Magnetic flow meter assembly with independent coil drive and control system

Abstract

A magnetic flow meter assembly with an independent coil drive and control system. A magnetic flow meter assembly has a tubular body having two opposing ends defining a fluid flow path for a conductive fluid therebetween. The magnetic flow meter assembly further includes a pair of coil assemblies configured to transmit a current as received from a voltage regulator via first and second coil drivers. The coil assembly can thereby generate a magnetic field, wherein a pair of measuring electrodes detects a voltage induced by the conductive fluid passing through the magnetic field. In addition, the coil assemblies are each electrically coupled to at least one sensor, the at least one sensor providing feedback to a corresponding voltage regulator via a proportional-integral-derivative (PID) controller, the proportional-integral-derivative (PID) controller being configured to minimize an error between a corresponding measured current and a target current.

Description

Technical Field

[0001] The present invention relates generally to the control and operation of sensors for measuring fluids, and more particularly to magnetic flow meters for performing fluid flow measurements. Background Art

[0002] Magnetic flow meters measure the velocity of a conductive fluid through a pipe by generating a magnetic field and measuring the resulting voltage. These flow meters rely on Faraday's law, in which the flow of a conductive fluid through a magnetic field causes a voltage signal that is sensed by electrodes and the sensed voltage is proportional to the fluid velocity.

[0003] Magnetic flow meter assemblies are generally insertion-type magnetic meters or full bore magnetic meters. Insertion-type magnetic meters typically include a sensor body placed into a fluid flow and electrodes disposed at the distal end of the sensor body. The sensor may include a conductive coil that generates a magnetic field, which in combination with the fluid flow generates an electromotive force (voltage) that is then sensed by the electrodes. A full bore magnetic meter typically includes a tubular body arranged in line along a fluid conduit, with a conductive coil disposed on the tubular body that generates a magnetic field across the body and electrodes inserted into the wall of the body.

[0004] Although these flow meters are generally effective, there are deficiencies. For example, these devices may be subject to temperature changes, which, assuming a constant flow rate, affects the resistance of the conductive coil, thereby affecting the current flowing through the coil and potentially altering the magnetic field within the fluid flow path and the resulting measured voltage. In addition, since the conductive coils can be paired, any deviation between the pair of coils potentially changes the symmetry of the magnetic field, also resulting in an altered magnetic field. These changes to the magnetic field may adversely affect the measurement accuracy of the flow meter.

[0005] Therefore, it should be appreciated that a need remains for a magnetic flow meter assembly that addresses these concerns. The present invention satisfies these needs and others. Summary of the invention

[0006] Briefly and generally, the present invention provides a system and related methods for generating a magnetic field for a magnetic flow meter. The system includes: a first coil driver for providing a first current through a first coil assembly, a second coil driver for providing a second current through a second coil assembly, and corresponding sensors for respectively measuring electrical properties associated with the first and second coil assemblies. The system is further configured to provide feedback to first and second voltage regulators in response to the corresponding measured electrical properties. As such, the first and second voltage regulators can independently modify the current through the first and second coil assemblies in response to the feedback signal, and thereby enable a prescribed magnetic field to be generated within a fluid flow path while taking into account any asymmetric conditions affecting the coil assemblies.

[0007] More specifically, by way of example and not limitation, the system includes a tubular body having opposing ends configured to enable fluid flow therebetween. A pair of measuring electrodes are attached to the tubular body to measure a voltage induced by a conductive fluid flowing through a magnetic field generated by a coil assembly. By using the measured voltage, fluid velocity and flow rate can be calculated using a processor electrically coupled to the measuring electrodes.

[0008] In a detailed aspect of an exemplary embodiment, the system includes: a corresponding instrumentation amplifier for scaling an electrical property measured by a corresponding sensor; an analog-to-digital converter for converting the electrical property; and an error amplifier for detecting a difference between the measured electrical property and a target (desired) electrical property for a corresponding coil assembly. Based on the detected error, a proportional-integral-derivative (PID) controller provides an output to a pulse width modulator (PWM) for minimizing the error detected using a system tuning process. The PWM output is filtered, buffered, and summed to go into control feedback for a voltage regulator, which then controls the voltage output and thereby controls the current through the corresponding coil driver and the corresponding coil assembly.

[0009] In another detailed aspect of the exemplary embodiment, the coil driver is configured to alternate the direction of current through each coil assembly, wherein one cycle in a given time period represents current flowing through each coil assembly in a first direction followed by current flowing through each coil assembly in a second direction.

[0010] In yet another detailed aspect of the exemplary embodiment, the corresponding sensor is embodied as a shunt resistor.

