CN211978011U

CN211978011U - Magnetic flowmeter for measuring fluid flow

Info

Publication number: CN211978011U
Application number: CN202020438284.3U
Authority: CN
Inventors: 科尔克·阿兰·亨特; 贾里德·詹姆斯·德雷尔
Original assignee: Micro Motion Inc
Current assignee: Micro Motion Inc
Priority date: 2019-09-05
Filing date: 2020-03-30
Publication date: 2020-11-20
Anticipated expiration: 2030-03-30
Also published as: CN112444296B; CN112444296A

Abstract

A magnetic flow meter for measuring fluid flow comprising: a flow tube assembly receiving a flow and having a coil with a first coil wire and a second coil wire for receiving a coil current and in response generating a magnetic field to generate an EMF representative of the flow rate from the fluid. The EMF sensor is arranged to sense the EMF and generate an output indicative of the flow rate. The current supply circuit applies a current supply signal to the coil. The load balancing boosting power supply part provides power for the current supply circuit. In another aspect, the power scavenging circuit recovers power from the coil.

Description

Magnetic flowmeter for measuring fluid flow

Technical Field

Embodiments of the present disclosure relate to magnetic flow meters, and more particularly, to techniques for controlling current used to generate a magnetic field used in flow rate measurements.

Background

Accurate and precise flow control is critical for a wide range of fluid processing applications, including bulk 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, adhesives, resins, and other fluid materials. The flow rate measurement technique used in each particular application depends on the fluid involved and the associated process pressure, temperature and flow rate.

Exemplary flow rate measurement techniques include: a turbine device for measuring flow rate based on the mechanical rotation; a pitot tube sensor and a differential pressure device that measure flow from the bernoulli effect or pressure drop across the flow restriction; eddy current devices and coriolis devices that measure flow based on the effects of vibration; and a mass flow meter that measures flow from thermal conductivity. Magnetic flowmeters differ from these technologies by characterizing the flow based on faraday's law, which relies on electromagnetic interactions rather than mechanical or thermodynamic effects. In particular, magnetic flowmeters rely on the conductivity of the process fluid, as well as the electromotive force (EMF) induced as the fluid flows through a region of the magnetic field.

A conventional magnetic flowmeter includes a sensor (or pipe) section and a transmitter section. The transmitter section includes a coil driver that drives a 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) across the flow that is proportional to the velocity of the flow. The magnetic flowmeter measures a flow rate based on the voltage difference detected by the sensor portion.

Magnetic flowmeters must work in conjunction with large inductive switching loads. These inductive loads cause large fluctuations in the current through the load. This presents a significant challenge to the internal power supply. If the dynamic load is not properly managed, it can cause input current to inrush into the transmitter, which creates potential power challenges for the power system used to power the magnetic flowmeter.

The accuracy of the flow velocity measurement depends on many factors, one of which is the accurate generation of a magnetic field across the flow. The operating set point instructs the coil driver to generate a current that will produce the desired magnetic field across the current. The current may be periodically sampled to ensure that it matches the operating set point.

SUMMERY OF THE UTILITY MODEL

A magnetic flow meter for measuring fluid flow comprising: a flow tube assembly receiving a flow and having a coil with a first coil wire and a second coil wire for receiving a coil current and in response generating a magnetic field to generate an EMF in the fluid representative of the flow rate. The EMF sensor is arranged to sense the EMF and generate an output indicative of the flow rate. The current supply circuit applies a current supply signal to the coil. The load balancing boosting power supply part provides power for the current supply circuit. In another aspect, the power scavenging circuit recovers power from the coil.

The present disclosure is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. The present disclosure is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.

Drawings

FIG. 1 is a simplified block 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 magnetic flowmeter.

Fig. 3 is a circuit diagram of the power controller of fig. 1.

Fig. 4 is a diagram illustrating a waveform of the power supply of fig. 1.

DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION

Embodiments of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. Elements identified using 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 use current through a sensor (coil) to generate a magnetic field and, according to faraday's law, when a conductive fluid passes through the magnetic field, an electric field proportional to the flow rate is generated. To eliminate the bias in the system, the current is periodically reversed (called the coil frequency), and in the simplest case, an average voltage is obtained to determine the flow rate. During current reversal, a back EMF will be generated that is proportional to the current and the inductance of the coil in the flow sensor. This back EMF causes the regulated power supply that powers the sensor to temporarily lose its ability to regulate the output voltage. As the amplitude of the back EMF increases, it may actually cause the power supply to shut down. When this occurs, the power supply must be turned back on and deliver a large current very quickly to keep the system stable and complete the current reversal. The current surge on the power supply system can be very severe and is not well supported by typical power supply systems. The utility model discloses a with the technique and the circuit of current regulation to the constant value. In one aspect, the present invention integrates a load balancing circuit into the boost supply to eliminate/reduce dynamic current surges. In addition, the circuit captures the back EMF energy stored in the inductive load and reuses this energy in the next switching cycle.

