Magnetic flowmeter with programmable bidirectional current generator

Abstract

A magnetic flowmeter includes a flow tube assembly and a programmable bidirectional current generator. The flow tube assembly receives a fluid flow and includes a coil and an electromotive force (EMF) sensor. The coil is configured to generate a magnetic field on the fluid flow in response to a coil current. The EMF sensor is arranged to sense an EMF on the fluid flow that is proportional to the flow rate and generate an output indicative of the induced EMF. The current generator includes a waveform generator that issues waveform commands, a power amplifier, and a controller. The controller is configured to control the power amplifier to generate coil current pulses that form a coil current that travels through the coil in alternating directions. The coil current pulses each have a current waveform based on the corresponding waveform command.

Description

Technical Field

[0001] Embodiments of the present disclosure relate to magnetic flowmeters, and more particularly, to techniques for controlling current waveforms used to generate magnetic fields during flow rate measurements. Background Art

[0002] Precise and accurate flow control is crucial for a wide variety of fluid handling applications, including bulk fluid handling, food and beverage preparation, chemical and pharmaceutical, water and air distribution, hydrocarbon extraction and processing, environmental control, and a range of manufacturing technologies that utilize thermoplastics, films, glues, resins, and other fluid materials. The flow rate measurement technology used in each specific application depends on the fluids involved and the associated process pressure, temperature, and flow rate.

[0003] Exemplary flow rate measurement technologies include turbine devices that measure flow based on mechanical rotation, pitot sensors and differential pressure devices that measure flow based on the Bernoulli effect or pressure drop across a flow restriction, vortex and Coriolis devices that measure flow based on vibration effects, and mass flow meters that measure flow based on thermal conductivity. Magnetic flowmeters distinguish themselves from these technologies by characterizing flow based on Faraday's law, which relies on electromagnetic interactions rather than mechanical or thermodynamic effects. Specifically, magnetic flowmeters rely on the conductivity of the process fluid and the electromotive force (EMF) induced when the fluid flows through a magnetic field.

[0004] Conventional pulsed direct current (DC) magnetic flowmeters include a sensor section and a transmitter section. The transmitter section includes a current generator or coil driver that generates a coil current with a current amplitude set based on the magnetic flowmeter's operating setpoint. Conventional coil drivers simply create a simple square wave pulse current waveform with a predetermined amplitude by reversing the polarity of the current in the coil. The coil current causes the coil to generate an alternating magnetic field on the fluid flow, thereby inducing an EMF or potential difference (voltage) on the fluid flow. This EMF or potential difference (voltage) is proportional to the flow velocity and is detected by the sensor section. The magnetic flowmeter determines the flow rate of the fluid flow based on the sensed EMF.

[0005] During coil current reversals, the current flowing through the coil does not change instantaneously due to the coil's inductance. This causes the coil current to initially exceed the level specified by the operating setpoint, causing the magnetic field generated by the coil to settle at an incorrect magnetic field strength. Consequently, accurate flow rate measurement is not possible until the coil current settles to a steady-state level that matches the operating setpoint. Summary of the Invention

[0006] Embodiments of the present disclosure relate to a magnetic flowmeter for measuring the flow rate of a fluid flow, and a method for measuring the flow rate of a fluid flow using the magnetic flowmeter. One embodiment of the magnetic flowmeter includes a flow tube assembly and a programmable bidirectional current generator. The flow tube assembly is configured to receive a fluid flow and includes a coil and an electromotive force (EMF) sensor. The coil is configured to generate a magnetic field on the fluid flow in response to a coil current. The magnetic field induces an electromotive force in the fluid flow that is proportional to the flow rate. The EMF sensor is arranged to sense the EMF and generate an output indicative of the induced EMF. The current generator includes a waveform generator configured to issue waveform commands, a power amplifier, and a controller. The controller is configured to control the power amplifier to generate coil current pulses that form a coil current that travels through the coil in alternating directions. Each coil current pulse has a current waveform over time based on the corresponding waveform command.

[0007] In one embodiment of the method, a fluid flow is received by a flow tube assembly having a coil. A waveform generator is used to issue waveform commands that define a current waveform that varies over time. Coil current pulses are generated using a programmable bidirectional current generator. Each coil current pulse has a current waveform that varies over time based on one of the waveform commands. The coil current pulses are driven through the coil in alternating directions. A magnetic field is generated on the fluid flow using the coil. The magnetic field induces an electromotive force (EMF) in the fluid flow that is proportional to the flow rate in response to the generated coil current pulses. An EMF sensor is used to generate an output indicative of the induced EMF.

