Patent Description:
<CIT> describes a method for testing a magnetic-inductive flowmeter with a measuring tube for guiding a fluid to be measured and with a magnetic field system.

<CIT> describes an electromagnetic flowmeter with a measuring tube, a coil arrangement and means for periodically changing the direction of current through the coil arrangement. The flowmeter may be tested by changing the current direction and measuring at least one parameter of the current rise.

<CIT> describes a magnetic flowmeter with a flowtube arranged to receive a flow of process fluid. A coil is positioned proximate the flowtube and arranged to apply a magnetic field to the process fluid in response to a drive current alternating direction.

<CIT> describes a flow meter, in particular to a water meter, designed for domestic applications.

<CIT> describes a magnetically inductive flow rate sensor function monitoring method. In a measurement mode, current pulses having a constant current value are applied to a pair of coils. In a monitoring mode, a time varying current may be applied to one of the coils and a response is measured by the other coil.

Precise and accurate flow control is critical to a wide range of fluid processing applications, including bulk fluid handling, food and beverage preparation, chemistry and pharmaceuticals, water and air distribution, hydrocarbon extraction and processing, environmental control, and a range of manufacturing techniques utilizing thermoplastics, thin films, glues, resins and other fluid materials, for example. Flow rate measurement technologies used in each particular application depend upon the fluids involved, and on the relevant process pressures, temperatures and flow rates.

Exemplary flow rate measuring technologies include turbine devices that measure flow as a function of mechanical rotation, pitot sensors and differential pressure devices that measure flow as a function of the Bernoulli effect or pressure drop across a flow restriction, vortex and Coriolis devices that measure flow as a function of vibrational effects, and mass flowmeters that measure flow as a function of thermal conductivity. Magnetic flowmeters are distinguished from these technologies by characterizing a flow based on Faraday's Law, which depends upon electromagnetic interactions rather than mechanical or thermodynamic effects. In particular, magnetic flowmeters rely upon the conductivity of the process fluid, and the electromotive force (EMF) induced as the fluid flows through a region of magnetic field.

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 having a current magnitude that is set based on an operating setpoint of the magnetic flowmeter. Conventional coil drivers only create simple square pulsed current profiles of pre-determined magnitude by reversing current polarity into the coil. The coil current causes the coil to generate an alternating magnetic field across the fluid flow, which induces an EMF or potential difference (voltage) across the fluid flow that is proportional to the velocity of the flow and is detected by the sensor section. The magnetic flowmeter determines the flow rate of the fluid flow based on the sensed EMF.

During a reversal of the coil current, the current through the coil does not change instantaneously due to the inductance of the coil. This causes the coil current to initially overshoot the level specified by the operating setpoint, which in turn causes the magnetic field generated by the coil to settle at an incorrect field strength. As a result, accurate flow rate measurements are not possible until the coil current settles to a steady state level that matches the operating setpoint.

The present invention provides a magnetic flowmeter and a method of measuring a flow rate of a fluid flow with the features of the independent claims. Further advantageous embodiments are subject matter of the dependent claims. Embodiments of the present disclosure are directed to magnetic flowmeters for measuring a flow rate of a fluid flow, and methods of measuring a flow rate of a fluid flow using a magnetic flowmeter. One embodiment of the magnetic flowmeter includes a flow tube assembly and a programmable bi-directional current generator. The flow tube assembly is configured to receive the fluid flow and includes a coil and an electromotive force (EMF) sensor. The coil is configured to produce a magnetic field across the fluid flow in response to a coil current. The magnetic field induces an EMF in the fluid flow that is proportional to the flow rate. The EMF sensor is arranged to sense the EMF and generate an output indicating the induced EMF. The current generator includes a profile generator configured to issue profile commands, a power amplifier and a controller. The controller is configured to control the power amplifier to generate coil current pulses forming the coil current that travel through the coil in alternating directions. Each coil current pulse has a current profile of voltage over time, such as the voltage across the coil, that is based on a corresponding profile command.