[0011] For the purpose of summarizing the present invention and the advantages achieved over the prior art, certain advantages of the present invention have been described herein. It is to be understood that not necessarily all such advantages can be achieved according to any particular embodiment of the present invention. Thus, for example, those skilled in the art will recognize that the present invention can be embodied or implemented in a manner that achieves or optimizes one advantage or a group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

[0012] All of these embodiments are intended to be within the scope of the invention disclosed herein. These and other embodiments of the invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments with reference to the accompanying drawings, the invention not being limited to any particular preferred embodiment disclosed. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Embodiments of the invention will now be described, by way of example only, with reference to the following drawings:

[0014] Figure 1 is a simplified perspective view of a magnetic flow meter assembly according to the present invention.

[0015] Figure 2 The time-varying magnetic field B generated within the fluid flow path of a magnetic flow meter is illustrated.

[0016] Figure 3 is a simplified diagram of a circuit used to independently drive and control the magnetic field of a magnetic flow meter.

[0017] Figure 4 is a simplified diagram of a circuit for an H-bridge coil driver configured to alternate the direction of current flowing through a coil assembly.

[0018] Figure 5 is a simplified perspective view depicting the operation of an independent coil driver according to the present invention.

[0019] Figure 6 The time-varying current (I) is illustrated, depicting the direction of the alternating current flowing through the coil assembly.

[0020] Figure 7 The time-varying magnetic field B within the fluid flow path based on the direction of the alternating current flowing through the coil assembly is illustrated.

[0021] Figure 8 The time-varying voltage measured between the measuring electrodes based on the direction of the alternating current flowing through the coil assembly is illustrated.

[0022] Fig. 9 A method for controlling a full bore magnetic flow meter according to the present invention is depicted.

[0023] Fig.10 is a simplified perspective view of a magnetic flow meter assembly according to the present invention, the magnetic flow meter assembly including a bracket coupled to a pair of coils that form a magnetic circuit that confines a conduit.

[0024] Fig.11 yes Fig.10 A simplified perspective view of a magnetic flow meter assembly further comprising a shield housing and an electronic assembly. DETAILED DESCRIPTION

[0025] Referring now to the drawings and in particular to Figure 1 , a magnetic flow meter assembly 10 is shown having a novel coil drive and control system. The magnetic flow meter assembly 10 has a tubular body (e.g., a pipe) 12 having two opposing ends 14 and 16 that are aligned along a horizontal axis (Ax) and define a fluid flow path therebetween. The magnetic flow meter assembly 10 includes a pair of coil assemblies (18, 20) coupled to a mid-region of the flow meter and configured to pass current as received from a voltage regulator (52, 54) via first and second coil drivers (32, 34). The coil assemblies (18, 20) can thus generate a magnetic field 22 within a fluid flow path 24 of the tubular body 12 via current passing therethrough. A pair of measurement electrodes 26 attached to the body 12 are configured to detect a voltage induced by a conductive fluid passing through the magnetic field 22. In addition, the coil assemblies are each electrically coupled to at least one sensor (36, 38), the at least one sensor (36, 38) providing feedback to a corresponding voltage regulator (52, 54) via a proportional-integral-derivative (PID) controller (48, 49), the proportional-integral-derivative (PID) controller (48, 49) being configured to maintain an error between a corresponding measured current and a target current at zero. As such, based on the corresponding received feedback, each corresponding voltage regulator (52, 54) can independently manipulate the current through the corresponding coil assembly (18, 20) to overcome factors that cause the drive current to deviate from the target current, thereby enabling a prescribed magnetic field to be generated within the fluid flow for accurate flow measurement.

[0026] Continue to refer Figure 1, the coil assembly (18, 20) can be externally coupled to the tubular body 12 and aligned along a vertical axis (Az) that is orthogonal to the longitudinal axis (Ax). The pair of measuring electrodes 26 can be aligned along an axis (Ay) that is orthogonal to the longitudinal axis (Ax) and the vertical axis (Az), and is configured to detect a voltage induced by electrical communication with the fluid within the fluid flow path. The magnetic flow meter assembly 10 further includes a plurality of auxiliary electrodes 19 (a, b, c), which include a first auxiliary electrode 19 (a) and a second auxiliary electrode 19 (b) arranged upstream of the pair of measuring electrodes 26. The first and second auxiliary electrodes are aligned with the axis (Az) on opposite sides of the pipe so that the axis (Ay) and the axis (Az) are coplanar. The third auxiliary electrode 19 (c) is arranged downstream of the pair of measuring electrodes 26. The measuring electrode and the auxiliary electrode are each mounted to a corresponding hole formed in the wall of the pipe 12.

