Comprehensive electromagnetic flowmeter

• US 20030056602A1
• Filed: 09/09/2002
• Published: 03/27/2003
• Est. Priority Date: 10/06/1999
• Status: Active Grant

• Current Assignee: Vincent J. Cushing
• Original Assignee: Vincent J. Cushing
• Inventors: Cushing, Vincent J.
• Granted Patent: US 6,973,840 B2
• Time in Patent Office: Days
• US Class Current: 73/861.17
• CPC Class Codes: G01F 1/60 Circuits therefor

Abstract

An electromagnetic flowmeter works with insulating liquids, and includes circuitry for handle drifting zero-point offset and triboelectric noise occurring in turbulently flowing dielectrics. Two signal processing schemes are presented—using high frequency induction and low frequency induction, but instead of measuring total voltage, the processor senses total voltage differentials, smooths the differentials, then integrates (sums) them such that the three components of total voltage are articulated—and, importantly, the flow voltage component itself is measured.

Claims

1. An electromagnetic flowmeter for measuring flow of a material, said flowmeter comprising:

a conduit of substantially insulative material for carrying said material;

a magnet for generating a magnetic induction in a flow measurement region of said conduit;

at least two electrodes disposed on an outer surface of said conduit in said region; and

a signal processing circuit for processing an output from each said electrode, said signal processing circuit including a compensation circuit for compensating for offsets.

2. A flowmeter according to claim 1, wherein said compensation circuit comprises:

an amplifier circuit processing an output from each electrode, each amplifier circuit comprising

a preamplifier; and

a regeneration amplifier having a gain G and having an output coupled

to an input of said preamplifier through a capacitance C_r;

wherein said gain G and capacitance Cr are selected such that (G−

1)C_r=4C₀ where C₀ is a capacitance between said electrodes when said conduit is empty.

3. A flowmeter according to claim 1, wherein said induction is an alternating induction, and the frequency of alternation is greater than a power mains frequency.

4. A flowmeter according to claim 3, wherein said frequency of alternation is a multiple of said power mains frequency.

5. A flowmeter according to claim 4, wherein said multiple is greater than 1.

6. A flowmeter according to claim 3, wherein said frequency of alternation is in the neighborhood of 1000 kHz.

7. A flowmeter according to claim 3, wherein said frequency of alternation is greater than 1000 kHz.

8. A flowmeter according to claim 1, wherein each of said electrodes is in the shape of a plate.

9. A flowmeter according to claim 8, wherein each said plate comprises an electrode grid.

10. A flowmeter according to claim 1, wherein said signal processing circuit further comprises an output sampling circuit for sampling a processed output of said electrodes, said signal processing circuit computing a plurality of difference signals by comparing pairs of time-offset samples.

11. A flowmeter according to claim 10, wherein said signal processing circuit comprises means for averaging a plurality of said difference signals.

12. A flowmeter according to claim 11, wherein said means for averaging includes means for averaging said difference signals over an integer number of cycles of a power mains frequency.

13. A flowmeter according to claim 1, wherein said signal processing circuit includes means for determining a voltage V_f=V−

V_d, where V_f represents measured flow, V represents a flow signal obtained from said electrodes and V_d represents a spurious voltage.

14. A flowmeter according to claim 13, wherein V_d=V_se⁻

t/τ

.

15. An electromagnetic flowmeter for measuring flow of a material, said flowmeter comprising:

a conduit of substantially insulative material for carrying said material;

a magnet for generating an alternating magnetic induction in a flow measurement region of said conduit;

at least two electrodes disposed on an outer surface of said conduit in said region; and

a signal conditioner for sampling and processing outputs from said electrodes, said signal conditioner sampling at least one of said electrode outputs plural times during each half cycle of said alternating magnetic induction.

16. An electromagnetic flowmeter for measuring flow of a material, said flowmeter comprising:

a conduit of substantially insulative material for carrying said material;

a magnet for generating a magnetic induction in a flow measurement region of said conduit;

at least two electrodes disposed on an outer surface of said conduit in said region; and

a signal processing circuit for processing an output from each said electrode, said signal processing circuit including a temporal differential module.

19. An electromagnetic flowmeter according to claim 16, further including a high frequency induction method circuit.

17. An electromagnetic flowmeter for measuring flow of a material, said flowmeter comprising:

a conduit of substantially insulative material for carrying said material;

a magnet for generating a magnetic induction in a flow measurement region of said conduit;

at least two electrodes disposed on an outer surface of said conduit in said region; and

a signal processing circuit for processing an output from each said electrode, said signal processing circuit including a high frequency induction method circuit.

18. An electromagnetic flowmeter for measuring flow of a material, said flowmeter comprising:

a conduit of substantially insulative material for carrying said material;

a magnet for generating a magnetic induction in a flow measurement region of said conduit;

at least two electrodes disposed on an outer surface of said conduit in said region; and

a signal processing circuit for processing an output from each said electrode, said signal processing circuit including a low frequency induction method circuit.