In one embodiment of the method, a fluid flow is received through a flow tube assembly having a coil. Profile commands are issued using a profile generator that defines a current profile of a voltage over time. Coil current pulses of a coil current are generated using a programmable bi-directional current generator. Each coil current pulse has a current profile of a voltage over time that is based on one of the profile commands. The coil current pulses are driven through the coil in alternating directions. A magnetic field is generated across 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 generating the coil current pulses. An output indicating the induced EMF is generated using an EMF sensor.

Embodiments of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. Elements that are identified using the same or similar reference characters refer to the same or similar elements. The various embodiments of the present disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art.

Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it is understood by those of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, circuits, systems, networks, processes, frames, supports, connectors, motors, processors, and other components may not be shown, or shown in block diagram form, in order to avoid obscuring the embodiments in unnecessary detail.

<FIG> is a simplified diagram of an exemplary industrial process measurement system <NUM>, in accordance with embodiments of the present disclosure. The system <NUM> may be used in the processing of a material (e.g., process medium) to transform the material from a less valuable state into more valuable and useful products, such as petroleum, chemicals, paper, food, etc. For example, the system <NUM> may be used in an oil refinery that performs industrial processes that can process crude oil into gasoline, fuel oil, and other petrochemicals.

The system <NUM> includes a pulsed direct current (DC) magnetic flowmeter <NUM> that is configured to sense a flow rate of a process fluid flow <NUM>, such as through a pipe <NUM>, for example. The magnetic flowmeter <NUM> includes an electromotive force (EMF) sensor section <NUM> and a transmitter <NUM>. The transmitter <NUM> is generally configured to control the sensor section <NUM> to measure the flow rate of the fluid flow <NUM>, and optionally communicate the measured flow rate to an external computing device <NUM>, such as a computerized control unit, which may be remotely located from the flowmeter <NUM>, such as in a control room <NUM> of the system <NUM>, for example.

The transmitter <NUM> may communicate with the external computing device <NUM> 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 <NUM>, or a wireless communication link. Communications between the external computing device <NUM>, and the transmitter section may be performed over the control loop <NUM> in accordance with conventional analog and/or digital communication protocols. In some embodiments, the two-wire control loop <NUM> includes a <NUM>-<NUM> milliamp control loop, in which a process variable may be represented by a level of a loop current IL flowing through the two-wire control loop <NUM>. Exemplary digital communication protocols include the modulation of digital signals onto the analog current level of the two-wire control loop <NUM>, such as in accordance with the HART® communication standard. Other purely digital techniques may also be employed including Foundation FieldBus and Profibus communication protocols. Exemplary wireless versions of the process control loop include, for example, a wireless mesh network protocol, such as WirelessHART® (IEC <NUM>) or ISA <NUM>. 11a (IEC <NUM>), or another wireless communication protocol, such as WiFi, LoRa, Sigfox, BLE, or any other suitable protocol.

Power may be supplied to the magnetic flowmeter <NUM> from any suitable power source. For example, the magnetic flowmeter <NUM> may be wholly powered by the loop current IL flowing through the control loop <NUM>. One or more power supplies may be utilized to power the process magnetic flowmeter <NUM>, such as an internal or an external battery. An electrical power generator (e.g., solar panel, a wind power generator, etc.) may also be used to power the magnetic flowmeter <NUM>, or charge a power supply used by the magnetic flowmeter <NUM>.

The transmitter <NUM> may be directly attached to the sensor section <NUM>, such as to a housing containing the sensor section <NUM>, or located remotely (e.g., <NUM>-<NUM> feet, which corresponds to approximately <NUM>-<NUM> meters) from the sensor <NUM>. When the transmitter <NUM> is remotely located from the sensor section <NUM>, electrical connections between the transmitter <NUM> and sensor section <NUM> may be provided by one or more connecting cables or transmission lines <NUM>, which may be formed by cables, wires, a data bus, a control bus, or other suitable connection for electrical and data communication.

<FIG> is a simplified diagram of the magnetic flowmeter <NUM>, in accordance with embodiments of the present disclosure. The sensor section <NUM> may include a flow tube assembly <NUM> having a pipe section <NUM>, through which the fluid flow <NUM> travels, as shown in <FIG>. The flow tube assembly <NUM> also includes an EMF sensor <NUM> having electrodes <NUM>, such as electrodes 124A and 124B, and the flow tube assembly <NUM> includes one or more field coils or coil wires <NUM>, such as field coils 126A and 126B. The electrodes 124A and 124B, and the coils 126A and 126B may be positioned on opposing sides of the pipe section <NUM>, as shown in <FIG>.

