Magnetic flowmeter

Abstract

The magnetic flowmeter includes a flow tube assembly, an electromotive force (EMF) sensor, a power amplifier, a current sampling circuit, and a controller. The flow tube assembly accommodates the fluid flow and includes a coil for receiving a coil current and inducing an EMF proportional to the flow rate in the fluid flow. The EMF sensor generates an output indicating the induced EMF. The power amplifier generates an unfiltered current pulse at a first frequency. The power amplifier includes a low-pass filter that attenuates the unfiltered current pulse, thereby forming a coil current pulse at a second frequency, which forms the coil current. The current sampling circuit samples the coil current pulse at a sampling frequency. The controller modifies the relationship between the sampling frequency and the first frequency and adjusts the coil current based on the samples.

Description

[0001] Cross-references to related applications

[0002] This application is based on and claims the benefit of U.S. Provisional Patent Application No. 62 / 896,124, filed September 5, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] Embodiments of this disclosure relate to magnetic flowmeters, and more specifically, to techniques for controlling the magnetic field used in flow rate measurements. Background Technology

[0004] Precise and accurate flow control is critical for a wide range of fluid handling applications, including bulk fluid processing, food and beverage preparation, chemicals and pharmaceuticals, water and air distribution, hydrocarbon extraction and treatment, and environmental control, as well as for a range of manufacturing technologies utilizing fluid materials such as thermoplastics, films, adhesives, resins, and others. The flow rate measurement technique used in each specific application depends on the fluid involved and the associated process pressure, temperature, and flow rate.

[0005] Exemplary flow rate measurement techniques include turbine devices that measure flow rate based on mechanical rotation, pitot tube sensors and differential pressure devices that measure flow rate based on the Bernoulli effect or pressure drop across a flow limit, eddy current and Coriolis devices that measure flow rate based on vibration effects, and mass flow meters that measure flow rate based on thermal conductivity. Magnetic flow meters differ from these techniques in that they characterize flow rate based on Faraday's Law, which depends on electromagnetic interactions rather than mechanical or thermodynamic effects. Specifically, magnetic flow meters rely on the electrical conductivity of the process fluid and the electromotive force (EMF) induced when the fluid flows through a region of magnetic field.

[0006] Traditional magnetic flowmeters consist of a sensor section and a transmitter section. The transmitter section includes a current generator that drives a current through a coil in the sensor section to generate a magnetic field that passes through the pipe section. This magnetic field induces an EMF, or potential difference (voltage), that crosses the flow in proportion to the flow velocity. The magnetic flowmeter measures the flow rate based on the voltage difference detected by the sensor section.

[0007] The accuracy of flow rate measurement depends on many factors, one of which is the accurate generation of the magnetic field across the flow. The operating setpoint guides a current generator to produce a current that generates the desired magnetic field across the flow. The current can be periodically sampled to ensure it matches the operating setpoint.

[0008] Current from the current generator can be transmitted from the current generator to the coil in the sensor section via a transmission line. In some cases, such as when the transmission line is long (e.g., 10–1000 feet), a mismatch may occur between the characteristic impedance of the transmission line and the current generator and / or sensor section. This impedance mismatch can cause voltage / current wave reflections at the mismatched impedance, which can generate current / voltage standing waves in the transmission line.

[0009] Such standing waves can adversely affect the accuracy of the current sample from the current generator. Therefore, the sampled current generator current may not match the actual current generator current supplied to the coil in the sensor section. Consequently, the current generator current and the corresponding magnetic field may not meet the desired operating parameters for a magnetic flowmeter used for accurate flow rate measurement. Summary of the Invention

[0010] Embodiments of this disclosure relate to a magnetic flowmeter for measuring the flow rate of a fluid flow and a method for controlling the magnetic flowmeter. In one embodiment, the magnetic flowmeter includes a flow tube assembly, an electromotive force (EMF) sensor, a power amplifier, a current sampling circuit, and a controller. The flow tube assembly includes a tube section for receiving the fluid flow and a coil for receiving a coil current and generating a magnetic field across the fluid flow, the magnetic field inducing an EMF proportional to the flow rate in the fluid flow. The EMF sensor is arranged to sense the EMF and generate an output indicating the induced EMF. The power amplifier is used to generate an unfiltered current pulse at a first frequency. The power amplifier includes a low-pass filter that attenuates the unfiltered current pulse to form a coil current pulse at a second frequency, the coil current pulse forming a coil current. The current sampling circuit is used to capture a series of samples of the coil current pulse at a sampling frequency. The controller is used to change the relationship between the sampling frequency and the first frequency and to adjust the coil current based on the samples.

