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

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

Conventional magnetic flowmeters include 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 across the pipe section. The magnetic field induces the EMF or potential difference (voltage) across the flow that is proportional to the velocity of the flow. The magnetic flowmeter measures the flow rate based on the voltage difference, which is detected by the sensor section.

Magnetic flowmeters must work with large inductive switching loads. These inductive loads cause large swings in current through the load. This creates extreme challenges on the internal power supplies. If the dynamic loads are not managed properly, they can cause input current surges to the transmitter which produce potential supply challenges for the power systems use to power the magnetic flowmeter.

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

<CIT> describes a magnetic flowmeter system comprising flow tube, two coils for generating a magnetic field across the tube, and circuitry for driving the coil and sensing flow. The circuitry comprises a transformer that includes a pair of secondary windings. The number of the two windings is selected to provide a relatively low voltage and a relatively high voltage to the coil.

<CIT> describes an electromagnetic flowmeter comprising a base unit comprising a flow channel, in which an insert is placed. The insert comprises a plurality of male terminals that are configured to engage slide terminals of the base unit. A coil drover circuit for creating a magnetic field in the flow meter comprises a two-level constant current source.

<CIT> describes an analysis circuit for an electromagnetic flow tube and transmitter. The circuit comprises a regulated current driver that is summed up at a node with a voltage booster source to form a coil drive current. A switch bridge comprising configured to alternate the direction of the coil drive current as it passes through the coil.

<CIT> describes an electromagnetic flow meter for detecting a flow rate of a fluid by the capacitance method. The flow meter comprises a switching circuit configured to convert a supplied DC power from a primary side into a predetermined power by a transformer based on a switching control circuit. The converted power is output to a secondary side in that an output current can be arbitrarily set by the switching circuit.

A magnetic flowmeter for measuring a fluid flow is provided by claim <NUM>. The magnetic flowmeter includes a flow tube assembly receiving the flow and having a coil with first and second coil wires for receiving a coil current and responsively producing a magnetic field thereby generating an EMF in the fluid representative of a flow rate. An EMF sensor is arranged to sense the EMF and generate an output indicating the flow rate. Current supply circuitry applies a current supply signal to the coil. A load leveling boost supply provides power to the current supply circuitry. In another aspect, additionally, power scavenging circuitry recovers power from the coil.

The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the Background.

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

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

Magnetic flowmeters utilize a current through the sensor (coil) to develop a magnetic field, and as a conductive fluid passes through this field, an electric field that is proportional to the flow rate is produced, in accordance to Faradays' Law. To cancel out offsets in the system, the current is reversed periodically (known as the Coil Frequency) and, in the simplest case, an average voltage is obtained to determine the flow rate. During the current reversal, a back-emf is 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 momentarily lose the ability to regulate the output voltage. As the magnitude of the back-emf increases, it can actually cause the power supply to turn off. When this happens, the power supply must very quickly turn back on and deliver a large current to keep the system regulated and to complete the current reversal. The current surges on the power supply system can be extreme and are not well supported by typical power systems. The present invention includes techniques and circuits that regulate the current to a constant value. The invention integrates load leveling circuitry into a boost supply to remove/reduce dynamic current surges. Additionally, the circuitry captures the counter EMF energy stored in the inductive load and reuses this energy on the next switching cycle.

The invention includes a magnetic flowmeter which includes a load leveling boost power supply circuit. In another aspect, the invention further includes a scavenging circuit which is configured to reuse the back EMF which is generated in a flow tube coil following a current reversal cycle.

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

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

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

Power may be supplied to the magnetic flowmeter <NUM> from any suitable power source. For example, the magnetic flowmeter <NUM> may be wholly powered by the loop current IL flowing through the control loop <NUM>. One or more power supplies may also be utilized to power the process magnetic flowmeter <NUM>, such as an internal or an external battery. An electrical power generator (e.g., solar panel, a wind power generator, etc.) may also be used to power the magnetic flowmeter <NUM>, or charge a power supply used by the magnetic flowmeter <NUM>. However, most flowmeters typically operate in what is known as a "four-wire" configuration in which two wires are used to provide the process control loop <NUM> and a second pair of wires are used to provide power to the flowmeter. The power can be provided by a local DC power source and is useful in providing the relatively large amount of power required to generate a strong magnetic field in the flow of process fluid.

