR with optical heterodyne detection technique to its tail by the use of single-mode fiber as sensing head
The Fresnel reflection characteristic at end is analyzed, so as to realize single-point or multiple spot progress level monitoring and alert.The sensor can be surveyed
Points are more, measurement range is big, reproducible, reliability is high, precision is high, and sensor fibre manufacture craft is simple, inexpensively.Suitable for pair
Setting liquid level is alarmed, instruction etc..
In order to solve the above-mentioned technical problem, the technical solution adopted in the present invention is：
A kind of point type liquid level sensor device based on optical frequency domain reflection technology, including linear frequency sweep laser, light are provided
Fine beam splitter, optical fiber circulator, sensing module, fiber coupler, photodetector, data collecting card, computer and alarm electricity
Road；Wherein：
The sweeping laser that the linear frequency sweep laser exports is divided into two-way by the fiber optic splitter, is all the way signal
Light, another way are reference light；Flashlight enters the optical fiber circulator, and reference light enters the fiber coupler；
The sensing module is connected by single-mode fiber with the optical fiber circulator, and flashlight is entered by single-mode fiber should
Sensing module；The sensing module includes fiber optic splitter, single or more sensor fibre, the tail end end of every sensor fibre
Face is smooth through transverse cuts, and the tail end of each sensor fibre is placed in the container of different set liquid level；Flashlight passes through the light
Fine beam splitter enters sensor fibre, is returned in Fresnel reflection signal caused by the tail end end of each sensor fibre along road
And through being coupled into single-mode fiber at fiber optic splitter, the backreflected signals light in single-mode fiber passes through the optical fiber circulator
The fiber coupler is imported, beat frequency interference occurs at the fiber coupler with reference light, produces beat frequency interference signal；
The beat frequency interference signal is converted into electric signal by the photodetector；
The data collecting card gathers the beat frequency interference signal in electric signal by multichannel simultaneously；
The computer enters row data communication with the linear frequency sweep laser, the data collecting card, and described in control
Linear frequency sweep laser and the data collecting card, the computer also carries out Treatment Analysis to beat frequency interference signal, and sends number
According to the warning circuit；
The data that the warning circuit issues according to the computer of reception, control indicator lamp and alarm.
Above-mentioned technical proposal is connect, the sweeping laser that the linear frequency sweep laser exports is divided into by the fiber optic splitter
50：50 two-way.
Present invention also offers a kind of point type liquid level sensor measuring method, comprise the following steps：
Linear scan laser sends the laser of optical maser wavelength periodicity linear change, and laser is divided into fiber optic splitter
Two-way light, light is flashlight all the way, is all the way reference light；
Reference light is directly coupled into an input in fiber coupler；
Flashlight enters optical fiber circulator and is transferred to single-mode fiber, enters sensing module, Mei Yigen by single-mode fiber
Fresnel reflection signal caused by the tail end end of sensor fibre returns along road, and coupling is combined into single mode at fiber optic splitter
Optical fiber, the backreflected signals light in single-mode fiber imports the fiber coupler by the optical fiber circulator, with reference light
Beat frequency interference occurs at the fiber coupler, produces beat frequency interference signal；
Beat frequency interference signal is converted to electric signal through photodetector, is gathered by data collecting card, is done soon by computer
Fast Fourier transformation obtains the spectrum information of beat signal.
Present invention also offers a kind of beat frequency interference signal demodulating method of point type liquid level sensor, comprise the following steps：
Convert to obtain corresponding along sensor fibre clap to the beat frequency interference signal progress non-uniform Fast Fourier of collection
Again and again spectrum；
Drop point processing is carried out to beat frequency frequency spectrum；
Beat frequency spectrum signal is smoothed, improves the difference of Fresnel reflection peak value and ambient noise；
Peak-seeking calculating is carried out to beat frequency frequency spectrum, the transverse and longitudinal that peak-seeking calculates all reflection peaks for including finding whole spectrogram is sat
Mark, i.e. distance and peak value size, the transverse and longitudinal coordinate of all Fresnel reflections calculated and preservation, as Local Reference Number；
A data are often gathered, mathematic interpolation are carried out with the Local Reference Number of preservation, when the peak value of this gathered data is big
When small and Local Reference Number peak value magnitude difference is more than given threshold, return judges numerical value 1, is otherwise 0, all binary number structures
Into truth table；
Truth table data corresponding to each reflection peak are sent to warning circuit, warning circuit control corresponding indicator lamp with
And alarm is alarmed.