[0011] Another embodiment of the magnetic flowmeter includes a flow tube assembly, an EMF sensor, a power amplifier, a current sampling circuit, and a controller. The flow tube assembly includes a tube section for receiving the fluid flow and a coil for receiving coil current and generating a magnetic field across the fluid flow, which induces an EMF proportional to the flow rate in the fluid flow. The EMF sensor is arranged to sense the EMF and generate an output indicating the induced EMF. The power amplifier is used to generate unfiltered current pulses of a first frequency. Within a pulse period, each of the unfiltered current pulses is generated after a pulse delay starting from the beginning of the pulse period. The power amplifier includes a low-pass filter that attenuates the unfiltered current pulses to form coil current pulses of a second frequency, which form the coil current. The current sampling circuit is used to capture a series of samples of the coil current pulses at a sampling frequency. The controller is used to adjust the pulse delay to change the relationship between the sampling frequency and the unfiltered current pulses, and to adjust the coil current based on the samples.

[0012] In one embodiment of the method, a fluid flow is contained within a segment of a flow tube assembly. An unfiltered current pulse of a first frequency is generated using a power amplifier. Each of the unfiltered current pulses is generated within a pulse period corresponding to the first frequency. The unfiltered current pulses are attenuated using a low-pass filter of the power amplifier to form a coil current pulse of a second frequency, which forms the coil current. The coil current pulse includes a residual signal from the unfiltered current pulse. The coil current pulse is driven through the coil of the flow tube assembly in alternating directions. A magnetic field is generated across the fluid flow, inducing an EMF proportional to the flow rate. One of the coil current pulses is sampled at a sampling point within each pulse period using a current sampling circuit. The relationship between the sampling point and the residual signal of the unfiltered current pulse is unique for each sampling point. The coil current is adjusted using a controller based on the current pulse samples.

[0013] This summary is provided to introduce, in a simplified manner, the selection of concepts further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to help determine the scope of the claimed subject matter. The claimed subject matter is not limited to embodiments that address any or all of the shortcomings mentioned in the background section. Attached Figure Description

[0014] Figure 1 This is a simplified diagram of an exemplary industrial process measurement system according to embodiments of the present disclosure.

[0015] Figure 2 This is a simplified diagram of an exemplary magnetic flowmeter according to embodiments of the present disclosure.

[0016] Figure 3 and Figure 4 This is a simplified diagram of an exemplary programmable bidirectional current generator according to embodiments of the present disclosure.

[0017] Figure 5 and Figure 6 This is a diagram illustrating exemplary control signals for a complementary switch pair from the controller to the H-bridge according to an embodiment of the present disclosure.

[0018] Figure 7A and Figure 7B These are voltage diagrams showing exemplary high-frequency unfiltered current pulses and corresponding coil current pulses according to embodiments of the present disclosure.

[0019] Figure 7C and Figure 7D It is shown in the Figure 7A and Figure 7B The voltage diagram of the line voltage obtained after filtering the unfiltered current pulse.

[0020] Figure 7E It is in response to Figure 7C and Figure 7D A diagram of the coil current pulses generated by the line voltage.

[0021] Figure 8 This is a schematic diagram of an exemplary magnetic flowmeter according to an embodiment of the present disclosure.

[0022] Figure 9 This is a diagram illustrating an example of voltage / current wave reflection caused by a mismatch between the characteristic impedance of the transmission line and the impedance of the current generator and coil.

[0023] Figure 10 This is a diagram illustrating an exemplary voltage / current standing wave that may form due to impedance mismatch.

[0024] Figure 11 This is a diagram illustrating an exemplary residual signal of a coil current pulse according to an embodiment of the present disclosure.

[0025] Figure 12 This is a voltage diagram illustrating an exemplary coil current pulse according to an embodiment of the present disclosure.

[0026] Figure 13 This is an exemplary residual signal of the coil current according to an embodiment of the present disclosure and a voltage diagram of current signal sampling points synchronized with the residual signal.

[0027] Figures 14 to 16 This is a voltage diagram showing an exemplary residual signal on a coil current pulse according to an embodiment of the present disclosure and a current signal sampling point desynchronized with the residual signal.

[0028] Figure 17 This is a flowchart illustrating a method for controlling a magnetic flowmeter according to an embodiment of the present disclosure. Detailed Implementation

[0029] Embodiments of this disclosure are described more fully below with reference to the accompanying drawings. Elements identified by the same or similar reference numerals refer to the same or similar elements. However, various embodiments of this disclosure may be implemented in many different forms and should not be construed as limiting oneself to the exemplary embodiments described. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0030] Specific details are set forth in the following description to provide a full understanding of the embodiments. However, those skilled in the art will understand that these embodiments can be practiced without these specific details. For example, circuits, systems, networks, processes, frames, supports, connectors, motors, processors, and other components may be omitted or shown in block diagram form to avoid obscuring the embodiments with unnecessary detail.