[0008] This summary is provided to introduce some concepts in a simplified form that are further described in the detailed description below. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages identified in the background. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a simplified diagram of an exemplary industrial process measurement system according to an embodiment of the present disclosure.

[0010] Figure 2 is a simplified diagram of an exemplary magnetic flowmeter according to an embodiment of the present disclosure.

[0011] Figure 3 and Figure 4 is a simplified diagram of an exemplary programmable bidirectional current generator according to an embodiment of the present disclosure.

[0012] Figure 5 and Figure 6is a diagram illustrating exemplary control signals from a controller to a complementary pair of switches of an H-bridge according to an embodiment of the present disclosure.

[0013] Figure 7A and Figure 7B are voltage graphs illustrating exemplary high frequency unfiltered current pulses and corresponding coil current pulses, respectively, according to embodiments of the present disclosure.

[0014] Figure 8 is a simplified current waveform diagram of an exemplary square wave coil current pulse.

[0015] Figure 9 Included are current waveform diagrams of exemplary square wave waveform commands and current waveform diagrams of resulting current waveforms of coil current pulses generated based on the square wave waveform commands.

[0016] Figure 10 is a simplified diagram of a current generator, flow tube kit, and exemplary waveform commands according to an embodiment of the present disclosure.

[0017] Figure 11 is a diagram illustrating a current level waveform of an exemplary trapezoidal waveform command according to an embodiment of the present disclosure.

[0018] Figure 12 A graph showing a current waveform of an exemplary trapezoidal waveform command and a graph showing a current waveform of a corresponding current pulse according to an embodiment of the present disclosure is shown.

[0019] Figure 13 is a flow chart illustrating a method of measuring the flow rate of a fluid flow according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] Hereinafter, the embodiments of the present disclosure will be described more fully with reference to the accompanying drawings. Elements identified with the same or similar reference numerals refer to the same or similar elements. However, the various embodiments of the present disclosure can be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure will be thorough and complete and will fully convey the scope of the present disclosure to those skilled in the art.

[0021] Specific details are given in the following description to provide a thorough understanding of the embodiments. However, one of ordinary skill in the art will appreciate that the embodiments can be practiced without these specific details. For example, circuits, systems, networks, processes, frameworks, supports, connectors, motors, processors, and other components may not be shown or may be shown in block diagram form to avoid obscuring the embodiments with unnecessary detail.

[0022] Figure 1is a simplified diagram of an exemplary industrial process measurement system 100 according to an embodiment of the present disclosure. System 100 can be used in the processing of materials (e.g., process media) to transform the materials from a lower-value state into higher-value, more useful products, such as petroleum, chemicals, paper, food, etc. System 100 can be used in refineries that perform industrial processes that process crude oil into gasoline, fuel oil, and other petrochemical products.

[0023] System 100 includes a pulsed direct current (DC) magnetic flowmeter 102 configured to sense the flow rate of a process fluid stream 104, for example, through a pipe 106. Magnetic flowmeter 102 includes an electromotive force (EMF) sensor portion 108 and a transmitter 110. Transmitter 110 is generally configured to control sensor portion 108 to measure the flow rate of fluid stream 104 and optionally communicate the measured flow rate to an external computing device 112, such as a computer control unit that may be remote from flowmeter 102 (e.g., located in a control room 114 of system 100).

[0024] The transmitter 110 can communicate with the external computing device 112 over a suitable process control loop. In some embodiments, the process control loop includes a physical communication link, such as a two-wire control loop 116, or a wireless communication link. Communication between the external computing device 112 and the transmitter portion over the control loop 116 can be performed according to conventional analog and / or digital communication protocols. In some embodiments, the two-wire control loop 116 includes a 4-20 mA control loop, wherein the process variable can be determined by the loop current I flowing through the two-wire control loop 116. L Exemplary digital communication protocols include, for example, The communication standard modulates the digital signal onto the analog current level of the two-wire control loop 116. Other purely digital technologies may also be used, including Foundation FieldBus and Profibus communication protocols. Exemplary wireless versions of process control loops include, for example, wireless mesh network protocols (e.g., (IEC 62591) or ISA 100.11a (IEC 62734)), or another wireless communication protocol (e.g., WiFi, LoRa, Sigfox, BLE), or any other suitable protocol.

[0025] The magnetic flowmeter 102 may be powered from any suitable power source. For example, the magnetic flowmeter 102 may be powered by a loop current I flowing through the control loop 116. L Fully powered. The process magnetic flowmeter 102 can be powered using one or more power sources (e.g., internal or external batteries). A generator (e.g., a solar panel, a wind turbine, etc.) can also be used to power the magnetic flowmeter 102 or to recharge a power source used by the magnetic flowmeter 102.

