Load balancing boost power supply for magnetic flowmeter

Abstract

A magnetic flowmeter 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 representing a flow rate. The EMF sensor is arranged to sense the EMF and generate an output indicative of the flow rate. A current supply circuit applies a current supply signal to the coil. A load balancing boost supply provides power to the current supply circuit. In another aspect, a power scavenging circuit recovers power from the coil.

Description

Technical Field

[0001] 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 Art

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

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

[0004] A conventional magnetic flowmeter includes a sensor (or pipe) portion and a transmitter portion. The transmitter portion includes a coil driver that drives current through the coil of the sensor portion to generate a magnetic field on the pipe portion. The magnetic field induces an EMF or potential difference (voltage) across the flow, which is proportional to the velocity of the flow. The magnetic flowmeter measures the flow velocity based on the voltage difference detected by the sensor portion.

[0005] Magnetic flow meters must operate in conjunction with large inductive switching loads. These inductive loads result in large fluctuations in the current through the load. This creates significant challenges for the internal power supply. If dynamic loads are not properly managed, it can cause input current to surge into the transmitter, creating potential power supply challenges for the power system used to power the magnetic flow meter.

[0006] The accuracy of flow rate 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 flow. The current can be sampled periodically to ensure that it matches the operating set point. Summary of the invention

[0007] A magnetic flowmeter 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 generating a magnetic field in response, thereby generating an EMF in the fluid representing a flow rate. The EMF sensor is arranged to sense the EMF and generate an output indicative of the flow rate. A current supply circuit applies a current supply signal to the coil. A load balancing boost supply provides power to the current supply circuit. In another aspect, a power scavenging circuit recovers power from the coil.

[0008] This Summary is provided to introduce some concepts in a simplified form, which are further described in the Detailed Description below. This Summary is neither intended to identify key features or essential features of the claimed subject matter nor to be used to help determine the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all of the disadvantages noted in the Background. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0010] Figure 2 is a simplified circuit diagram of a magnetic flowmeter.

[0011] Figure 3 yes Figure 1 Circuit diagram of the power controller.

[0012] Figure 4 It is shown Figure 1 Figure 2 is a diagram of the power supply waveform. Specific embodiments

[0013] Embodiments of the present disclosure are described more fully below with reference to the accompanying drawings. Elements identified with the same or similar reference numerals refer to the same or similar elements. However, the various embodiments of the present disclosure can be embodied in many different forms and should not be interpreted as being limited to the embodiments set forth herein. On the contrary, these embodiments are provided to make the present disclosure comprehensive and complete, and to fully convey the scope of the present disclosure to those skilled in the art.

[0014] Specific details are given in the following description to provide a comprehensive understanding of the embodiments. However, it should 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, frameworks, supports, connectors, motors, processors, and other components may not be shown or may be shown in block diagram form to avoid obscuring the embodiments in unnecessary detail.

[0015] Magnetic flow meters use current passing through the sensor (coil) to generate a magnetic field, and according to Faraday's law, when a conductive fluid passes through this magnetic field, an electric field proportional to the flow rate is generated. In order to eliminate deviations in the system, the current will be reversed periodically (called the coil frequency), and in the simplest case, the average voltage is obtained to determine the flow rate. During the current reversal, a back EMF will be generated, which 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 the 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 happens, the power supply must be reconnected very quickly and deliver a large current to keep the system stable and complete the current reversal. The current surge on the power supply system can be very severe, and typical power supply systems cannot support it well. The present invention includes techniques and circuits for regulating the current to a constant value. In one aspect, the present invention integrates a load balancing circuit into the boost power supply to eliminate / reduce dynamic current surges. In addition, the circuit captures the back EMF energy stored in the inductive load and reuses the energy in the next switching cycle.

[0016] In one aspect, the invention includes a magnetic flow meter including a load balancing boost supply circuit. In another aspect, the invention includes a sweeping circuit configured to reuse a back EMF generated in a flow tube coil after a current reversal period.

