Title of Invention

A APPARATUS USING AN ORIFICE AND A NON-CONTACT TRANSDUCER TO MEASURE FLOW RATE OF FLUIDS THROUGH PIPELINES

Abstract

This invention relates to an apparatus using an orifice and a non-contact transducer for measuring flow-rates of fluids through pipelines, The apparatus consists of (i) a flow sensing tube (1) with flange (6) through which the flow rate is to be determined, (ii) conducting. means (2) and (7) for establishing contact with bridge circuit and signal conditioner; (iii) metallic orifice (3); (iv) fixing means (4); (v) insulating gasket (5) and (vi) bridge circuit with signal conditioner (8) for registering fluid flow date. The apparatus of this invention has been illustrated in Figs.l and. 3 of the drawings.

Full Text

The present invention relates to an improved apparatus using an orifice and a non-contact transducer to measure flow rate of fluids through pipelines. More particularly this invention pertains to a novel-non-contact impedance type transducer for the orifice type flow sensor of fluids flowing through pipelines, metallic or non-metallic, which plays an . important role in process industries. Flow rate of a process fluid, commonest being water, flowing through a pipeline happens to be one of the most important variables to be measured and controlled in any process industry and the design of a suitable flow transducer with sufficient accuracy and precision is important even to this date. A large number of techniques has been evolved for utilising various effects of a fluid flowing through a pipeline to determine accurately the fluid flow rate , such as for instance, the effect of energy associated with a flowing fluid through a pipeline, Doppler effect, anemometer effect and effect of speed of the fluid suction pump on the flow rate, etc. In the vortex flowmeter, the effect of a blunt obstruction post to the flowing fluid through a pipeline has been utilised , which has established experimentally that the frequency of the vortices produced behind a blunt post inserted into a flowing fluid is linearly proportional to the velocity of the fluid. Hence the volume flow rate of the fluid is directly proportional to the frequency. In the coriolis flow meter , the coriolis force produced by a flowing fluid changes the tilting frequency of a vibrating tube, which is proportional to the flow rate. Even though both the vortex and coriolis flow transducers are quite sensitive and accurate as the frequency is being measured, these are very costly and have to be handled with care. Other flow transducers like orifice, venturi and nozzle type transducers, electromagnetic flow type transducer, etc. are in demand as they are less costly , simpler in design and easy to handle In the conventional orifice transducer, the pressure difference between upstream and downstream tapping points of the orifice is sensed by a diaphragm type differential pressure ( herein after abbreviated as "DP") cell. The pressure difference is produced due to the flow of fluid through the orifice according to Bernoulli's theorem. Movement of the diaphragm due to such pressure difference is converted into a pneumatic or electric signal by using flapper nozzle system, piezo-resistance or strain gauge system type converter. This DP-cell may thus suffer from errors due to change of elastic property of the diaphragm, corrosive effect and the temperature effect of the process fluid, mounting defect of the diaphragm cell, leakage of the fluid through the joints, etc. Moreover, there may be some maintenance problems due to the choking of the connecting tubes and trapping of the gaseous components of the process fluid in the connecting pipe line, etc. The principal object the present invention is to provide a novel apparatus which is cost effective and capable of overcoming the defects encountered in the measuring equipmentsoised heretofore. A further object of the invention is to provide a (novel) apparatus using a non-contact type transducer to measure flow rate of fluids flowing tnrough pipelines by using orifice. A still frurther object of the present invention is to provide an improved apparatus using a noovel non contact type transducer which does not need any diaphragm type DP cell. Another object of this invention is to provide a novel pparatus wherein the non-contact transducer may have an insulated metallic orifice in a flow sensing tube made of conducting material installed in a metallic pipeline with a conducting liquid flowing through it. 2 Another object of this invention is to provide a novel apparatus wherein the non-contact transducemay have a metallic orifice in a flow sensing tube made of insulating material installed in a non-metallic pipeline with a conducting liquid flowing through it. Yet another object pf this invention is to provide a novel apparatus wherein the non-contact transducer may have an insulated metallic orifice and a perforated metallic flow streamliner plate mounted close to the orifice in a flow sensing tube made of conducting material with an insulating fluid flowing through it. The foregoing objects are achieved by this present invention according to which there is provided an apparatus using an orifice and a non-contact transducer to measure