The transmitter <NUM> may include, for example, a signal processor <NUM>, a digital processor <NUM> and programmable bi-directional current generator <NUM>. In some embodiments, the transmitter <NUM> includes a communication interface <NUM>. The digital processor <NUM> may represent one or more processors that control components of the magnetic flowmeter <NUM> to perform one or more functions described herein in response to the execution of instructions, which may be stored in non-transitory, patent eligible memory. In some embodiments, the digital processor <NUM> provides control signals to the current generator <NUM> based on an operating setpoint of the magnetic flowmeter <NUM>, and the current generator <NUM> produces a DC coil current IC that includes DC current pulses that are delivered through the one or more coils <NUM> in alternating directions.

The coil current IC is delivered through the field coils 126A and 126B of the flow tube <NUM> through a suitable electrical connection, such as the transmission line <NUM> shown in <FIG> and <FIG>. This causes the coils 126A and 126B to generate an alternating magnetic field across the fluid flow <NUM> traveling through the pipe section <NUM>, which functions as a moving conductor that induces an EMF in the fluid in accordance with Faraday's law of electromagnetic induction. The electrodes 124A and 124B, which are either capacitively coupled to the conductive process fluid or in direct electrical contact with the process fluid, pick up the voltages present in the fluid flow <NUM>. The difference in the voltages at the electrodes 124A and 124B is proportional to the rate of the fluid flow <NUM> and forms an output of the EMF sensor <NUM>.

The signal processor <NUM> of the transmitter <NUM> is connected to the electrodes 124A and 124B to receive the output from the sensor <NUM> in the form of a differential voltage. The digital processor <NUM> controls the signal processor <NUM> to sample the voltage difference between the electrodes 124A and 124B, and provide the measured voltage difference to the digital processor <NUM>, using any suitable technique. This may involve converting an analog differential voltage signal to a digital value that is supplied to the digital processor <NUM>, for example. The digital processor <NUM> may perform additional signal processing of measured differential voltage to establish a measurement of the flow rate of the process fluid flow <NUM>, which may be communicated to the computing device <NUM> using the communications interface <NUM>.

In some embodiments, the current generator <NUM> includes a controller <NUM>, a power amplifier <NUM>, and a profile generator <NUM>. The controller <NUM> may represent one or more processors that control components of the power amplifier <NUM> to perform one or more functions described herein, such as in response to control signals from the digital processor <NUM>, profile commands <NUM> from the profile generator <NUM>, and/or in response to the execution of instructions, which may be stored in non-transitory, patent eligible memory represented by the controller <NUM>. For example, the controller <NUM> may control the power amplifier <NUM> to produce the coil current pulses that form the coil current IC based on signals from the digital processor <NUM>, which may be based on the operating setpoint for the magnetic flowmeter <NUM>, and control a current profile for each of the coil current pulses based on the profile commands <NUM> from the profile generator <NUM>. As used herein, the "current profile" of the coil current IC or the coil current pulses corresponds to a voltage across or to one side of the coils <NUM> over time that corresponds to the coil current IC through the coils <NUM>.

<FIG> are simplified diagrams of an exemplary power amplifier <NUM>, in accordance with embodiments of the present disclosure. The power amplifier <NUM> may be in the form of a voltage controlled current source, or another suitable current source. In the illustrated example, the power amplifier <NUM> includes a power supply <NUM>, an H bridge <NUM> and a low pass filter (LPF) <NUM>. The H bridge is configured to receive an unfiltered current IPS from the power supply <NUM> (e.g., voltage source) that travels in the direction indicated in <FIG>. In some embodiments, the H bridge <NUM> comprises pairs of complementary switches <NUM> including a switch 156A and its complementary switch 156A', and a switch 156B and its complementary switch 156B'. The complementary nature of the switch pairs 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 the complementary switches 156B and 156B'.

