Magnetic flowmeter having a programmable bi-directional current generator

Patent metadata

Field	Value
Publication number	US-11204268-B2
Application number	US-201916588012-A
Country	US
Kind code	B2
Filing date	Sep 30, 2019
Priority date	Sep 5, 2019
Publication date	Dec 21, 2021
Grant date	Dec 21, 2021

Abstract

A magnetic flowmeter includes a flow tube assembly and a programmable bi-directional current generator. The flow tube assembly receives the fluid flow and includes a coil and an electromotive force (EMF) sensor. The coil is configured to produce a magnetic field across the fluid flow in response to a coil current. The EMF sensor is arranged to sense an EMF across the fluid flow that is proportional to the flow rate, and generate an output indicating the induced EMF. The current generator includes a profile generator that issues profile commands, a power amplifier and a controller. The controller is configured to control the power amplifier to generate coil current pulses forming the coil current that travel through the coil in alternating directions. Each coil current pulse has a current profile that is based on a corresponding profile command.

First claim

What is claimed is:

1. A magnetic flowmeter for measuring a flow rate of a fluid flow, comprising:
a flow tube assembly configured to receive the fluid flow and including:
a coil configured to produce a magnetic field across the fluid flow in response to a coil current, the magnetic field induces an electromotive force (EMF) in the fluid flow that is proportional to the flow rate; and
an EMF sensor arranged to sense the EMF and generate an output indicating the induced EMF; and

a programmable bi-directional current generator comprising:
a profile generator configured to issue at least one of a plurality of different profile commands;
a power amplifier; and
a controller to control the power amplifier to generate coil current pulses forming the coil current that travel through the coil in alternating directions, each coil current pulse having a current profile of voltage over time that is based on the at least one of a plurality of different profile commands from the profile generator.

2. The magnetic flowmeter of claim 1 , wherein:
the power amplifier comprises:
a power supply;
an H bridge coupled to the power supply; and
a low pass filter configured to receive unfiltered current pulses from the H bridge through first and second conductors, attenuate high frequency components of the unfiltered current pulses to form the coil current pulses; and

the controller is configured to actuate pairs of complementary switches of the H bridge at varying duty cycles to generate the unfiltered current pulses based on the profile commands and alternate the direction of the coil current pulses through the coil.

3. The magnetic flowmeter of claim 2 , wherein the unfiltered current pulses have a frequency of 10-100 kHz.

4. The magnetic flowmeter of claim 2 , wherein the H bridge includes:
a first switch configured to actuate coupling the first conductor and a first terminal of the power supply;
a second switch that is complementary to the first switch and is configured to actuate coupling the first conductor to a second terminal of the power supply;
a third switch configured to actuate coupling of the second conductor to the first terminal of the power supply; and
a fourth switch that is complementary to the third switch and is configured to actuate coupling the second conductor to the second terminal of the power supply.

5. The magnetic flowmeter of claim 4 , wherein:
the controller actuates the first and second switches at a higher duty cycle than the third and fourth switches to deliver the coil current pulses in a first direction through the coil; and
the controller actuates the third and fourth switches at a higher duty cycle than the first and second switches to deliver the coil current pulses in a second direction, which is opposite the first direction, through the coil.

6. The magnetic flowmeter of claim 4 , wherein:
the controller actuates the first and second switches at a first duty cycle to produce first unfiltered current pulses having a first average voltage on the first conductor based on the profile commands;
the controller actuates the third and fourth switches at a second duty cycle to produce second unfiltered current pulses having a second average voltage on the second conductor based on the profile commands; and
a difference between the first and second average voltages determines the direction coil current pulses travel through the coil.

7. The magnetic flowmeter of claim 4 , wherein each of the coil current pulses travels in a single direction through the coil and has a current profile of a voltage level that varies with time in accordance with the corresponding profile command.

8. The magnetic flowmeter of claim 7 , wherein:
the controller actuates the first and second switches at a first duty cycle that varies over time to produce first unfiltered current pulses having a first average voltage level at the first conductor that varies over time based on the profile commands; or
the controller actuates the third and fourth switches at a second duty cycle that varies over time to produce second unfiltered current pulses having a second average voltage at the second conductor that varies over time based on the profile commands.

9. The magnetic flowmeter of claim 1 , wherein the profile commands include commands to produce the coil current pulses, each coil current pulse having a current profile of a voltage over time selected from the group consisting of a square current profile, a non-square current profile, a trapezoidal current profile, a sinusoidal current profile, and an irregular current profile.

10. The magnetic flowmeter of claim 9 , wherein each profile command corresponds to a non-square current profile having a leading portion, in which the voltage level gradually rises to a set point level over time.

11. The magnetic flowmeter of claim 10 , wherein the non-square current profile includes a trailing portion, in which the current level gradually falls from the set point level over time.

12. The magnetic flowmeter of claim 9 , wherein:
the EMF sensor comprises first and second electrodes positioned on opposing sides of the fluid flow; and
the magnetic flowmeter includes:
a signal processor configured to receive voltages sensed by the first and second electrodes and generate a digital voltage signal indicating a voltage difference between the first and second electrodes that is proportional to the EMF and the flow rate of the fluid flow; and
a digital processor configured to process the digital voltage signal and establish a flow rate of the fluid flow.

13. The magnetic flowmeter of claim 12 , including a communications interface configured to communicate the flow rate to an external computing device over a two-wire process control loop that powers the magnetic flowmeter.

14. The magnetic flowmeter of claim 1 , wherein the profile commands are based on an inductance of the coil.

15. The magnetic flowmeter of claim 1 , wherein the profile commands are based on a maximum voltage of a power supply of the power amplifier.

16. The magnetic flowmeter of claim 1 wherein a profile command is selected from the plurality of different profile commands to reduce errors in the coil current that travels through the coil.

17. A method of measuring a flow rate of a fluid flow comprising:
receiving the fluid flow through a flow tube assembly having a coil;
issuing at least one of a plurality of different profile commands defining a current profile of a voltage over time using a profile generator;
generating coil current pulses of a coil current using a programmable bi-directional current generator, each coil current pulse having a current profile of a voltage over time that is based on the at least one of the plurality of different profile commands, wherein the coil current pulses are driven through the coil in alternating directions;
generating a magnetic field across the fluid flow using the coil that induces an electromotive force (EMF) in the fluid flow that is proportional to the flow rate in response to generating the coil current pulses; and
generating an output indicating the induced EMF using an EMF sensor.

18. The method of claim 17 , wherein generating the coil current pulses comprises:
actuating pairs of complementary switches of an H bridge at different duty cycles to generate unfiltered current pulses based on the profile commands and alternate the direction the coil current pulses travel through the coil; and
filtering the unfiltered current pulses using a low pass filter to form the coil current pul

Assignees

• Micro Motion Inc

Inventors

• Ameri Masoud

Classifications

• G01F1/60 Primary

  Circuits therefor · CPC title

• G01F1/586 Primary

  constructions of coils, magnetic circuits, accessories therefor (G01F1/582 takes precedence; magnet; inductances; transformers; selection of materials for their magnetic properties per se H01F) · CPC title

• G01F1/584

  constructions of electrodes, accessories therefor · CPC title