AUSTRALIA 5 Patents Act 1990 10 15 COMPLETE SPECIFICATION INNOVATION PATENT 20 25 FLOW METERS 30 35 The following statement is a full description of this invention, including the best method of performing it known to me.
TITLE FLOW METERS 5 FIELD OF THE INVENTION This invention relates to the field of flow measuring devices. In particular, this invention relates to electromagnetic flow measuring 10 devices. DEFINITIONS OF TERMS USED IN THE SPECIFICATION The expression 'flow meter' in this specification is used to refer to a device 15 that is used for measuring the flow of a fluid or the amount of fluid that travels past a given location through a restricted space like a pipe or a conduit. The expression 'electromagnetic flow meter' in this specification is used to 20 refer to a device that derives the flow velocity by measuring the change in induced voltage of a conductive fluid passing across a controlled magnetic field. Electromagnetic flow meters are also sometimes referred to as magmeters or induction flow meters. 25 The expression 'potting' in this specification is used to refer to a process of filling a complete electronic assembly with a solid compound for resistance to shock and vibration, and for exclusion of moisture and corrosive agents. These definitions are in addition to those expressed in the art. 30 1 BACKGROUND OF THE INVENTION AND PRIOR ART The need to measure has been a part of our lives since the earliest days of 5 mankind. A value is assigned to a product after you measure it. For instance, to buy a bag of grains, it has to be weighed. Likewise, with development in technology and engineering, the need to measure fluids and gases has also become imperative. Measurement of fluids are typically carried out for various purposes like determining the quantity of fluid for billing purposes, 10 for ensuring that a process is operating satisfactorily, for calculations that can be used for improving the existing process, and to ensure that the critical parameters of a process operate as desired. Flow meters were invented to fulfill this need. The tools used for flow 15 measurement have to be accurate and reliable since these measurements ultimately form part of a bigger system that can be hampered if the measurements are erroneous. Various technologies have been used for flow measurement like magnetic, 20 vortex and ultrasonic. The most common flow meter is the electromagnetic flow meter and is based on Faraday's Law of Electromagnetic Induction. According to Faraday's law of electromagnetic induction, any change in the magnetic field with time induces an electric field perpendicular to the changing magnetic field: 25 E = -N d4/dt = -N d(BA)/dt where E is the induced voltage, B is the external magnetic field, A is the cross sectional area of the coil and N is the number of turns of the coil. 2 For electromagnetic flow meters, the number of turns N and the strength of the external magnetic field B are fixed. Thus Faraday's law can be expressed as E = -NB dA/dt = -NB dl/dt D = -NBVD 5 where D is the distance between the two electrodes and V is the flow velocity. If all the fixed parameters viz., N, B and D are combined into a single factor K = -NBD, we have E =KV 10 Hence it can be inferred that the induced voltage is proportional to the flow velocity. A typical electromagnetic flow meter places electric coils around or near the pipe through which the flow of fluid is to be measured. A pair of electrodes 15 is set across the pipe wall or at the tip of the flow meter. When the conductive fluid flows through the pipe, it is equivalent to a conductor cutting across a magnetic field. This induces a change in the voltage reading between the electrodes. The higher the flow speed, the higher is the voltage induced. 20 Electromagnetic flow meters cater to most kinds of fluids, the only requirement being it should be a conductive fluid. Electromagnetic flow meters are relatively cost-efficient and easy to install. Furthermore, since there are no moving parts, they are easy to maintain and offer relatively good 25 accuracy. The electromagnetic flow meters known in the art typically include double coil arrangements thereby making the flow meters bulky. 3 Several attempts have been made to make compact electromagnetic flow meters. US patent 5767418 discloses an electromagnetic flow meter with a single bobbin coil that generates a magnetic field through a central channel of a 5 spool through which the liquid whose flow is to be measured flows. This disclosure requires the pipe or conduit carrying the liquid to be cut and the flow meter disclosed in US patent 5767418 to be fitted such that the liquid flows through the above mentioned central channel of the spool. 10 Again, US patent 7213467 describes an electromagnetic flow meter configured as an insert for insertion into an in-situ housing connected in a flow line. Apart from requiring an in-situ housing already connected in the flow line, the flow meter in this disclosure also requires diverting a part of the flow away from the duct to make the meter compact. The measurement 15 is therefore based on a small portion of the flow rather than the actual flow through the flow line. Further, US patent application US2008/0060447 describes an electromagnetic flow meter which also includes a single coil for generating a 20 magnetic field across the measuring section of the flow meter. The flow meter in this disclosure again requires insertion of this device into the conduit or pipe carrying a fluid thereby necessitating cutting of the conduit or pipe. Also, the fluid needs to be conditioned by providing a restriction at the inlet of the flow meter thereby changing the flow of the fluid. 