flow rate of fluids through pipelines which comprises the following: (a) flow sensing tube through which flows the fluid, the flow rate of which is to be measured under given conditions' (b) conducting means for establishing contact with bridge circuit signal conditioner; (c) metallic orifice; (d) perforated metallic streamliner plate, (e) fixing means like screws, bolts and/or nuts, and (f) bridge circuit with signal conditioner for registering data for measuring flow rate of fluid through pipelines. As discussed above , the apparatus of the present invention uses a non-contact impedance type transducer. The said transducer is in the form of an impedance between an insulated metallic orifice and the conducting pipeline with or without the perforated metallic streamliner plate or between a metallic orifice and a very close grounded metallic ring surrounding the insulating pipeline of the flow head connected with the grounded metallic main pipe line. When a fluid flows through an orifice a vena-contracta region is formed and the distance and diameter of this vena-contracta region depends on flow rate. Hence the impedance in the form of parallel combination of a capacitance and resistance between an insulated orifice and an electrode very close to the orifice within the vena-cotracta region changes with flow rate. Since the pipeline is usually made of conducting material like cast iron, galvanised iron, stainless steel, carbon steel, etc. . the pipeline itself may be made the second electrode of this sensing impedance. With a view to measure a very small change in the capacitance, resistance or impedance of an impedance sensor, the invention has evolved a modified bridge network capable of measuring the changes in impedance of the flow sensor. The invention will now be further illustrated by the accompanying drawings in which- Fig. 1 shows a non-contact transducer of an insulating flange mounted orifice in an insulating non-metallic pipe line connected with the grounded metallic main pipeline for flow measurement. Fig.2 shows a non-contact transducer of a screw mounted orifice in an insulating non-metallic pipe line connected with the grounded main pipeline for flow measurement. Fig.3 shows a non-contact transducer of a conducting flange mounted insulated orifice in a conducting metallic pipeline with or without a perforated metallic streamliner plate connected with the grounded metallic main pipeline for flow measurement Fig.4 shows a modified Wein bridge network with signal conditioner for measurement of flow of fluid. In Fig.l, 1 is the insulating flow sensing tube, 2 is the conducting ring, 3 is tht metallic orifice, 4 is the fixing nut and bolt, 5 is the insulating material gasket, 6 is tht insulating flange and 7 is metallic terminal screw. In Fig.2, 1 is the insulating flow sensing tube, 2 is the conducting ring, 3 is the metallic orifice, 4 is the fixing screw of the orifice. In. Fig.3, 1 is the metallic flow sensing tube, 2 is the perforated metallic streamliner plate ( optional ), 3 is the metallic orifice, 4 is the insulated fixing nut & bolt. 5 is the material gasket, 6 is the metallic flange and 7 is metallic terminal screw. For all the Figs.l, 2 and 3, DS is the orifice plate with AB as the circular orifice hole. In Figs. 1 and 2, HK is a thin copper ring surrounding the insulating pipeline very close to the orifice. When a liquid flows through the pipeline, a vena - contracta region is formed and the diameter and distance of this region depends on flow rate. From this basic principle, the theoretical background of the present invention will be discussed hereafter: Lei the vena - contracta region be concentrated at an imaginary vertex point C and the cross-section of the conical flowing liquid in the plane of the ring HK in Fig.l or 2, or in the plane of the flange ( or streamliner plate ) HK in Fig.3, be EF. Let the vena -contracta vertex point C be at a distance x from the orifice plate, so that, (do/d) = (x-xo)/x where 'do' is the diameter ( E F) of the flowing liquid at the plane H K, (d' is the diameter of the orifice hole AB and V is the distance of the plane HK from the orifice. Hence the cross section Ao of the flowing liquid at the plane H K will be Ao= (p cdo2/4)= (p /4)(l-xo/x)2d2 (1) Since X0 A0 =( p /4)(l-2x0/x)d2 (2) Now the region outside E F in the plane H K inside the pipeline is only filled with the liquid at turbulence. Since the liquid is in the grounded pipeline and ring HK is grounded so the capacitance and resistance between the ring HK in Fig.l or 2 (or the-metallic flange HK in Fig.3 ) and the orifice plate DJ may be assumed to be equal to the capacitance (Cx) and resistance (Rx) between the orifice plate and the section EF of the flowing liquid. Hence these capacitance and resistance may be assumed to be given by the following equations (3) and (4) respectively. Cx = e o K Ao / Xo (J) And Rx = xo/Ao (4) where e 0 is the permittivity of the vacuum, k is the dielectric constant of the fluid and a is the conductivity of the fluid. Combining the equations (2) and (3) we have, Cx = (p e 0k d2/4x0) (1-2x0/ x) (5) Now at higher volume flow rate, the diameter of the vena-contrcta region decreases and hence the distance 'x' of the vena- contracta