Integrally molded magnetic flowmeter

The present invention relates to a type of flow meter used to detect and measure the flow rate of a process fluid in an industrial process plant. More specifically, the present invention relates to the measurement of flow rate using a magnetic flow meter.

Magnetic flow meters are commonly used to measure the flow rate of a conductive process fluid through an electrically isolated flow tube. According to Faraday's law of electromagnetic induction, when a conductive process fluid moves vertically in a magnetic field, a voltage is induced in the fluid that is proportional to the velocity of the process fluid and the strength of the applied magnetic field. A magnetic field can be generated by applying an electric current to a coil made of a single wire formed in a number of loops that are closely spaced apart. At this time, a pair of electrodes is used to measure the voltage induced by the movement of the process fluid.

<p num="0003"> Many flowmeters require a rigid flow tube (such as metal) to achieve the strength required to adapt to high pressures. In many cases, arranging and arranging electrodes and magnetic coils can be difficult and consumes a lot of time during manufacturing. Additional metal components, such as metal flow tubes, result in magnetic eddy current loss between the magnetic coil and the process fluid. In addition, the alignment and placement of coils and electrodes requires various joining steps, including welding.</p>

<p num="0004"> A magnetic flow meter for measuring the flow rate of a process fluid includes a magnetic coil arranged to apply a magnetic field to the process fluid. A pair of electrodes are electronically connected to the process fluid and are arranged to detect the voltage induced in the process fluid in relation to the applied magnetic field and the flow rate of the process fluid.<u style="single">Using a removable mold</u>Non-conductive material<u style="single">Formed by filling</u>A molded flow tube is arranged to accept the flow of process fluid. Molded flow tubes are molded around a magnetic coil and a pair of electrodes,<u style="single">The filled non-conductive material</u>It is configured to support a magnetic coil and a pair of electrodes. The flowmeter circuit is configured to apply a current to the magnetic coil and receive the voltage detected by a pair of electrodes.</p>

<p num="0005"> According to this configuration, partial or complete removal of stainless steel conduits for pressure containment, removal possibility of welded housings or other machined housings on the outside of the coil, magnetism between the coil and the process fluid. It offers a variety of benefits, including reduced eddy current loss and an overall simplification of the manufacturing process in which electrodes, coils, and associated wires are easily assembled in the mold and the polymer is injected or poured into the mold. ..</p>

<figref num="1">It is a figure which shows the process control system including a magnetic flow meter.</figref><figref num="2">It is a partial cut-out cross-sectional perspective view of the magnetic flowmeter of FIG.</figref><figref num="3">It is a partial cut-out cross-sectional front view of the magnetic flowmeter of FIG.</figref><figref num="4A">It is an exploded perspective view of the mold used for manufacturing the flow tube of the magnetic flowmeter of FIG.</figref><figref num="4B">It is a perspective view of the mold used for manufacturing the flow tube of the magnetic flowmeter of FIG.</figref><figref num="5">It is a schematic circuit diagram of the magnetic flowmeter of FIG.</figref>

The present invention provides a magnetic flow meter used to measure the flow rate of a conductive process fluid in an industrial process. In some embodiments, the present invention allows the coils and electrodes of the flowmeter to be arranged as required, and the configuration of the molded flow tube provides pressure containment. In certain embodiments, this is achieved with a configuration known as a "wafer" type vessel in which the vessel is secured between the two flanges at the opposing ends of the two process conduits.

In one example, the coils, electrodes, and related wiring are all molded or cast into solid polymer molded tubing or "rings" arranged in a "doughnut" shape, between the two process flanges of the pipeline. Can be attached to. The particular polymer can be selected as required based on the pressure of the process fluid, the size of the orifice, the ease of molding and the like. In some configurations, additional materials can be used to achieve structural reinforcement. For example, an "auxiliary ring" of metal or other material may extend around the outer circumference of the polymer tube. This can aid pressure containment and provide the polymer tubing with additional stability. The metals that can be used include, for example, stainless steel or carbon steel. Carbon steel, like any other material, has the advantage of providing a magnetic feedback path for the magnetic field. The polymer ring itself consists of, for example, polyurethane, PFA, non-conductive polyphenylene sulfide, and may optionally include conductive polyphenylene sulfide electrodes. Polyphenylene sulfide is commercially available from Ryton® and Techtron. It is known by the trade name (registered trademark). In general, any combination of electrodes, including electrodes of conductive polymers and non-conductive polymers, can be used to carry out the present invention.