The controller <NUM> may include a microprocessor and gate driver that controls the switch pairs 156A and 156A' and 156B and 156B' to generate high frequency (e.g., <NUM>-<NUM>) unfiltered current pulses from the unfiltered current IPS, which are delivered to the LPF <NUM> over conductors <NUM> or <NUM>. The low pass filter (LPF) <NUM> operates to attenuate the high frequency unfiltered current pulses from the H bridge <NUM> output on conductors <NUM> or <NUM>, to form the low frequency (e.g., <NUM>-<NUM>) coil current pulses that form the coil current IC.

The controller <NUM> controls the direction the filtered coil current IC flows through the one or more coils <NUM> by modulating a duty cycle of the switches <NUM>. For example, <FIG> are charts illustrating exemplary control signals from the controller <NUM> to the switches <NUM> that cause the coil current IC to flow in the direction indicated in <FIG>, respectively. A high signal in the charts corresponds to a closed state for the switches <NUM>, and a low signal in the charts corresponds to an open state. As indicated in <FIG>, the duty cycle for the switch 156A is less than the duty cycle for the switch 156B. As a result, the duty cycle for the switch 156A' is greater than the duty cycle for the switch 156B'. This causes the average voltage in the line <NUM> to be greater than the average voltage in line <NUM>, resulting in the coil current IC flowing in the direction indicated in <FIG>. In <FIG>, the duty cycle for the switch 156A is greater than the duty cycle for the switch 156B, and the duty cycle for the switch 156A' is less than the duty cycle for the switch 156B'. This causes the average voltage in the line <NUM> to be greater than the average voltage in line <NUM>, resulting in the coil current IC flowing in the direction indicated in <FIG>. This configuration is distinct from conventional power amplifiers of magnetic flowmeters <NUM> that use an H bridge to simply route a current from a power supply in alternating directions through coils of a flow tube assembly.

<FIG> are voltage charts respectively illustrating exemplary high frequency unfiltered current pulses PL and PH output from the H bridge <NUM> at line <NUM> or <NUM>, and the corresponding voltage on a side of the coils <NUM> after the LPF <NUM>, in accordance with embodiments of the present disclosure. The unfiltered pulses each have a pulse width that may be adjusted to generate the desired voltage level for the coil current IC. For example, a series of high frequency voltage pulses PL on the line <NUM> or <NUM> from the H bridge <NUM> may each have a pulse width WL, as shown in <FIG>. Over the course of a pulse or excitation period T, at which the coil current IC changes direction, the pulses PL have average voltage VL. The LPF <NUM> filters the voltage pulses PL to produce a coil current pulse PCL of the coil current IC having the low DC voltage level VL, as shown in <FIG>. Likewise, a series of high frequency voltage pulses PH from the H bridge <NUM> may each have a pulse width WH, as shown in <FIG>. Over the course of the period T, the average voltage pulses PH have an average voltage VL. The LPF <NUM> filters the voltage pulses PH to produce the voltage pulse PCH of the coil current Ic having a high DC voltage level of VH, as shown in <FIG>. Accordingly, the duty cycle at which the controller <NUM> actuates the switches <NUM> of the H bridge <NUM>, can be varied by the controller <NUM> to not only control the direction the coil current pulses travel through the coils <NUM>, but also the current profile of the coil current pulses.

<FIG> is a chart of simplified current profiles of exemplary square coil current pulses <NUM> that may be produced by the current generator <NUM>. The controller <NUM> may control the duty cycle at which complementary pairs of switches <NUM> of the H bridge <NUM> are actuated to produce unfiltered current pulses that, when filtered using the LPF <NUM>, produce the coil current pulses <NUM> having a voltage level <NUM> that may be set based on an operating setpoint of the flowmeter <NUM>, for example. The controller <NUM> may also adjust the excitation frequency at which the pulses <NUM> change direction based on the duty cycle at which the complementary pairs of switches <NUM> are actuated. For example, positive current pulses <NUM> (unshaded) of the coil current IC may flow through the coils <NUM> in the direction indicated in <FIG> and <FIG>, and negative current pulses <NUM> (shaded) of the coil current IC may flow through the coils <NUM> in the direction indicated in <FIG>. Additionally, the current profile of the pulses <NUM> may be controlled by the profile commands <NUM> from the profile generator <NUM>. As discussed below, the current profile of the pulses <NUM> may include a time-varying voltage level.

