Variable frequency magnetic flowmeter

• US 20130006544A1
• Filed: 06/28/2011
• Published: 01/03/2013
• Est. Priority Date: 06/28/2011
• Status: Active Grant

• Current Assignee: Micro Motion Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Rovner, Bruce David
• Granted Patent: US 9,182,258 B2
• Time in Patent Office: Days
• US Class Current: 702/45
• CPC Class Codes: G01F 1/58 by electromagnetic flowmeters
• CPC Class Codes: G01F 1/60 Circuits therefor

Abstract

An apparatus 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, and an electrode for sensing an electromotive force induced across the process flow by the magnetic field. The current source energizes the coil at a plurality of different pulse frequencies. A processor calculates a function of the electromotive force at the plurality of different pulse frequencies, and generates a flow output based on the function.

Claims

1. An apparatus comprising:

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, wherein the current source energizes the coil at a plurality of different pulse frequencies;

an electrode for sensing an electromotive force induced across the process flow by the magnetic field; and

a processor for calculating a function of the electromotive force at the plurality of different pulse frequencies, and for generating a flow output based on the function.

2. The apparatus of claim 1, wherein the function comprises a common mean of the electromotive force at each of the different pulse frequencies.

3. The apparatus of claim 2, wherein the plurality of different pulse frequencies comprises at least three different pulse frequencies.

4. The apparatus of claim 1, wherein the function comprises a weighted average of the electromotive force at the plurality of different pulse frequencies.

5. The apparatus of claim 4, wherein the weighted average is weighted based on a difference between the electromotive force at each of the different pulse frequencies and a common mean.

6. The apparatus of claim 5, wherein the weighted average excludes at least one of the different pulse frequencies based on the difference.

7. The apparatus of claim 5, wherein the flow output comprises an alarm indicator based on the difference.

8. The apparatus of claim 5, wherein the weighted average comprises weightings of zero and one based on a difference between a value of the electromotive force at a particular pulse frequency and the common mean, wherein a weighting of zero excludes the value of the electromotive force at the particular frequency from the flow output, and wherein a weighting of one includes the value of the electromotive force at the particular frequency in the flow output.

9. The apparatus of claim 1, wherein the electrode senses the electromotive force at a plurality of different phases.

10. The apparatus of claim 9, wherein the function comprises an average of the electromotive force at the plurality of different phases.

11. A magnetic flowmeter comprising:

a pipe section, the pipe section having an inner diameter and an outer diameter;

a coil proximate the outer diameter of the pipe section;

a pulsed current source connected to the coil, wherein the pulsed current source provides a plurality of different pulse frequencies;

electrodes extending from the outer diameter of the pipe section to the inner diameter of the pipe section, wherein the electrodes sense an electromotive force across the pipe section; and

a processor connected to the electrodes, wherein the processor generates a flow output as a function of the electromotive force at the plurality of different pulse frequencies.

12. The flowmeter of claim 11, further comprising a lining on the inner diameter of the pipe section, wherein the electrodes extend through the lining to contact a process flow.

13. The flowmeter of claim 11, wherein the function comprises a common mean of the electromotive force at each of the different pulse frequencies.

14. The flowmeter of claim 11, wherein the function comprises a weighted average of the electromotive force at the plurality of different pulse frequencies.

15. The flowmeter of claim 14, wherein the weighted average excludes at least one of the plurality of different pulse frequencies based on a difference from a common mean.

16. The flowmeter of claim 15, wherein the flow output comprises an alarm based on the difference.

17. The flowmeter of claim 11, wherein the function comprises an average of the electromotive force at a plurality of different phases.

18. A method of measuring flow, the method comprising:

generating a pulsed magnetic field across a process flow;

sensing an electromotive force induced across the process flow by the pulsed magnetic field;

varying a frequency of the pulsed magnetic field, wherein the pulsed magnetic field has a plurality of different pulse frequencies;

calculating an average of the electromotive force at the plurality of different pulse frequencies; and

generating a flow output based on the average.

19. The method of claim 18, wherein calculating an average comprises calculating a weighted average based on a difference between the electromotive force at each of the different pulse frequencies and a common mean.

20. The method of claim 19, wherein the weighted average excludes at least one frequency of the plurality of different pulse frequencies, based on the difference.

21. The method of claim 19, further comprising generating an alarm based on the difference.

22. The method of claim 18, wherein sensing an electromotive force comprises sensing the electromotive force at a plurality of different phases, and wherein calculating an average comprises calculating an average of the electromotive force at the plurality of different pulse frequencies and the plurality of different phases.