Magnetic flowmeter with automatic adjustment based on sensed complex impedance

• US 9,696,188 B2
• Filed: 03/14/2013
• Issued: 07/04/2017
• Est. Priority Date: 03/14/2013
• Status: Active Grant

• Current Assignee: Micro Motion Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Rogers, Steven Bruce, Rovner, Bruce D., Foss, Scot Ronald
• Primary Examiner(s): Satanovsky, Alexander
• Assistant Examiner(s): Suarez, Felix
• Application Number:
  US13/826,839
• Publication Number:
  US 20140260662A1
• Time in Patent Office: 1,573 Days
• Field of Search: 702 12, 702 45, 702 46, 702 49, 702100, 702108, 7315218, 331 65
• CPC Class Codes: G01F 1/58 by electromagnetic flowmeters
• CPC Class Codes: G01F 1/60 Circuits therefor

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.

Claims

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.