CN86205428U - Plug-in vortex street flowmeter - Google Patents

Abstract

An inserted vortex street flowmeter belongs to an instrument for measuring flow. A flowmeter for measuring the flow of a full pipe by a point flow velocity method using a sensor is provided. The flowmeter uses a screw rod capable of adjusting the insertion depth, a vortex flow sensor is fixed at the lower end of the screw rod, and a sensitive element of the sensor is a piezoelectric wafer for detecting stress. The sensor adopts a double-vortex generator structure, thereby greatly improving the signal-to-noise ratio of vortex street signals and greatly expanding the lower limit of flow velocity measurement. The flowmeter is suitable for measuring the flow of large-diameter pipelines, the maximum pipe diameter can reach 2 meters, the measurement precision is high, the gas and liquid are universal, and the flowmeter can reliably work in dusty and corrosive severe environments.

Description

Plug-in vortex street flowmeter

Belong to the instrument of measuring flow.

The plug-in type vortex shedding flow meter is a kind of instrument of measuring fluid flow.The industrial flow that uses both at home and abroad is in respect of the vortex shedding flow meter of restriction flowmeter, insert type turbine flowmeter, electromagnetic flowmeter, pitot tube and late nineteen seventies appearance at present.The measurement range of restriction flowmeter is narrow, and the pressure loss is big, the energy consumption height; The cost height of major diameter restriction device, installation difficulty, winter need add the heat-preserving anti-freezing measure.Though the insert type turbine flowmeter stated accuracy is higher, the medium cleanliness are required harshness, and require often to demarcate, operational reliability is not high.Electromagnetic flowmeter is only applicable to liquid medium, and the caliber product involves great expense greatly, is difficult to promote.Though the pitot tube cost is low and energy-conservation, range ratio is little, and the phenomenon that freezes is unsuitable in sewage and the medium-term and long-term work of dusty gas.The first generation vortex shedding flow meter that U.S. Eeastech company and Japanese Yokogawa Motor company release has respectively had at present that range ratio is wide, crushing is little, precision is high, repdocutbility is good, a simple structure, reliable, outstanding advantage such as gas-liquid is general, thermal adaptability is good.All there are the product that shows unique characteristics in West Germany E-H company, Britain Kent company, U.S. Foxboro company, Fischer﹠Por-ter company etc.But know according to open report institute, these companies mostly have only caliber at present less than 200 millimeters product, can not be used for big flow measurement.According to the U.S. 4,248,098 patent introduction: Japanese Yokogawa Motor company the stress of the seventies development in latter stage detect the formula piezoelectric sensor solved preferably flow measurement sensitivity and wide-range than between contradiction, but when measuring low flow rate of gas still signal too a little less than, present wild effect, its air velocity measurement lower limit is 6 meter per seconds, can not satisfy the needs that some low flow rate of gas is measured.Because stochastic factor, the flow signal that the living body structure of single-shot sends has bigger amplitude scintillation, even occurs intermittency once in a while, and is particularly serious when hanging down flow velocity, influenced the stable and repeated of flow measurement, reduced precision index.For the major diameter gas pipeline, for energy-conservation and minimizing crushing, often below 6 meter per seconds, this industrial flowmeter for existing vortex shedding flow meter and other kind all is difficult to be competent at working flow rate.

The objective of the invention is to overcome above-mentioned shortcoming, and release an a kind of plug-in type vortex shedding flow meter that is suitable for measuring greater than 200 mm dia pipelines, usefulness point flow velocity method the full packages flow, its service condition can be with reference to international standard ISO-7145.The present invention adopts a kind of new vortex pair generation body structure, so that still can obtain the stable flow rate signal in low flow rate of gas is measured, improves the waviness of signal, improves signal to noise ratio (S/N ratio).