In one aspect, the present invention includes a magnetic flowmeter that includes a load balancing boost power supply circuit. In another aspect, the present invention includes a scavenging circuit configured to reuse a back EMF generated in a current coil after a current reversal period.

FIG. 1 is a simplified block diagram of an example industrial process measurement system 98 in accordance with an embodiment of the present disclosure. The system 98 may be used in the processing of materials (e.g., processing media) to transform the materials from a lower value state to a higher value and more useful product, such as petroleum, chemicals, paper, food, and the like. For example, the system 98 may be used in a refinery executing 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, magnetic flowmeter 100 is configured to sense a flow rate of a process fluid flow 101, for example, through a pipe or flowtube 102. Magnetic flowmeter 100 includes an electromotive force (EMF) sensor (107 in fig. 2) and flowmeter electronics (transmitter) 106. The sensor is generally configured to measure or sense a flow rate 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, such as a computer control unit, which may be located remotely from the flow meter 100, such as 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, such as a 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 includes a 4-20 mA control loop, wherein a process variable in the control loop may be determined by a loop current I flowing through the two-wire control loop 115_LIs expressed in terms of the level of (c). Exemplary digital communication protocols include, for example, according to

The communication standard modulates a digital signal onto the analog current level of the two-wire control loop 115. Other purely digital technologies including FieldBus and Profibus communication protocols may also be employed. For treatingAn exemplary wireless version of a process control loop includes: e.g. wireless mesh network protocols, e.g.

(IEC 62591) or ISA 100.11a (IEC 62734); or another wireless communication protocol such as WiFi, LoRa, Sigfox, BLE, or any other suitable protocol.

Magnetic flowmeter 100 may be supplied with power 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. One or more power sources, such as an internal battery or an external battery, can also be utilized to power process magnetic flow meter 100. A generator (e.g., a solar panel, a wind generator, etc.) may also be utilized to power magnetic flow meter 100 or to charge a power source used by magnetic flow meter 100. However, most flow meters typically operate in a so-called "four-wire" configuration, in which two wires are used to provide process control loop 115, and a second pair of wires are used to provide power to the flow meter. The power may be provided by a local DC power source and is useful for providing the relatively large amount of power required to generate a strong magnetic field in the process fluid stream.

Fig. 2 is a simplified block diagram of magnetic flowmeter 100. Magnetic flowmeter 100 includes a flowtube 102, flowtube 102 configured to receive a flow of process fluid therethrough. A coil 104 is disposed in the flow tube 102 and is configured to apply a magnetic field to the moving process fluid. An electrode 107 is disposed in the flow tube 102 and is exposed to the process fluid. These electrodes 107 sense the EMF generated in response to a magnetic field applied to the moving process fluid. As discussed above, the EMF is proportional to the flow rate of the process fluid.

In the configuration shown in fig. 2, the differential amplifier 108 is configured to sense and amplify a voltage difference generated between the two electrodes 107. In one configuration, the differential amplifier 108 includes an analog-to-digital converter that provides a digital output related to the sensed EMF. In either case, the output from element 108 is related to the sensed EMF, which is proportional to the flow rate of the process fluid.

Measurement circuitry 110 receives the output from differential amplifier 108 and provides an output related to the flow of the process fluid. The measurement circuit 110 may be implemented in digital and/or analog circuitry and may include a microprocessor or the like. In one configuration, the output from the measurement circuitry 110 is of the type used in a process control environment. For example, as discussed above, the output may comprise an output on a two-wire process control loop comprising, for example, a 4mA-20mA process control loop. The control loop may be based on

A communication protocol, Fieldbus protocol, or other hardwired protocol. In addition, the process control loop may also include a wireless control loop in which signals are transmitted wirelessly. In some configurations, the same process control loop is used to provide power to magnetic flowmeter 100.

The current applied to the coil 104 of the magnetic flowtube 102 is controlled by a current supply circuit 120. As discussed herein, the current supply circuit 120 operates as a load-balancing boost supply.