These configurations include partial or complete removal of stainless steel conduits for pressure containment, removal potential of welded or other machined housings on the outside of the coil, magnetic eddies between the coil and the process fluid. It offers a variety of benefits, including reduced current loss and an overall simplification of the manufacturing process in which electrodes, coils, and associated wires are easily assembled in the mold to inject or pour the polymer into the mold.

In some embodiments, the magnetic flowmeter includes a flow tube arranged to accept the flow of process fluid. Further, the flow meter preferably includes a plurality of coils arranged adjacent to the flow pipe. The controller is configured to apply a magnetic field to the process fluid using multiple coils. The first and second electrodes are arranged to detect the potential of the process fluid, which is related to the applied magnetic field and the flow rate of the process fluid. The sensor is configured to detect the voltage between the first electrode and the second electrode. The controller is configured to calculate the flow rate of the process fluid based on the voltage detected by the sensor between the first and second electrodes.

In FIG. 1, a typical environment for the magnetic flowmeter 102 is illustrated at 100. More specifically, in FIG. 1, the magnetic flow meter 102 is connected to the process pipe 104, and further, the process pipe 104 is connected to the control valve 112. As shown in FIG. 1, the flow tube 108 of the flowmeter 102 is a "wafer" type flow tube, in which case it is secured between the flange 120 of the process conduit 104 and the opposing flange 130. As such, it does not have a flange. Flange 120 and 130 include bolt holes 122 and 132, respectively. Bolts 140 are arranged to be accepted through holes 122 and 132, which secure the flow pipe 108 between the flanges 120 and 130. The flow tube may also be provided with a sleeve 141 that receives the bolt, through which the flow tube 108 can be located in the center between the flanges 120 and 130.

In a magnetic flow meter, the process variable monitored is related to the velocity of the process fluid flowing through the flow tube 108. The magnetic flowmeter 102 can be configured to provide an output for long-distance transmission to a controller or indicator via the communication bus 106. In a typical processing plant, the communication bus 106 is a 4-20mA current loop, fieldbus connection, pulse output / frequency output, HART® protocol communication, to a controller or other device such as the system controller / monitor 110. A wireless communication connection (such as a wireless HART® communication protocol conforming to the IEC62591 standard), Ethernet®, or optical fiber connection, or other communication channel. The system controller 110 is programmed as a process monitoring device that displays flow rate information to a human operator, or as a process controller that controls a process using the control valve 112 via the communication bus 106.

FIG. 2 is a partially cutaway perspective view of the magnetic flowmeter 102, and FIG. 3 is a partially cutaway front view of the magnetic flowmeter 102. As shown in FIGS. 2 and 3, the magnetic flowmeter 102 includes a flow tube 108 connected to an electronics housing 240. The flow tube 108 is formed by a ring or tube 200 that internally holds the magnetic coils 222A and 222B. The coils 222A and 222B are arranged to generate a magnetic field inside the tube 200, which applies the magnetic field to the process fluid. Electrodes 224A and 224B are located within tube 200. The ends of the electrodes 224A and 224B extend at least to the edge of the tube 200, which allows the electrodes 224A and 224B to make electrical contact with the process fluid. FIG. 2 also shows a magnetic flow tube 108 disposed adjacent to a flange 120 that includes a bolt hole 122. As mentioned in connection with FIG. 1, the flange 120 and the flange 130 are used to secure the magnetic flow tube 108 between the portions of the pipe 104. In FIGS. 2 and 3, coils 222A and 222B having a saddle-shaped or "C-shaped" shape are illustrated. However, the present invention is not limited to this configuration. Furthermore, the present invention is not limited to a configuration having two coils and two electrodes, and any number of coils and electrodes can be used as required. In addition, as mentioned above, an optional outer support ring 202 may be used to achieve additional strength. In one example, the support ring 202 is made of metal. However, the support ring 202 may be formed from other materials and may partially or wholly extend around the ring 200.

4A and 4B show the molding process in which the mold 204 is used to form the tube 200. The mold 204 is arranged to allow the liquid polymer to be poured into the space formed within the mold 204 and the ring 202. Prior to filling this space with polymer, coils 222A, 222B, electrodes 224A, 224B, and their associated wiring are arranged as required within space 208 of mold 204. Molded electrodes of conductive polymers can also be formed by molding. Once the molding material has solidified, the final tube 200 is formed and the mold 204 is removed from the part and finished as required. After the molding process, additional processing (eg, additional machining or polishing of the ring 200) may be required. In FIGS. 4A and 4B, element 240 shows a connection housing used to electrically connect to the transmitter.