The controller <NUM> may periodically receive current level measurements of the coil current IC from a current monitoring circuit <NUM> as feedback to determine if an adjustment to the coil current IC is required to match the setpoint level <NUM> (dashed lines in <FIG>) for the magnetic flowmeter <NUM>, which is necessary for accurate flow rate measurements. The current monitoring circuit <NUM> may take on any suitable form. For example, the current monitoring circuit <NUM> may operate to sense a voltage that is related to the coil current IC and convert the sampled voltage to a digital signal using an analog-to-digital converter that is presented to the controller <NUM> as a measured current level, for example. The controller <NUM> may adjust the coil current IC based on the measured current level in an attempt to match the current level of the coil current IC to the setpoint current level directed by the operating setpoint of the magnetic flowmeter <NUM>. The voltage sampled by the circuit <NUM> over time may define the current profile of the coil current IC or the coil current pulses and may be used to form the current profile charts described herein.

It may be desirable to generate the current pulses <NUM> shown in <FIG> having square current profiles as the DC coil current IC, by actuating the switches <NUM> of the H bridge <NUM> at a continuous duty cycle for the phases shown in <FIG>, based on a square profile command from the controller <NUM>. However, due to the inductance of the coils <NUM>, the measured current profile of the current pulses of the coil current IC that are driven through the coils <NUM> do not match an ideal square profile shown in <FIG>.

This is generally illustrated in <FIG>, which includes a current profile chart of an exemplary square profile command <NUM> from the profile generator <NUM> and the resulting current profile <NUM> of a coil current pulse <NUM> that is generated based on the command <NUM> and driven through the coils <NUM> of the flow tube assembly <NUM>. As shown in <FIG>, a leading portion <NUM> of the command signal <NUM> substantially instantaneously transitions from a negative square current pulse profile <NUM>, to a positive square current pulse profile <NUM>. This causes the controller <NUM> to adjust the fixed duty cycles applied to the switches <NUM> to switch the voltage levels in the lines <NUM> and <NUM>, and change the direction of the coil current IC. For example, the command <NUM> may cause the controller <NUM> to transition from the duty cycles shown in <FIG> to the duty cycles shown in <FIG> to switch the direction of the coil current IC from the direction indicated in <FIG> to the direction indicated in <FIG>.

Due to the inductance of the coils <NUM>, it is not possible for the coil current IC to instantly make the direction change in accordance with the profile command <NUM>. Instead, a leading portion <NUM> of the current pulse <NUM> has a level that gradually increases over time toward the setpoint level <NUM>, and then overshoots the setpoint level <NUM>. Thus, the leading portion <NUM> of the current profile of the current pulse <NUM> includes a leading error region <NUM> (shaded) corresponding to the difference from the leading portion <NUM> of the profile command <NUM>. Likewise, a trailing portion <NUM> of the measured current profile of the current pulse <NUM> cannot match the corresponding trailing portion <NUM> of profile command <NUM>, resulting in a trailing error region <NUM> (shaded) corresponding to the difference from the trailing portion <NUM> of the profile command <NUM>.

This kind of overshoot can result from an integral part of proportional-integral-derivative (PID) control algorithms, which may be implemented by the controller <NUM>. The integrator part of PID control algorithms make sure the current feedback tracks the profile command <NUM> exactly - or there is no error between the command profile <NUM> and the feedback from the monitoring circuit <NUM>. However, when the feedback current falls behind the commanded current, the integrator tries to compensate for this error by creating another error in the opposite sign such that the "sum" of the error is zero. This phenomenon is well known by control engineers designing classical PID controllers.

