阅读说明：本技术 用于磁流量计的连续自适应数字线圈驱动器 (Continuous adaptive digital coil driver for magnetic flowmeter ) 是由 埃默里·马苏德 于 2020-02-03 设计创作，主要内容包括：一种用于测量流体流量的磁流量计,包括接收流量的流管组件,该流管组件具有用于接收线圈电流以在流体中产生磁场的线圈,线圈具有第一线圈绕线和第二线圈绕线。这会在流体中生成表示所述流量的EMF。EMF传感器被布置为感测所述EMF并生成与流量有关的输出。电流供应电路响应于命令信号向线圈的第一线圈绕线和第二线圈绕线提供线圈电流。数字控制电路根据控制算法向电流供应电路提供命令信号。在一方面,控制算法对线圈的电参数的改变进行适应。还提供了一种实现磁流量计的方法。(A magnetic flow meter for measuring fluid flow includes a flow tube assembly receiving the flow, the flow tube assembly having a coil for receiving a coil current to generate a magnetic field in the fluid, the coil having a first coil winding and a second coil winding. This generates an EMF in the fluid that is representative of the flow. An EMF sensor is arranged to sense the EMF and generate an output related to the flow. The current supply circuit supplies a coil current to the first and second coil windings of the coil in response to the command signal. The digital control circuit provides a command signal to the current supply circuit according to a control algorithm. In one aspect, the control algorithm adapts to changes in the electrical parameters of the coil. A method of implementing a magnetic flowmeter is also provided.)

1. A magnetic flow meter for measuring fluid flow comprising:

a flow tube assembly receiving the flow, the flow tube assembly having a coil for receiving a coil current, the coil having a first coil winding and a second coil winding, the coil current producing a magnetic field that generates an EMF in the fluid that is representative of the flow;

an EMF sensor arranged to sense the EMF and generate an output indicative of the flow;

a current supply circuit configured to provide the coil current to first and second coil windings of the coil in response to a command input; and

a digital control circuit providing the command input to the current supply circuit according to a control algorithm.

2. The magnetic flow meter of claim 1, wherein the current supply circuit comprises a current source and at least one switch for selectively coupling the current source to the coil.

3. The magnetic flow meter of claim 2, wherein the command input comprises a PWM pulse width modulated signal applied to the at least one switch.

4. The magnetic flow meter of claim 1, further comprising a low pass filter connecting the current supply circuit to the coil to provide a substantially DC coil current to the coil.

5. The magnetic flow meter of claim 1, wherein the command input applied to the current supply circuit reverses the direction of the coil current through the coil.

6. The magnetic flow meter of claim 1, wherein the command input comprises a PWM pulse width modulated signal.

7. The magnetic flow meter of claim 1, wherein the control algorithm is configured to control the command input according to a current profile.

8. The magnetic flow meter of claim 7, wherein the current profile comprises at least one of an amplitude, a frequency, a waveform, and an overshoot.

9. The magnetic flow meter of claim 1, wherein the digital control circuit comprises an impedance identification algorithm configured to determine an impedance of the coil, and the command input is a function of the determined impedance.

10. The magnetic flow meter of claim 9, wherein the impedance identification algorithm receives a current feedback signal related to the current through the coil for determining the impedance of the coil.

11. The magnetic flow meter of claim 1, wherein the current supply circuit comprises four switches configured to control the current through the coil.

12. The magnetic flow meter of claim 11, wherein the command input comprises four signals applied individually to each of the four switches.

13. The magnetic flow meter of claim 11, wherein the command input comprises two signals applied to two pairs of the four switches.

14. The magnetic flow meter of claim 1, wherein the control algorithm is configured to generate the command input as a function of a sensed current flowing through the coil, and the digital control circuit comprises an impedance identification algorithm,

the impedance identification algorithm is configured to identify an impedance of the coil and responsively control a parameter of the control algorithm as a function of the sensed current and the command input.