Above-mentioned technical proposal is connect, it is corresponding with the sensor fibre end face to clap before and after liquid level and sensor fibre end contact
Step evolution saltus step occurs for the intensity of frequency interference signal, is judged by analyzing the change of the sensor fibre end face beat frequency interference signal
Whether testing liquid has reached setting liquid level.
Compared with prior art the advantageous effect of present invention is that：The present invention proposes the point type liquid level of OFDR technologies
Sensing technology.The present invention is combined using OFDR technologies with optical heterodyne detection technique, carrys out the phenanthrene of detection analysis single-mode fiber tail end
Nie Er reflection characteristics, realize point type level gauging.Sensor fibre uses general single mode fiber, no add-on assemble, and measurement range is big
In 100 meters, measurement accuracy is better than 20um.Due to the general single mode fiber that sensing head uses, manufacture craft is simple, therefore measure
It is reproducible, reliability is high.Sensing head fixed form of the present invention is simple, it is only necessary to is pasted and fixed on sensor fibre with seccotine
On the support bar placed vertically or on testing liquid chamber wall.The present invention can also realize multiple spot level gauging, measurement points
It is unrestricted, only it need to can realize that multiple spot liquid level is surveyed in the sensor fibre that the more root long degree of fiber optic splitter output end connection differ
Amount.It is particularly suitable in industrial production accurately measuring the inflammable and explosive setting liquid level for waiting dangerous liquid.
Brief description of the drawings
The embodiment of the present invention is described in further detail below by accompanying drawing.
Fig. 1 is the point type level gauging structural representation of the present invention；
Fig. 2 is Fresnel reflection peak figure when liquid level separates with sensor fibre end face in single-point level sensing of the present invention；
Fig. 3 is liquid level and Fresnel reflection peak figure during sensor fibre end contact in single-point level sensing of the present invention；
Fig. 4 is multiple spot liquid level Fresnel reflection peak figure of the present invention；
In Fig. 1：1 it is linear frequency sweep laser, 2 is fiber optic splitter (50：50) 3 it is, optical fiber circulator, 4 is single-mode optics
It is fine, 5 be sensing module, 6 be fiber coupler (1x2), 7 be photodetector, 8 be data collecting card, 9 be computer, 10 be
Warning circuit, 11 be fiber optic splitter (1xN), 12 be sensor fibre, 13 be sensor fibre end face, 14 be liquid level.
Embodiment
The invention will be further described for example below combination accompanying drawing.
Point type liquid level sensor of the embodiment of the present invention based on OFDR, as shown in figure 1, including linear frequency sweep laser 1, light
Fine beam splitter (50：50) 2, optical fiber circulator 3, single-mode fiber 4, sensing module 5, fiber coupler (1x2) 6, photodetector
7th, data collecting card 8, computer 9.
Linear scan laser 1 and fiber optic splitter (50：50) 2 inputs connect, fiber optic splitter (50：50) output end
The a ports with a ports of optical fiber circulator and fiber coupler (1x2) are connected respectively.The b mouths and single-mode fiber of optical fiber circulator
Connection, c mouths are connected with the b mouths of fiber coupler (1x2).Single-mode fiber 4 is connected with sensing module 5.
Referred to based on OFDR technologies：Linear scan laser 1 sends optical maser wavelength periodicity linear change as light source
Laser, narrow linewidth laser, scanning range 1520nm-1630nm, sweep velocity 2nm/s-2000nm/s can be used.Laser enters
Enter fiber optic splitter (50：50) 2 points are two-way light.Light is flashlight all the way, is all the way reference light.Reference light is directly coupled into
A mouths in fiber coupler (1x2) 6.Flashlight enters a mouths of optical fiber circulator 3 and is transferred to single-mode fiber 4.Flashlight enters
Sensor fibre 12 is entered back into after entering fiber optic splitter (1xN) 11.In whole pickup arm back scattering, back scattering occur for flashlight
Guang Yan roads return to optical fiber circulator 3 and enter the b mouths of fiber coupler (1x2) 6 by the c mouths outgoing of optical fiber circulator 3.Two-way
Light interferes at fiber coupler (1x2) 6.Because reference light is different with the light path of rear orientation light, time delay is introduced, then
Contain beat signal in interference signal.After photodetector 7, interference light signal is converted to electric signal, is adopted by data collecting card 8
Collection, and do Fast Fourier Transform (FFT) in the computer 9 and obtain the spectrum information of beat signal.