concentration point 'C ' from the orifice plate decreases. Let us assume that V is inversely proportional to the volume flow rate 'q'. i.e. x a I/q or x = k1 / q (6) where k1 is an arbitrary constant. Combining the equations (5) & (6), we have, Cx = (p e 0okd2/4xo)(l-2xoq/k1) (7) Or Cx=CX9(l-aq) (8) where Cxo = p e 0k d2/4 xo and a = 2xo/k1 (9) Hence if the flow rate increases then the capacitancce plate DJ and the grounded copper ring HK or the pipe flange HK may be assumed to decrease linearly which is verified from the practical experimet Similarly from the equation (4), we have, 1/RX = (p d2/4xo)(l-2xoq/k1) (10) or 1/RX -(l/RX0)(l-aq) (11) where 1 /Rxo = (p d2/4 Xo)and a = (2xo/k1) (12) These capacitance Cx and resistance Rx have been measured by a modified Wein Bridge Network ABDE as shown in Fig.4 of the drawings. In Fig.4, C ' denotes circuit common and A denotes ground terminal of the sensing jnipedanee=Zx.compIetely isolated from the circuit common C '. The sensing impedance may be assumed to be lumped parameter equivalent "of the parallel combinationoitnecapacitance Cx and resistance Rx as shown in Fig.4. The bridge is excited by a sinusoidal stabilised ac signal at a frequency f . Let the current passing through the arm AB, AE, .B,P and DE of the bridge network be I1, I2, I3 and I4 respectively. The linear 6p-Amps A1 and A2 maintain the bridge output nodal points B and E at the same virtual ground potentials. Hence the effect of stray capacitance between these two nodal points is reduced to a minimum value. Let the impedances of the arms AB and AE of the bridge network be respectively Zx and Z and the potentials at the output terminals of A1 and A2 be V1 and Vo respectively for the stabilised supply voltage V. Hence, I1=V/Zx I2 = V/Z,I3 = V,/P and l4 =V1, /Qand If= Vp/Rf (13) From KirchhofPs current law, we have I1 + I3 = 0 (14) and I2 + I4 +If =0 (15) From equations (13), (14) and (15), we have V/Z-(P/Q)V/Zx + V0/Rf =0 Or Vo = (VRf / Q) ( P/Zx- Q/Z ) (16) From fig.4, we have 1/Z= I/R+jCand I/Zx= !/Rx + jCx Hence the equation (16) is reduced to Vo - (VRfQ ) [P {( 1/ Rx) - (I/R)} - jQ (Cx - C ) ] (17) From the equations (8) and (11), the above equation (17) is reduced to Vo= (VRf/Q) [P {(l/Rx)(l-aq) - 1/R } - jQ {Cxo( 1 -aq ) - C}] (18) If the bridge be balanced at no flow condition when values of Rx and Cx are respectively Rxo and Cxo, then Vo = 0 when R = Rxo, C=Cx0 and q = 0. Hence the bridge output at any flow q is given by, Vo = (VRfQ ) [ (- P aq / Ro ) + jQ (Cxoaq )] (19) or Vo= - (VRfa / Q ) [ (P / Rxo) - jQ Cxo ] q (20) or V0 = k2q (21) where k2 = - (VRf a / Q ) [ (P / Rso ) - jcoQ Cxo ] = constant (22) 6 Hence the bridge output is linearly related with the flow rate. The bridge sensitivity factor k2 can be adjusted by varying the value of the feed back resistance Rf. As pointed earlier, the transducer of the orifice of the present invention does not need any diaphragm type DP cell and can be used in both ways ,e.g. (i) a non contact transducer of orifice with flow sensing tube made of insulating material like PVC, nylon, fibre glass, HDP, polypropylene or coplymers thereof and the like as showri and Fig.2 of the drawings or (ii) with flow sensing tube maae~oF a conducting material like galvaised steel, stainless steel, carbon steel etc., as illustrated in Fig.3 of the drawings. In Fig.l ami Fig.2, the sensing pipeline is made of a non-conducting, insulating material as described above which is a part of the grounded metallic pipeline of the same diameter. In Fig.l, the orifice plate is fixed in position between the conventional flanges made of insulating material by means of the fixing nuts and bolts whereas in Fig.2, The orifice plate is fixed in position by the terminal screw from outside, and the void or gap between the pipeline and the orifice, if any, is filled with epoxy adhesive 'Araldite'. In both Fig.l and Fig.2, a copper ring is fixed in position by soldered joints very close to the orifice surrounding the pipe. Two lead wires are connected with the orifice and the grounded copper ring. Referring to Fig.3, the orifice plate is fixed in position between the metallic flanges in a grounded metallic pipeline. The orifice is insulated from the metallic flanges and the fixing metallic nuts & bolts by suitable insulating material like Teflon", asbestors, fiberglass, HDP, polyacrylamide, PVC, PVA and paper coated with epoxy adhesive. Two lead wires are connected with the orifice plate and the pipeline. The invention will be further described with the help of the following example which is given by way of illustration and not by way of limitation. Example A flow pipeline is selected which is a uniform PVC tube having external and internal diameter of 25 and 20 mm. respectively. The orifice S.S. plate of 5-mm thickness and 20mm diameter, filled with a S.S. screw of dia. 3mm. The orifice hole diameter is 6mm with a chamfering angle of 13 degree in the downstream side. The orifice is mounted in the middle portion of the pipeline of length 1-meter kept in horizontal position. The orifice plate is fixed in position by the terminal screw from outside, and the void or gap between the pipeline and the orifice, if any, is filled with epoxy adhesive 'Araldite'. The