CN1168955C - Single optical fiber tracing type high precision continuous liquid level measuring method - Google Patents
Single optical fiber tracing type high precision continuous liquid level measuring method Download PDFInfo
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- CN1168955C CN1168955C CNB011387890A CN01138789A CN1168955C CN 1168955 C CN1168955 C CN 1168955C CN B011387890 A CNB011387890 A CN B011387890A CN 01138789 A CN01138789 A CN 01138789A CN 1168955 C CN1168955 C CN 1168955C
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Abstract
The present invention relates to a single optical fiber tracing type high precision continuous liquid level measuring method which belongs to the technical fields of measurement and control. The end part of a single multimode fiber is made into a cone-point which is used as a sensing head by the method of electric arc smelting pull or optical grinding, and a servo mechanism which is controlled by a computer is combined to realize liquid level continuous measurement. The present invention is characterized in that the servo mechanism which drives an optical fiber sensing head to move is composed of a stepping motor, a threaded rod, a slide block and an outer sleeve pipe with a guide groove; the move direction of the sensing head is determined by the intensity of feedback signals of the sensing head to track liquid levels; positions of the liquid levels are calculated according to the corresponding step number of the stepping motor when the sensing head passes a two-phase interface of gas and liquid and optical feedback signals are changed. The actual measurement precision of the single optical fiber tracing type high precision continuous liquid level measuring method is within the range of 2m and is superior to (+/-) 0.1mm. The single optical fiber tracing type high precision continuous liquid level measuring method can be used for directly measuring the liquid levels and can not be affected by the change of liquid density. Thus the problem of long term drift does not exist. The present invention has the advantages of simple structure and strong reliability, and can be widely used for the liquid level measurement and control of small liquid cans of petrochemical industry systems.
Description
Technical field
The invention belongs to the observation and control technology field, is a kind of continuous liquid level measuring method based on optical fiber frustrated total internal reflection sensing, relates to the accurate measurement and the control of liquid level in the petrochemical complex industry.
Background technology
The traditional relatively electric sensor of Fibre Optical Sensor has many advantages, and as the detection sensitivity height, anti-electromagnetic interference (EMI) and essential safety etc. are used widely in Aero-Space and petrochemical complex industry in recent years.The continuous liquid level measuring of petrochemical industry at present adopts the method for measuring pressure conversion liquid level mostly, and this method exists measurement result to be subject to the influence of liquid density variation influence and sensor long term drift, is difficult to realize high-acruracy survey.Another kind method is to utilize optical fiber frustrated total internal reflection sensor measurement liquid level, as patent (95231166.6) and patent (00229488.5), though such sensor has very high bearing accuracy, can only carry out the discrete discontinuous measurement usually or do fixed point warning or control.
Summary of the invention
The objective of the invention is,, provide a kind of method of new, rift-free, continuous and direct measuring liquid level in conjunction with the highly sensitive characteristics of single fiber frustrated total internal reflection liquid level sensor and the accurate mechanical positioning and the tracking technique of micro-processor controlled feed service system.
Technical scheme of the present invention is, adopt arc welding to draw the method for awl directly to make cone angle in the end of common multi-mode communication optical fiber and spend to gas, liquid two-phase interface sensing head between 90 degree, make the gas/liquid two-phase signal contrast of sensing head reflected back surpass 10dB 80.In order to realize continuous liquid level measuring, sensing head need be installed to one micro-processor controlled can pinpoint servo control mechanism on, this is raised clothes mechanism and mainly is made up of the sleeve pipe and the explosion-resistant enclosure of micro-step motor, screw rod, slide block, band guide groove.Sensing head is fixed on the slide block, drive by stepper motor-screw mechanism, the optical signal magnitude that feeds back to according to optical fiber sensor head is determined the direction of motion of sensing head, when sensing head contact liquid level, computing machine promptly demonstrates the liquid level of this moment stepper motor position correspondence, keeps the tracking of liquid level simultaneously according to transducing signal.System controlled by computer and process of measurement partly are made up of pulse generation and counting, umber of pulse-liquid level conversion and demonstration, variable step tracking, bound warning and historical data demonstration record etc.
