Electromagnetic flowmeter having low power consumption

• US 6,237,424 B1
• Filed: 10/15/1999
• Issued: 05/29/2001
• Est. Priority Date: 04/25/1997
• Status: Expired due to Term

• Current Assignee: Elster Water Metering Limited (Honeywell International Inc.)
• Original Assignee: ABB Metering Ltd. (Honeywell International Inc.)
• Inventors: Jin, Wu, Salmasi, Zareh Soghomonian, Howarth, Craig Timothy, Gregg, Ronald David, MacManus, Gerard
• Primary Examiner(s): Patel, Harshad
• Assistant Examiner(s): PATEL, JAGDISH C
• Application Number:
  US09/419,334
• Time in Patent Office: 592 Days
• Field of Search: 73/861.08, 73/861.11, 73/861.12, 73/861.13, 73/861.16, 73/861.17
• US Class Current: 73/861.17
• CPC Class Codes: G01F 1/002 wherein the flow is in an open channel
• CPC Class Codes: G01F 1/58 by electromagnetic flowmeters
• CPC Class Codes: G01F 1/586 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 Class Codes: G01F 1/60 Circuits therefor

Abstract

An electromagnetic flow meter and method of operating the same. There is provided a flow measurement duct, a magnetic circuit including pole pieces for generating a magnetic field in fluid flowing in a direction in the duct across the direction of flow, and an electrical circuit including at least one sensing electrode for measuring a voltage thereby induced in the fluid to provide an output indicative of the flow. The method comprises measuring a series of pairs of outputs of the electrical circuit, each pair of outputs comprising an output when the magnetic field is present and an output when the magnetic field is absent, and determining from the measured series of pairs of outputs whether fluid is present or absent in the duct.

Claims

1. A method of operating an electromagnetic flow meter comprising a flow measurement duct, a magnetic circuit including pole pieces on opposite sides of the duct, a path for magnetic flux and a coil for generating a magnetic field in fluid flowing in a direction in the duct across the direction of flow, and an electrical circuit including a pair of sensing electrodes and a signal progressing circuit branch for measuring a voltage thereby induced in the fluid to provide an output indicative of the flow, the method comprising the steps of measuring a series of pairs of outputs of said electrical circuit, each pair of outputs comprising an output when said magnetic field is present and an output when said magnetic field is absent, and determining from the measured series of pairs of outputs whether fluid is present or absent in the duct.

2. An electromagnetic flow meter comprising a flow measurement duct, a magnetic circuit including pole pieces on opposite sides of the flow measurement duct, a structure operatively connected to the pole pieces and providing a path for magnetic flux, and a coil disposed on one of the pole pieces for generating a magnetic field across fluid flowing in the duct, an electrical circuit including a coil drive circuit branch connected to the coil, a pair of sensing electrodes in spaced relation and in fluid communication with the duct and a signal processing circuit branch connected to the electrodes for measuring a voltage induced in the fluid, for deriving a flow measurement therefrom, and for sensing presence or absence of fluid in the duct from a series of pairs of outputs of the electrical circuit, each pair of outputs comprising an output of the electrical circuit when the magnetic circuit is active and an output of the electrical circuit when the magnetic circuit is inactive.

3. An electromagnetic flow meter according to claim 2 wherein the electrical circuit responds to noise signifying that the duct is empty of said fluid.

4. An electromagnetic flow meter according to claim 3 wherein the electrical circuit measures said voltage for short periods of time separated by relative long intervals, such periods having a frequency of occurrence such that the flow measured by the electrical circuit during said periods is representative of the flow during the relatively long intervals.

5. An electromagnetic flow meter according to claim 4 wherein the electrical circuit measures said voltage during some of said periods to identify said noise, when the magnetic circuit is inactive.

6. An electromagnetic flow meter according to claim 5, further comprising a processor operatively associated with said electrical circuit for varying duration of said intervals according to a measured flow rate, and/or according to a variation in the measured flow rate.