The power supply circuit 120 includes a power supply 122, the power supply 122 providing an input voltage V_InAnd an input current I_INInput current I_INIs applied to inductor L1. The output of inductor L1 may be selectively shorted to electrical ground using switch SW1, which switch SW1 is formed by gate driver 124 and transistor switch 126. The power supply 122 may be internal or external to the device. The circuit may reduce or eliminate current surges drawn from power supply 122. Inductor L1, diode D1, capacitor C1, and switch SW1 operate together to provide a boost supply configuration in which the DC input voltage V is_INIs raised to a higher voltage V1. The instantaneous current through the inductor increases the voltage beyond that provided by the power supply 122. Capacitor C1 is used to smooth out voltage spikes. The voltage V1 is connected to the H-bridge driver 128 through a diode D2. Diodes D1 and D2 are connected to electrical ground through capacitors C1 and C2, respectively. Further, the controller 130 is configured to sense using resistors R1 and R2Measuring feedback voltage V_FB. The H-bridge driver 128 includes a switch 140, the switch 140 being controlled by the measurement circuit 110 according to known techniques. More specifically, the direction of the current applied to the coil 104 through the low pass filter 142 may be switched by alternating operation of the switches on either side of the H-bridge 128.

The controller 130 is configured to sense a current (I) applied to the H-bridge through the low pass filter 150 using the current sensor 132_In) And the current output (I) of the H-bridge through the low pass filter 152 using the current sensor 134_Out). One example configuration of controller 130 is shown in fig. 3, where controller 130 includes

amplifiers

160, 162, and 164. The differential amplifier 160 provides an output related to the difference between the input current and the output current. Amplifier 162 is based on a voltage reference V_refTo amplify the current difference. The amplified output from amplifier 162 is then coupled to feedback voltage V_fbA comparison is made and the control output is applied to switch SW 1.

During operation, the load-balancing boost supply 120 operates in a boost switching power supply configuration, in which the input voltage V is employed_INAnd stepped up (boosted) to a higher output voltage V1 or V2. For equalizing (level) the input current I_INThe net output current I must be determined_OUT. For most of this period, current flows from the boost circuit. However, during the back EMF time when the direction of current through the coil 104 is reversed, current flows back into the boost circuit. The actual boost load current is the time-averaged sum of these two currents (net load current). The low pass filter 152 is used to average the net load current over a number of coil frequency transitions. The low pass filter 152 is therefore a very low frequency filter.

If the back EMF current does flow back to the boost circuit 120, the output voltage V2 increases and the control circuit 130 detects that the voltage V2 is too high. When this occurs, the controller 130 controls the output by decreasing the duty cycle of the switch SW 1. A blocking diode D2 is used with an additional capacitor C2 on the circuit output to "sink" this reverse current. The excess current is stored in capacitor C2 and reused during the next cycle of the H-bridge 128. It is to be noted that the output voltage V2 must be able to increase over the entire coil frequency period. Therefore, the output voltage V2 is not a well-regulated voltage.

Now the net load current (I) is determined_LOAD) The control circuit 130 of the boost circuit 120 forcibly maintains the boost voltage to provide the required load current I_LOAD. This is achieved by allowing the output voltage V2 to increase while normally turning off the boost, thereby keeping the input current constant. If the net load current is not used, but only the output current is monitored, the net energy stored in the system will continue to increase with each cycle and the voltage will increase uncontrollably.

FIG. 4 is a V illustrating the circuit shown in FIG. 2₁、V₂Sensing 2 and I_INAnd the amplitude versus time of the control, and illustrates the operation of the controller 130 as discussed above. From a power supply V, given a constant output load_inThe boosted input current of (a) varies indirectly with the supply voltage. When switch SW 1126 is conductive, it causes current to flow through inductor L1. This current causes energy to be stored in inductor L1. The time that inductors L1 and SW 1126 are on is referred to as the on-time and the remainder of the switching cycle is referred to as the off-time. Diode D1 is reverse biased and therefore non-conductive. During the off-time, diode D1 is forward biased and allows the energy stored in inductor L1 to flow to the output and charge capacitor C1. The average value of the current passing through D1 is the load current of the boost power supply portion (current sense 1). The load current is independent of the input supply voltage Vin. Current (I) flowing into the power supply by sensing the load current (current sense 2) and forcing the net current to be the same as the load current sensed at current sense 2_in) Will be continuous and nearly constant as shown in fig. 4.

With this configuration, the input current I can be actively controlled_INTo reduce or eliminate large periodic current surges that can range from zero (0) amps input to many amps input in a few milliseconds. It can be considered as a dc power factor correction circuit.