[0031] Figure 1 This is a simplified diagram of an exemplary industrial process measurement system 100 according to embodiments of the present disclosure. System 100 can be used to process materials (e.g., process media) to transform them from a lower-value state into more valuable and useful products, such as petroleum, chemicals, paper, food, etc. For example, system 100 can be used in oil refineries where industrial processes can be carried out to process crude oil into gasoline, fuel oil, and other petrochemical products.

[0032] System 100 includes, for example, a pulsed DC magnetic flowmeter 102 for sensing the flow rate of process fluid 104, for example, through pipe 106. Magnetic flowmeter 102 includes an electromotive force (EMF) sensor portion 108 and a transmitter 110. Sensor portion 108 is typically used to measure or sense the flow rate of fluid 104. Transmitter 110 is typically used to control the sensor to measure the flow rate and optionally transmits the measured flow rate to an external computing device 112, such as a computerized control unit, which may be located remotely from the flowmeter 102, such as in a control room 114 of system 100.

[0033] Transmitter 110 can communicate with external computing device 112 via 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 can be performed on control loop 116 according to conventional analog and / or digital communication protocols. In some embodiments, 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 two-wire control loop 116. L The level representation. Exemplary digital communication protocols include, for example, those based on... The communication standard modulates the digital signal onto the analog current level of the two-wire control loop 116. Other purely digital technologies can also be used, including Foundation Fieldbus and Profibus communication protocols. Exemplary wireless versions of the process control loop include, for example, wireless mesh network protocols, such as... (IEC 62591) or ISA 100.11a (IEC 62734), or another wireless communication protocol, such as WiFi, LoRa, Sigfox, BLE, or any other suitable protocol.

[0034] The magnetic flowmeter 102 can be powered from any suitable power source. For example, the magnetic flowmeter 102 can be powered entirely by the loop current I flowing through the control loop 116. L Power supply. The process magnetic flowmeter 102 can also be powered by one or more power sources (such as internal or external batteries). A generator (e.g., solar panel, wind turbine, etc.) can also be used to power the magnetic flowmeter 102 or to charge the power source used by the magnetic flowmeter 102.

[0035] The transmitter 110 may be directly attached to the sensor portion 108, for example, to a housing containing the sensor portion 108, or disposed away from the sensor portion 108 (e.g., 10 to 1000 feet). When the transmitter 110 is disposed away from the sensor portion 108, the electrical connection between the transmitter 110 and the sensor portion 108 may be provided by one or more connecting cables or transmission lines 118, which may be formed by cables, wires, data buses, control buses, or other suitable connections for electrical and data communication.

[0036] Figure 2 This 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 pipe section 122 through which the fluid flow 104 travels, such as... Figure 1As shown. The flow tube assembly 120 also includes an EMF sensor 123 with electrodes 124 (e.g., electrodes 124A and 124B), and the flow tube assembly 120 includes one or more field coils or coil lines 126 (e.g., coils 126A and / or 126B). Electrodes 124A and 124B and coils 126A and 126B can be positioned on opposite sides of the tube segment 122, as shown. Figure 2 As shown.

[0037] Digital processor 130 may represent one or more processors that control components of magnetic flowmeter 102 in response to the execution of instructions to perform one or more functions described herein, the instructions of which may be stored in a non-transitory, patent-compliant memory. In some embodiments, digital processor 130 provides control signals to current generator 132 based on the operating setpoint of magnetic flowmeter 102 to generate coil current I. C Coil current I C This includes alternating DC square wave current pulses that pass through coil 126.

[0038] In some embodiments, the current generator 132 includes a controller 140, a power amplifier 142, and a profile generator 144. The controller 140 may represent, for example, one or more processors that control components of the power amplifier 142 to perform one or more functions described herein in response to control signals from a digital processor 130 and / or in response to the execution of instructions, which may be stored in a non-transitory, patent-compliant memory represented by the controller 140.

[0039] The controller 140 can periodically receive the coil current I from the current sampling circuit 143. C The measured current level is used as feedback to determine whether the coil current I needs to be adjusted. C To match the setpoint level of the magnetic flowmeter 102, which is necessary for accurate flow rate measurement. The current sampling circuit 143 can take any suitable form. For example, the current sampling circuit 143 can be used, for example, in... Figure 2 The operation is performed at the location shown to sense the coil current I. C The relevant voltage is sampled and converted into a digital signal using an analog-to-digital converter. This digital signal is provided to the controller 140, for example, as a measured current level. The controller 140 can then adjust the coil current I based on the measured current level. C In an attempt to reduce the coil current I C The current level matches the setpoint current level guided by the operating setpoint of the magnetic flowmeter 102. The change in the sampled voltage over time can also be used to generate the coil current I described herein. C A diagram showing the current distribution of a coil current pulse.

[0040] Figure 3 and Figure 4 This 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 illustrated example, the power amplifier 142 includes a power supply 145, an H-bridge 146, and a low-pass filter (LPF) 148. The H-bridge is used to receive an unfiltered current I from the power supply 145 (e.g., a voltage source). PS The unfiltered current I PS exist Figure 3 and Figure 4 The H-bridge 146 travels in the direction shown. In some embodiments, the H-bridge 146 includes a pair of complementary switches 156, each including switch 156A and its complementary switch 156A', and switch 156B and its complementary switch 156B'. The complementary nature of the 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'.