[0026] The transmitter 110 can be directly attached to the sensor portion 108 (e.g., to a housing containing the sensor portion 108), or can be located remotely (e.g., 10-1000 feet) from the sensor portion 108. When the transmitter 110 is located remotely from the sensor portion 108, electrical connections between the transmitter 110 and the sensor portion 108 can be provided by one or more connecting cables or transmission lines 118, which can be formed by cables, wires, a data bus, a control bus, or other suitable connections for electrical and data communication.

[0027] Figure 2 is a simplified diagram of a magnetic flowmeter 102 according to an embodiment of the present disclosure. The sensor portion 108 may include a flow tube assembly 120 having a tube segment 122 through which the fluid flow 104 travels, such as Figure 1 As shown. The flow tube assembly 120 also includes an EMF sensor 123 having electrodes 124 (e.g., electrodes 124A and 124B), and the flow tube assembly 120 includes one or more field coils or coil wires 126, such as field coils 126A and 126B. The electrodes 124A and 124B and the coils 126A and 126B can be located on opposite sides of the pipe section 122, such as Figure 2 shown.

[0028] The transmitter 110 may include, for example, a signal processor 128, a digital processor 130, and a programmable bidirectional current generator 132. In some embodiments, the transmitter 110 includes a communication interface 134. The digital processor 130 may represent one or more processors that control the components of the magnetic flowmeter 102 to perform one or more functions described herein in response to the execution of instructions, which may be stored in a non-transitory, patent-eligible memory. In some embodiments, the digital processor 130 provides a control signal to the current generator 132 based on an operating set point of the magnetic flowmeter 102, and the current generator 132 generates a DC coil current I C , the DC coil current I C This includes pulses of DC current passing through the one or more coils 126 in alternating directions.

[0029] Coil current I C By suitable electrical connections (e.g. Figure 1 and Figure 2118) is transmitted through magnetic field coils 126A and 126B of flow tube 120. This causes coils 126A and 126B to generate an alternating magnetic field on fluid stream 104 flowing through pipe section 122, with fluid stream 104 acting as a moving conductor that induces an EMF in the fluid according to Faraday's law of electromagnetic induction. Electrodes 124A and 124B, which are capacitively coupled to or in direct electrical contact with the conductive process fluid, pick up the voltage present in fluid stream 104. The voltage difference at electrodes 124A and 124B is proportional to the flow rate of fluid stream 104 and forms the output of EMF sensor 123.

[0030] Signal processor 128 of transmitter 110 is connected to electrodes 124A and 124B to receive the output from sensor 123 in the form of a differential voltage. Digital processor 130 controls signal processor 128 using any suitable technique to sample the voltage difference between electrodes 124A and 124B and provide the measured voltage difference to digital processor 130. For example, this may involve converting an analog differential voltage signal into a digital value that is provided to digital processor 130. Digital processor 130 may perform additional signal processing on the measured differential voltage to establish a measurement of the flow rate of process fluid stream 104, which may be communicated to computing device 112 using communication interface 134.

[0031] In some embodiments, the current generator 132 includes a controller 140, a power amplifier 142, and a waveform generator 144. The controller 140 may represent one or more processors that control components of the power amplifier 142 to perform one or more functions described herein, such as in response to control signals from the digital processor 130, waveform commands 145 from the waveform generator 144, and / or in response to the execution of instructions represented by the controller 140 that may be stored in a non-transitory, patent-compliant memory. For example, the controller 140 may control the power amplifier 142 to generate a coil current I based on a signal from the digital processor 130 (which may be based on an operating set point of the magnetic flowmeter 102). C The coil current pulses are generated by the coil current generator 144 and the current waveform of each coil current pulse is controlled based on the waveform command 145 from the waveform generator 144. As used herein, the coil current I C The “current waveform” or coil current pulse corresponds to the voltage across the coil 126 or on one side of the coil 126 over time, which corresponds to the coil current I through the coil 126. C .