insertion depth of the fixing screw is kept at around 5mm to eliminate possibility of leakage of the fluid through the terminal screw, which is utilized as one electrode of the sensing impedance. The other electrode of the sensing impedance is a thin copper ring of 0.5 mm thickness fixed in position surrounding the PVC tube very close to the orifice plate. One lead wire is soldered with the copper ring and other lead wire is connected with the fixing screwj)f_the_orifice plate. The modified Wien's bridge networg including a signal conditionersproduces an amplified bridge output with adjustable sensitivity factor. Hence the need of a pre amplifier may not be essential. The signal conditioner is required to convert the AC output of the bridge network of the flow sensor into 1-5 volt DC voltage so that it can be converted to a 4-20mA DC current signal and transmitted to a remote receiver or controller. In the present instance 1-5 volts DC signal is produced and the signal conditioner uses op-amp based circuit consisting of a rectifier, filter network and a zero and span adjustment network. The bridge output terminals are both at virtual common potentials and hence the effect of stray capacitance is minimised. The static characteristic of the variation of output AC voltage of the bridge output with flow rate has been found to be linear, as envisaged by the theoretical equation (19), and the percentage error from ideal linearity has also been found to be negligible. The flow tube along with the sensor is mounted horizontally with the grounded supply pipeline through which tap water is sent from a constant head overhead tank. The flowrate of water is increased in steps by means of a manual valve connected in series with the pipeline. In each step, the capacitance between the sensor output terminals is measured by a three and half digit LCR meter with an accuracy of +- 1%. The static characteristic graph has been obtained by plotting the capacitance measured by the LCEL,meter against flow rate, yielding a straight line. It is interesting to note that the static characteristic graph of the variation of the capacitance Cx of the sensor with theflowratelthnost follows the ideal theoretical equation(7), and the value of Cxo obtaine a from this ideal experimental graph is almost equal to the value obtained from equation(9), which establishes the correctness and reliability of the mathematical model presented herein above. To know the measurement errors at different flow rates, the flow of water through'the pipeline from the constant head tank is increased in steps by means of a manual valve connected in series and in each step the actual flow rate of water is measured and the corresponding bridge output and signal conditioner output are recorded. The static characteristics of the bridge network and the signal conditioner by plotting the output against the flow rate have been found to be linear. The method of operation of the apparatus is quite simple. The two lead wires are_ connected with the based modified Wein's Bridge circuit at the two points A and B as shown in Fig-4. The bridge is supplied from a stabilised sinusoidal AC source at 1000 Hz and the output of the bridge network is an AC voltage signal. The magnitude of the voltage signal may be adjusted by adjusting the feedback resistance Rf of the op-amp A2. The AC signai after rectification and filtration can be converted to DC voltage signal which is directly sent to the display unit at the control room or it may be converted into a 4-20mA current signal and then transmitted to the control room. The signal may also be digitized for communication with personal computer by using suitable communication techniques. During operation, the transducer is connected to the bridge circuit with signal conditioner as shown in Fig.4 of the drawings. The bridge is first balanced to have a minimum output when there is no flow of a particular fluid in the pipeline and the pipe is filled with the fluid at rest. Under this condition the signal conditioner is adjusted to have I volt DC voltage signal. Now with the help of a constant speed pump or a constant head overhead tank the maximum flow of fluid is allowed to flow through the pipeline and the actual maximum flowrate is measured by direct collection method or by any other accurate flow meter. Now the span and gain of the signal conditioner circuit is adjusted to have 5 volt DC signal at the output. The same procedure is repeated several times until stabilised results are obtained. The apparatus is now ready for measuring any unknown flow rate of the particular fluid. 8 Advantages: 1. As the sensing electrodes are outside the pipeline and have no contact with the liquid, errors due to corrosive effect of the liquid on diaphragm material, leakage effect of the process fluid through the DP cell joints, choking and gas trapping effects in the connecting pipelines, etc., are totally eliminated. 2. The effects of the elastic property of the diaphragm material and that of fluid temperature will be absent. 3. The design of the subject apparatus is such that it is rugged, has much longer life compared to conventional equipment's such as DP cell type transducer, has very good repeatability, resolution and stability. 