[0041] Controller 140 may include a microprocessor and a gate driver that controls switches 156A and 156A' and 156B and 156B' to draw current I from... PS A high-frequency (e.g., 10–100 kHz) current pulse is generated and transmitted to the LPF 148 via conductors 157 or 159. The low-pass filter (LPF) 148 operates to attenuate the high-frequency current pulse output from the H-bridge 146 on conductors 157 or 159 to form a low-frequency (e.g., 5–200 Hz) coil current pulse, which forms the coil current I. C .

[0042] Controller 140 controls the filtered coil current I by modulating the duty cycle of switch 156. C The direction of flow through coil 126. For example, Figure 5 and Figure 6 This is a diagram illustrating an exemplary control signal from controller 140 to switch 156, which causes the coil current I... C respectively along Figure 4 and Figure 3 The flow direction is shown in the diagram. The high-level signal in the diagram corresponds to the closed state of switch 156, and the low-level signal corresponds to the open state. (As shown...) Figure 5As shown, the duty cycle of switch 156A is less than that of switch 156B. As a result, the duty cycle of switch 156A' is greater than that of switch 156B'. This causes the average voltage in line 159 to be greater than the average voltage in line 157, resulting in a coil current I... C along Figure 4 The flow direction is shown in the diagram. Figure 6 In this circuit, the duty cycle of switch 156A is greater than that of switch 156B, and the duty cycle of switch 156A' is less than that of switch 156B'. This causes the average voltage in line 157 to be greater than the average voltage in line 159, resulting in a coil current I... C along Figure 3 The flow direction is shown in the diagram. This configuration differs from the conventional power amplifier of the magnetic flowmeter 102, which uses an H-bridge to simply route current from the power supply through the coils of the flow tube assembly in alternating directions.

[0043] Figure 7A and Figure 7B This illustrates an embodiment of the present disclosure where, prior to LPF 148, the voltage from H-bridge 146 is on line 157 having a voltage Vpa. Figure 7A ) and on line 159 with voltage Vpb ( Figure 7B The voltage diagram shows an exemplary high-frequency current pulse 160 (e.g., pulses 160A and 160B) output by the H-bridge 146. For example, a series of voltage pulses 160A from line 157 of the H-bridge 146 during the pulse or excitation period T1, each having a corresponding frequency with a period Tp and 1 / Tp (e.g., 10–100 kHz), can each have a pulse width W. L ,like Figure 7A As shown. With coil current I... C During the period T1 of the pulse that changes direction, pulse 160A has an average voltage V. L Similarly, during pulse period T2, a series of high-frequency voltage pulses 160B from line 157 of H-bridge 146 can each have a pulse width W. H ,like Figure 7B As shown. During period T2, the average voltage pulse 160B has an average voltage V. H Line 159 from H-bridge 146 has pulse 160B during pulse period T1 and pulse 160A during pulse period T2. These pulses 160B and 160A are complementary to the pulses on line 157 during the same period, as... Figure 7B As shown.

[0044] Figure 7C and Figure 7D The voltages Va and Vb after LPF 148 are shown. Figure 2 , Figure 3 and Figure 4 LPF 148 attenuates the high-frequency pulses 136A and 136B on lines 157 and 159. Voltages Va and Vb determine the coil current I. C The direction and amplitude of the coil current pulse. For example, during the pulse period T1, the voltage Va is less than the voltage Vb. This causes the coil current I... C along Figure 4 The flow direction is shown. During period T2, voltage Va is greater than voltage Vb, thus causing the coil current I... C along Figure 2 and Figure 3 The flow direction is shown.

[0045] Figure 7E This is a voltage graph showing the coil current pulse voltage (such as the voltage sampled by current sampling circuit 143) within periods T1 and T2. Figure 7E As shown, the voltage of coil current pulse P1 in period T1 is negative, and the voltage of coil current pulse P2 in period T2 is positive.

[0046] Coil current I C Through appropriate electrical connection (e.g.) Figure 1 and Figure 2 The transmission line 118 shown is transmitted to the excitation coils 126A and 126B of the flow tube 120. This causes coils 126A and / or 126B to generate a magnetic field on the tube segment 122, which changes direction at an excitation frequency (e.g., 1 / T). The process fluid flow 104 passing through the interior of the tube segment 122 acts as a moving conductor, inducing an EMF in the fluid according to Faraday's law of electromagnetic induction. Electrodes 124A and 124B, capacitively coupled to or in direct electrical contact with the conductive process fluid, pick up the voltage present in the fluid flow 104. The voltage difference at electrodes 124A and 124B is proportional to the velocity of the fluid flow 104.