<FIG> is a simplified block diagram of magnetic flowmeter <NUM>. Magnetic flowmeter <NUM> includes flow tube <NUM> configured to receive a flow of process fluid therethrough. A coil <NUM> is positioned in the flow tube <NUM> and is configured to apply a magnetic field for the moving process fluid. Electrodes <NUM> are carried in the flow tube <NUM> and are exposed to the process fluid. These electrodes <NUM> sense an EMF generated in response to the magnetic field applied to the moving process fluid. As discussed above, this EMF is proportional to the flow rate of the process fluid.

In the configuration illustrated in <FIG>, a differential amplifier <NUM> is configured to sense and amplify the voltage difference generated between the two electrodes <NUM>. In one configuration, the differential amplifier <NUM> includes an analog to digital converter which provides a digital output related to the sensed EMF. In either case, the output from element <NUM> is related to the sensed EMF which in turn is proportional to the flow rate of the process fluid.

Measurement circuitry <NUM> receives the output from differential amplifier <NUM> and provides an output related to the flow of the process fluid. The measurement circuitry <NUM> can be implemented in digital and/or analog circuitry and can include a microprocessor or the like. In one configuration, the output from measurement circuitry <NUM> is of the type used in a process control environment. For example, as discussed above, the output can comprise an output on a two-wire process control loop including, for example, a <NUM>-<NUM> mA process control loop. The control loop may operate in accordance with the HART® communication protocol, a Fieldbus protocol, or other hardwired protocol. Further, the process control loop can also comprise a wireless control loop in which signals are communicated wirelessly. In some configurations, the same process control loop is used to provide power to the magnetic flowmeter <NUM>.

The current applied to the coil <NUM> of the magnetic flow tube <NUM> is controlled by current supply circuitry <NUM>. As discussed herein, current supply circuitry <NUM> operates as a load leveling boost supply.

The current supply circuitry <NUM> includes a power source <NUM> which provides an input voltage VIn and an input current IIN which is applied to an inductor L1. The output of inductor L1 can be selectively shorted to electrical ground using switch SW1 which is formed by a gate driver <NUM> and a transistor switch <NUM>. Power source <NUM> can be loaded internally or externally to the device. The circuitry can reduce or eliminate current surges drawn from a power source <NUM>. Inductor L1, diode D1, capacitor C1 along with switch SW1 operate to provide a boost power supply configuration in which a DC input voltage VIN is boosted to a higher voltage V1. The transient current through the inductor causes the voltage to increase beyond that provided by the power supply <NUM>. Capacitor C1 operates to smooth voltage spikes. The voltage V1 is connected to an H-bridge driver <NUM> through diode D2. Diodes D1 and D2 are connected to electrical ground through capacitors C1 and C2 respectively. Further, a controller <NUM> is configured to sense a feedback voltage VFB using resistors R1 and R2. The H-bridge driver <NUM> includes switches <NUM> which are controlled by measurement circuitry <NUM> in accordance with known techniques. More specifically, by alternating operation of switches on either side of the H-bridge <NUM>, the direction of the current applied to the coil <NUM> through a low pass filter <NUM> can be switched.

The controller <NUM> is configured to sense a current (IIn) applied to the H-bridge using a current sensor <NUM> through a low pass filter <NUM> as well as the current output of the H-bridge (IOut) using current sensor <NUM> through low pass filter <NUM>. One example configuration of the controller <NUM> is shown in <FIG> which includes amplifiers <NUM>, <NUM> and <NUM>. Differential amplifier <NUM> provides an output related to a difference between the input and output currents. Amplifier <NUM> amplifies this current difference based upon a voltage reference Vref. The amplified output from amplifier <NUM> is then compared to the feedback voltage Vfb and a control output is applied to switch SW1.