Effect of the present invention and benefit are, the single fiber frustrated total internal reflection sensing head that use is done through the electric arc melting and pulling by common multimode optical fiber, level detection sensitivity reaches the micron number magnitude, and compare with two optical fiber frustrated total internal reflection sensing heads, structure and manufacture craft are simple, good reliability, cost is low.The measuring accuracy of whole measuring system mainly by the machining accuracy decision of screw rod, slide block and guide groove, under the standard machinery processing conditions, can guarantee to make the measuring accuracy of total system to be higher than ten thousand/(2m measurement range).This measuring method is a kind of method of direct measuring liquid level, the not influence of liquid body variable density, there is not the long term drift problem, can be widely used in the level gauging and the control of the multiple liquid of petrochemical system, be specially adapted to the liquid level accurate measurement of miniature liquid jar.
Description of drawings
Accompanying drawing is the structure and the principle of work synoptic diagram of single optical fiber tracing type liquid level sensor.(1) microcomputer among the figure, (2) step motor drive control, the light emission, light-receiving and detection of electrons case, (3) led light source, (4) PIN photodetector, (5) 1 fens 2 fiber couplers, (6) single fiber cable, (7) 5 core safety cables, (8) aluminium alloy explosion-resistant enclosure, (9) 5 phase micro-step motors, (10) hermetic fiber articulation, (11) motor shaft-screw rod adapter sleeve, (12) screw rod (13) 90 degree tapered cylindrical optical fiber probes, (14) carry the slide block that fibre-optical probe is followed the tracks of motion of melt surface, (15) with the stainless steel sleeve pipe of vertical guide groove, liquid (17) screw rod bottom end bearing and end cap in (16) horizontal liquid tank.
Embodiment
Describe most preferred embodiment of the present invention in detail below in conjunction with accompanying drawing.
The centre wavelength of sending as LED in the accompanying drawing (3) is that the light signal of 850nm is transferred to the fibre-optical probe (13) of fluid reservoir internal fixation on slide block (14) through fiber coupler (5), single fiber cable (6).Sensing probe is to draw or the epiconuses of 80 to 90 degree that abrasive method is made into electric arc is molten in the end of common multi-mode communication optical fiber.When probe placed air, a part of light can transmit back PIN photodetector (4) via same optical fiber (6) and coupling mechanism (5) in the most advanced and sophisticated formation of awl total reflection, and the intensity of establishing this signal is I
0When sensing probe places liquid (17), because liquid refractive index is higher than the refractive index of air, make light destroyed at the total reflection condition at sensing head place, most of light leaks in the liquid, and the light signal strength of return detector (4) is weakened, and is made as I
1Common contrast R=10Log (I
0/ I
1) can reach more than the 20dB, utilize and return the tangible difference of light intensity in both sides, gas-liquid two-phase interface, the position that promptly can tell liquid level.Because the SENSITIVE SIZE of fiber tip only is about 60 μ m, adds the suction-operated when fiber tip contacts with liquid level, this sensing head can reach the micron number magnitude to the orientation sensing precision of liquid level.
What need explanation a bit is, because the difference of manufacture craft level, the angle of fibre-optical probe point or shape may depart from 90 desirable degree cone shapes, this can cause that the R value diminishes, though the R value can make system works within a large range, the too small meeting of R value influence the reliability and the serviceable life of system.Therefore utilize electric arc to draw awl or grinding fibre-optical probe, should make it as far as possible near desirable 90 degree cone shapes.