Sensing module 5 include fiber optic splitter (1xN) 11, single or more sensor fibre 12, for realize single-point or
Multiple spot level gauging.Wherein, sensor fibre 12 is general single mode fiber, is connected simultaneously with the output end of fiber optic splitter (1xN) 11
Fixed placement is in testing liquid.
In order that obtaining being reflected into for sensor fibre end vertically reflects (intensity vertically reflected is most strong, easily differentiates),
Sensor fibre tail end is handled with optical fiber cutter transverse direction flat cut, and in vertical fixed placement testing liquid.Testing liquid
Rise or decline, liquid level can pass through sensor fibre tail end end face.
The measuring method of point type liquid level sensor of the embodiment of the present invention based on optical frequency domain reflection technology：Linear scan laser
Device 1 sends the laser of optical maser wavelength periodicity linear change, and laser enters fiber optic splitter (50：50) 2 points are two-way light.All the way
Light is flashlight, is all the way reference light.Reference light is directly coupled into an input in fiber coupler 6.Flashlight enters
Enter optical fiber circulator 3 and be transferred to single-mode fiber 4.Back scattering occurs on single-mode fiber 4 for flashlight, and rear orientation light is along road
Return to optical fiber circulator 3 and enter another input of fiber coupler 6 by the c mouths outgoing of optical fiber circulator.Two-way light
Interfered at fiber coupler 6.Because the light path of two-way light return signal is different, time delay is introduced, then in interference signal
Contain beat signal.After photodetector 7, interference light signal is converted to electric signal, is gathered by data collecting card, and does quick
Fourier transformation obtains the spectrum information of beat signal.
The light velocity and laser sweep speed determine that the beat signal frequency measured can be mapped as physical distance, and beat frequency is believed
Number intensity proportional is in the intensity of reflected signal.
Rear orientation light is mainly Rayleigh scattering and Fresnel reflection.Due to Fresnel reflection be by light in transmitting procedure
Caused by medium refraction index is undergone mutation, and it is poor to be proportional to medium refraction index.When sensor fibre tail end is in air, optical fiber
Refractive index and the refringence of air refraction are larger, have stronger Fresnel reflection.When liquid level to be measured rise or fall with
When sensor fibre tail end contacts, optical fiber tail-end exit end medium refraction index is undergone mutation, now optical fiber and testing liquid refractive index
Difference diminishes.And then Fresnel reflection dies down, then step change type saltus step is presented in the beat signal intensity at optical fiber tail-end, and the beat frequency is believed
Number enter Row-Action algorithm analysis, can determine whether liquid level to be measured reaches the sensor fibre tail end end face, realize level gauging.
In sensing module 5, the output end of fiber optic splitter (1xN) 11 can connect the sensor fibre that more root long degree differ, and realize multiple spot liquid level
Measurement.
The operation principle of the present invention is to be based on optical frequency domain reflection technology.It will be put after the tail end transverse direction flat cut of sensor fibre 12
Put and containing at testing liquid.When the tail end of sensor fibre 12 contacts front and rear with testing liquid, rolled at the exit end of sensor fibre end face
The rate of penetrating is undergone mutation so that the incidence end of sensor fibre end face 13 changes with refringence at exit end, so as to use probe beam deflation
Step evolution saltus step occurs for the beat signal amplitude at the end-position of sensor fibre 12 of technology detection.By analyzing the beat signal
To judge whether testing liquid reaches the height of setting liquid level 13.
Spatial resolution can be achieved in tens micron dimensions in optical frequency domain reflection technology in 100 meters of Distance-sensings, therefore
The precision of point type level monitoring of the present invention is very high.The distance sensing of optical frequency domain reflection technology is even thousands of up to hundreds of meters simultaneously
Rice, thus the scope of point type level monitoring of the present invention is very wide.
Generally, the big I of beat signal frequency that optical frequency domain reflection technology measures is mapped as physical distance, short distance
Spatial resolution, while can also long distance monitoring in tens micron dimensions.The beat signal that optical frequency domain reflection technology measures is strong
Degree is then proportional to the intensity of reflected signal.