Although preference has been given toAlthough the present invention has been described with reference to exemplary 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. In the structure shown herein, the capacitor C₂A power scavenging circuit is provided to store power from the coil when the direction of the drive current is reversed. However, other power storage and scavenging techniques may be used, including those of inductors or batteries. With the configuration proposed here, a boost supply is provided by inductor L1, diode D1, switch SW1, and capacitor C1. A low pass filter 152 is used to provide time averaging of the load current. The output current from the boost supply is also sensed and applied to low pass filter 150, low pass filter 150 having a shorter time constant than low pass filter 152. The controller 130 compares the two filtered signals and controls the operation of the switch SW1 to input the current I_INMaintained at a relatively constant level as shown in fig. 4.

Claims

1. A magnetic flow meter for measuring fluid flow, wherein the magnetic flow meter comprises:

a flow tube assembly receiving a flow, the flow tube assembly having a coil with a first coil wire and a second coil wire for receiving a coil current and in response generating a magnetic field to generate an EMF in the fluid representative of the flow rate;

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

a current supply circuit configured to apply a current supply signal to the coil; and

a load-balancing boost power supply section configured to supply power to the current supply circuit and regulate an input current from a DC power supply to be almost constant.

2. The magnetic flow meter of claim 1, wherein the current supply circuit comprises: first and second switches respectively coupling the first and second coil wires to a first supply conductor; and third and fourth switches respectively coupling the first and second coil wires to a second supply conductor.

3. The magnetic flow meter of claim 1, wherein the load-balancing boost supply comprises a power storage element configured to scavenge power from the coil when the direction of the current supply signal through the coil is reversed.

4. The magnetic flow meter of claim 3, wherein the power storage element comprises a capacitor.

5. The magnetic flow meter of claim 1, wherein the load-balancing boost supply comprises a current sensor configured to sense current flowing into the coil and, in response, to control the current supply signal based on the sensed current.

6. The magnetic flow meter of claim 1, wherein the load-balancing boost supply comprises a current sensor configured to sense current flowing from the coil and, in response, to control the current supply signal based on the sensed current.

7. The magnetic flow meter of claim 1, wherein the load-balancing boost supply comprises a current sensing circuit configured to sense a difference between current flowing into the coil and current flowing out of the coil, and in response, to control the current supply signal based on the sensed current difference.

8. The magnetic flow meter of claim 1, wherein the load-balancing boost supply senses a voltage related to a voltage on the coil and, in response, controls the current supply signal based on the sensed voltage.

9. The magnetic flow meter of claim 8, wherein the load-balancing boost supply determines a difference between current flowing into the coil and current flowing out of the coil, and further in response, controls the current supply signal based on the difference.

10. The magnetic flow meter of claim 1, wherein the load-balancing boost supply is coupled to an input voltage and configured to apply a voltage to the coil that is greater than the input voltage.

11. The magnetic flow meter of claim 10, wherein the load-balancing boost supply comprises a switch configured to selectively couple an inductor to electrical ground and thereby generate a voltage greater than the input voltage.

12. The magnetic flow meter of claim 1, wherein the load-balancing boost supply comprises a diode for preventing current from the coil from flowing into components of the load-balancing boost supply when the direction of the current supply signal applied to the coil is reversed.

13. The magnetic flow meter of claim 1, wherein the load-balancing boost supply comprises a voltage sensor for sensing a back EMF flowing from the coil into the load-balancing boost supply as a result of a reversal of direction of the current supply signal flowing through the coil.

14. The magnetic flowmeter of claim 13, wherein the load-balancing boost supply comprises a switch configured to control the current supply signal as a function of the sensed back EMF.

15. A magnetic flow meter for measuring fluid flow, wherein the magnetic flow meter comprises:

a power scavenging circuit configured to recover power from the coil.

16. The magnetic flow meter of claim 15, wherein the power scavenging circuit comprises a power storage element.

17. The magnetic flow meter of claim 16, wherein the power storage element comprises a capacitor.

18. The magnetic flow meter of claim 15, wherein the magnetic flow meter comprises a load-balancing boost supply having a current sensor configured to sense current flowing into the coil and, in response, to control the current supply signal based on the sensed current.

19. The magnetic flow meter of claim 15, wherein the magnetic flow meter comprises a load-balancing boost supply having a current sensor configured to sense current flowing from the coil and, in response, to control the current supply signal based on the sensed current.

20. The magnetic flow meter of claim 15, wherein the load-balancing boost supply comprises a switch configured to switch off the current supply signal in dependence on the sensed back EMF.