15. The magnetic flow meter of claim 1, wherein the parameters of the control algorithm accommodate changes in the electrical parameters of the coil.

16. A method for measuring process fluid flow using a magnetic flow meter, comprising:

receiving a flow of process fluid through a flowtube assembly having a coil for receiving a coil current, the coil having a first coil winding and a second coil winding, responsively generating a magnetic field and generating an EMF in the fluid indicative of the flow;

sensing the EMF with a sensor and generating an output indicative of flow;

providing the coil current to first and second coil windings of the coil using a current supply circuit in response to a command input; and

generating the command input applied to the current supply circuit using a digital control circuit in response to a control algorithm.

17. The method of claim 16, wherein the command input comprises a PWM pulse width modulated signal.

18. The method of claim 16, wherein the control algorithm is configured to control the command input according to a current profile.

19. The method of claim 18, wherein the current profile comprises at least one of an amplitude, a frequency, a waveform, and an overshoot.

20. The method of claim 16, wherein the digital control circuit includes an impedance identification algorithm for determining the impedance of the coil, and the command input is a function of the determined impedance.

21. The method of claim 20, wherein the impedance identification algorithm receives a current feedback signal related to the current through the coil for determining the impedance of the coil.

Technical Field

Embodiments of the present disclosure relate to magnetic flowmeters, and more particularly, to techniques for controlling current used to generate a magnetic field for flow measurement.

Background

Accurate and precise flow control is critical for a wide range of fluid processing applications, including bulk fluid (bulk fluid) fluid processing, food and beverage preparation, chemistry and pharmaceuticals, water and air distribution, hydrocarbon extraction and processing, environmental control, and a range of manufacturing techniques utilizing, for example, thermoplastics, films, glues, resins, and other fluid materials. The flow rate measurement technique used in each particular application depends on the fluids involved and the associated process pressures, temperatures and flow rates.

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

A conventional magnetic flowmeter includes a sensor section and a transmitter section. The transmitter section includes a coil driver that drives current through a coil of the sensor section to generate a magnetic field on the pipe section. The magnetic field induces an EMF or potential difference (voltage) on the flow that is proportional to the flow rate. The magnetic flowmeter measures a flow rate based on the voltage difference detected by the sensor portion.

A current supply circuit in the flow meter is used to apply alternating current to the electromagnetic coil. The supply circuit includes an H-bridge transistor circuit having a first switch and a second switch that couple one of the first coil wire and the second coil wire to the supply conductor. Third and fourth switches of the bridge circuit couple the other of the first and second coil windings to the second supply conductor. The control circuit periodically alternates the first switch, the second switch, the third switch, and the fourth switch on and off alternately to reverse the polarity of the coil current. The alternating current applied to the inductive load may be difficult to control and may introduce errors in the flow measurements.

Disclosure of Invention

A magnetic flow meter for measuring fluid flow includes a flow tube assembly receiving the flow, the flow tube assembly having a coil for receiving a coil current to generate a magnetic field in the fluid, the coil having a first coil winding and a second coil winding. This generates an EMF in the fluid that is representative of the flow. An EMF sensor is arranged to sense the EMF and generate an output related to the flow. The current supply circuit supplies a coil current to the first and second coil windings of the coil in response to the command signal. The digital control circuit provides a command signal to the current supply circuit according to a control algorithm. In one aspect, the control algorithm adapts to changes in the electrical parameters of the coil. A method of implementing a magnetic flowmeter is also provided.

This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended 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 noted in the background.

Drawings

FIG. 1 is a simplified diagram of an example industrial process measurement system according to an embodiment of the present disclosure.

Fig. 2 is a simplified circuit diagram of a prior art coil driver for a magnetic flowmeter.

Fig. 3 is a block diagram of a current source for a magnetic flowmeter current driver.

Fig. 4A and 4B are simplified schematic diagrams of a coil drive circuit for driving a coil in a magnetic flow meter using Pulse Width Modulation (PWM).