[0017] Figure 1 is a simplified block diagram of an exemplary 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 materials from a lower value state into a higher value and more useful product, such as petroleum, chemicals, paper, food, etc. For example, the system 98 may be used in a refinery performing an industrial process that processes crude oil into gasoline, fuel oil, and other petrochemical products.

[0018] System 98 includes a pulsed direct current (DC) magnetic flowmeter 100, for example, configured to sense the flow rate of a process fluid flow 101, for example, through a pipe or flow tube 102. Magnetic flowmeter 100 includes an electromotive force (EMF) sensor ( Figure 2 107) and flow meter electronics (transmitter) 106. The sensor is typically configured to measure or sense the flow rate of the fluid stream 101. The electronics 106 are typically configured to control the applied magnetic field to measure the flow rate and optionally transmit the measured flow rate to an external computing device 111, such as a computer control unit, which can be located remote from the flow meter 100, such as in a control room 113 of the system 98.

[0019] The electronic device 106 can communicate with the external computing device 111 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 115 or a wireless communication link. The communication between the external computing device 111 and the flow meter 100 can be performed on 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 mA-20 mA control loop, wherein the process variable in the control loop can be determined by the loop current I flowing through the two-wire control loop 115. L Exemplary digital communication protocols include, for example, The communication standard modulates the digital signal onto the analog current level of the two-wire control loop 115. Other purely digital technologies including FieldBus and Profibus communication protocols may also be used. Exemplary wireless versions of process control loops 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.

[0020] The magnetic flow meter 100 may be powered from any suitable power source. For example, the magnetic flow meter 100 may be powered entirely by the loop current I flowing through the control loop 115. L Powered. One or more power sources, such as internal batteries or external batteries, may also be used to power the process magnetic flowmeter 100. A generator (e.g., a solar panel, a wind turbine, etc.) may also be used to power the magnetic flowmeter 100 or to charge the power source used by the magnetic flowmeter 100. However, most flowmeters are typically operated in a so-called "four-wire" configuration, in which two wires are used to provide the process control loop 115, and a second pair of wires is used to provide power to the flowmeter. Power may be provided by a local DC power source, and the power is useful for providing the relatively large amounts of power required to generate a strong magnetic field in the process fluid flow.

[0021] Figure 2 1 is a simplified block diagram of a magnetic flowmeter 100. The magnetic flowmeter 100 includes a flow tube 102 configured to receive a process fluid flow therethrough. A coil 104 is disposed in the flow tube 102 and is configured to apply a magnetic field to the moving process fluid. Electrodes 107 are disposed in the flow tube 102 and are exposed to the process fluid. These electrodes 107 sense an EMF generated in response to the magnetic field applied to the moving process fluid. As discussed above, the EMF is proportional to the flow rate of the process fluid.

[0022] exist Figure 2In the configuration shown, the differential amplifier 108 is configured to sense and amplify the 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 the element 108 is related to the sensed EMF, which is proportional to the flow rate of the process fluid.

[0023] The measurement circuit 110 receives the output from the differential amplifier 108 and provides an output related to the flow rate of the process fluid. The measurement circuit 110 may be implemented in digital and / or analog circuitry and may include a microprocessor, etc. In one configuration, the output from the measurement circuit 110 is of a type used in a process control environment. For example, as discussed above, the output may include an output on a two-wire process control loop, including, for example, a 4mA-20mA process control loop. The control loop may be based on 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 the magnetic flow meter 100.

[0024] The current applied to the coil 104 of the magnetic flow tube 102 is controlled by the current supply circuit 120. As discussed herein, the current supply circuit 120 operates as a load-balancing boost supply.