[0027] The housing is coupled to the exterior of the body and is configured to hold at least one processor (e.g., Fig.11 ). In an exemplary embodiment, each of the two measuring electrodes 26 is followed by a signal conditioning path that includes a high sensitivity operational amplifier and an adjustable gain instrumentation amplifier. The measured voltage potential (the difference measured between the two measuring electrodes) is further processed by a high resolution analog to digital converter and a processor. The digitally converted voltage potential is further scaled and processed by a second processor to accurately display and / or provide multiple outputs proportional to the flow rate, i.e., digital output, 4-20 mA analog output.

[0028] In certain embodiments of the present invention, the magnetic flowmeter assembly can be configured as described and claimed in the following applicant's co-pending patent application: U.S. application No. 16 / 146,090, filed on September 28, 2018, entitled "FULL BOREMAGNETIC FLOWMETER ASSEMBLY," which is hereby incorporated by reference for all purposes.

[0029] The magnetic flow meter assembly 10 relies on Faraday's law of electromagnetic induction for measuring the velocity of an electrically conductive fluid in a tubular body. Specifically, Faraday's law states that the voltage induced on any conductor moving at right angles through a magnetic field is proportional to the velocity of the conductor.

[0030] Ue and Proportional

[0031] in:

[0032] Ue = Induced voltage (i.e. signal voltage)

[0033] v = average velocity of the conducting fluid

[0034] B = Magnetic field strength

[0035] L = length of the conductor (i.e. the distance between the electrodes)

[0036] Alternatively, the fluid velocity v is related to Proportional.

[0037] The flow of the conductive liquid through the magnetic field B generates a voltage signal Ue, which can be sensed by the pair of measuring electrodes (26) and can in turn be used to calculate the velocity v of the conductive fluid. Magnetic flow meters are generally very accurate (e.g., <1% measurement error). As described by the Faraday equation, changes in the magnetic field strength B can cause significant errors in the measurement of the fluid velocity v.

[0038] As previously mentioned, the magnetic field can be generated by a pair of coil assemblies coupled to a magnetic flow assembly. Furthermore, it is known that for a Helmholtz coil pair, the magnetic field B is proportional to the current I and the number of loops (e.g., the number of turns), and the direction of the magnetic field is determined by the current polarity based on the right-hand rule. It is also known that the larger the magnetic field, the larger the voltage induced by the current as measured via the electrodes.

[0039] Thus, variations in the magnetic field B strength can introduce significant errors into the fluid flow measurement. These variations can be caused by a number of factors including, among others, temperature changes in the coil, differences in the electrical properties of the coil, drift of the drive electronics, and dimensional changes in the fluid flow path. For example, the coil resistance R coil is a function of the temperature of the coil.

[0040]

[0041] From this equation we see: Coil resistance R coil It increases linearly with temperature change, increasing when the temperature increases and decreasing when the temperature decreases.

[0042] refer to Figure 2 , an exemplary depiction of the magnitude of the magnetic field B within the flow field is shown for a given flow meter assembly that is not perfectly symmetrical (e.g., The magnitude is not equal to ). Ideally, The absolute value of will be equal to The absolute value of , thereby making the time-varying magnetic field B uniform over time. Separate values ​​of B1 and B2 are generated by alternating the direction of current flow through each coil assembly (18, 20), that is, B1 is the magnetic field generated by current flowing through the two coil assemblies in a first direction, and B2 is the magnetic field generated by current flowing through the two coil assemblies in a second direction (as further described below). In addition, the current flow through each coil assembly (18, 20) follows the right-hand rule, and as such, each coil assembly generates a corresponding magnetic field that combines together to obtain a corresponding magnetic field (B1, B2) that exists across the fluid. For example, by a first coil assembly (e.g. Figure 1 18) can be directed inwardly toward the fluid, while the magnetic field generated by the second coil assembly (e.g. Figure 1 The magnetic field generated by 20) goes outward from the body 12 and is oriented around the tubular body, thereby increasing the magnetic field of the first coil assembly as its value. The total, absolute magnetic field over a given time period Can be based on and Furthermore, as noted earlier, each magnetic field generated by each coil assembly is proportional to the corresponding drive current, and thus, by regulating the individual coil drive currents, a uniform magnetic field can be achieved.

[0043] Reference again Figure 1 The coil drive system includes: first and second coil drivers (32, 34) driving current through first and second coil assemblies (18, 20); first and second sensors (36, 38) for measuring electrical properties associated with the coil assemblies; first and second voltage sources (39, 41) coupled to first and second voltage regulators (52, 54) respectively for outputting a desired voltage to each coil driver (32, 34) based on feedback received from first and second PID controllers (48, 49). Each PID controller (48, 49) is responsive to a corresponding sensed electrical property.