In single-point level gauging, any one optical fiber of fiber optic splitter (1xN) 11 output end connection is chosen as biography
Photosensitive fine 12 are placed in testing liquid, make sensor fibre end face 13 at setting liquid level.The liquid level now set is high
Degree is at the position of sensor fibre end face 13 of sensor fibre 12.When liquid level 14 is located at 13 lower section of sensor fibre end face, pass
It is air to feel at the exit end of fiber end face 13, refractive index 1.When liquid level 14 rises and is contacted with sensor fibre end face 13, pass
It is testing liquid to feel at the exit end of fiber end face 13, refractive index nliquid, optical fibre refractivity n is vertical according to Fresnel reflection
End face reflection rate R formula when incident：
Wherein n1And n2It is the refractive index of medium before and after incident end face respectively.
Substitute into medium refraction index n at optical fibre refractivity n and the exit end of sensor fibre end face 13XAnd abbreviation can obtain Fei Nie
End face reflection rate R during your reflective vertical incidence
Wherein n is optical fibre refractivity, nXMedium refraction index at the exit end of sensor fibre end face 12.
When the exit end of sensor fibre end face 13 is air, nXFor 1, when the exit end of sensor fibre end face 13 is testing liquid
When, nXFor nliquid.And nliquidMore than 1.
Therefore, before and after testing liquid liquid level 14 rises and contacted with sensor fibre end face 13, sensor fibre end face 13 is emitted
Step evolution saltus step occurs for reflectivity at end, so as to which Fresnel reflection intensity is undergone mutation.
Because the beat signal frequency of optical frequency domain reflection technology detection is mapped as physical distance, intensity proportional is in reflected signal
Intensity.Therefore, before and after liquid level 14 contacts with sensor fibre end face 13, beat signal corresponding at sensor fibre end face 13 is strong
Step evolution saltus step occurs for degree.Judge whether testing liquid reaches by analyzing the change of the beat signal of sensor fibre end face 13
Set liquid level.
As shown in Fig. 2 this monitoring result is liquid level 14 when being located at 13 lower section of sensor fibre end face, sensor fibre end face 13
Put the Fresnel reflecting peak of place's (i.e. 9.48564 meters of opening positions of distance setting starting point).Now testing liquid and sensor fibre end face
13 separation, are air at the exit end of sensor fibre end face 13, refractive index 1.It is anti-according to end face during Fresnel reflection vertical incidence
Penetrate rate R formula：
Wherein n is optical fibre refractivity, nXFor medium refraction index at the exit end of sensor fibre end face 13.
According to reflectance formula, the reflectivity of sensor fibre end face 13 and testing liquid now connect with sensor fibre end face 13
Reflectivity contrast when touching, reflectivity are higher.Reflected signal is demodulated, show that the Fresnel reflection intensity of the opening position is larger,
And then it is higher to obtain the opening position Fresnel reflection peak amplitude.
It can be seen that setting 9.48564 meters of opening positions of starting point as the Fresnel reflection of sensor fibre end face 12 in distance in Fig. 2
Beat signal corresponding to signal, its intensity are -84.8dBm.
As shown in figure 3, this monitoring result is liquid level 14 when being located at 13 top of sensor fibre end face, sensor fibre end face 13
Put the Fresnel reflecting peak of place's (i.e. 9.48564 meters of opening positions of distance setting starting point).Now at the exit end of sensor fibre end face 13
Medium refraction index nXFor nliquid, and nliquidMore than 1.Therefore, the beat signal intensity at the sensor fibre end face 13 is jumped
Become, and then saltus step occurs for the Fresnel reflection peak intensity of the opening position, saltus step is -94.6dBm.Fresnel reflecting peak after saltus step
Amplitude it is relevant with testing liquid refractive index, Fig. 3 is that testing liquid is pure water.
Comparison diagram 2 and Fig. 3 can be seen that testing liquid liquid level 14 and contacted with sensor fibre end face 13 front and rear, be set in distance
Determine corresponding to the reflected signal of sensor fibre end face 13 of 9.48564 meters of opening positions of starting point that there occurs step evolution jump for beat signal intensity
Become, and then saltus step occurs for the opening position Fresnel reflection peak intensity.The position of sensor fibre end face 13 is setting liquid level
Position.
Changed in a computer by the intensity of the reflected signal of the Algorithm Analysis opening position, it can be determined that liquid level to be measured is
The no height of liquid level 14 for reaching setting, and will determine that result is sent to slave computer by computer, and control corresponding indicator lamp and
Warning device.So as to realize monitoring, the alarm to liquid level.