Plug-in type vortex shedding flow meter configuration such as Fig. 1 on pipeline.Flow sensor 1 inserts in the tested pipeline 3 by screw mandrel 2, is immersed among the detected fluid, regulates screw mandrel 2, changes the insertion depth of sensor.The screw flange seat 5 of screw mandrel 2 is fixed on the ball valve 4, to realize continuing to flow also detachable sensor.The other end at screw mandrel 2 then is equipped with instrument amplifier box 7, with indicator stem 6 indication fluid flow directions.Flow sensor 1 is formed (Fig. 2) by cylinder 10, preceding generation body 13, back generation body 9, sensitive element 12, briquetting 11.Body 9 takes place in the back is that a section is trapezoidal cylinder, and upper end and cylinder 10 weld together, and by being threaded in the end of screw mandrel 2, solid dead with pin 8 again.Bodies 9, cylinder 10 and screw mandrel 2 will the back take place and couple together (as Fig. 4) in also available bolt 16.Screw mandrel 2 should have enough rigidity, drops on outside the vortex street frequency range with the mechanical natural frequency of vibration that guarantees whole insertion parts.Plastic spacer 14 seals, and prevents that fluid from entering the inside that body takes place in the back.In the thorax hole, inside of back generation body 9 piezoelectric chip 12 is housed, for example can stacking briquetting 11 on the wafer with making such as PZT piezoelectric ceramics, with bonding agent that the three is fixed as a whole, briquetting plays a part to strengthen convered structure rigidity.According to the medium working temperature, can select adhesive materials such as epoxy resin, high temperature inorganic adhesive.The lower end of back generation body 9 is unsettled, when the vortex lift alternating action that the body both sides take place takes place on the body 9 in the back, the inner bending normal stresses that produces of body is taking place, this stress produces the alternation electric charge on bonding piezoelectric chip 12, draw with lead 15 by electrode, the frequency of alternation electric charge is the vortex street frequency.The flow signal that this cantilever Beam structure is produced is than United States Patent (USP) 4,248, and the end described in 098 is fixed, and the flow signal that an end freely-supported Beam structure is produced is big more than 10 times.The present invention takes the back that body 9 bottom hollows take place, and top installs briquetting 11 measures such as grade additional, and the center of gravity that body 9 takes place after making is increased to the installation position place of piezoelectric chip, so that the vibration interference of non-flow signal is limited in less degree.Preceding generation body 13 is a rhombus section cylinder, and its upper and lower side can be fixed on the housing of cylinder 10 with welding, riveted joint or screw, the equal symmetry of body takes place before and after must guaranteeing be installed on the axis of cylinder.Because the synergy of body takes place in front and back, curl increases, and signal amplitude strengthens 5～10 times than the living body structure of single-shot, has fundamentally eliminated signal fluctuation and intermittency.Under the situation that guarantees sensor accuracy ± 1%, the air velocity measurement lower limit can reach 3 meter per seconds, and the fluid-velocity survey lower limit of water can reach 0.4 meter per second, range ratio is 20:1, repeatability is up to ± 0.06%, and this moment is if be reduced into 10:1 with range ratio, then precision can reach ± 0.5%.In view of the main effect of preceding generation body 13 is to produce vortex, when design, just can suitably reduce size and the quality that body 9 takes place in the back, thus the minimizing vibration interference.In order to obtain good measurement effect, recommend following parameters relation (Fig. 3): the inside diameter D of sensor cylinder 10 ₁With internal diameter of the pipeline D ₂Ratio be not more than 0.11, insert the unlikely excessive flow field analysis that influences behind the pipeline to guarantee sensor.In order to form stable vortex, the length L of sensor cylinder 10 is (1.4-1.6) D ₂, when using in the flow field of vortex is arranged, lengthening L can improve the stability of vortex frequency, but the L value conference influence the linearity of instrument.The trapezoidal cross-section two hypotenuse angle theta that body 9 takes place in the back equal 60 °, its fluoran stream surface width d ₂With cylinder 10 inside diameter D ₁Ratio be 0.27.Because the existence of preceding generation body 13 excessively strengthens d ₂Enhancing signal be there is no remarkable effect, d ₂Excessively also will increase resistance.The length l of body 9 downbeams takes place in the back ₂Should be greater than its width d ₂, otherwise to the expansion lower flow rate limit, to improve accuracy of instrument unfavorable, best relation is l ₂Equal 0.74d ₂l ₃Existence for the serviceability of regime flow meter, make fluoran stream surface width dimensions d ₂The unlikely variation rapidly under fluid erosion is necessary, generally gets l ₃Equal (0.1～0.15) d ₂The section configuration of preceding generation body 13 and size have a significant impact the performance of vortex shedding flow meter.A large amount of evidences, its optimum shape is the right angle rhombus, this shape can guarantee that the flow signal that piezoelectric chip picks up almost is a constant amplitude, no fluctuation, crushing is also little.The length of side d of rhombus ₁Fluoran stream surface width d with back generation body 9 ₂Ratio be 0.45～0.85, optimum value is 0.6.Two take place between the body apart from l ₁The same length of side d that body 13 takes place ₁Between should get the relation that adapts, d ₁Littler, l ₁Should be littler.Along with l ₁Shortening, Strouhal number St is more stable, the crushing that helps improving precision and reduce sensor.Its optimum value is l ₁Equal (2.2～2.4) d ₁, so just broken United States Patent (USP) 4,350, the l of regulation in 047 ₁Be at least 4d ₁Saying, thereby can be applied to the dual occurrence body structure in the sensor of plug-in type vortex shedding flow meter.

