Magnetic flowmeter with automatic adjustment based on sensed complex impedance

Patent metadata

Field	Value
Publication number	US-9696188-B2
Application number	US-201313826839-A
Country	US
Kind code	B2
Filing date	Mar 14, 2013
Priority date	Mar 14, 2013
Publication date	Jul 4, 2017
Grant date	Jul 4, 2017

Abstract

A magnetic flowmeter comprises a pipe section for process flow, a coil for generating a magnetic field across the pipe section, a current source for energizing the coil to generate the magnetic field at a coil drive frequency, and electrodes for sensing voltage induced across the process flow by the magnetic field. A processor calculates a function of the sensed voltage and generates a flow output based on the function. The processor adjusts an operating parameter of the flowmeter, such as electrode voltage sampling period, the coil drive frequency, or a phase shift, as a function of a sensed electrode-to-electrode or electrode-to-ground complex impedance.

First claim

The invention claimed is:

1. A magnetic flowmeter comprising:
a pipe section having an inner diameter and an outer diameter;
a coil proximate the outer diameter of the pipe section;
a current source connected to the coil to produce an alternating magnetic field at a coil drive frequency;
electrodes extending from the outer diameter of the pipe section to the inner diameter of the pipe section; and
a processor that generates a flow output as a function of a sensed voltage between the electrodes, wherein the processor adjusts one of a coil drive frequency, an electrode voltage sampling period, or a phase shift of an electrode signal as a function of a sensed complex impedance of a process fluid flowing within the pipe section, the complex impedance sensed between the electrodes or between one or more of the electrodes and ground.

2. The magnetic flowmeter of claim 1 , wherein the processor adjusts the coil drive frequency in an inverse relationship to the sensed complex impedance.

3. The magnetic flowmeter of claim 1 , wherein the processor adjusts the electrode voltage sampling period in an inverse relationship to the sensed complex impedance.

4. The magnetic flowmeter of claim 1 , wherein the current source is a pulsed DC current source.

5. The magnetic flowmeter of claim 1 , wherein the current source is an AC current source.

6. A method of measuring flow, the method comprising:
generating an alternating magnetic field across a flow of a process fluid;
sensing a voltage induced between sensing electrodes by the alternating magnetic field;
generating a flow output based on the voltage sensed;
sensing a complex impedance of the process fluid, the complex impedance sensed between sensing electrodes or between one or more of the sensing electrodes and ground; and
varying one of a coil drive frequency, an electrode voltage sampling period, or a phase shift of an electrode signal as a function of the sensed complex impedance.

7. The method of claim 6 , wherein the electrode voltage sampling period is adjusted in an inverse relationship to the sensed complex impedance.

8. The method of claim 6 , wherein the coil drive frequency is adjusted in an inverse relationship to the sensed complex impedance.

9. A method of operating a magnetic flowmeter, the method comprising:
sensing a complex impedance of a process fluid, the complex impedance sensed between sensing electrodes or between one or more of the sensing electrodes and ground; and
automatically adjusting one of a coil drive frequency, an electrode voltage sampling period, or a phase shift of an electrode signal of the magnetic flowmeter as a function of the sensed complex impedance.

10. The method of claim 9 , wherein the electrode voltage sampling period is adjusted in an inverse relationship to the sensed complex impedance.

11. The method of claim 9 , wherein the coil drive pulse frequency is adjusted in an inverse relationship to the sensed complex impedance.

Assignees

• Rosemount Inc

Inventors

• Rogers Steven Bruce
• Rovner Bruce D
• Foss Scot Ronald

Classifications

• G01F1/60 Primary

  Circuits therefor · CPC title

• G01F1/58

  by electromagnetic flowmeters · CPC title