However, when the controller <NUM> tries to compensate for the error caused by the fast commanded current profile, and a slow feedback response, it may need to apply a large voltage to bring the error to zero. If the required error-compensating voltage exceeds the maximum of the power supply <NUM> (e.g., when the pulse width modulated duty cycle is about <NUM> percent), the power supply <NUM> may become "saturated" such that it can't apply more voltage across the inductor anymore. In this case, the integrator part of the controller <NUM>, after attempting to apply all of the power supply's voltage across the load (coil <NUM>), is unable to bring the current under control and an error between the commanded current (command profile <NUM>) and the feedback current gets larger and larger. This can result in instability of the controller <NUM> and ringing as the integrator portion of the PID controller <NUM> continues to try to bring the total accumulated error (between the command and feedback) back to zero by creating another error with "opposite sign.

The current level in the leading and trailing error regions <NUM> and <NUM> of the measured current profile of the current pulse <NUM> exceed the setpoint current level <NUM>. This overshoot of the coil current level causes the magnetic field generated by the one or more coils <NUM> in response to the current pulse <NUM> to settle to the wrong field strength, which may result in inaccurate flow rate measurements. Additionally, the current level overshoot in the regions <NUM> and <NUM> may cause the power amplifier <NUM> to exceed its maximum voltage, which can saturate the power amplifier <NUM> and prevent proper regulation of the power amplifier <NUM>.

Embodiments of the present disclosure operate to reduce the mismatch errors between the commanded current profile <NUM> and the measured current profile of the coil current IC. This results in a reduction in current level overshoot and improved flow rate measurement accuracy. Additionally, the commanded current profiles may be configured to prevent the power amplifier <NUM> from exceeding its maximum voltage to avoid regulation issues.

As mentioned above, the controller <NUM> controls the voltage level and current profile of the coil current pulses based on the profile commands <NUM> from the profile generator <NUM>, as indicated in <FIG>. The profile generator <NUM> operates to issue profile commands <NUM> to the controller <NUM> to control the current profile of the DC pulses of the coil current IC, as indicated in the simplified diagram of <FIG>, in which the power amplifier <NUM> is represented by a programmable bi-directional current source <NUM>, which may be formed in accordance with the embodiments described above. In some embodiments, the profile generator <NUM> is configured to produce different complex profile commands <NUM>, such as square current profile commands 145A, trapezoidal current profile commands 145B, irregular current profile commands 145C, sinusoidal current profile commands 145D, and/or other complex profile commands, as indicated in <FIG>.

In some embodiments, the profile commands <NUM> are tailored to the inductance of the coils <NUM>, such that the measured current profiles closely match the commanded profiles. The inductance of the coils <NUM> may be either empirically derived from family characteristics of a population of the magnetic flowmeters <NUM>, or an empirically derived factory characterization of the magnetic flowmeter <NUM>, for example. In some embodiments, the profile commands <NUM> are programmed as factory settings and stored in non-transitory, patent eligible memory of the magnetic flowmeter <NUM>, such as memory represented by the controller <NUM> or the digital processor <NUM>, for example.

Additionally, the profile commands may be tailored to the maximum voltage of the power amplifier <NUM>, such as the power supply <NUM> (<FIG>), to reduce the likelihood of a current overshoot of the pulse current that exceeds the maximum voltage of the power amplifier <NUM>. The profile generator <NUM> calculates a slope of a current level ramp that is practically achievable based on the estimated inductance of the coils <NUM> and, optionally, the maximum voltage of the power amplifier <NUM>, and uses this slope to generate profile commands having a non-square current profile that can be substantially matched by the current pulses of the coil current IC.

<FIG> is a chart illustrating current profiles <NUM> of exemplary trapezoidal profile commands <NUM> that may be issued by the profile generator <NUM> to the power amplifier <NUM>, in accordance with embodiments of the present disclosure. The current profiles <NUM> each have a leading portion <NUM>, in which the current level gradually rises to the set point current level <NUM> over a rise time period tR, and a trailing portion <NUM>, in which the current level gradually returns to zero over a fall time period tF. The slope of the leading and trailing portions <NUM> and <NUM> is determined by the profile generator <NUM> based upon the estimated inductance of the coils <NUM> and, optionally, the maximum voltage of the power amplifier <NUM>.