The present invention is suitable for the measurement of large-diameter pipeline flow, maximum caliber can reach 2 meters, and has a range ratio wide (20:1), advantages such as energy-conservation, thermal adaptability is good, can in-20～+ 300 ℃ of scopes, work, precision height, gas-liquid are general, reliable operation in many dirt and mordant rugged surroundings.

Claims (8)

1, a kind of vortex shedding flow meter that utilizes sensor to measure fluid flow, it is characterized in that said sensor (1) is to be packed in screw mandrel (2) lower end of scalable insertion depth with screw thread and pin (8) or with bolt (16), body (9), sensitive element (12) and briquetting (11) take place by cylinder (10), preceding generation body (13), back and form in sensor.

2, according to the described back of claim 1 body (9) taking place is that section is trapezoidal cylinder, and its upper end is welded or is connected on the cylinder (10) with bolt (16), and the lower end is unsettled.

3, be that section is the cylinder of right angle rhombus according to the described preceding generation body of claim 1 (13), its upper and lower side can be fixed on the cylinder (10) with welding, riveted joint or screw, and its diagonal line and cylinder (10) axis coincides.

4, be the high-temperature piezoelectric ceramic component according to the described sensitive element of claim 1 (12), with the high temperature inorganic adhesive body (9) taken place for ceramic component and back and be connected to an integral body.

5, according to the inside diameter D of the described cylinder of claim 1-3 (10) ₁Inside diameter D with pipeline (3) ₂Ratio be not more than 0.11, cylinder (10) length L and its inside diameter D ₁Ratio be 1.4～1.6.

6, the angle theta according to claim 1 or 2 described back generation body (9) trapezoidal cross-section two hypotenuses is 60 °, its fluoran stream surface width d ₂With cylinder (10) inside diameter D ₁Ratio be 0.27, its downbeam length l ₂With fluoran stream surface width d ₂Ratio be 0.74.

7, according to claim 1 or the 3 described preceding length of side d that body (13) rhombus takes place ₁Body (9) fluoran stream surface width d takes place with the back ₂Ratio be 0.45～0.85.

8, according between the described forward and backward generation body of claim 1-3 apart from l ₂With preceding generation body section rhombus length of side d ₁The best ratio be 2.2～2.4.

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