[0032] Figure 3 and Figure 41 is a simplified diagram of an exemplary power amplifier 142 according to an embodiment of the present disclosure. The power amplifier 142 may be in the form of a voltage-controlled current source or another suitable current source. In the example shown, the power amplifier 142 includes a power supply 147, an H-bridge 146, and a low-pass filter (LPF) 148. The H-bridge is configured to receive an edge signal from the power supply 147 (e.g., a voltage source). Figure 3 and Figure 4 The unfiltered current I PS In some embodiments, H-bridge 146 includes pairs of complementary switches 156, including switch 156A and its complementary switch 156A', and switch 156B and its complementary switch 156B'. The complementarity of switch pair 156A and 156A' means that when switch 156A is open, switch 156A' is closed, and when switch 156A is closed, switch 156A' is open. This also applies to complementary switches 156B and 156B'.

[0033] The controller 140 may include a microprocessor and a gate driver that controls the switch pairs 156A and 156A' and 156B and 156B' according to the unfiltered current I PS To generate high frequency (e.g., 10-100kHz) unfiltered current pulses, the unfiltered current pulses are passed to the low pass filter (LPF) 148 via conductors 157 or 159. The low pass filter (LPF) 148 works to attenuate the high frequency unfiltered current pulses output from the H bridge 146 on conductors 157 or 159 to form the coil current I C Low frequency (e.g. 5-100 Hz) coil current pulses.

[0034] The controller 140 controls the filtered coil current I by adjusting the duty cycle of the switch 156. C The direction of flow through the one or more coils 126. For example, Figure 5 and Figure 6 is a diagram showing exemplary control signals from the controller 140 to the switch 156, which respectively cause the coil current I C along Figure 4 and Figure 3 The high signal in the graph corresponds to the closed state of the switch 156, and the low signal in the graph corresponds to the open state. Figure 5 As shown, the duty cycle of switch 156A is less than the duty cycle of switch 156B. Therefore, the duty cycle of switch 156A' is greater than the duty cycle of switch 156B'. This causes the average voltage in line 159 to be greater than the average voltage in line 157, resulting in the coil current I C along Figure 3 Flow in the direction shown. Figure 6In the example, the duty cycle of switch 156A is greater than the duty cycle of switch 156B, and the duty cycle of switch 156A′ is less than the duty cycle of switch 156B′. This causes the average voltage in line 157 to be greater than the average voltage in line 159, which in turn causes the coil current I C along Figure 4 This configuration differs from conventional power amplifiers for magnetic flowmeter 102, which use an H-bridge to simply route current from a power supply through the coils of the flow tube assembly in alternating directions.

[0035] Figure 7A and Figure 7B is a voltage diagram showing exemplary high frequency unfiltered current pulses P output from the H-bridge 146 at lines 157 or 159, respectively, according to an embodiment of the present disclosure. L and PH, and the corresponding voltage on one side of coil 126 after LPF 148. The unfiltered pulses each have a voltage adjustable to generate coil current I C The pulse width of the desired voltage level. For example, Figure 7A As shown, a series of high frequency voltage pulses P on line 157 or 159 from H bridge 146 L Each may have a pulse width W L . The coil current I C During the pulse or excitation period T in which the direction is changed, the pulse P L With an average voltage V L . LPF 148 responds to voltage pulse P L Filtering is performed to generate the coil current I C With low DC voltage level V L The coil current pulse P CL ,like Figure 7B Similarly, a series of high frequency voltage pulses P from the H bridge 146 H Each may have a pulse width W H ,like Figure 7A As shown. During the period T, the average voltage pulse P H With an average voltage V H The LPF 148 filters the voltage pulse PH to generate the coil current I C With a high DC voltage level V H The voltage pulse P CH ,like Figure 7B Thus, the controller 140 can vary the duty cycle at which the controller 140 actuates the switches 156 of the H-bridge 146 to control not only the direction of the coil current pulses flowing through the coil 126 but also the current waveform of the coil current pulses.

[0036] Figure 8is a simplified current waveform diagram of an exemplary square wave coil current pulse 152 that can be generated by the current generator 142. For example, the controller 140 can control the duty cycle at which the complementary switch pair 156 of the H-bridge 146 is actuated to generate an unfiltered current pulse that, after being filtered using the LPF 148, produces the coil current pulse 152 having a voltage level 158 that can be set based on the operating set point of the flow meter 102. The controller 140 can also adjust the excitation frequency at which the pulse 152 changes direction based on the duty cycle used to actuate the complementary switch pair 156. For example, the coil current I C A positive current pulse 152 (not shaded) may be generated along Figure 2 and Figure 3 The direction shown flows through the coil 126, and the coil current I C The negative current pulse 152 (shaded) can be Figure 4 The direction shown is through coil 126. Additionally, the current waveform of pulse 152 can be controlled by waveform command 145 from waveform generator 144. As described below, the current waveform of pulse 152 can include a voltage level that varies with time.