Fig. 5A and 5B are diagrams illustrating exemplary control signals from a microcontroller to switches of an H-bridge according to embodiments of the present disclosure.

Fig. 6 is a block diagram of an adaptive coil drive digital circuit.

Detailed Description

Embodiments of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. Elements identified with the same or similar reference numbers refer to the same or similar elements. 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 disclosure to those skilled in the art.

In the following description specific details are given to provide a thorough understanding of the embodiments. However, it will be 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.

Magnetic flowmeters are used to measure the flow of a fluid. The magnetic flow meter operates according to faraday's law of electromagnetic induction to measure the flow of conductive liquid through the pipe. In a magnetic flowmeter, a coil is used to apply a magnetic field to a conductive fluid. According to faraday's law, the movement of the conductive fluid by the magnetic field generates an EMF (voltage) that can be sensed using the sensing electrode. The magnitude of this voltage is proportional to the flow rate of the conductive process fluid.

In a magnetic flowmeter, high frequency current reversal is required in order to increase the signal-to-noise ratio (1/f). The coil driver needs to control the current in a minimal/no overshoot manner and provide a fast settling time before measuring the electrode voltage. A tight optimum (light optimum) current control loop is critical to improve system performance. Magnetic flow tube coil drivers are required for use with flow tubes of different sizes. Flow tube parameters change with time and temperature. The coil driver system identifies the impedance of the attached flow tube at power up, continuously monitors any parameter changes and provides optimal current control.

FIG. 1 is a simplified diagram of an example industrial process measurement system 98, according to an embodiment of the present disclosure. The system 98 may be used in the processing of materials (e.g., process media) to transform the material from a less valuable state to a more valuable and useful product, such as petroleum, chemicals, paper, food, and the like. For example, the system 98 may be used in a refinery that performs industrial processes that can process crude oil into gasoline, fuel oil, and other petrochemicals.

System 98 includes a pulsed Direct Current (DC) magnetic flowmeter 100, for example, the pulsed DC magnetic flowmeter 100 configured to sense a flow of a process fluid flow 101, such as through a pipe or flowtube 102. Magnetic flowmeter 100 includes an electromotive force (EMF) sensor 316 (see fig. 4A, 4B) and flowmeter electronics 106. The sensor 316 is generally configured to measure or sense the flow of the fluid flow 101. The electronics 106 are generally configured to control the applied magnetic field to measure the flow rate and, optionally, communicate the measured flow rate to an external computing device 111 (e.g., a computer control unit), which external computing device 111 may be located remotely from the flow meter 100, for example, in a control room 113 of the system 98.

The electronic device 106 may communicate with an external computing device 111 over a suitable process control loop. In some embodiments, the process control loop includes a physical communication link (e.g., two-wire control loop 115) or a wireless communication link. Communication between the external computing device 111 and the flow meter 100 can be performed over the control loop 115 according to conventional analog and/or digital communication protocols. In some embodiments, the two-wire control loop 115 comprises a 4-20 milliamp control loop, wherein the process variable can be determined by a loop current I flowing through the two-wire control loop 115_LIs represented by the level of (c). Exemplary digital communication protocols include, for example, according toThe communications standard modulates a digital signal onto the analog current level of the two wire control loop 115. Other purely digital technologies may also be employed, including FieldBus and Profibus communication protocols. Exemplary wireless versions of process control loops include, for example, wireless mesh network protocols(for example,(IEC 62591) or ISA 100.11a (IEC 62734)), or another wireless communication protocol (e.g., WiFi, LoRa, Sigfox, BLE), or any other suitable protocol.

Magnetic flowmeter 100 may be powered from any suitable power source. For example, magnetic flowmeter 100 may be completely powered by loop current I flowing through control loop 115_LAnd (5) supplying power. Process magnetic flow meter 100 can also be powered by one or more power sources, such as internal or external batteries. A generator (e.g., a solar panel, a wind generator, etc.) may also be used to power magnetic flow meter 100 or to charge a power source used by magnetic flow meter 100.