The block diagram of FIG. 5 shows an embodiment of a magnetic flow meter 102 for measuring the flow rate of the conductive process fluid 184 through the flow tube 108. The coils 222A and 222B are configured to apply an external magnetic field to the flow of the fluid according to the drive current given by the coil driver 230. The coil 222 is powered by either alternating current (AC) or direct current (DC). Electrodes (EMF sensors) 224A, 224B are electrically coupled to the fluid flow and provide the amplifier 232 with an EMF signal output 234 related to EMF generated in the fluid flow due to the applied magnetic field and fluid velocity. .. The analog-to-digital converter 242 feeds the digitized EMF signal to the controller system 248 (such as a microprocessor). A signal processor 250 is mounted within the microprocessor system 248 of the flowmeter electronic device 240, which is combined with an EMF output 234 to provide an output 252 related to fluid velocity. Memory 278 is used to store program instructions or other information.

The microprocessor system 248 calculates the velocity through the flow tube 108 according to the relationship between the EMF output 234 and the flow velocity, as described in Faraday's law. V = E / (kBD) Equation 1 Here, E is the EMF output 234, V is the velocity of the fluid, D is the diameter of the flow tube 108, B is the strength of the magnetic field in the fluid, and k is the constant of proportionality. .. The microprocessor system 248 calculates the flow rate of the process fluid according to a well-known technique. The digital-to-analog converter 258 connected to the microprocessor system 248 produces an analog transmitter output 260 for coupling to the communication bus 106. The digital communication circuit 262 produces a digital transmitter output 264.

In some configurations, the magnetic flowmeters of the present invention are configured to conform to the characteristics of the flanges 120 and 130 (see Figure 1) (where the magnetic flowmeter is fixed between them). When the magnetic field is not completely contained in the flow tube 108 of the present invention, the adjacent flange changes the magnetic field based on the magnetic permeability of the flange. This affects the calibration of the flowmeter. For example, if the flange is carbon steel, the flowmeter needs to be calibrated differently than if the flange were stainless steel.

In some embodiments, the microprocessor 248 is configured to detect whether adjacent flanges are made of carbon steel or stainless steel. More specifically, it changes the inductance of the magnetic circuit made by the coils 222A and 222B. This inductance is greater when carbon steel flanges are used than when stainless steel flanges are used. The increase in inductance is detected by monitoring the rate of change of the coil current as the polarity of the current reverses. Higher inductance values correlate with more gradual rate of change. The inductance of the magnetic circuit can be measured at the time of manufacture and different calibration values can be stored in the memory of the microprocessor 248. Software implemented in microprocessor 248 may be used to measure the inductance of the magnetic circuit and select the appropriate calibration value at startup when the flow tube begins operation. This adjustment can be done automatically at startup, or it can be done on the basis of other techniques, such as periodic inspections or command-based inspections received via the data bus 106.

In an alternative method for detecting the composition of the flange, the hysteresis of the magnetic circuit is measured upon reversal of the magnetic field. Hysteresis changes when the flange is made of carbon steel rather than made of stainless steel. The microprocessor 248 can analyze different hysteresis signals and select an appropriate compensation value. In one example, the coils 222A and 222B are driven by a special signal to make the detection of hysteresis easier. For example, the change in hysteresis can be detected more easily by adding a higher frequency signal at the start-up of the device.

Although the present invention has been described for preferred embodiments, one of ordinary skill in the art will recognize that modifications of form and detail may be made without departing from the spirit and scope of the invention. More specifically, embodiments of the present invention have been described as including two coils and two electrodes, but the number of coils and electrodes that can be used in the present invention is not limited thereto. The flowmeter coil can be configured as required. The coil may have a conical seat, an inverted conical seat, a labyrinth, or the like. In the above, two methods for selecting an appropriate calibration value have been described, but other methods including manual selection can be used. In another example, the calibration value is calculated based on the magnetic properties of the adjacent flanges. For example, the calibration value for a flow meter is polynomial characterization. It may be related to magnetic properties detected based on an equation such as equation). Similarly, compensation may be adjusted if the metal ring is used to reinforce the molded flow tube. As used herein, a wafer-type flowmeter means a flowmeter that has a flow tube at its end that does not have a flange.

102 Magnetic flow meter, 104 Process piping, 106 Communication bus, 108 Molded flow tube, 110 System controller / monitor, 112 Control valve, 120, 130 Flange, 122,132 Bolt hole, 140 Bolt, 141 Sleeve, 200 Ring or pipe, 202 Outer support ring, 222,222A, 222B Magnetic coil, 224,224A, 224B Electrode, 230 Coil driver, 240 Flow meter circuit, 248 Controller system, 258 Digital / analog converter, 262 Digital communication circuit