<FIG> illustrates a chart of a current profile <NUM> of an exemplary trapezoidal profile command <NUM> from the profile generator <NUM>, and a chart of the current profile <NUM> of the corresponding current pulse <NUM> generated by the power amplifier <NUM>, which may be measured using the monitoring circuit <NUM>, for example. Due to the slope of the leading and trailing portions <NUM> and <NUM> of the profile command <NUM> being tailored to the inductance of the coils <NUM>, the measured current profile <NUM> includes leading and trailing portions <NUM> and <NUM> that closely match the leading and trailing portions <NUM> and <NUM> of the current profile <NUM> of the profile command <NUM>, resulting in smaller leading error region <NUM> (shaded area) and trailing error region <NUM> (shaded area) relative to when square current profile commands <NUM> (<FIG>) are used. As a result, the current pulses <NUM> of the coil current Ic have a reduced current overshoot in the regions <NUM> and <NUM>, thereby driving the magnetic field generated by the coils <NUM> to settle to the desired field strength indicated by the current level setpoint <NUM>, and improving flow rate measurement accuracy.

Additionally, the profile commands <NUM> may be tailored to maintain the voltage of the power amplifier <NUM> below its maximum voltage when producing the current pulses <NUM> in response to the profile commands <NUM>, including during the production of the current overshoot in the error regions <NUM> and <NUM>. As a result, issues with the regulation of the power amplifier <NUM> can be reduced.

<FIG> is a flowchart illustrating a method of measuring a flow rate of a fluid flow using a magnetic flowmeter <NUM>, in accordance with embodiments of the present disclosure. At <NUM> of the method, a fluid flow <NUM> is received through the flow tube assembly <NUM>, such as through the pipe section <NUM>, as shown in <FIG> and <FIG>. Profile commands <NUM> are issued at <NUM> that define a current profile <NUM> (<FIG>) of a voltage over time using the profile generator <NUM>. In some embodiments, the profile commands <NUM> are based on an inductance of the coils <NUM>. In some embodiments, the profile commands <NUM> are also based on a maximum voltage of the power amplifier <NUM>.

At <NUM> of the method, current pulses are generated using the power amplifier <NUM> based on the profile commands <NUM>, and are driven through the coils <NUM> of the flow tube assembly <NUM> in alternating directions. This may be accomplished in accordance with techniques described above, such as by actuating pairs of complementary switches <NUM> of an H bridge of the power amplifier <NUM> at different duty cycles, for example. In some embodiments, the current pulses each have a non-square current level profile, such as indicated by the current pulse <NUM> shown in <FIG>.

At <NUM>, a magnetic field is generated across the fluid flow <NUM>, and an EMF is induced in the fluid flow <NUM>. The induced EMF is proportional to the flow rate of the fluid flow <NUM>.

Claim 1:
A magnetic flowmeter (<NUM>) for measuring a flow rate of a fluid flow (<NUM>), comprising:
a flow tube assembly configured to receive the fluid flow (<NUM>) and including:
a coil (<NUM>) configured to produce a magnetic field across the fluid flow (<NUM>) in response to a coil current, the magnetic field induces an electromotive force, EMF, in the fluid flow (<NUM>) that is proportional to the flow rate; and
an EMF sensor (<NUM>) arranged to sense the EMF and generate an output indicating the induced EMF; and
a programmable bi-directional current generator (<NUM>) comprising:
a memory configured to store multiple different profile commands (<NUM>), wherein each profile command (<NUM>) defines a current profile of a voltage over time, wherein a current profile corresponds to a voltage over time that corresponds to the coil current;
a profile generator (<NUM>) configured to issue at least one of the profile commands (<NUM>);
a power amplifier (<NUM>); and
a controller (<NUM>) to control the power amplifier (<NUM>) to generate coil current pulses forming the coil current that travel through the coil (<NUM>) in alternating directions, each coil current pulse having a current profile of voltage over time that is based on a corresponding profile command,
wherein the coil current formed by the generated coil current pulses causes the magnetic field generated by the coil (<NUM>) for measuring the flow rate,
characterized in that
the profile commands (<NUM>) are tailored to the inductance of the coils (<NUM>) and the maximum voltage of the power amplifier (<NUM>) to reduce the likelihood of a current overshoot of the pulse current that exceeds the maximum voltage of the power amplifier (<NUM>).