In multiple spot level gauging of an alternative embodiment of the invention based on optical frequency domain reflection technology, fiber optic splitter
(1xN) 11 output end connects the sensor fibre that more root long degree differ.Selection and tested point can be determined according to prepare liquid number of sites
The fiber optic splitter (1xN) 11 of number matching.In theory, the branch's number that can be added is unrestricted, the sense light in each branch
Fibre 12 chooses length according to setting liquid level.The selection principle of length is:So that the sensor fibre end of every sensor fibre 12
Face is located at each setting liquid level of liquid level to be measured.Each sensor fibre 12 and the testing liquid height one of each setting
One correspondence.Because the beat signal frequency that optical frequency domain reflection technology measures can be mapped as physical distance, the sense light of different length
The sensor fibre end face 1 of fibre 12 corresponds to different distances.In multiple spot level monitoring, the output end of fiber optic splitter (1xN) 11
Connect the sensor fibre that more root long degree differ.Fresnel reflection letter at the sensor fibre endface position of each sensor fibre 12
Number returned along road, coupling is combined into single-mode fiber 4 at fiber optic splitter (1xN) 11, the backreflected signals in single-mode fiber 4
Fresnel reflection information at sensor fibre endface position with each sensor fibre 12.Back reflected laser exists with reference light
Interfered at fiber coupler (1x2) 6, interference signal is converted to electric signal into photodetector 7, by data collecting card 8
Collection.Analysis is demodulated to beat signal corresponding to the sensing end face opening position of every sensor fibre 12, every can be obtained
Whether the Fresnel reflection intensity at the sensor fibre endface position of sensor fibre 12 changes, and then judges that testing liquid is
The no sensor fibre end face for reaching any one sensor fibre 12.Because the sensor fibre 12 of each different length corresponds to not
With setting liquid level, therefore, the Fresnel reflection intensity of the sensor fibre end by analyzing every sensor fibre 12
Change to judge whether liquid level reaches corresponding setting liquid level, realize multiple spot level gauging.
Single-mode fiber 4 can use general single mode fiber, 1550 communication bands, for optical signal transmission.
If Fig. 4 is multiple spot level gauging schematic diagram.It is anti-to sensor fibre end face 12 in 4 sensor fibres 12 of different length
Signal is penetrated to be demodulated to obtain 4 Fresnel reflecting peaks.Each Fresnel reflecting peak corresponds at 4 sense light at setting height
The Fresnel reflection of fine end face 12.It can monitor whether testing liquid reaches by the Strength Changes for monitoring each Fresnel reflecting peak
To the corresponding height of setting liquid level 13.
Beat frequency interference signal demodulating method based on above-mentioned point type liquid level sensor specifically includes several steps
The first step, using optical heterodyne detection technique, to backscatter signal along sensor fibre (Rayleigh scattering and Fresnel
Reflection) it is acquired with the interference signal after reference arm generation beat frequency interference.
Second step, the beat signal gathered using computer to the first step progress non-uniform Fast Fourier are converted and passed
Photosensitive fine beat frequency frequency spectrum corresponding along the line.
3rd step, drop point processing is carried out to beat frequency frequency spectrum, it is therefore an objective to reduce whole spectrum number strong point, accelerate computing speed
Degree.
4th step, beat frequency spectrum signal is smoothed, improves the difference of Fresnel reflection peak value and ambient noise.
It is easy to accurately find the position of each reflection peak.
5th step, peak-seeking calculating is carried out to beat frequency frequency spectrum.Peak-seeking, which calculates, to be included finding all reflection peaks of whole spectrogram
Transverse and longitudinal coordinate, i.e. distance and peak value size.The transverse and longitudinal coordinate of all Fresnel reflections calculated and preservation, as local ginseng
Examine value.
6th step, peak value magnitude difference compare.A data are often gathered, it is poor to be carried out with the Local Reference Number that step 5 preserves
Value calculates.When the peak value size of this gathered data is more than given threshold (given threshold with Local Reference Number peak value magnitude difference
Depending on testing liquid refractive index, due to liquid level to be measured and sensor fibre end contact whether Fresnel reflecting peak strength difference can
Up to 10dB, therefore given threshold scope is very wide, and measurement accuracy is high) when, return judges numerical value 1, is otherwise 0.All binary systems
Number forms truth table.
7th step, the truth table data corresponding to each reflection peak are sent to slave computer.The corresponding instruction of slave computer control
Lamp and warning device
As it will be easily appreciated by one skilled in the art that drawings and Examples described herein are only illustrating the technology of the present invention
Scheme rather than its limitations, it is all do not depart from the present invention program spirit and principle within made any modification, equivalent substitution and
Improve etc., it all should cover among the claimed technical scheme scope of the present invention.