[0044] Two coil assemblies (18, 20) are driven simultaneously by two independently controlled and operated coil drivers (32, 34), each of which provides a respective time-varying drive current. The coil drivers (32, 34) are each electrically coupled to a respective voltage source (39, 41) having a voltage output, which is regulated in real time by a respective voltage regulator (52, 54) based on feedback from a sensor (36, 38) that measures electrical properties of the coil assemblies. This ensures that a constant drive current is provided by the coil drivers (32, 34) to the coil assemblies (18, 20), regardless of environmental and physical changes to the coil assemblies. The drive current through the coils can have a frequency range of nearly zero (0 Hz) to the kilohertz range, and a magnitude generally less than ten (10) amperes.

[0045] refer to Figure 3 , showing in more detail the coil drive system (30, 31) for each coil assembly (18, 20). It should be noted that most Helmholtz coils use direct current (DC) to generate a static magnetic field. However, for this flow meter application, a time-varying magnetic field is used to avoid material migration of the coil assemblies (18, 20) (described below).

[0046] As previously mentioned, the drive systems (30, 31) each include: a pair of coil drivers (32, 34) for driving the first and second coil assemblies (18, 20); sensors that may be embodied as shunt resistors (36, 38) for measuring respective currents driving the coil assemblies; a pair of instrumentation amplifiers (40, 42) for scaling respective measured drive currents; a pair of A to D converters (ADCs) (44, 46) for converting analog signals to digital signals; and a pair of proportional-integral-derivative (PID) controllers (48, 49) for controlling the output voltage to each coil driver circuit via a pair of pulse width modulators (PWMs) (50, 51) and voltage regulators (52, 54). The voltage regulators (52, 54) enable the voltage from each respective voltage source (39, 41) to be regulated to output a desired voltage to each coil driver circuit.

[0047] The two coil drivers (32, 34) are energy management integrated circuits (ICs) that provide active power pulse outputs. The coil drivers can be fully integrated ICs or bridges built using discrete components, namely power MOSFETs. In an exemplary embodiment, the coil drivers can be embodied as H-bridge drivers, which are configured with very low resistance and thus low voltage drop during coil drive. As such, the coil drivers are capable of alternating the direction of the current through each coil assembly (described further below), thereby affecting the direction of the magnetic field emitted from each coil. Alternating the direction of the current, and thus the magnetic field, is achieved in order to avoid the electrochemical phenomenon of electrode migration.

[0048] The shunt resistors (36, 38) produce a voltage drop proportional to the current flowing through them. The shunt resistors have a fairly low resistance to limit power dissipation losses and minimize the effect on the magnetic field B. For example, a 0.1 ohm resistor in a 10A circuit will drop 1 volt.

[0049] Additionally and / or alternatively, the resistance across the shunt resistors (36, 38) may be manipulated to help more quickly obtain a stable drive current and thus a stable magnetic field. Given that the current driven through the coil assembly may be time-varying, obtaining a stable current more quickly will extend the time required to achieve a stable magnetic field. Figure 2 and Figure 7 and thereby maximize the conditions for obtaining accurate flow measurements in a given time period, as in Figure 8 As depicted by the corresponding area measured by the stable voltage.

[0050] As seen in the following equation, current (I) can be defined as a function of voltage (V), resistance (R), inductance (L), and time (t):

[0051]

[0052] The resistance across the coil driver system can be based on the resistance across the shunt resistors (36, 38), and the resistance within each coil assembly (18, 20), i.e., the coil resistance. The inductance is based on the coil assembly configuration, i.e., the coil inductance. Specifically, the coil resistance and coil inductance are unique to each coil assembly (18, 20) and are determined by the number of coil turns and the coil geometry within the corresponding coil assembly (18, 20). Referring to the equation for current (I) listed above, it is apparent that a larger resistance will provide a stable current faster. Thus, the shunt resistor can be manipulated using resistance, which will optimally provide a stable current faster without significantly affecting the magnetic field due to power dissipation losses, which come from a higher voltage drop.

[0053] Reference now Figure 3 , two instrumentation amplifiers (40, 42) receive respective voltages across shunt resistors (36, 38) and then scale the respective voltages of the shunt resistors (36, 38) in a manner that enables the received voltages to be processed. The instrumentation amplifiers (40, 42) amplify the signals and maintain a linear relationship between the respective input currents and the respective output voltages. The analog-to-digital converters (44, 46) receive the analog outputs from the instrumentation amplifiers (40, 42) and convert them into digital signals. The analog information is transmitted by modulating a continuous transmit signal and amplifying the signal strength or changing its frequency to add data to the transmit signal.

[0054] In an exemplary embodiment, the digital data from the two A / D converters (44, 46) represent the drive current through the corresponding coil driver system (30, 31) measured by the shunt resistor (36, 38). The error amplifier (56, 58) identifies the corresponding target (reference) current (I ref ) (60, 62) and the corresponding measured current, and outputs an error signal. The target (reference) current (I ref ): 1) stronger magnetic field (B) and 2) effective power consumption (i.e. I). Higher power may be inefficient, such as due to unintentional heat generation. On the other hand, given that the strength of the magnetic field applied to the fluid decreases as the pipe size increases, a higher power output may be required.