7. An electromagnetic flow meter according to claim 2, wherein the electrical circuit derives a series of time-spaced flow measurement signals from voltages induced in the fluid, each signal comprising a component representative of the flow and a variable DC component unrelated to the flow, the electrical circuit further comprising a processor for determining the DC component of said signal and for adjusting DC level of a subsequent said signal in response to said DC component.

8. An electromagnetic flow meter according to claim 7 wherein the processor predicts the DC component of the subsequent signal from a plurality of values of the DC component obtained from a previous signal.

9. An electromagnetic flow meter according to claim 8 wherein the flow measurement signal comprises a plurality of pulses, the processor predicting the DC component of the subsequent signal by applying an algorithm to values of the DC component each obtained from a respective pulse.

10. An electromagnetic flow meter according to claim 2, wherein the pole pieces are of a material exhibiting preferential crystalline anisotropy.

11. An electromagnetic flow meter according to claim 10 wherein the crystalline anisotropy is aligned with a direction of the magnetic field in the pole pieces.

12. An electromagnetic flow meter according to claim 11, wherein the pole pieces are of a magnetically soft material.

13. An electromagnetic flow meter according to claim 10, wherein the pole pieces are of a magnetically soft material.

14. An electromagnetic flow meter according to claim 13 wherein the pole pieces are of a material containing 0.03% wt or less of carbon.

15. An electromagnetic flow meter according to claim 2, wherein the structure comprises an enclosure containing the pole pieces, the coil, and the flow measurement duct.

16. An electromagnetic flow meter according to claim 2, wherein the sole pieces are shared to generate the magnetic field in alternating directions, the magnetic circuit further comprising a conductive element on at least one of the pole nieces for suppressing noise in a signal representative of flow induced electromagnetically by a change in direction of the magnetic field.

17. An electromagnetic flow meter according to claim 16 wherein the element for suppressing comprises a conductive ring encircling one of the pole pieces adjacent to the flow measurement duct.

18. An electromagnetic flow meter according to claim 16 wherein the conductive element comprises a conductive member in which eddy currents are generated, said eddy currents moderating rate of change of the magnetic field.

19. An electromagnetic flow meter according to claim 18, wherein the conductive member encircles said at least one of the pole pieces.

20. An electromagnetic flow meter according to claim 18, wherein the conductive member comprises a conductive ring encircling one of the pole pieces adjacent the flow measurement duct.

21. An electromagnetic flow meter according to claim 18, wherein the conductive member comprises a disc of diameter substantially equal to the diameter of the coil.

22. An electromagnetic flow meter according to claim 21, wherein the disc is at an axial end of the coil facing towards another one of the pole pieces.

23. An electromagnetic flow meter according to claim 21, wherein the conductive member encircles said at least one of the pole pieces.

24. An electromagnetic flow meter according to claim 2, wherein said flow measurement duct comprises a flow measurement portion and a flow tube having walls, said flow measurement portion having a smaller cross-sectional area than a portion of the flow tube, said portions being joined by a convergent or divergent section of the flow tube walls which are defined by reverse transition curves with a point of inflection therebetween.

25. An electromagnetic flow meter according to claim 24, wherein the measurement portion has at least one pair of opposing parallel planar walls.

26. An electromagnetic flow meter according to claim 2, wherein said flow measurement duct comprises a flow measurement portion and a flow tube having walls, said flow measurement portion having a smaller cross-sectional area than a portion of the flow tube, said portions being joined by a convergent or divergent section of the flow tube walls which at any location axially thereof have an included angle of not more than nine degrees, the walls of the convergent or divergent section being defined by one or more transition curves.

27. An electromagnetic flow meter according to claim 26, wherein the measurement portion is of substantially rectangular cross-section.

28. An electromagnetic flow meter according to claim 27, wherein said portion is of circular cross-section.

29. An electromagnetic flow meter according to claim 2, further comprising a battery connected to the electrical circuit.