Fig. 2 is a simplified block diagram of the coil driver circuit 120. Flow tube 102 includes a coil 104, and the coil 104 is electrically connected to a driver circuit 120. The driver circuit 120 includes an analog current source 108 connected to an H-bridge circuit 110. The H-bridge circuit 110 includes four switches (typically transistors) driven by a polarity command signal source 112. The output of the signal source is fed through the switch driver 114 so that at any given time, current is applied to the coil 104 in the direction indicated by the arrow in fig. 2 or in the opposite direction.

In a conventional magnetic flowmeter coil driver, a current source 108 and an H-bridge 110 are used to inject a square wave current into the coil 104 of the flowtube 102. The magnetic flowmeter controls the current set point and the H-bridge 110 is used to set the polarity (direction) of the current applied to the coil 104. Since one coil drive circuit design can be used to power different sized flowtubes, after identifying the impedance of the attached flowtube, the driver circuit 120 can be configured by selecting one of several different control schemes to control the current flowing into the coil 104, which changes the current profile to compensate for parameter variations between flowtubes 102. Each control scheme may control the current to a set of flow tubes. However, for any given flow tube, the control scheme may not be optimal. In addition, when the current is reversed, the current source 108 may become unstable due to the freewheeling current in the induction coil 104. During this time, the operating voltage range of the controller may be exceeded until the coil driver is restored. In addition, the coil driver circuit 120 may not work with newly designed flowtube configurations, thus requiring the circuit to be redesigned.

Fig. 3 shows a configuration of a typical conventional current source 108 used in a magnetic flowmeter coil driver for generating a desired current profile. The control scheme is selected based on knowledge of the flow tube impedance. In the diagram of fig. 3, the controller 200 uses the respective switches 208-1, 208-2, 208-3.. 208-N to select the desired current control scheme 202-1, 202-2, 202-3.. 202-N. The control scheme may be implemented as an analog circuit. A current set point 204 is used and the current is applied to the coil of flow tube 102 through a regulator 206. The feedback current is applied to the control scheme for use by the selected control algorithm. The particular control scheme may be in accordance with known control algorithm techniques. For example, PID (proportional integral derivative) algorithms, including those using feedback and/or feedforward signals, may be used. Generally, a good controller is one that minimizes response time and/or tracks command signals as closely as possible.

When the flowtube is installed, the appropriate control scheme 202-1 to 202-N is selected using the particular impedance and desired current drive characteristics. The controller 200 may include a microcontroller or other circuitry as desired. However, this configuration is limited to a predetermined control scheme. Furthermore, since the electrical characteristics of the coils of the flowtube 102 change over time, typical conventional control schemes cannot accommodate these changes.

Unlike conventional coil drivers, in which the current through an inductive load is controlled primarily by analog circuitry, a fully digital coil driver is provided, as shown in fig. 4A and 4B. Fig. 4A illustrates a magnetic flow meter 300 using a digital coil driver circuit according to an example embodiment. Components in FIGS. 4A and 4B that are similar to components shown in FIG. 2 retain their numbering. With the digital coil driver set forth herein, the current profile can be controlled by controlling the signals used to operate the H-bridge circuit, as opposed to the predetermined fixed control scheme implemented by the conventional controller 200, which cannot be adapted to change the flow tube parameters. More specifically, a PWM (pulse width modulation) command input signal may be used to control the switches in the H-bridge.

As shown in fig. 4A, the H-bridge driver 110 is connected between the bus voltage and electrical ground and includes four switches 302A, 302B, 302C, and 302D, such as field effect transistors or the like. Switch 302B is complementary to switch 302A, and switch 302D is complementary to switch 302B. The switch driver 114 is shown as four analog driver circuits 304A, 304B, 304C, and 304D. Each switch driver 304A-304D receives a PWM command from microcontroller 308. Fig. 4B shows a slightly different configuration of the flow meter 300, in which the switch drivers 304A and 304C are inverting drivers. This configuration allows the microcontroller 308 to apply two PWM command signals, as opposed to the configuration of fig. 4A, which uses four such command signals.