[0047] The signal processor 128 of transmitter 110 is connected to electrodes 124A and 124B. The flow tube assembly 120 may be electrically grounded to pipe segment 122, to a flange or segment upstream or downstream of pipe segment 122, or to another suitable ground connection. Digital processor 130 controls signal processor 128 to sample the voltage difference between electrodes 124A and 124B using any suitable technique and provides the measured voltage difference to digital processor 130. For example, this may involve converting an analog differential voltage signal into a digital value provided to digital processor 130. Digital processor 130 may perform further signal processing on the measured differential voltage to establish a flow rate measurement of the flow rate of process fluid flow 104. The measured flow rate may be transmitted to computing device 112 using communication interface 134, for example, via one of the wired or wireless communication protocols discussed above.

[0048] Figure 8 This is a schematic diagram of the power amplifier 142 of the transmitter 110, the coil 126 of the sensor section 108, and the transmission line 118 connecting the power amplifier 142 to the coil 126. The power amplifier 142 consists of a current source 149 and an impedance Z. S This indicates that one or more coils 126 are controlled by impedance Z. C This indicates that transmission line 118 has a characteristic impedance Z0. When the impedance Z of the current generator... S and / or the impedance Z of the coil C When there is a mismatch with the characteristic impedance Z0 of the transmission line, a coil current I may occur. C Reflection. This impedance mismatch is most likely to occur when the sensor section 108 is connected to the transmitter 110 via a long transmission line 118 (e.g., 10 to 1000 feet).

[0049] LPF 148 cannot fully handle high-frequency or unfiltered pulses 160 ( Figure 7A and Figure 7B Attenuation. As a result, the residual portion of the unfiltered pulse 160 passes through LPF 148 and appears in the coil current I. C The top of the coil current pulse P (or its harmonics). As a result, the coil current I that occurs under the aforementioned impedance mismatch. C The reflections include the reflection of the high-frequency residual portion of the unfiltered pulse 160, which may result in standing waves reflecting voltage / current waves along transmission line 118.

[0050] Figure 9 This illustrates the difference between the characteristic impedance Z0 of transmission line 118 and the impedance Z of current generator 132. S and the impedance Z of one or more coils 126 C The mismatch between them, the residual signal 162 of the unfiltered pulse 160 that was not attenuated by LPF 148, in the coil current I C A diagram illustrating an example of voltage / current wave reflection. Figure 10 Includes a diagram showing a simplified example of the formation of voltage / current standing waves that can occur due to impedance mismatch.

[0051] like Figure 9 As shown, when the residual signal 162 is transmitted from the interface 164 of the transmission line 118 and the power amplifier 142 to the coil 126, due to the impedances Z0 and Z at the interface 166... C Due to the mismatch between the two, a portion of signal 162 is reflected back along transmission line 118 from the interface 166 between transmission line 118 and coil 126 as a reflected voltage signal 162A. This is because the impedances Z0 and Z2A at interface 164... CDue to the mismatch, a portion of signal 162A is reflected back along transmission line 118 as voltage signal 162B. The resulting standing wave signal 168 can be observed along transmission line 118 as "ringing," and the resulting standing wave signal 168 includes peaks 170 and troughs 172, as shown... Figure 10 As shown. The result is that the coil current I... C It may include a high-frequency voltage signal having a form similar to that of residual wave signal 168, such as Figure 11 As shown. These residual wave signals 168 are formed on top of the coil current pulse P, as... Figure 12 As shown in the figure.

[0052] In some implementations, the controller 140 causes the coil current I... C The sampling and control of the H-bridge switches 156 and the generation of pulses 160 by the controller 140 are synchronized with the pulse period Tp or update cycle. This results in a fixed interval between the residual wave signal 168 and the sampling point, at which the current sampling circuit 143 samples the coil current I. C The pulse P is sampled. In the case where current / voltage standing wave reflection occurs in transmission line 118 due to impedance mismatch, thus forming a residual wave signal 168 on the coil current pulse P, such as... Figure 12 As shown, synchronization between signal 168 and the sampling point can cause the sampling point to be at the same position as signal 168.

[0053] Figure 13 An example of this situation is shown, in which the current sampling circuit 143 fixes the sampling delay t relative to the start of each pulse period Tp of each current pulse 160 or residual wave signal 168. S The coil current I was measured at sampling point 174. C Sampling is performed. In the example shown, sampling the coil current pulse P in this manner results in sampling point 174 being located at the trough of the residual wave signal 168, but it could also occur at another location along each signal 168, such as at a peak. Therefore, each of the sampled coil current levels could deviate from the actual average current level 176 by an offset 178.