[0037] The controller 140 may periodically receive the coil current I from the current monitoring circuit 150. C The current level measurement result is used as feedback to determine whether the coil current I C Adjustments are made to match the set point level 158 of the magnetic flow meter 102 ( Figure 8 The current monitoring circuit 150 may be in any suitable form. For example, the current monitoring circuit 150 may be operable to sense the coil current I C The sampled voltage is converted into a digital signal using an analog-to-digital converter, for example, and presented to the controller 140 as the measured current level. The controller 140 can adjust the coil current I based on the measured current level. C , in an attempt to make the coil current I C The current level of the coil 150 matches the set point current level indicated by the operating set point of the magnetic flow meter 102. The voltage sampled over time by the circuit 150 can define the coil current I C or current waveforms of coil current pulses, and can be used to form the current waveform graphs described herein.

[0038] It is expected that based on the square wave waveform command from the controller 140, Figure 5 and Figure 6 The continuous duty cycle of the phase shown is used to actuate the switch 156 of the H bridge 146, generating Figure 8The current pulse 152 having a square wave current waveform is shown as the DC coil current I C However, due to the inductance of coil 126, the coil current I driven through coil 126 is C The measured current waveform of the current pulse is similar to that of Figure 8 The ideal square wave shape shown is not matched.

[0039] This is Figure 9 It is generally shown in Figure 9 A current waveform diagram includes an exemplary square wave waveform command 145 from the waveform generator 144 and a resulting current waveform 162 of a coil current pulse 164 generated based on the command 145 and driven through the coil 126 of the flow tube assembly 120. Figure 9 As shown, the front portion 164 of the command signal 145 transitions substantially immediately from the negative square wave current pulse waveform 166 to the positive square wave current pulse waveform 168. This causes the controller 140 to adjust the fixed duty cycle applied to the switch 156 to switch the voltage levels in the lines 157 and 159 and change the coil current I C For example, command 145 may cause controller 140 to Figure 6 The duty cycle shown transitions to Figure 5 The duty cycle shown is to change the coil current I C Direction from Figure 4 The direction shown switches to Figure 3 direction shown.

[0040] Due to the inductance of coil 126, the coil current I C It is not possible to immediately change direction according to waveform command 145. Instead, the level of front portion 170 of current pulse 162 gradually increases over time toward setpoint level 158 and then exceeds setpoint level 158. Therefore, front portion 170 of the current waveform of current pulse 162 includes a front error region 172 (shaded), which corresponds to the difference from front portion 164 of waveform command 145. Similarly, rear portion 174 of the measured current waveform of current pulse 162 fails to match a corresponding rear portion 176 of waveform command 145, resulting in a rear error region 178 (shaded), which corresponds to the difference from rear portion 176 of waveform command 145.

[0041] This overshoot can be caused by the integrator portion of a proportional-integral-derivative (PID) control algorithm, which can be implemented by controller 140. The integrator portion of the PID control algorithm ensures that the current feedback accurately tracks waveform command 145, or that there is no error between waveform command 145 and the feedback from monitoring circuit 150. However, when the feedback current lags behind the command current, the integrator attempts to compensate for this error by creating another error with the opposite sign so that the sum of the errors is zero. This phenomenon is well known to control engineers who design classic PID controllers.

[0042] However, when controller 140 attempts to compensate for the error caused by the fast command current waveform and slow feedback response, it may be necessary to apply a large voltage to bring the error to zero. If the desired error compensation voltage exceeds the maximum value of power supply 147 (for example, when the pulse width modulation duty cycle is approximately 100%), power supply 147 may become "saturated" and unable to apply any more voltage to the inductor. In this case, after attempting to apply all of the power supply voltage to the load (coil 126), the integrator portion of controller 140 is unable to control the current and the error between the command current (command waveform 145) and the feedback current becomes increasingly larger. This can lead to instability and ringing in controller 140 as the integrator portion of PID controller 140 continues to try to bring the total accumulated error (between command and feedback) back to zero by creating another error with an "opposite sign."

[0043] The current levels in the front error region 172 and the rear error region 178 of the measured current waveform of the current pulse 162 exceed the setpoint current level 158. The overshoot of the coil current level causes the magnetic field generated by the one or more coils 126 in response to the current pulse 162 to settle to an erroneous field strength, which may result in an incorrect flow rate measurement. In addition, the current level overshoot in regions 172 and 178 may cause the power amplifier 142 to exceed its maximum voltage, which may saturate the power amplifier 142 and prevent the power amplifier 142 from properly regulating.