25 Furthermore, US patent 7421908 discloses an electromagnetic flow sensing apparatus and method comprising a flow tube that is placed within a flow system for conducting a flowing media using already existing process 4 connections or the flow tube may be welded to the mating pipe work. The flow sensor in this disclosure includes a fixed portion attached to a sidewall of the flow tube and a removable cartridge portion with sensor terminals adapted to be in electrical communication with the stationary electrodes of 5 the fixed portion. This device also necessitates some kind of invasion of the conduit or pipe carrying the flowing media. As seen in the disclosures described herein above, the flow meters known in the art have to be specifically designed to match the pipe or conduit that 10 carries the fluid. Apart from making the flow meter complicated and non standard, it also sometimes requires that the pipe or conduit be cut to install the flow meter. Moreover, flow meters known in the art use stainless steel pipes with an electrical insulating lining provided inside. 15 There is thus a need for a flow meter that can be moulded in-situ and which is cost effective and compact apart from being non-invasive and standard and also use the standard polymeric pipes available in the market as a flow tube. 20 OBJECTS OF THE INVENTION An object of this invention is to provide a compact device for measurement of flow of conductive fluids. 25 Another object of this invention is to provide a flow meter which is cost effective. 5 Still one more object of this invention is to provide a device for flow measurement which is easy to mount or assemble on the pipe through which flow is to be measured. 5 One more object of this invention is to provide a flow meter which is robust. Another object of this invention is to provide a device for flow measurement which is accurate. 10 Still one more object of this invention is to provide a device for flow measurement which conforms to industry standards and conventions. Yet another object of this invention is to provide a flow meter which is non invasive and does not require cutting of conduits or pipes. 15 One more object of this invention is to provide a flow meter which uses available standard polymeric pipes as the flow tube. SUMMARY OF THE INVENTION 20 In accordance with the present invention, there is provided a flow meter adaptable for measuring the flow of a fluid through a polymeric conduit, comprising: * a sensing assembly comprising: 25 - a core of magnetic material having a body fitted on a location adjacent to the outer surface of a polymeric tube and integral limbs extending from the body on either side 6 of the tube, the tube being mounted in line with the conduit; - a coil of conductive material wound around the body of 5 the core having terminals connected to a power source; - the coil and the core adapted to generate a magnetic field with a component passing through a plane across the cross section of the tube at the specific location; 10 - at least two sensing electrodes fitted in the tube diametrically opposite to each other and adapted to be in contact with the fluid passing through the tube; the sensing electrodes further adapted to define a sensing 15 axis orthogonal to the plane of the magnetic field; - a grounding electrode fitted in the tube; and - a closed loop formation adapted to enclose the magnetic 20 field created by the coil and the core; and * a housing formed around the sensing assembly. Preferably, in accordance with this invention, the tube and the conduit are of 25 the same polymeric material. Preferably, in accordance with this invention, the tube is an integral part of the conduit. 7 Typically, in accordance with this invention, the terminals of the sensing electrodes are connected to a signal sensing device. Typically, in accordance with this invention, the closed loop formation is a 5 metallic structure. Typically, in accordance with this invention, the closed loop formation is clamped to the coil. 10 Typically, in accordance with this invention, the closed loop formation is welded to the coil. Typically, in accordance with this invention, the closed loop formation is adapted to hold the coil in close proximity to the tube. 15 Preferably, in accordance with this invention, the flow meter is moulded in situ on the polymeric conduit serving as the tube. Typically, in accordance with this invention, the housing is of a polymeric 20 material. Typically, in accordance with this invention, the housing is a mould fitted over the sensing assembly and filled with a thermosetting resin. 