[0054] Coil current I C This error in the measured level can cause the controller 140 to adjust the coil current I. CThe voltage level is set to deviate from the desired level guided by the digital processor 130 based on the operating setpoint of the magnetic flowmeter 102. As a result, the magnetic field generated by the coil 126 in response to the deflected coil current will be different from the magnetic field required to accurately measure the flow rate of the fluid flow 104 guided by the operating setpoint. Therefore, the measured voltage difference between electrodes 124A and 124B may not accurately indicate the flow rate of the fluid flow 104.

[0055] The embodiments of this disclosure operate to improve the coil current I. C Measurements, such as those performed in cases where a residual waveform signal 168 exists due to the aforementioned impedance mismatch, are used to improve the accuracy of flow rate measurements. Typically, the controller 140 of the current generator 132 is used to alter the relationship between the pulse 160 output from the H-bridge 146, which has a period Tp or a frequency 1 / Tp, and the sampling point 174 (e.g., desynchronization), at which the coil current pulse P is sampled by the sampling circuit 143. As a result, the sampling circuit 143 samples different portions of the signal 168, rather than the same portion of the pulse 136 that appears at the sampling point 174 synchronized with the period Tp or the frequency 1 / Tp. Figure 13 Sampling was performed.

[0056] Multiple sampled voltages of each coil current pulse P can be used to establish the average voltage level of the coil current pulse P, which more accurately represents the coil current I supplied to one or more coils 126. C The actual voltage level is 176. As a result, the current generator 132 can more accurately set the coil current pulse P to the voltage level required for the operation set point of the magnetic flowmeter 102, thereby providing improved control over the magnetic field generated by the coil 126 and more accurate flow rate measurement.

[0057] Different techniques for changing the relationship or desynchronizing sampling point 174 with residual signal 168 will be referred to... Figures 14 to 16 To discuss, Figures 14 to 16 This is a diagram illustrating a portion of an exemplary coil current pulse P, including the residual signal 168 of the unfiltered current pulse 160. In some embodiments, the relationship between the residual signal 168 and the sampling point 174 can be altered or desynchronized by introducing a phase shift or delay relative to the residual signal 168 to the sampling point 174. For example, when the residual signal 168 is generated at the beginning of each pulse period Tp and has a pulse frequency (1 / Tp), the controller 140 can change the sampling delay t of each sampling point 174 measured from the beginning of each pulse period Tp. S Sampling delay t S The delay can vary from zero to the pulse period Tp. Therefore, the coil current pulse P can be sampled with a delay t from the start of the pulse period. S1Sampling is performed at sampling point 174. The second sampling point 174 can be delayed by a sampling delay t from the next pulse period Tp. S2 The third sampling point 174 can be sampled from the next pulse period Tp with a delay t. S3 Furthermore, the fourth sampling point 174 can be sampled with a delay t from the next pulse period Tp. S4 And so on, where the delay t S1 t S2 t S3 and t S4 Each is different, such as Figure 14 and Figure 15 As shown in the figure. This makes the corresponding sampling delay t S1 To t S4 Different portions of the residual signal 168 are sampled by the sampling circuit 143 and used by the controller 140 to determine the coil current level measurement. As a result, repeated sampling of the coil current pulse P at the peaks or troughs of the residual pulse 168 is avoided, and the error in the average value (dashed line) of the current sampling approaches zero over time.

[0058] In one implementation, the controller 140 delays the sampling by t within a series of unfiltered current pulse cycles or loops Tp. S Randomization, typically as Figure 14 As shown. Alternatively, the sampling delay can be programmed so that sampling point 174 is positioned at discrete intervals along the pulse period Tp, to effectively perform a controlled sweep within the pulse period Tp of the residual signal 168, as shown. Figure 15 As shown. Here, the sampling delay t S1 To t S4 Each sampler can be offset by a predetermined period, which allows the sampling circuit 143 to sample a portion or all of the pulse period T. This can result in a more accurate measurement of the coil current level than when the sampling point 174 is randomized.

[0059] According to another embodiment, a phase shift or pulse delay t is introduced from the beginning of the pulse period Tp to the generation of the current pulse 160. P Meanwhile, by fixing the sampling delay t from the beginning of each current pulse period T. S This is done to maintain a fixed sampling frequency and to synchronize the relationship between the residual signal 168 or the unfiltered current pulse 160 and the sampling point 174. An example of this technique is... Figure 16 The figure shows that the residual signal 168 shown corresponds to different pulse delays t starting from the corresponding pulse period Tp. P (such as t) P1 t P2 and t P3The unfiltered current pulse 160 generated after sampling delay t S This keeps the sampling point 174 fixed. This ensures that each sampling point 174 corresponds to a different portion of the current pulse 136 on a series of current pulses 136. As a result, repeated sampling of the residual signal 168 within the peaks or troughs is avoided, and the coil current I can be reflected more accurately. C The average level is obtained by sampling over a time period of 176. Therefore, using this technique, the error in coil current level measurement is close to zero.