[0025] The power supply circuit 120 includes a power supply 122, which provides an input voltage V In and input current I IN , input current I IN is applied to the inductor L1. The output of the inductor L1 can be selectively shorted to electrical ground using a switch SW1 formed by a gate driver 124 and a transistor switch 126. The power supply 122 can be loaded internally or externally to the device. The circuit can reduce or eliminate current surges drawn from the power supply 122. The inductor L1, diode D1, capacitor C1 and switch SW1 operate together to provide a boost supply configuration, where the DC input voltage V IN is raised to a higher voltage V1. The instantaneous current through the inductor causes the voltage to increase to a voltage that exceeds the voltage provided by the power supply 122. Capacitor C1 is used to smooth the voltage spike. Voltage V1 is connected to the H-bridge driver 128 through diode D2. Diodes D1 and D2 are connected to electrical ground through capacitors C1 and C2, respectively. In addition, the controller 130 is configured to sense the feedback voltage V using resistors R1 and R2 FBThe H-bridge driver 128 includes switches 140 that are controlled by the measurement circuit 110 according to known techniques. More specifically, by alternating operation of the switches on either side of the H-bridge 128, the direction of the current applied to the coil 104 through the low pass filter 142 can be switched.

[0026] The controller 130 is configured to sense the current (I In ) and the current output (I Out ).exist Figure 3 An example configuration of the controller 130 is shown in FIG. 1 , which 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. The amplifier 162 is based on a voltage reference V ref Then, the amplified output from amplifier 162 is combined with the feedback voltage V fb A comparison is made and a control output is applied to switch SW1.

[0027] During operation, the load-balanced boost power supply 120 operates in a boost switching power supply configuration, wherein the input voltage V IN and gradually increase (boost) it to a higher output voltage V1 or V2. In order to balance the input current I IN , the net output current I OUT For most of the cycle, current flows out of the boost circuit. However, during the back EMF time when the direction of current through 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 (the net load current). The low pass filter 152 is used to average the net load current over multiple coil frequency transitions. Therefore, the low pass filter 152 is a very low frequency filter.

[0028] If the back EMF current does flow back into 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 reducing the duty cycle of the switch SW1. A blocking diode D2 is used with an additional capacitor C2 on the output of the circuit to "absorb" this reverse current. The excess current is stored in the capacitor C2 and reused during the next cycle of the H-bridge 128. Note that the output voltage V2 must be able to increase over the entire coil frequency cycle. Therefore, the output voltage V2 is not a well-regulated voltage.

[0029] The net load current (I LOAD), the control circuit 130 of the boost circuit 120 forces the boost circuit 120 to maintain the boost voltage to provide the required load current I LOAD This is accomplished by allowing the output voltage V2 to increase while the boost is normally shut down, thereby keeping the input current constant. If the net load current is not used, and 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.

[0030] Figure 4 It is shown Figure 2 The circuit shown in FIG. 1 shows V1, V2, sense 2 and I IN The magnitude of V is plotted against time and illustrates the operation of the controller 130 as discussed above. Given a constant output load, the voltage from the power supply V in The input current of the boost varies indirectly with the supply voltage. When switch SW1 126 is turned on, it causes current to flow through inductor L1. This current causes energy to be stored in inductor L1. The time that inductor L1 and SW1126 are turned on is called the on-time, and the rest of the switching cycle is called the off-time. Diode D1 is reverse biased and therefore does not conduct. 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 this current through D1 is the load current of the boost supply (current sense 1). The load current is independent of the input supply voltage Vin. 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, the current (I in ) will be continuous and almost constant, such as Figure 4 shown.

[0031] With this configuration, the input current I IN , to reduce or eliminate large periodic current surges that can range from zero (0) amp input to many amp input in a few milliseconds. Think of it as a DC power factor correction circuit.

[0032] Although the present invention has been described with reference to preferred embodiments, those skilled in the art will recognize that modifications may be made in form and detail without departing from the spirit and scope of the invention. In the structure shown herein, capacitor C2 provides a power sweeping circuit to store power from the coil when the direction of the drive current is reversed. However, other power storage and sweeping techniques may be used, including those of inductors or batteries. Using the configuration proposed herein, a boost power 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 power supply is also sensed and applied to a low pass filter 150, which has a shorter time constant than the low pass filter 152. The controller 130 compares the two filtered signals and controls the operation of the switch SW1 to convert the input current I IN Maintain a relatively constant level, such as Figure 4 shown.