[0055] Continue to refer Figure 3 , the PID controller (48, 49) is configured to receive the corresponding error signal and apply proportional, integral and derivative (PID) factors so that the target current (I ref The difference between the current (60, 62) and the corresponding measured current (for the respective coil assembly) is kept to a minimum, in particular seeking to eliminate any difference (ie seeking I ref = corresponding measured current). Specifically, the PID controller uses a combination of: 1) specifying an output proportional to the detected error (proportional controller), 2) minimizing the steady state error by limiting the response rate of the system so as not to over-shoot the system corrected response (integral controller), and 3) predicting the system response based on the output (derivative controller). As such, the PID controller is configured to implement a "system tuning process" that enables a better target output to be achieved for minimizing the error signal. The PID controller (48, 49) will then output a command to the pulse width modulator (PWM) (50, 51).

[0056] In an alternative embodiment, a microprocessor may receive digital data from two A / D converters (44, 46), process the data using instructions stored in corresponding memories, and provide the result as an output. Such data processing may include comparing the measured electrical property (i.e., current) against the target electrical property, wherein the processor then calculates the PID output and subsequently outputs a series of commands for the pulse width modulator (50, 51). The microprocessor is any embedded microcontroller capable of performing the previously mentioned tasks. An example of a microprocessor is the Raspberry Pi single board computer developed by the Raspberry Pi Foundation. However, it should be appreciated that the current measurement may be processed by a general purpose processor (e.g., an x86 device), a microcontroller, a gate array, an application specific integrated circuit (ASIC), or other type of computer processor.

[0057] Reference now Figure 3 , pulse width modulation (PWM) is used to control the current supplied to the two coil drivers (32, 34) via outputs from corresponding PID controllers (or microprocessors, microcontrollers, etc.). The pulse width modulators (50, 51) control the average voltage output (and thereby regulate the current through each corresponding coil assembly (18, 20)) by rapidly switching between supply and load based on commands received from the PID controllers (48, 49). Each PWM (50, 51) can be configured with a duty cycle ranging from 0 to 100%, and a frequency that can range in kHz to bring the error to zero. In addition, the use of PWM ensures that power losses in the switching device are low, and there is a minimum current delivered to the coil assembly when the switch is "off".

[0058] The PWM signal is then filtered (64, 66) and converted to a buffered (68, 70) DC voltage which is then used to control a voltage regulator (52, 54) for outputting a voltage to a corresponding coil driver circuit in such a manner that the current through the coil assembly is kept constant at (or as close as possible to) a target current (I ref ). In this way, a prescribed magnetic field (B) will be generated which overcomes the presence of factors that may affect the magnetic field and thus enables a more accurate flow measurement.

[0059] The voltage sources (39, 41) coupled to the respective voltage regulators (52, 54) are dependent or controlled voltage sources that generally maintain a fixed voltage independent of the output current. In an alternative embodiment, the voltage sources (39, 41) are controlled in real time based on control signals received from the respective pulse width modulators (50, 51).

[0060] An advantage in using separate coil drivers for each coil assembly is that the required voltage output can be reduced by as much as half compared to a configuration in which a single coil driver is used to pass current through the series connected coil assemblies. More specifically, the required voltage headroom when using separate coil drivers will be calculated based on:

[0061]

[0062] Where R Coil1 represents the coil resistance of the first coil assembly, R Sensor represents the corresponding sensor resistance, and I represents the current through the first coil assembly. In contrast, a common coil driver with coil assemblies in a series arrangement would require a voltage headroom based on:

[0063]

[0064] As such, a lower voltage source for each coil driver may be used. For example, the required voltage may potentially be lower than that required for a car battery, such as 10.8V.

[0065] Another advantage to using an independent coil drive system for each coil assembly includes the ability of each system to compensate if the flow meter assembly is subjected to asymmetric conditions, such as asymmetric environmental effects. Yet another advantage to using independent coil drive systems is the ability to isolate one coil drive system at a time during a rough median flow measurement, thereby saving energy. Additionally, each coil drive system and assembly can be independently monitored for diagnostic purposes.