[0060] Figure 17 This is a flowchart illustrating a method for controlling a magnetic flowmeter 102 according to an embodiment of the present disclosure. At point 190 of the method, a fluid flow 104 is received through a pipe section 122 of the flow tube assembly 120, such as... Figure 1 As shown. At position 192, a power amplifier 142 using a current generator 132 generates an unfiltered current pulse 160. Figure 7A and Figure 7B As described above, the unfiltered current pulse 160 is generated at a high frequency (e.g., 10–100 kHz), and each pulse 160 is generated within a pulse period Tp. Figure 7A and Figure 7B At position 194, the unfiltered current pulse 160 is attenuated using the LPF 148 of power amplifier 142. Figure 3 and Figure 4 To form coil current I C The coil current pulse P( Figure 7E and Figure 12 The coil current pulse P includes a residual signal 168 from the unfiltered current pulse 160 that has not been fully attenuated by the LPF 148, such as... Figure 12 As shown.

[0061] At point 196 of the method, a coil current pulse P is driven through one or more coils 126 in an alternating direction. The formation of positive and negative coil current pulses P traveling through one or more coils 126 in an alternating direction can be generated by a current generator 132 using the above-described technique. Figure 7E ).

[0062] At 198 of the method, in response to step 186, a magnetic field is generated across the fluid flow 104 within the pipe segment 122, and an EMF proportional to the flow rate of the fluid flow 104 is induced in the fluid flow 104.

[0063] At point 200 of this method, a current sampling circuit 143 is used to sample one of the coil current pulses P at sampling point 147 within each pulse period Tp. According to one of the aforementioned techniques, a controller 140 is used to desynchronize the relationship between sampling point 174 and the corresponding current pulse, ensuring that sampling point 174 has a unique relationship with the residual signal 168. As a result, sampling point 174 is not synchronized with the residual signal 168, such as... Figure 12 As shown. Therefore, this method avoids the same location (e.g., at the peak 170 or trough 172 of the residual signal) Figure 11 Repeated sampling of the residual signal 168.

[0064] At position 202, controller 140 is used to adjust the coil current I based on the sample. C This is to match the operating setpoint of the magnetic flowmeter 102. For example, the controller 140 can determine the coil current level measurement (such as the voltage of the coil current pulse P) based on samples of the coil current pulse P acquired by the sampling circuit 143 (such as the average value of the voltage level indicated by the samples). This is synchronized with the sampling point 174 and the residual signal 168. Figure 13 At different times, the current samples captured by this method cover various portions of the residual signal 168. The average value of the obtained samples provides the coil current I. C The approximation of the residual signal 168 level is more accurate than when the residual signal 168 is repeatedly sampled at the same peak or trough. The controller 140 can compare the measured coil current level with the desired coil current level based on the operating setpoint of the magnetic flowmeter 102, and adjust the coil current accordingly in step 202.

[0065] Although embodiments of the present disclosure have been described with reference to preferred embodiments, those skilled in the art will recognize that changes in form and detail may be made 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, the magnetic flowmeter comprising: A flow tube assembly comprising a tube segment for receiving the fluid flow and a coil for receiving coil current and generating a magnetic field across the fluid flow, the magnetic field inducing an electromotive force (EMF) in the fluid flow proportional to the flow rate. An EMF sensor is arranged to sense the EMF and generate an output indicating the induced EMF; as well as A power amplifier for generating an unfiltered current pulse of a first frequency and including a low-pass filter that attenuates the unfiltered current pulse to form a coil current pulse of a second frequency, the coil current pulse forming the coil current. A current sampling circuit is used to capture a series of samples of the coil current pulses at a sampling frequency; as well as A controller is used to change the relationship between the sampling frequency and the first frequency, and to adjust the coil current based on the sample.

2. The magnetic flowmeter according to claim 1, wherein, Each of the unfiltered current pulses has a pulse period corresponding to the first frequency; The current sampling circuit samples the coil current pulse with a sampling delay starting from each pulse cycle; and The controller changes the sampling delay to alter the relationship between the sampling frequency and the first frequency.

3. The magnetic flowmeter according to claim 2, wherein, The controller randomizes the sampling delay.

4. The magnetic flowmeter according to claim 2, wherein, The controller shifts the sampling delay across the series of samples.

5. The magnetic flowmeter according to claim 2, wherein, The power amplifier includes: power supply; An H-bridge, coupled to the power supply; and A low-pass filter is used to receive unfiltered current pulses from the H-bridge; and The controller is used to manipulate the complementary switching pairs of the H-bridge with varying duty cycles to generate the unfiltered current pulses and to alternate the direction of the coil current pulses passing through the coil.

6. The magnetic flowmeter according to claim 5, wherein, The first frequency is 10–100 kHz; and The second frequency is 5 to 200 Hz.