Claims

1. A magnetic flowmeter (100) for measuring fluid flow, comprising: a flow tube assembly (102) receiving a fluid flow, the flow tube assembly having a coil (104) with a first coil wire and a second coil wire for receiving a coil current and generating a magnetic field in response, thereby generating an electromotive force (EMF) in the fluid representative of the flow velocity; an EMF sensor (107) arranged to sense the EMF and generate an output indicative of the flow rate; An H-bridge circuit (128) configured to apply a current supply signal to the coil and to switch a direction of the current supply signal flowing through the coil; as well as A load balancing boost power supply unit (120), the load balancing boost power supply unit is configured to provide power to the H-bridge circuit and regulate input current from a DC power supply (122), the load balancing boost power supply unit comprising: an inductor (L1) coupled in series with the input current; a switch (Sw1) arranged to selectively connect the inductor to electrical ground, thereby increasing the voltage provided by the DC power source; a current sensing circuit (132, 134) arranged to measure the net current flowing into and out of the coil; and The controller (130) controls the operation of the switch based on the measured net current so that the input current is constant.

2. The magnetic flowmeter according to claim 1, wherein: The H-bridge circuit includes: a first switch and a second switch, the first switch and the second switch respectively coupling the first coil wire and the second coil wire to a first supply conductor; and a third switch and a fourth switch, the third switch and the fourth switch respectively coupling the first coil wire and the second coil wire to a second supply conductor.

3. The magnetic flowmeter according to claim 1, wherein: The load-balancing step-up power supply section includes a power storage element configured to sweep power from the coil when a direction of the current supply signal through the coil is reversed.

4. The magnetic flowmeter according to claim 3, wherein: The power storage element includes a capacitor.

5. The magnetic flowmeter according to claim 1, wherein: The load-balancing boost power supply includes a current sensor configured to sense current flowing into the coil and, in response, control the current supply signal based on the sensed current.

6. The magnetic flowmeter according to claim 1, wherein: The load-balancing boost power supply includes a current sensor configured to sense current flowing from the coil and, in response, control the current supply signal based on the sensed current.

7. The magnetic flowmeter according to claim 1, wherein: The load-balancing boost supply senses a voltage related to the voltage across the coil and, in response, controls the current supply signal based on the sensed voltage.

8. The magnetic flowmeter according to claim 1, wherein: The load balancing boost power supply unit includes a diode for preventing current from the coil from flowing into components of the load balancing boost power supply unit when a direction of a current supply signal applied to the coil is reversed.

9. The magnetic flowmeter according to claim 1, wherein: The load balancing boost power supply unit includes a voltage sensor for sensing a back EMF flowing from the coil into the load balancing boost power supply unit due to a direction reversal of the current supply signal flowing through the coil.

10. The magnetic flowmeter according to claim 9, wherein: The controller controls the switch based on the sensed back EMF from the coil.

11. A magnetic flowmeter (100) for measuring fluid flow, comprising: a flow tube assembly (102) receiving a fluid flow, the flow tube assembly having a coil (104) with a first coil wire and a second coil wire for receiving a coil current and generating a magnetic field in response, thereby generating an electromotive force (EMF) in the fluid representative of the flow velocity; an EMF sensor (107) arranged to sense the EMF and generate an output indicative of the flow rate; an H-bridge circuit (128) configured to apply a current supply signal to the coil and, in response, reverse the direction of the current supply signal through the coil, thereby generating a back EMF, causing a back EMF current to flow out of the coil; as well as A power sweeping circuit is configured to recover power from the coil by charging a capacitor (C2) using the back EMF current.

12. The magnetic flow meter of claim 11, comprising a load balancing boost power supply having a current sensor configured to sense current flowing into the coil and, in response, control the current supply signal based on the sensed current.

13. The magnetic flow meter of claim 11, comprising a load balancing boost power supply having a current sensor configured to sense current flowing from the coil and, in response, control the current supply signal based on the sensed current.

14. The magnetic flow meter of claim 11, comprising a load balancing boost power supply including a switch configured to cut off the current supply signal according to the sensed back EMF.

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