[0066] Reference now Figure 4 , shows the corresponding coil driver ( Figure 3 32, 34) in which current based on the output voltage from the corresponding voltage regulator (52, 54) can flow through the corresponding coil assembly (18, 20) through one of two paths. Based on the first path labeled I1, the H-bridge driver will be configured to direct the current to flow clockwise through the coil assembly by preventing the current from flowing through the second path labeled I2 within the driver. Conversely, based on the second path (I2), the H-bridge driver will direct the current to flow counterclockwise through the coil assembly by preventing the current from flowing through the first path within the driver. In this manner, the right-hand rule is followed, and as Figure 5 As depicted in , the direction of the magnetic field 22 will alternate based on the direction of the current flow, and thus, the direction of the voltage potential as measured by the electrode 26 will also alternate. Figure 6 As seen in the time period A complete cycle of the alternating current flow direction through the coil assembly is indicated, i.e., clockwise flow through the coil assembly followed by counterclockwise flow. In addition, Figure 7-8 The time period of the alternating current flow direction cycle is further depicted accordingly. Correspondingly, the magnetic field generated by the coil assembly and the characteristics of the voltage potential measured by the electrodes.

[0067] The coil driver further features an integrated on-chip voltage reference, ultra-low temperature drift (<15 ppm / C o ) and are highly reliable. The driver may include a serial SPI interface for accessing digital data.

[0068] Reference now Figure 5-8 , we will explain how the coil drive system enables U E Return to zero and establish a uniform magnetic field B in the fluid flow field. Figure 5 , the voltage potential U across the conducting fluid E At the measuring electrode U E1 and U E2 As pointed out earlier, when U E When is zero, a constant magnetic field B is achieved across the fluid flow v.

[0069]

[0070] refer to Figure 6 , an illustrative drive current (I) is shown having magnitude (I1, I2) and period . As noted earlier, each coil driver is individually controllable and drives a single coil assembly. Drive current I1 represents the current driven by the coil driver in a first direction, and drive current I2 represents the current driven by the coil driver in a second direction. The drive currents can have a frequency range from nearly zero (0 Hz) to the kilohertz range, and a magnitude generally below ten (10) amperes. In this example, the magnitudes of the drive currents (I1, I2) are equal. However, we will later describe how to modulate the drive currents (I1, I2) for each coil driver to produce a constant, time-varying magnetic field B.

[0071] refer to Figure 7 , an illustrative time-varying magnetic field is shown as having magnitude (B1, B2) and period As pointed out earlier, the magnetic field Changes in can introduce errors into the fluid velocity measurement. Therefore, it is important that changes in the magnetic field are corrected in real time to ensure that the fluid flow measurement is accurate and consistent over time. In this example, we see: and have the same absolute magnitude, and the period is consistent over time.

[0072] Reference now Figure 8 , illustrative drive voltage U E is shown as having magnitude (U E1 ,U E2 ) and the same period as the magnetic field B As discussed earlier, U E The separate measuring electrode U E1 and U E2 The voltage difference between the E When the magnetic field B is zero, a constant magnetic field B (for example, U E1 and U E2 In this example, we see that: U E1 and U E2 The absolute magnitude of is the same, and the period is consistent over time.

[0073] Reference now Fig. 9 , describes a method for controlling a full bore magnetic flow meter. The method begins by providing drive currents to two coil assemblies using first and second coil drivers (step 80). The respective drive currents generate (step 81) corresponding magnetic fields based on the drive currents through the coils.

[0074] The sensor measures (step 82) an electrical property in the corresponding coil assembly, which is then scaled by an instrumentation amplifier and converted from analog to digital using an A / D converter. The digital signal of the corresponding measured electrical property is compared against the target (desired) electrical property using an error amplifier. If the measured electrical property is the same as the desired electrical property (e.g., I ref = measured electrical property), then the measured current through the coil assembly is generating the desired magnetic field, and the voltage regulator continues to operate at the same output voltage ("no" branch). Alternatively, if an error signal is detected between the desired electrical property and the measured electrical property (e.g., I ref ≠ the measured electrical property), then modify the output voltage (“yes” branch) (step 84).

[0075] Using a PID controller, a system tuning process (step 86) is applied to minimize the detected error signal, wherein the tuning process provides an output that enables a target system response that efficiently resolves the measured error. The output from the PWM is provided to a voltage regulator, which modifies the corresponding drive voltage (step 88). As such, each coil assembly is driven via a modified drive voltage, with a current that seeks to generate the desired magnetic field (step 81) and minimize the error between the target reference currents.

[0076] Reference now Fig.10 , the coil assemblies 18, 20 are coupled to the tubular body (pipe) 12 in the middle region of the tubular body (pipe) 12. The coil assemblies are assembled to the outside of the pipe, aligned along the axis (Az). More specifically, each coil is held in place by a bracket 21, which constrains the pipe 12. The poles 25 are arranged between each coil 18 and the pipe. The poles are formed of a conductive material, such as the same metal as the magnetic bracket, a soft magnetic carbon steel with Fe% > 99.4, and are shaped to conform to the pipe. Non-conductive (air gap) gaskets 27 are arranged on opposite ends of the coils. In the case of each coil, a first air gap gasket 27 is sandwiched between the coil and the corresponding pole 25, and a second air gap gasket 27 is sandwiched between the coil and the bracket 21. In each coil, there is a magnetic core made of a material with good magnetic properties. These cores transfer flux lines from the coil to the pole shoes and the magnetic bracket.