Slide block in the accompanying drawing (14) is used for carrying fibre-optical probe (13) and moves up and down and follow the tracks of liquid level, and the motion of slide block is that when screw rod rotated, slide block moved up and down along the guide groove (15) of sleeve pipe by screw rod (12) driving that is connected with stepper motor (9).The lower end of screw rod is supported by a teflon bearing (17).The minimum step angle of miniature 5 phase step motors (9) is 0.36 degree, if adopt the screw rod of 2m stroke, pitch is 1.25, the minimum theoretical resolution that its optical fiber is followed the tracks of liquid level can reach 1.25 μ m, in fact consider the machining accuracy of screw rod (12) and guide groove and the factors such as influence of surface tension of liquid, actual level gauging absolute precision can be better than ± 0.1, when range is two meters relative accuracy can reach ± 5 * 10
-5The outstanding feature of this measuring method is a level gauging precision height, does not have the problem of long term drift.Owing to only transmit the light signal of nW level at the fibre-optical probe of fluid reservoir inside, the micro-step motor of external container is the brushless machine of low voltage drive (24V), and taked the explosive-proof sealed structure of teflon between motor shaft and ring flange, belong to the essential safe type sensor, the liquid level that can be applicable to the multiple liquid container of petrochemical enterprise is accurately measured.
Claims (1)
1. single optical fiber tracing type continuous liquid level measuring method, it is characterized in that the single optical fiber tracing type liquid level sensor comprises by single multimode optical fiber draws or cone angle that the method for mechanical lapping is made into is the pointed sensing heads of circular cone of 80～90 degree through electric arc is molten, signal transmission fiber, 1 minute 2 fiber coupler, the light emission, light-receiving and header detection signal and by computer-controlled step motor drive mechanism, wherein step motor drive mechanism comprises stepper motor, screw rod, the outer tube of slide block and band guide groove, sensing head and slide block are fixed together, with slide block along the guide groove vertical motion; Its measuring method comprises the steps: to be reflected back toward described detection case after the light signal of light emitted reaches sensing head, computing machine is determined sensing head direction of motion according to the intensity of reflected signal, thereby control step motor-driven screw rod-slide block drives sensing head trend motion of melt surface, the Continuous Tracking level change, simultaneously according to sensing head during through liquid level the change step number of pairing stepper motor of return signal calculate and show liquid level.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB011387890A CN1168955C (en) | 2001-12-06 | 2001-12-06 | Single optical fiber tracing type high precision continuous liquid level measuring method |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB011387890A CN1168955C (en) | 2001-12-06 | 2001-12-06 | Single optical fiber tracing type high precision continuous liquid level measuring method |
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| Publication Number | Publication Date |
|---|---|
| CN1352378A CN1352378A (en) | 2002-06-05 |
| CN1168955C true CN1168955C (en) | 2004-09-29 |
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| Application Number | Title | Priority Date | Filing Date |
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| CNB011387890A Expired - Fee Related CN1168955C (en) | 2001-12-06 | 2001-12-06 | Single optical fiber tracing type high precision continuous liquid level measuring method |
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Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102914347B (en) * | 2012-11-09 | 2015-02-25 | 中国计量学院 | Liquid level sensor having self-calibration function and sensing method thereof |
| CN104034393A (en) * | 2013-10-16 | 2014-09-10 | 王琪伟 | Optical fiber liquid level dynamic monitor |
| CN104677462A (en) * | 2015-02-10 | 2015-06-03 | 浙江沁园水处理科技有限公司 | Self-adapted non-immersion type liquid level detection device and detection method |
| CN104729628B (en) * | 2015-03-25 | 2017-08-22 | 浙江工业大学 | A kind of liquid level sensor and level measuring method based on optical fiber |
| CN106989796A (en) * | 2017-04-20 | 2017-07-28 | 常熟理工学院 | Liquid level sensor |
| CN112304393B (en) * | 2020-10-28 | 2023-08-08 | 浙江传媒学院 | Liquid level measuring device and method, oiling machine verification system and method |
| CN113916326A (en) * | 2021-10-05 | 2022-01-11 | 桂林电子科技大学 | Inclined to one side double-core optic fibre level gauge |
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