4. The electrode part of the instrument is simple and involves little cost, thereby rendering the entire apparatus extremely cost effective. 5. Sensitivity of the apparatus can be selected to any value and thus its resolution is very high. 6. The apparatus can be converted into a smart unit by adopting proper communication technique and can be linked to a computer in DCS or PLC-based system. Additional modifications and improvements of the present invention may also be apparent to those skilled in the art. Thus, the particular combination of the parts described and illustrated herein is intended to represent only one embodiment of the present invention, and is not intended to serve as limitation of alternative devices within the spirit and scope of the invention. Having described the invention in detail with particular reference to the accompanying drawings and illustrative example given above, it will now be more specially defined by means of claims appended hereafter. 9 I claim:, 1. A novel apparatus using an orifice and a non-contact transducer to measure flow rate of fluids through pipelines which comprises tne fofiowing:- (a)flow sensing tube (1) with flange (6) through which flows the fluid, the flow rate of which is to be measured under given conition. (b) conducting fneans (2) and'(7) for establishing contact with bridge circuit and signal conditioner. (c)metallic orifice(3); (d) fixing means(4) like screws and/or nut and bolt, (e)insulating gasket (5) and (0 bridge circuit with 'signal conditioner (8) for registering data for measuring flow of fluid through pipelines. 2. An apparatus as claimed in Claim 1, wherein the is made of insulating . material like PVC, Nylon, glass, fiberglass, HDP, polypropylene or copolymers thereof. 3. An apparatus as claimed in Claims I and 2, wherein the s made of insulating material which is a part of the grounded metallic pipeline of tfie same diameter. 4. An apparatus as claimed in Claims Ito3, wherein an orifice plate is fixed in position inside the insulating pipeline by a screw from outside with the space between the orifice and the pipe wall completely sealed with a suitable sealing material, a conducting metallic ring is mounted close to the said orifice plate surrounding the pipe and two lead wires are connected with the fixing screw and the said metallic ring. 5. An apparatus as claimed in Claims I to 4, wherein the orifice plate is fixed between the insulating flanges of the insulating pipeline and metallic ring mounted close to the orifice is made of copper. 6. An apparatus as claimed in Claim 1, wherein the flow sensing tube is made of metal carrying an insulated fixing nut and bolt (4), an insulated material gasket (5), a metallic orifice plate(3), a metallic flange (6) and two lead wires connected with the orifice plate and the pipeline which are connected to the bridge circuit and signal conditioner (8) 7. An apparatus as claimed in Claim 1, wherein the flow sensing tube is made of metal carrying an insulated fixing nut and bolt (4), an insulated material gasket (5), a metallic orifice plate(3), a metallic flange (6), a perforated,metallic streamliner plate (2) and two lead wires connected with the orifice plate and the pipeline which are connected to bridge circuit and the signal conditioner (8) 8. An apparatus as claimed in Claims 1 and 7, wherein the signal conditioner converts the AC output voltage of the flow sensor into DC voltage so that it can be converted into a DC current signal and transmitted to a remote receiver or controller. 9. An apparatus as claimed in Claim 8, wherein the signal conditioner is designed using op-amp based circuit consisting of a rectifier and filter network and a zero and span. JO 10. An apparatus as claimed in Claims 1 and 7 to 9, wherein the non-contact transducer with flow sensing tube is made of conducting material like galvanized iron (GI), stainless steel (SS), carbon steel (CS), and the like. 11. An apparatus as claimed in Claim l0, wherein the orifice plate is fixed in position between the flange joints and the orifice is insulated from the metallic flanges and fixing nuts and bolts by suitable insulating material. 12. An apparatus as claimed in Claim 11, wherein the insulating material is selected from the group of Teflon, asbestos, fiberglass, HDP, polyacrylomitrile, PVC, PVA and paper with epoxy adhesive. 13. A novel apparatus using non-contact impedance type transducer to measure flow rate of flulds through pipelines, substantially as herein before described with particular reference to the drawings and appended examples. 11 Dated 20th day of . octorber,2003. This invention relates to an apparatus using an orifice and a non-contact transducer for measuring flow-rates of fluids through pipelines, The apparatus consists of (i) a flow sensing tube (1) with flange (6) through which the flow rate is to be determined, (ii) conducting. means (2) and (7) for establishing contact with bridge circuit and signal conditioner; (iii) metallic orifice (3); (iv) fixing means (4); (v) insulating gasket (5) and (vi) bridge circuit with signal conditioner (8) for registering fluid flow date. The apparatus of this invention has been illustrated in Figs.l and. 3 of the drawings.