During operation, the Load-levelling Boost Supply <NUM> operates in a boost switching power supply configuration that takes an input voltage VIN, and steps it up (boosts it) to a higher output voltage V1 or V2. In order to level the input current IIN, the net output current IOUT must be determined. For the majority of the cycle, current is flowing out of the boost circuit. However, during the back-emf time when the direction of current through coil <NUM> is reversed, the 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 <NUM> is used to average the net load current over multiple coil frequency transitions. As such, it is a very low frequency filter.

If a back-emf current does flow back into the boost circuit <NUM>, the output voltage V2 increases, and the control circuit <NUM> detects that the voltage V2 is too high. When this occurs, the controller <NUM> controls the output by lowering the duty cycle of switch SW1. Blocking diode D2 is used with an additional capacitor C2 on the output of the circuit to "absorb" this reverse current. The extra current is stored in capacitor C2 and reused during the next cycle of the H-bridge <NUM>. 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.

Now that the net load current (ILOAD) is determined, the control circuit <NUM> for the boost circuit <NUM> forces the boost to stay on to supply the load current ILOAD that is needed. This is done by allowing the output voltage V2 to increase while the boost would normally be off, to thereby keep 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 keep increasing with each cycle, and the voltage will increase out of control.

<FIG> is a graph showing amplitude of V<NUM>, V<NUM>, Sense <NUM> and IIN versus time for the circuit shown in <FIG> and illustrates the operation of the controller <NUM> as discussed above. The input current of the boost from the supply source Vin varies indirectly with the supply voltage given a constant output load. When the Switch SW1 <NUM> turns on, it causes current to flow through the inductor L1. This current causes energy to be stored in the inductor L1. The time that the inductor L1 and SW1 <NUM> are on is known as the on-time, and the remainder of the switching cycle is referred to as the off-time. Diode D1 is reversed biased, and therefore does not conduct. During the off-time, diode D1 is forward biased and the energy stored in the inductor L1 is allowed to flow to the output and charge capacitor C1. The average of this current through D1 is the Boost Supply's load current (Current Sense <NUM>). The load current is independent of the input supply voltage Vin. By sensing the load current (Current Sense <NUM>) and forcing the net current to be the same as the load current sensed at Current Sense <NUM>, the current in to the supply (Iin) will be continuous and nearly constant as shown in <FIG>.

With this configuration, the input IIN current is actively controlled to reduce or eliminate large, periodic current surges which can range from zero (<NUM>) Amps input, to many Amps input in a matter of milliseconds. This can be considered a DC Power Factor Correction circuit.

Claim 1:
A magnetic flowmeter (<NUM>) for measuring a fluid flow, comprising:
a flow tube assembly (<NUM>) receiving the fluid flow and having a coil (<NUM>) with first and second coil wires for receiving a coil current and responsively producing a magnetic field thereby generating an EMF in the fluid representative of a flow rate;
an EMF sensor (<NUM>) arranged to sense the EMF and generate an output indicating the flow rate;
an H-bridge driver (<NUM>) configured to apply a current supply signal to the coil (<NUM>) and switch the direction of the current applied to the coil (<NUM>); and
a load leveling boost supply (<NUM>) configured to provide power to the H-bridge driver (<NUM>) and condition the input current (IIN) from a DC source, wherein the load leveling boost supply (<NUM>) is coupled to an input voltage (VIN) and is configured to apply a voltage (V1) to the coil (<NUM>) which is greater than an input voltage (VIN),
wherein the load leveling boost supply (<NUM>) includes:
a switch (SW1) configured to selectively couple an inductor (L1) to electrical ground and thereby generate the voltage (V1) which is greater than the input voltage (VIN), wherein the H-bridge driver (<NUM>) is connected to the voltage (V1), and
a controller (<NUM>) configured to sense the input current (IIN) using a first current sensor (<NUM>) through a first low pass filter (<NUM>) and a current output (IOut) of the H-bridge driver (<NUM>) using a second sensor (<NUM>) through a second low pass filter (<NUM>), wherein the controller (<NUM>) is configured to compare signals of the first and second current sensor (<NUM>, <NUM>) and control operation of the switch (SW1) to maintain the input current (IIN) at a relatively constant level.