25 In accordance with the present invention, there is provided a method for providing a flow meter on a polymeric conduit through which the flow of a fluid is to be measured comprising the following steps: - providing a core of magnetic material having a body fitted on a 30 location adjacent to the outer surface of a tube of the same 8 material as the conduit and integral limbs extending from the body on either side of the tube; - providing a coil of conductive material wound around the body 5 of the core having terminals connected to a power source; - connecting the terminals of the coil to a source of power for generating a magnetic field with a component passing through a plane across the cross section of the tube at the specific 10 location; - providing at least two sensing electrodes in the tube diametrically opposite to each other defining a sensing axis orthogonal to the plane of the magnetic field; 15 - connecting the terminals of the sensing electrodes to a signal sensing device; - providing a grounding electrode in the tube; 20 - providing a closed loop formation for enclosing the magnetic field generated by the core and the coil; - holding the coil in close proximity to the tube by clamping or 25 welding the closed loop formation; and - providing a housing and potting it by introducing a thermosetting resin forming a flow meter. 30 In accordance with another embodiment of the present invention, there is provided a method for providing a flow meter on a polymeric conduit 9 through which the flow of a fluid is to be measured comprising the following steps: - providing a core of magnetic material having a body fitted on a 5 location adjacent to the outer surface of a polymeric tube and integral limbs extending from the body on either side of the tube; - providing a coil of conductive material wound around the body 10 of the core having terminals connected to a power source; - connecting the terminals of the coil to a source of power for generating a magnetic field with a component passing through a plane across the cross section of the tube at the specific 15 location; - providing at least two sensing electrodes in the tube diametrically opposite to each other defining a sensing axis orthogonal to the plane of the magnetic field; 20 - connecting the terminals of the sensing electrodes to a signal sensing device; - providing a grounding electrode in the tube; 25 - providing a closed loop formation for enclosing the magnetic field generated by the core and the coil; - holding the coil in close proximity to the tube by clamping or 30 welding the closed loop formation; and 10 - providing a housing and potting it by introducing a thermosetting resin forming a flow meter. In accordance with one more embodiment of the present invention, there is 5 provided a method for providing a moulded in-situ flow meter on a polymeric conduit serving as a flow tube through which the flow of a fluid is to be measured comprising the following steps: - providing a core of magnetic material having a body fitted on a 10 location adjacent to the outer surface of the conduit and integral limbs extending from the body on either side of the conduit; - providing a coil of conductive material wound around the body of the core having terminals connected to a power source; 15 - connecting the terminals of the coil to a source of power for generating a magnetic field with a component passing through a plane across the cross section of the conduit at the specific location; 20 - providing at least two sensing electrodes in the conduit diametrically opposite to each other defining a sensing axis orthogonal to the plane of the magnetic field; 25 - connecting the terminals of the sensing electrodes to a signal sensing device; - providing a grounding electrode in the conduit; 11 - providing a closed loop formation for enclosing the magnetic field generated by the core and the coil; - holding the coil in close proximity to the conduit by clamping 5 or welding the closed loop formation; and - providing a housing and potting it by introducing a thermosetting resin forming a flow meter. 10 BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The invention will now be described in relation to the accompanying drawings, in which: 15 FIGURE 1 illustrates a cross section of a conduit; FIGURE 2 illustrates a cross section of a conduit with holes drilled for inserting electrodes in accordance with the present invention; 20 FIGURE 3 illustrates a cross section of a conduit with electrodes inserted into the drilled holes in accordance with the present invention; FIGURE 4 illustrates a cross section of a conduit along with a coil, core and connecting wires arranged in accordance with the present invention; 25 FIGURE 5 illustrates a cross section of a conduit wherein a metallic polygonal structure is clamped in accordance with the present invention; and FIGURE 6 illustrates a cross section of a flow meter encased in a housing in 30 accordance with the present invention. 12 DETAILED DESCRIPTION OF THE ACCOMPANYING DRAWINGS 5 The invention will now be described with reference to the embodiment shown in the accompanying drawings. The embodiment does not limit the scope and ambit of the invention. The description relates purely to the exemplary preferred embodiment of the invention and its suggested application. 10 The flow meter in accordance with the present invention is typically used with conduits made of materials like PVC (Polyvinyl chloride), PVDF (Polyvinylidene Fluoride), glass, carbide, and ceramic. Conventional flow meters use stainless steel conduits through which the fluid whose flow rate is 15 to be measured is flowing. These flow meter pipes need to be provided with an insulating liner. These liners are bonded with the stainless steel pipe. Often there is a mismatch between the flow meter pipes and the pipes of the system. This mismatch occurs in various parameters like resistance to pressure, temperature, reaction of the fluid on the conduit, chemical 20 resistance of the material of conduit and desired flow characteristics. The flow meter in accordance with the present invention uses the available standard polymeric pipe itself as the flow tube; separate flow tubes with appropriate matching is not required. 