[0044] Embodiments of the present disclosure operate to reduce the command current waveform 145 and the coil current I C This can reduce current level overshoot and improve flow rate measurement accuracy. Additionally, the command current waveform can be configured to prevent the power amplifier 142 from exceeding its maximum voltage to avoid regulation issues.

[0045] As described above, the controller 140 controls the voltage level and current waveform of the coil current pulses based on the waveform command 145 from the waveform generator 144, such as Figure 2The waveform generator 144 operates to issue a waveform command 145 to the controller 140 to control the coil current I C The current waveform of the DC pulse is as follows Figure 9 , where the power amplifier 142 is represented by a programmable bidirectional current source 154, which can be formed according to the above-described embodiments. In some embodiments, the waveform generator 144 is configured to generate different complex waveform commands 145, such as a square wave current waveform command 145A, a trapezoidal current waveform command 145B, an irregular current waveform command 145C, a sinusoidal current waveform command 145D, and / or other complex waveform commands, such as Figure 10 shown.

[0046] In some embodiments, waveform command 145 is adapted to the inductance of coil 126 so that the measured current waveform closely matches the commanded waveform. The inductance of coil 126 can be empirically derived, for example, from the overall family characteristics of magnetic flowmeter 102 or from the factory characteristics of magnetic flowmeter 102. In some embodiments, waveform command 145 is programmed as a factory setting and stored in a non-transitory, patent-compliant memory of magnetic flowmeter 102, such as represented by controller 140 or digital processor 130.

[0047] Additionally, the waveform command may be adapted to the power amplifier 142 (eg, power supply 147 ( Figure 3 and Figure 4 )) to reduce the possibility of the current overshoot of the pulse current exceeding the maximum voltage of the power amplifier 142. The waveform generator 142 calculates the slope of the current level ramp that can actually be achieved based on the estimated inductance of the coil 126 and (optionally) the maximum voltage of the power amplifier 142, and uses this slope to generate a waveform command with a non-square wave current waveform, which can be compared with the coil current I C The current pulses are basically matched.

[0048] Figure 11 1 is a diagram illustrating a current waveform 184 of an exemplary trapezoidal waveform command 145 that may be issued by the waveform generator 144 to the power amplifier 142 according to an embodiment of the present disclosure. The current waveforms 184 each have a front portion 186 and a rear portion 190, in which the current level rises during a rising period t R During the period, the current level gradually rises to the set point current level 188; in the latter part 190, the current level falls during the period t F The waveform generator 144 determines the slopes of the front portion 186 and the rear portion 190 based on the estimated inductance of the coil 126 and (optionally) the maximum voltage of the power amplifier 142 .

[0049] Figure 12 14. A diagram of a current waveform 184 of an exemplary trapezoidal waveform command 145 from the waveform generator 144 and a diagram of a current waveform 192 of a corresponding current pulse 194 generated by the power amplifier 142, which may be measured, for example, using the monitoring circuit 150. Because the slopes of the front portion 186 and the rear portion 190 of the waveform command 145 are adapted to the inductance of the coil 126, the measured current waveform 192 includes a front portion 195 and a rear portion 196 that closely match the front portion 186 and the rear portion 190 of the current waveform 184 of the waveform command 145, resulting in a current waveform 192 that is closer to the inductance of the coil 126 than when a square wave current waveform command 145 is used. Figure 9 ) smaller front error region 197 (shaded area) and rear error region 198 (shaded area). As a result, the coil current I C The current pulse 194 has reduced current overshoot in regions 197 and 198, thereby stabilizing the magnetic field generated by the drive coil 126 to the desired magnetic field strength indicated by the current level set point 188 and improving flow rate measurement accuracy.

[0050] Additionally, when generating current pulse 194 in response to waveform command 145 (including during current overshoots in error regions 197 and 198), waveform command 145 can be adapted to maintain the voltage of power amplifier 142 below its maximum voltage. As a result, regulation issues with power amplifier 142 can be reduced.

[0051] Figure 13 FIG. 1 is a flow chart illustrating a method for measuring the flow rate of a fluid flow using a magnetic flowmeter 102 according to an embodiment of the present disclosure. In step 200 of the method, Figure 1 and Figure 2 As shown, the fluid flow 104 is received by the flow tube assembly 120 (eg, through the tube segment 122). In 202, the waveform generator 144 is used to issue a waveform command 145 that defines a current waveform 184 (voltage versus time) of the current waveform 184. Figure 9 and Figure 10 In some embodiments, waveform command 145 is based on the inductance of coil 126. In some embodiments, waveform command 145 is also based on the maximum voltage of power amplifier 142.