The H-bridge 110 is configured to receive unfiltered current from the bus voltage or power supply. The microcontroller 308 controls the switch pairs 302A and 302C and 302B and 302D to generate high frequency (e.g., 10-100kHz) current pulses from the unfiltered current that are passed to a Low Pass Filter (LPF)312 over conductors 320 and 322. Low Pass Filter (LPF)312 operates to attenuate high frequency current pulses output from H-bridge 110 on lines 320A and 322A to form low frequency (e.g., 5-100Hz) coil current pulses on corresponding lines 320B and 322B that form the coil current delivered by coil 104.

The microcontroller 308 controls the direction of the filtered coil current flowing through the coil 104 by modulating the duty cycle of the switch 302. Fig. 5A and 5B are graphs showing exemplary control signals from the microcontroller 308 to the switch 302 that cause coil current to flow in opposite directions through the coil 104. Typically, a series of narrow (short duration, low duty cycle) pulses for either switch 302A or switch 302B will result in corresponding short current pulses in either line 320A or line 322A. These high frequency short current pulses, when passed through the LPF 312, result in a low DC voltage on the corresponding line 320B or line 322B. Similarly, a series of wide (long duration, high duty cycle) pulses will cause a high DC voltage to be applied to the corresponding line 320A or 322A. These high frequency long current pulses, when passed through the LPF 312, result in a high DC voltage on the corresponding line 320B or 322B. For example, when the switches 302A-302D are actuated by the microcontroller 308, as shown in fig. 5A, the duty cycle of the switch 302A is greater than the duty cycle of the switch 302B, and the duty cycle of the switch 302C is less than the duty cycle of the switch 302D. This causes the average voltage in line 320B to be greater than the average voltage in line 322B, causing the coil current to flow in the direction shown in fig. 4A. When the control signal is consistent with that shown in fig. 5B, the duty cycle of the switch 302A is smaller than that of the switch 302D. This causes the average voltage in line 322B to be greater than the average voltage in line 320B, causing the coil current to flow in the opposite direction to that shown in fig. 4A.

Thus, by controlling the PWM command signal applied to the H-bridge 110, the microcontroller 308 can control the amplitude, rate of change, and shape of the current signal applied to the coil 104. This technique is used to adjust the direction and magnitude of the coil current, unlike the conventional power amplifier of magnetic flow meter 102, which uses an H-bridge to simply direct current from a power source through the coils of the flow tube assembly in alternating directions.

The current sensor 310 is used to sense the current applied to the coil 104. This sensed current provides a feedback signal to an analog-to-digital converter (ADC) of the microcontroller 308. The current sensor 310 may be based on any suitable technique, such as a voltage drop measured across a series resistance.

Figure 4A also shows an EMF sensor 316 that is electrically coupled to the fluid in the flow tube 102 and may include, for example, electrodes. A differential amplifier 318 receives the output signal from the EMF sensor 316 and provides an amplified differential signal to an analog-to-digital converter (ADC) of the microcontroller 308. As previously described, the magnitude of the voltage between EMF sensors 316 is related to the flow rate of the process fluid through flowtube 102.

In the digital coil driver configuration of fig. 4A, 4B, the microcontroller 308 uses PWM commands applied to the H-bridge circuit 110 to control the current flowing into the flow tube 102. Further, the PWM command may be determined based on current feedback sensed by current sensor 310, and the control algorithm implemented digitally in microcontroller 308. This is illustrated in fig. 6, which fig. 6 is a diagram of a continuous adaptive digital coil driver 400. The diagram of fig. 6 shows that the microcontroller 308 is coupled to a "load" 402, which "load" 402 is the effective load from the coil 104 and other components in the current path, as seen by the microcontroller circuit 308 at the switch driver 114. The current through the load 402 is sensed by the sensor 310, which provides current feedback 404. The sensed current feedback 404 is converted to a digital value using an analog-to-digital converter 406 and applied to a control algorithm 408 and an impedance identification algorithm 410. The control algorithm 408 operates according to a selected current profile 412 to control the operation of the switches 302A-302D in the H-bridge 110, which are represented in fig. 6 as PWM 416 along with the LPF 312. The control algorithm provides a command signal 414 to the PWM 416 and impedance identification algorithm 410. The impedance identification algorithm 410 determines the impedance of the load 402 by comparing the digitized current feedback 404 to the command signal 414 provided by the control algorithm 408. Based on the impedance identified by the impedance identification algorithm 410, the impedance identification algorithm adjusts the control parameters used by the control algorithm 408 to accommodate the particular impedance provided by the load 402.