25 This present invention envisages a device for measuring the flow of fluids through restricted spaces like a conduit and will be described in detail with reference to FIGURES 1 to 6. 13 FIGURE 1 illustrates a cross section of a conduit 22 through which a fluid flows. The conduit 22 is made of an electrically non conductive material. Two holes 26 are drilled diametrically opposite to each other in the conduit 22 as illustrated in FIGURE 2. Two sensing electrodes 16 are inserted into 5 the holes drilled in the conduit 22 as illustrated in FIGURE 3 to define a sensing axis. These holes are sealed after the sensing electrodes 16 are inserted to be in contact with the fluid passing through the conduit 22. FIGURE 4 illustrates a cross section of the conduit 22 along with the 10 arrangement of a coil 14, a core 30 and connecting wires in accordance with the present invention. An earthing / grounding electrode 24 is inserted into the conduit 22. The core 30 is made of magnetic material and provided with a body fitted at a location adjacent to the outer surface of the conduit 22 and integral limbs extending from the body on either side of the conduit 22. The 15 coil 14 of conductive material is wound around the body of the core 30. Terminals 12 of the coil 14 are taken out and connected to a source of power (not shown). The coil wound around the body of the core 30 generates a magnetic field 20 with a component passing through a plane across the cross section of the conduit 22 at the specific location. Terminals 10 of the sensing electrodes 16 are taken out and connected to a signal sensing device (not shown). The sensing axis defined by the sensing electrodes 16 is orthogonal to the plane through which the magnetic field passes. 25 FIGURE 5 illustrates a cross section of a conduit wherein a metallic polygonal structure is clamped in accordance with the present invention. A closed loop formation 20 defining an enclosed path is provided to enclose 14 the field produced by the coil 14 wound around the body of the core 30. Typically, the closed loop formation 20 is a metallic polygonal structure which is clamped or welded to the coil 14 using screws thereby holding the coil 14 in close proximity to the conduit 22. 5 FIGURE 6 illustrates a cross section of a flow meter encased in a housing by potting the sensing assembly. A mould is fitted over the entire sensing assembly and a thermosetting resin like fiber glass or molten polypropylene is poured into it. This resin after setting forms the housing 18. Once the resin 10 is set the mould is removed and a flow meter housing 18 is formed. The polymeric material of the housing 18 may be same as or different from the polymeric material of the conduit 22. Also the housing 18 may be moulded around the actual flow conduit 22 after drilling the holes for the 15 electrodes in the conduit 22 or alternatively, a flow meter may be mounted in the pipeline having a polymeric flow tube around which the housing is moulded. When a conductive fluid flows through a conduit, a small voltage is 20 generated across the sensing electrodes. This voltage is then given to a signal sensing device which includes an amplifier. The output of the amplifier is typically about 3-4 microvolt. This voltage is then converted in terms of current in the range of 4- 20 mA. The current rating corresponds to the velocity of the fluid and depends on the type of pipeline for which 25 measurements are being taken. This current is supplied to a display means which is calibrated to display the flow rate. 15 Although, the present invention has been described herein above for a moulded in-situ flow meter, wherein the conduit itself serves as a flow tube for the flow meter, the same can be applied to a flow meter provided with a flow tube made of the same polymeric material as the conduit or 5 alternatively of a different polymeric material. The flow tube may be designed to be an integral part of the conduit. TECHNICAL ADVANCEMENT A flow meter as described in the present invention has several technical 10 advantages including but not limited to the realization of: " a compact device; " a cost effective device; 15 " a device which is easy to mount or assemble on the pipe through which flow is to be measured; " a device which is robust; 20 " a device for flow measurement which is accurate; " a device for flow measurement which uses available standard polymeric pipes in the market as a flow tube. 25 " a device for flow measurement which conforms to the standards and conventions; and 16 * a non invasive device which does not require cutting of conduits or pipes. 5 While considerable emphasis has been placed herein on the various components of the preferred embodiment, it will be appreciated that many alterations can be made and that many modifications can be made in the preferred embodiment without departing from the principles of the 10 invention. These and other changes in the preferred embodiment as well as other embodiments of the invention will be apparent to those skilled in the art from the disclosure herein, whereby it is to be distinctly understood that the foregoing descriptive matter is to be interpreted merely as illustrative of the invention and not as a limitation. 15 17