7. The magnetic flowmeter according to claim 5, wherein, The EMF sensor includes a first electrode and a second electrode positioned on opposite sides of the fluid flow, each of the first electrode and the second electrode being used to sense the voltage of the fluid flow; and The magnetic flowmeter includes: A signal processor is configured to receive voltages sensed by the first electrode and the second electrode, and generate a digital voltage signal indicating the voltage difference between the first electrode and the second electrode in proportion to the flow rate of the EMF and the fluid flow. as well as A digital processor for processing the digital voltage signal and establishing the flow rate of the fluid flow.

8. The magnetic flowmeter according to claim 7, wherein, The magnetic flowmeter includes a communication interface for transmitting the flow rate to an external computing device via a two-wire process control loop that powers the magnetic flowmeter.

9. A magnetic flowmeter for measuring the flow rate of a fluid flow, the magnetic flowmeter comprising: A flow tube assembly comprising a tube segment for receiving the fluid flow and a coil for receiving coil current and generating a magnetic field across the fluid flow, the magnetic field inducing an electromotive force (EMF) in the fluid flow proportional to the flow rate. An EMF sensor is arranged to sense the EMF and generate an output indicating the induced EMF; as well as A power amplifier for generating unfiltered current pulses of a first frequency and including a low-pass filter that attenuates the unfiltered current pulses to form coil current pulses of a second frequency, the coil current pulses forming the coil current, wherein each of the unfiltered current pulses is generated after a pulse delay from the start of the pulse period within the pulse period. A current sampling circuit for capturing a series of samples of the coil current pulses at a sampling frequency; and A controller is used to adjust the pulse delay to change the relationship between the sampling frequency and the unfiltered current pulse, and to adjust the coil current based on the sample.

10. The magnetic flowmeter according to claim 9, wherein, The controller randomizes the pulse delay.

11. The magnetic flowmeter according to claim 9, wherein, The controller delays and shifts the pulse for each of the current pulses corresponding to the series of samples.

12. The magnetic flowmeter according to claim 9, wherein, The power amplifier includes: power supply; An H-bridge, coupled to the power supply; and A low-pass filter is used to receive the unfiltered current pulses from the H-bridge through a first conductor and a second conductor; and The controller is used to manipulate the complementary switching pairs of the H-bridge with varying duty cycles to generate the unfiltered current pulses and to alternate the direction of the coil current pulses passing through the coil.

13. The magnetic flowmeter according to claim 12, wherein, The first frequency is 10–100 kHz; and The second frequency is 5 to 200 Hz.

14. The magnetic flowmeter according to claim 13, wherein, The EMF sensor includes a first electrode and a second electrode positioned on opposite sides of the fluid flow, each of the first electrode and the second electrode being used to sense the voltage of the fluid flow; and The magnetic flowmeter includes: A signal processor is configured to receive voltages sensed by the first electrode and the second electrode, and generate a digital voltage signal indicating the voltage difference between the first electrode and the second electrode in proportion to the flow rate of the EMF and the fluid flow. as well as A digital processor for processing the digital voltage signal and establishing the flow rate of the fluid flow.

15. The magnetic flowmeter according to claim 14, wherein, The magnetic flowmeter includes a communication interface for transmitting the flow rate to an external computing device via a two-wire process control loop that powers the magnetic flowmeter.

16. A method for controlling a magnetic flowmeter, the method comprising: To accommodate fluid flow through the pipe section of the flow tube assembly; An unfiltered current pulse at a first frequency is generated using a power amplifier, with each unfiltered current pulse generated within a pulse period corresponding to the first frequency. The power amplifier's low-pass filter is used to attenuate the unfiltered current pulse, thereby forming a coil current pulse of a second frequency, which forms a coil current, wherein the coil current pulse includes a residual signal of the unfiltered current pulse. The current pulses drive the coil through the coil of the flow tube assembly in alternating directions; In response to a current pulse driving the coil through the coil, a magnetic field is generated across the fluid flow, and an electromotive force (EMF) proportional to the flow rate of the fluid flow is induced in the fluid flow. The coil current pulse is sampled at sampling points within each pulse cycle using a current sampling circuit, wherein the relationship between the sampling point and the residual signal of the unfiltered current pulse is unique for each sampling point; and The controller adjusts the coil current based on samples of the coil current pulses.

17. The method according to claim 16, wherein, Starting from each pulse cycle, the sampling point for each sample is located at the sampling delay; and The method includes using the controller to adjust the sampling delay for each sample.

18. The method according to claim 17, wherein, Adjusting the sampling delay for each sample includes using the controller to randomize the sampling delay for each sample.

19. The method of claim 17, wherein, Adjusting the sampling delay for each sample includes using the controller to shift the sampling delay for each sample.

20. The method of claim 17, wherein, The unfiltered current pulse is generated after a pulse delay starting from the beginning of each pulse cycle; The sampling point for each sample is located at a fixed sampling delay starting from the beginning of each pulse cycle; and the method includes adjusting the pulse delay for each current pulse using the controller.

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