[0077] The bracket 21 further serves as a magnetic circuit for the magnetic field generated by the coils (18, 20), which conducts the magnetic field outward to the pipe to be added to the magnetic field going inward. The bracket has a generally octagonal shape, which is beneficial to the assembly and the operation of the assembly 10. More specifically, the bracket 21 is formed by two, generally c-shaped parts 29 that are slidably mated with each other about the pipe to couple to each other. In this way, the bracket 21 can be used on pipes with different diameters. An attachment (e.g., a bolt) couples the coil to the bracket along the axis (Az).

[0078] The assembly 10 is configured to generate a strong alternating magnetic field (flux) B that is evenly distributed over the cross section of the pipe. The alternating magnetic field is used to avoid electrode material migration. The configuration of the bracket 21, including, for example, the shape and material, promotes the resulting magnetic field (flux) B within the pipe 12. In an exemplary embodiment, the bracket 21 is formed of a "soft" magnetic material, such as a soft iron material, which refers to a relative magnetic permeability, meaning that it has no residual magnetization when it is turned off. As such, magnetic losses are minimized for the magnetic field that goes outward from the pipe and is added to the magnetic field that goes inward to the pipe.

[0079] Reference now Fig.11 , the assembly 10 further includes a housing 72 configured to protect the magnetic field generator (which includes the coils 18, 20 and the bracket 21) from environmental exposure. The assembly 10 further includes an electronics assembly 74 attached to the housing of the assembly. The electronics assembly is in electrical communication with the electrodes (19, 26) and the coil assembly (18, 20) to operate the assembly 10. In an exemplary embodiment, the electronics assembly can house components such as, among others: a driver (32, 34), an operational amplifier (40, 42), an A to D converter (ADC) (44, 46), a PID controller (48, 49) (or a microprocessor), and a pulse width modulator (PWM) (50, 51).

[0080] It should be appreciated from the foregoing that the present invention provides a magnetic flow meter assembly having a novel coil drive and control system. The magnetic flow meter assembly has a tubular body (e.g., a pipe) having two opposite ends, and it is aligned along a horizontal axis (Ax) and defines a fluid flow path between them. The magnetic flow meter assembly includes a pair of coil assemblies, which are coupled to the middle area of ​​the flow meter and are configured to transmit a current such as received from a voltage regulator via a first and a second coil driver. The coil assembly can thus generate a magnetic field within the fluid flow path of the tubular body via a current passing therethrough. A pair of measuring electrodes attached to the body are configured to detect a voltage induced by a conductive fluid passing through the magnetic field. In addition, each of the coil assemblies is electrically coupled to at least one sensor, and the at least one sensor provides feedback to a corresponding voltage regulator via a proportional-integral-differential (PID) controller, and the proportional-integral-differential (PID) controller is configured to keep the error between the corresponding measured current and the target current to zero. As such, based on the received feedback, the respective voltage regulator may manipulate the current through the corresponding coil assembly to overcome factors causing the drive current to deviate from the target current, thereby enabling a prescribed magnetic field to be generated within the fluid flow for accurate flow measurement.

[0081] The present invention has been described above in terms of currently preferred embodiments so that an understanding of the present invention can be conveyed. However, there are other embodiments to which the present invention is applicable that are not specifically described herein. Therefore, the present invention should not be considered to be limited to the form shown, which will be considered to be illustrative rather than restrictive.

[0082] Although the present invention has been disclosed in detail with reference only to exemplary embodiments, those skilled in the art will appreciate that various other embodiments may be provided without departing from the scope of the present invention, including any and all combinations of the features discussed herein.

Claims

1. An assembly for controlling a flow meter, the flow meter being configured to measure the velocity of an electrically conductive fluid in a flow path, the assembly comprising: A first coil assembly circuit that generates a first magnetic field adjacent to the flow path, the first coil assembly circuit comprising: A first voltage source providing a first voltage output; a first coil driver configured to provide a first current to the first coil assembly based on the first voltage output; and a first sensor configured to measure a first electrical property associated with the first coil assembly, the first voltage source configured to modify a first voltage output in response to a first feedback signal received based on the first electrical property to obtain a prescribed first current and generate a prescribed first magnetic field; and A second coil assembly circuit that generates a second magnetic field adjacent to the flow path, the second coil assembly circuit comprising: A second voltage source providing a second voltage output; a second coil driver configured to provide a second current to the second coil assembly based on the second voltage output; and a second sensor configured to measure a second electrical property associated with the second coil assembly, the second voltage source configured to modify a second voltage output in response to a second feedback signal received based on the second electrical property to obtain a prescribed second current and generate a prescribed second magnetic field, the first and second prescribed magnetic fields configured to maintain a constant magnetic field adjacent to the fluid flow path, wherein the two coil assemblies are driven simultaneously by two independently controlled and operated coil drivers, and each coil assembly generates a corresponding magnetic field, and the corresponding magnetic fields combined together obtain a corresponding magnetic field existing across the fluid, and Wherein the first and second coil assemblies are aligned along a vertical axis orthogonal to the flow path, and a pair of measurement electrodes are configured to detect a voltage induced by a conductive fluid in the flow path.