[0052] At 204 of the method, current pulses are generated using the power amplifier 142 based on the waveform command 145 and driven in alternating directions through the coil 126 of the flow tube assembly 120. This can be accomplished, for example, according to the techniques described above, such as by actuating the complementary switch pairs 156 of the H-bridge of the power amplifier 142 at different duty cycles. In some embodiments, the current pulses each have a non-square wave current level waveform, such as Figure 12This is indicated by the current pulse 194 shown in FIG.

[0053] At 206, a magnetic field is generated on the fluid flow 104 and an EMF is induced in the fluid flow 104. The induced EMF is proportional to the flow rate of the fluid flow 104.

[0054] At 208, the EMF sensor 123 ( Figure 2 ) generates an output (e.g., a differential voltage) indicative of the flow rate of the fluid flow 104. As described above. Figure 2 As shown, the output of the EMF sensor 123 may be processed by a signal processor 128 and a digital processor 130 and transmitted to the external computing device 112 using a communication interface 134 .

[0055] Although embodiments of the present disclosure have been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the present disclosure.

Claims

1. A magnetic flowmeter for measuring the flow rate of a fluid flow, comprising: a flow tube kit configured to receive the fluid flow and comprising: a coil configured to generate a magnetic field on the fluid flow in response to a coil current, the magnetic field inducing an electromotive force (EMF) in the fluid flow that is proportional to the flow rate; and an EMF sensor arranged to sense the EMF and generate an output indicative of the induced EMF; and Programmable bidirectional current generator, including: a waveform generator configured to issue at least one waveform command among a plurality of different waveform commands; power amplifiers; and a controller that controls the power amplifier to generate coil current pulses, the coil current pulses forming a coil current traveling in alternating directions through the coil, each coil current pulse having a current waveform over time based on the at least one waveform command of the plurality of different waveform commands from the waveform generator, The waveform command is adapted to the inductance of the coil or the maximum voltage of the power amplifier to reduce the possibility that the current overshoot of the current pulse exceeds the maximum voltage of the power amplifier.

2. The magnetic flowmeter according to claim 1, wherein: The power amplifier comprises: power supply; An H-bridge coupled to the power supply; and a low-pass filter configured to receive an unfiltered current pulse from the H-bridge through a first conductor and a second conductor, and to attenuate a high-frequency component of the unfiltered current pulse to form the coil current pulse; and The controller is configured to actuate complementary switch pairs of the H-bridge at varying duty cycles to generate the unfiltered current pulses based on the waveform command and to alternate the direction of the coil current pulses through the coil.

3. The magnetic flowmeter according to claim 2, wherein: The unfiltered current pulses have a frequency of 10-100 kHz.

4. The magnetic flowmeter according to claim 2, wherein: The H-bridge comprises: a first switch configured to facilitate coupling of the first conductor to a first terminal of the power supply; a second switch, complementary to the first switch, and configured to facilitate coupling of the first conductor to a second terminal of the power supply; a third switch configured to facilitate coupling of the second conductor to the first terminal of the power supply; and A fourth switch is complementary to the third switch and is configured to facilitate coupling of the second conductor to a second terminal of the power supply.

5. The magnetic flowmeter according to claim 4, wherein: the controller actuating the first switch and the second switch at a higher duty cycle than the third switch and the fourth switch to pass the coil current pulses through the coil in a first direction; as well as The controller actuates the third switch and the fourth switch at a higher duty cycle than the first switch and the second switch to pass the coil current pulses through the coil in a second direction opposite to the first direction.

6. The magnetic flowmeter according to claim 4, wherein: the controller actuating the first switch and the second switch at a first duty cycle based on the waveform command to generate a first unfiltered current pulse having a first average voltage on the first conductor; the controller actuating the third switch and the fourth switch at a second duty cycle based on the waveform command to generate a second unfiltered current pulse having a second average voltage on the second conductor; as well as The difference between the first average voltage and the second average voltage determines the direction in which the coil current pulses travel through the coil.

7. The magnetic flowmeter according to claim 4, wherein: Each of the coil current pulses travels in a single direction through the coil and has a current waveform that varies with time according to a corresponding waveform command.

8. The magnetic flowmeter according to claim 7, wherein: the controller actuating the first switch and the second switch at a first time-varying duty cycle based on the waveform command to generate a first unfiltered current pulse having a first time-varying average voltage level on the first conductor; or The controller actuates the third switch and the fourth switch at a second time-varying duty cycle based on the waveform command to generate a second unfiltered current pulse having a second time-varying average voltage on the second conductor.

