Spectral diagnostics in a magnetic flow meter

• US 6,615,149 B1
• Filed: 05/23/2000
• Issued: 09/02/2003
• Est. Priority Date: 12/10/1998
• Status: Expired due to Term

• Current Assignee: Micro Motion Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Wehrs, David L.
• Primary Examiner(s): Hoff, Marc S.
• Assistant Examiner(s): Raymond, Edward
• Application Number:
  US09/576,450
• Time in Patent Office: 1,197 Days
• Field of Search: 702/76, 702/12, 702/17, 702/35, 702/38, 702/45, 702/70, 702/75, 702/77, 702/79, 702/100, 738/611--86
• US Class Current: 702/76
• CPC Class Codes: G01D 3/032 affecting incoming signal, e.g. by averaging; gating undesired signals
• CPC Class Codes: G01D 3/0365 the undesired influence being measured using a separate sensor, which produces an influence related signal
• CPC Class Codes: G01F 1/58 by electromagnetic flowmeters
• CPC Class Codes: G01F 1/60 Circuits therefor
• CPC Class Codes: G01F 25/10 of flowmeters

Abstract

A magnetic flow transmitter provides a coil driver output at a selected fundamental to a coil on a flow tube carrying a flow of a liquid. An amplifier amplifies an electrode signal from the flow tube and an A/D converter converts the amplified electrode signal. A digital signal processor (DSP) uses a spectral transform such as a Fourier type transform to generate a flow output based on spectral components at or near the fundamental and a noise diagnosing output based on components at or near a noise frequency.

Claims

1. A magnetic flow transmitter, comprising:

a driver adapted to provide a driver output at a selected fundamental to a coil on a flow tube carrying a flow of a liquid;

an amplifier having an amplifier input adapted to couple to electrodes on the flow tube, the amplifier having an amplifier output;

an analog-to-digital converter having a digital output related to the amplifier output; and

a digital processor that receives the digital output and generates spectral components of the digital output that extend over both the fundamental and a frequency of a known potential noise source different than the fundamental;

the processor providing a flow output as a function of at least one spectral component at or near the fundamental, the processor further providing a diagnostic output as a function of at least one spectral component at or near the frequency of the noise source.

2. The magnetic flow transmitter of claim 1 wherein the processor comprises a digital signal processor.

3. The magnetic flow transmitter of claim 1 wherein the processor comprises a microprocessor.

4. The magnetic flow transmitter of claim 1 wherein the processor generates the spectral components in the frequency domain as a transform function of time domain data at the digital output.

5. The magnetic flow transmitter of claim 4 wherein the transform function is a Fourier type transform.

6. The magnetic flow transmitter of claim 5 wherein the Fourier type transform is a fast Fourier transform.

7. The magnetic flow transmitter of claim 5 wherein the Fourier type transform function is a discrete Fourier transform.

8. The magnetic flow transmitter of claim 1 wherein the driver output is substantially a rectangular wave with a fundamental Fo.

9. The magnetic flow transmitter of claim 8 wherein the spectral components are generated in synchronization with the driver output.

10. The magnetic flow transmitter of claim 9 further comprising a synchronization line coupled between the driver and the processor.

11. The magnetic flowmeter of claim 1 further comprising a control line coupled from the processor to the driver, the line controlling the fundamental.

12. The magnetic flow transmitter of claim 1 wherein the flow and diagnostic outputs are galvanically isolated from the amplifier input.

13. The magnetic flow transmitter of claim 1 wherein the digital processor comprises digital filters controlled as a function of the diagnostic output.

14. A method of operation of magnetic flow transmitter, the method comprising:

driving a coil on a flow tube carrying a flow of a liquid, the driving having a repetition frequency at a selected fundamental Fo;

amplifying a signal from electrodes on the flow tube to provide an amplifier output;

converting the amplifier output to a digital output;

digitally processing the digital output to generate spectral components of the digital output that extend over both the fundamental and a frequency of a known potential noise source that is different than Fo;

generating a flow output as a function of at least one spectral component at or near the fundamental; and

generating a diagnostic output as a function of at least one spectral component at or near the frequency of the noise source.

15. The method of claim 14 further comprising:

selecting the fundamental Fo as a function of the diagnostic output.

16. The method of claim 14 further comprising:

adjusting the digital processing as a function of the diagnostic output.

17. The method of claim 14 further comprising:

communicating the diagnostic output to a location remote from the magnetic flow transmitter.

18. The method of claim 14 further comprising:

displaying the diagnostic output on a display on the magnetic flow transmitter.

19. A magnetic flow transmitter, comprising:

a driver adapted to provide a driver output at a selected fundamental to a coil on a flow tube carrying a flow of a liquid;

an amplifier having an amplifier input adapted to couple to electrodes on the flow tube, the amplifier having an amplifier output;

an analog-to-digital converter receiving the amplifier output and generating a digital output; and

processor means receiving the digital output and digitally generating spectral components of the digital output extending over both the fundamental and a frequency of a known potential noise source that is different than the selected fundamental;

the processor means generating a flow output as a function of at least one spectral component at or near the fundamental, and the processor means further generating a diagnostic output as a function of at least one spectral component at or near the frequency of the noise source.

20. A computer readable medium having stored thereon a plurality of sequences of instructions, the plurality of sequences of instructions including sequences which, when executed by a processor in a magnetic flow transmitter, cause the processor to perform the sequence:

receiving digital output representing a time domain amplified flow signal obtained from electrodes on a magnetic flow tube;

digitally generating spectral components of the digital output extending over both a fundamental of a coil drive on the flow tube and a frequency of a known potential noise source that is different than the fundamental;

generating a flow output as a function of at least one spectral component at or near the fundamental; and

generating a diagnostic output as a function of at least one spectral component at or near the frequency of the noise source.