2. The assembly as defined in claim 1, further comprising: a first voltage regulator, which regulates a first voltage output based on a corresponding voltage source and a corresponding feedback signal; and a second voltage regulator, which regulates a second voltage output based on a corresponding voltage source and a corresponding feedback signal.

3. An assembly as defined in claim 2, wherein the first and second feedback signals are output by first and second pulse width modulators (PWM), respectively, each PWM being electrically coupled to a corresponding voltage regulator.

4. An assembly as defined in claim 3, wherein first and second proportional-integral-derivative (PID) controllers output commands to first and second PWMs, respectively, for creating corresponding feedback signals, each output command being based on a corresponding measured electrical property and a target electrical property.

5. The assembly as defined in claim 4, further comprising first and second error amplifiers configured to provide a calculated difference between a respective measured electrical property and a target electrical property to a respective PID controller.

6. The assembly as defined in claim 3, further comprising first and second processors configured to: calculate a difference between the respective measured electrical properties and the target electrical properties; and The PID output command to the corresponding PWM is calculated to create the corresponding feedback signal.

7. An assembly as defined in claim 5, wherein each PWM output is filtered and buffered before being transmitted to a corresponding voltage regulator.

8. The assembly as defined in claim 1, wherein each coil driver is embodied as an H-bridge driver configured to alternate the direction of current to the respective coil assembly.

9. An assembly as defined in claim 1, wherein the first and second electrical properties measured are first and second currents in the first and second coil assemblies, respectively.

10. An assembly as defined in claim 1, wherein the first and second coil drivers operate independently of each other.

11. An assembly as defined in claim 1, wherein the first and second voltage outputs are each less than 10.8V.

12. A method for operating a flow meter configured to measure a velocity of an electrically conductive fluid in a flow path, the method comprising: driving a first coil assembly using a first current from a first coil driver, the first current being generated from a first voltage output from a first voltage source; driving the second coil assembly with a second current from a second coil driver, the second current being generated from a second voltage output from a second voltage source; measuring first and second electrical properties associated with the first and second coil assemblies, respectively; modifying first and second currents via first and second voltage sources in response to the first and second measured electrical properties; as well as maintaining a constant magnetic field adjacent to the fluid flow path by controlling first and second currents driving first and second coil assemblies in response to respective measured electrical properties, wherein the two coil assemblies are driven simultaneously by two independently controlled and operated coil drivers, and each coil assembly generates a corresponding magnetic field, the corresponding magnetic fields combined together obtain a corresponding magnetic field existing across the fluid, and wherein the first and second coil assemblies are aligned along a vertical axis orthogonal to the flow path, and a pair of measuring electrodes are configured to detect a voltage induced by the conductive fluid in the flow path.

13. The method as defined in claim 12, further comprising regulating the first and second voltage outputs using first and second voltage regulators, respectively, based on the corresponding measured electrical properties.

14. The method as defined in claim 13, further comprising outputting feedback signals from first and second pulse width modulators (PWMs) based on the respective measured electrical properties, the output feedback signals being configured to modify the first and second currents via the first and second voltage regulators.

15. The method as defined in claim 14, further comprising outputting commands from first and second proportional-integral-derivative (PID) controllers to the first and second PWMs, respectively, the output commands being based on the corresponding measured electrical properties and the target electrical properties.

16. The method as defined in claim 15, further comprising: calculating, using first and second error amplifiers, error signals between respective measured electrical properties and target electrical properties, and The corresponding calculated error signal is transmitted to the corresponding PID controller.

17. The method as defined in claim 16, further comprising: amplifying the respective measured electrical properties using first and second instrumentation amplifiers; converting the corresponding amplified measured electrical properties from analog signals to digital signals using first and second analog-to-digital converters; as well as The corresponding digital signals are transmitted to the first and second error amplifiers.

18. The method as defined in claim 17, further comprising: Filtering the output feedback signal using the first and second filters; as well as The filtered feedback signal is buffered for use in a corresponding voltage regulator.

19. The method as defined in claim 12, wherein driving the first coil assembly with the first current and driving the second coil assembly with the second current are performed independently of each other.

20. The method as defined in claim 12, wherein the first and second voltage outputs are each less than 10.8V.

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