9. The magnetic flowmeter according to claim 1, wherein: The waveform commands include commands to generate the coil current pulses, each coil current pulse having a time-varying current waveform selected from a square wave current waveform and a non-square wave current waveform.

10. The magnetic flowmeter according to claim 9, wherein: The non-square current waveform includes a front portion where the current level gradually increases over time to a set point level.

11. The magnetic flowmeter according to claim 10, wherein: The non-square current waveform includes a rear portion where the current level gradually decreases from the set point level over time.

12. The magnetic flowmeter according to claim 1, wherein The waveform command is based on the inductance of the coil.

13. The magnetic flowmeter according to claim 1, wherein The waveform command is based on a maximum voltage of a power supply of the power amplifier.

14. The magnetic flowmeter according to claim 9, wherein: The EMF sensor includes a first electrode and a second electrode located on opposite sides of the fluid flow; as well as The magnetic flowmeter comprises: a signal processor configured to receive the voltages sensed by the first electrode and the second electrode and generate a digital voltage signal indicative of a voltage difference between the first electrode and the second electrode, the voltage difference being proportional to the EMF and a flow rate of the fluid flow; as well as A digital processor is configured to process the digital voltage signal and establish a flow rate of the fluid flow.

15. The magnetic flow meter of claim 14, comprising a communication interface configured to communicate the flow rate to an external computing device via a two-wire process control loop that powers the magnetic flow meter.

16. A method of measuring the flow rate of a fluid flow, comprising: receiving the fluid flow through a flow tube assembly having a coil; issuing, using a waveform generator, at least one waveform command of a plurality of different waveform commands, the plurality of different waveform commands defining a current waveform that varies with time; generating coil current pulses of the coil current using a programmable bidirectional current generator, each coil current pulse having a current waveform over time based on the at least one waveform command of the plurality of different waveform commands, wherein the coil current pulses are driven through the coil in alternating directions; generating a magnetic field on the fluid flow using a coil in response to generating the coil current pulses, the magnetic field inducing an electromotive force (EMF) in the fluid flow that is proportional to the flow rate; as well as using an EMF sensor to generate an output indicative of the induced EMF, The waveform command is adapted to the inductance of the coil or the maximum voltage of the power amplifier to reduce the possibility that the current overshoot of the current pulse exceeds the maximum voltage of the power amplifier.

17. The method according to claim 16, wherein Generating the coil current pulse comprises: actuating complementary switch pairs of an H-bridge at different duty cycles to generate unfiltered current pulses based on the waveform command and to alternate the direction of the coil current pulses through the coil; and The unfiltered current pulses are filtered using a low pass filter to form the coil current pulses.

18. The method according to claim 17, wherein: The unfiltered current pulses have a frequency of 10-100 kHz.

19. The method of claim 17, wherein: The H-bridge comprises: a first switch configured to facilitate coupling of the first conductor to the first terminal of the power supply; a second switch, complementary to the first switch, and configured to facilitate coupling of the first conductor to a second terminal of the power supply; a third switch configured to facilitate coupling of a second conductor to the first terminal of the power supply; and a fourth switch, complementary to the third switch, and configured to facilitate coupling of the second conductor to a second terminal of the power supply; and Actuating the complementary switch pair includes: actuating the first switch and the second switch at a first duty cycle based on the waveform command using a controller to generate a first unfiltered current pulse having a first average voltage on the first conductor; and actuating, using the controller, the third switch and the fourth switch at a second duty cycle based on the waveform command to generate a second unfiltered current pulse having a second average voltage on the second conductor; The difference between the first average voltage and the second average voltage determines the direction in which the coil current pulses travel through the coil.

20. The method of claim 17, wherein: Actuating the complementary switch pairs of the H-bridge at different duty cycles includes: actuating the complementary switch pairs at different duty cycles that vary over time based on the waveform command; and The coil current pulses each have a current waveform that varies with time.

21. The method of claim 17, comprising: processing the output of the EMF sensor using a signal processor; as well as processing the digital output signal from the signal processor using a digital processor to establish a flow rate of the fluid flow; as well as The flow rate is communicated to an external computing device using a communication interface.

22. The method according to claim 16, wherein The waveform commands include commands to generate the coil current pulses, each coil current pulse having a time-varying current waveform selected from the group consisting of a square wave current waveform and a non-square wave current waveform.

23. The method according to claim 16, wherein The waveform command is based on the inductance of the coil.

24. The method according to claim 16, wherein The waveform command is based on a maximum voltage of a power supply of the current generator.

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