Claims (5)
1. the point type liquid level sensor device based on optical frequency domain reflection technology, it is characterised in that including linear frequency sweep laser, light
Fine beam splitter, optical fiber circulator, sensing module, fiber coupler, photodetector, data collecting card, computer and alarm electricity
Road；Wherein：
The sweeping laser that the linear frequency sweep laser exports is divided into two-way by the fiber optic splitter, is all the way flashlight, separately
It is reference light all the way；Flashlight enters the optical fiber circulator, and reference light enters the fiber coupler；
The sensing module is connected by single-mode fiber with the optical fiber circulator, and flashlight enters the sensing by single-mode fiber
Module；The sensing module includes fiber optic splitter, single or more sensor fibre, the tail end end face warp of every sensor fibre
Transverse cuts are smooth, and the tail end of each sensor fibre is placed in the container of different set liquid level；Flashlight passes through the optical fiber point
Beam device enters sensor fibre, returns and passes through along road in Fresnel reflection signal caused by the tail end end of each sensor fibre
It is coupled into single-mode fiber at fiber optic splitter, the backreflected signals light in single-mode fiber is imported by the optical fiber circulator
The fiber coupler, beat frequency interference occurs at the fiber coupler with reference light, produces beat frequency interference signal；
The beat frequency interference signal is converted into electric signal by the photodetector；
The data collecting card gathers the beat frequency interference signal in electric signal by multichannel simultaneously；
The computer enters row data communication with the linear frequency sweep laser, the data collecting card, and controls described linear
Frequency swept laser and the data collecting card, the computer also carries out Treatment Analysis to beat frequency interference signal, and sends data to
The warning circuit；
The data that the warning circuit issues according to the computer of reception, control indicator lamp and alarm.
2. point type liquid level sensor device as claimed in claim 1, it is characterised in that the fiber optic splitter will be described linear
The sweeping laser of frequency swept laser output is divided into 50：50 two-way.
3. a kind of point type liquid level sensor measuring method based on claim 1 or 2, it is characterised in that comprise the following steps：
Linear scan laser sends the laser of optical maser wavelength periodicity linear change, and laser is divided into two-way into fiber optic splitter
Light, light is flashlight all the way, is all the way reference light；
Reference light is directly coupled into an input in fiber coupler；
Flashlight enters optical fiber circulator and is transferred to single-mode fiber, enters sensing module, each sensing by single-mode fiber
Fresnel reflection signal caused by the tail end end of optical fiber returns along road, and coupling is combined into single-mode optics at fiber optic splitter
Fibre, the backreflected signals light in single-mode fiber import the fiber coupler by the optical fiber circulator, existed with reference light
Beat frequency interference occurs at the fiber coupler, produces beat frequency interference signal；
Beat frequency interference signal is converted to electric signal through photodetector, is gathered by data collecting card, and quick Fu is by computer
In leaf transformation obtain the spectrum information of beat signal.
A kind of 4. beat frequency interference signal demodulating method of the point type liquid level sensor based on claim 1 or 2, it is characterised in that
Comprise the following steps：
Convert to obtain corresponding beat frequency frequency along sensor fibre to the beat frequency interference signal progress non-uniform Fast Fourier of collection
Spectrum；
Drop point processing is carried out to beat frequency frequency spectrum；
Beat frequency spectrum signal is smoothed, improves the difference of Fresnel reflection peak value and ambient noise；
Peak-seeking calculating is carried out to beat frequency frequency spectrum, peak-seeking calculates the transverse and longitudinal coordinate for all reflection peaks for including finding whole spectrogram,
That is distance and peak value size, the transverse and longitudinal coordinate of all Fresnel reflections calculated and preservation, as Local Reference Number；
Often gather a data, mathematic interpolation carried out with the Local Reference Number of preservation, when this gathered data peak value size with
When Local Reference Number peak value magnitude difference is more than given threshold, return judges numerical value 1, is otherwise 0, and all binary numbers form true
It is worth table；
Truth table data corresponding to each reflection peak are sent to warning circuit, warning circuit controls corresponding indicator lamp and report
Alert device is alarmed.
5. according to the method for claim 4, it is characterised in that before and after liquid level and sensor fibre end contact, with the biography
Step evolution saltus step occurs for the intensity for feeling beat frequency interference signal corresponding to fiber end face, is done by analyzing the sensor fibre end face beat frequency
The change of signal is related to judge whether testing liquid has reached setting liquid level.
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