In operation, when powered up, the impedance of the load connected to the coil driver may be unknown. To identify the electrical characteristic (impedance) of the connected load, the microcontroller 408 first excites the load in an open loop (based on feedback-free control) using a small excitation signal (voltage) and measures the current feedback. In non-ideal situations where there is a non-linear relationship between voltage and current (most inductor core materials exhibit hysteresis characteristics, and the impedance of the coil 104 is a function of its operating current), the microcontroller 308 increases the applied voltage and measures the current until the desired operating current set point is reached. The impedance identification algorithm 410 then calculates the "load" impedance using known techniques, after which the microcontroller calculates the settings for the optimal parameters of the control loop. For example, a stepped voltage input may be applied to the coil 104. By monitoring the rise time of the resulting current using the current sensor 110, the value of the inductance of the coil 104, as well as any parasitic resistance, can be determined. The microcontroller 308 then closes the current loop using the initially calculated settings of the parameters. The impedance of the flow tube 102 will change over time due to the environment (e.g., the temperature of the flow tube 102) while the impedance identification algorithm 410 continuously measures the impedance of the flow tube while operating in a closed loop. After the new impedance passes through the low pass filter, the microcontroller calculates new optimal control loop parameters for the already implemented control scheme. In this way, the magnetic flowmeter coil driver operates continuously with optimal performance. This may reduce or substantially eliminate overshoot and may also provide a fast settling time, thereby achieving a fast coil frequency response.

Thus, the microcontroller uses knowledge of the current feedback to calculate the impedance of the flow tube and to derive the optimum tuning parameters (for the control law applied) after power-up. With continuous impedance measurements, the microcontroller can maintain such optimum performance by adjusting the settings of the parameters as the parameters (impedance) of the flow tube change due to, for example, changing environmental conditions (e.g., temperature) and aging effects. Since the control law is implemented digitally inside the microcontroller, the microcontroller can also decode the appropriate PWM signal or command and apply it directly to the switches of the H-bridge switch to control the current through the flow tube. In addition, the magnetic flow meter may be adapted to operate automatically with a new flow tube without the need for a predetermined control scheme as with conventional magnetic flow meters.

Although the present invention has 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 invention. This configuration may provide optimal performance for any attached flow tube. In addition, the system accommodates changes in the flow tube parameters due to temperature changes and aging. The microcontroller may be according to any technology, for example, may be implemented in a microcontroller. In the magnetic flow meter set forth herein, a square (or trapezoidal) current waveform is created by the coil driver. It is desirable that the system reach steady state as soon as possible after the current/magnetic field transition. In a steady state magnetic field, the flow tube electrode voltage is sensed and the flow calculated. It is assumed that the magnetic field is known when the current is in steady state (or shortly thereafter). The higher the frequency of flow measurement, the lower the "1/f" noise (pink noise). Therefore, it is desirable to optimize (or minimize) the settling time of the magnetic field (or current). Furthermore, if the current overshoots in the coil, in some magnetic materials the magnetic field may settle (settle) to a different magnetic field strength than without the overshoot. Since in a flow tube the magnetic field strength is measured in terms of current amplitude, in some systems current overshoot can lead to measurement errors. The digital control circuit set forth herein may be used to control the current applied to the coil to optimize the above factors.