Documents:

00554-kol-2003-abstract.pdf

00554-kol-2003-claims.pdf

00554-kol-2003-correspondene.pdf

00554-kol-2003-description(complete).pdf

00554-kol-2003-drawings.pdf

00554-kol-2003-form-1.pdf

00554-kol-2003-form-19.pdf

00554-kol-2003-form-2.pdf

00554-kol-2003-form-3.pdf

00554-kol-2003-p.a.pdf

554-KOL-2003-CORRESPONDENCE-1.1.pdf

554-KOL-2003-CORRESPONDENCE.pdf

554-KOL-2003-FORM 27.pdf

554-kol-2003-granted-abstract.pdf

554-kol-2003-granted-claims.pdf

554-kol-2003-granted-correspondence.pdf

554-kol-2003-granted-description (complete).pdf

554-kol-2003-granted-drawings.pdf

554-kol-2003-granted-examination report.pdf

554-kol-2003-granted-form 1.pdf

554-kol-2003-granted-form 18.pdf

554-kol-2003-granted-form 2.pdf

554-kol-2003-granted-form 3.pdf

554-kol-2003-granted-letter patent.pdf

554-kol-2003-granted-pa.pdf

554-kol-2003-granted-reply to examination report.pdf

554-kol-2003-granted-specification.pdf