Electrode leakage diagnostics in a magnetic flow meter

• US 6,611,775 B1
• Filed: 05/23/2000
• Issued: 08/26/2003
• 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., Coursolle, Thomas P.
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): Washburn, Douglas N
• Application Number:
  US09/576,719
• Time in Patent Office: 1,190 Days
• Field of Search: 738/61, 738/610.2, 738/610.8, 738/611.1, 738/611.2, 702/38, 702/45, 702/50, 702/51, 702/57, 702/65, 702/100, 702/183
• US Class Current: 702/65
• 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 meter has a diagnostic circuit that indicates leakage from flowtube electrodes. The diagnostic circuit couples to the electrodes and to ground. The diagnostic circuit samples diagnostic potentials between each electrode and ground, and then generates a sum of the diagnostic potentials between a first and a second electrode that indicates the leakage. The flowtube includes an insulated tube and an electromagnet. A transmitter circuit couples to the electromagnet and electrodes, and then generates a transmitter output representing a flow rate, which can be corrected for the leakage.

Claims

1. A magnetic flow meter, comprising:

a flowtube having an insulated tube adapted to carry a flowing liquid that is coupled to a ground, the flowtube having an electromagnet, and an electrode circuit including first and second electrodes;

a transmitter circuit coupled to the electromagnet, to the electrode circuit and to the ground, the transmitter circuit generating a transmitter output representing a flow rate of the liquid as a function of a differential potential on the electrode circuit; and

a diagnostic circuit coupled to the electrode circuit and to the ground, the diagnostic circuit sensing a first diagnostic potential between the first electrode and ground, and sensing a second diagnostic potential between the second electrode and ground, and generating a diagnostic output indicating leakage from the electrode circuit as a function of a sum of the first and second diagnostic potentials.

2. The magnetic flow meter of claim 1 wherein the leakage is from the electrode circuit to ground.

3. The magnetic flow meter of claim 1 wherein the leakage is from the electrode circuit to the electromagnet.

4. The magnetic flow meter of claim 1 wherein the diagnostic output indicates electrode-to-ground leakage when the sum of diagnostic potentials is in a first range, and indicates electrode-to-electromagnet leakage when the sum of diagnostic potentials is in a second range larger than the first range.

5. The magnetic flow meter of claim 1 wherein transmitter circuit couples a drive output to the electromagnet, and the diagnostic circuit calculates a sampled sum that is sampled in synchronization with the drive output.

6. The magnetic flow meter of claim 5 wherein the diagnostic circuit calculates an absolute value of the sampled sum.

7. The magnetic flow meter of claim 1 wherein the transmitter circuit includes a correction circuit generating a corrected transmitter output as a function of the transmitter output and the diagnostic output.

8. The magnetic flow meter of claim 7 wherein the correction circuit scales the corrected transmitter output as a function of a ratio of the diagnostic output to the transmitter output when the diagnostic output is in the first range.

9. The magnetic flow meter of claim 8 wherein the transmitter output is corrected according to the equation:

10. A magnetic flow meter, comprising:

a flowtube having an insulated tube adapted to carry a flowing liquid that is coupled to ground, the flowtube having an electromagnet, and first and second electrodes;

a transmitter circuit coupled to the electromagnet, the first and second electrodes and the ground, the transmitter circuit generating a transmitter output representing a flow rate of the liquid as a function of a differential potential between the first and second electrodes; and

diagnostic means coupled to the electrodes and the ground for sensing a first diagnostic potential between the first electrode and ground, and for sensing a second diagnostic potential between the second electrode and ground, and for generating a diagnostic output indicating electrode leakage as a function of a sum of the first and second diagnostic potentials.

11. 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 meter, cause the processor to perform the sequence:

receiving a first diagnostic potential between a first electrode of a magnetic flow meter and ground;

receiving a second diagnostic potential between a second electrode of a magnetic flow meter and ground; and

generating a diagnostic output indicating a presence of electrode leakage as a function of a sum of the first and second diagnostic potentials.

12. The computer readable medium of claim 11, further having sequences of instructions that perform the following sequence:

summing the first and second diagnostic potentials;

sampling the diagnostic potentials;

calculating an absolute value of the diagnostic potentials;

comparing the absolute value of diagnostic potentials to a stored reference;

indicating electrode leakage as a function of the comparing; and

correcting the transmitter output for the indicated leakage.

13. A process for operating a magnetic flow transmitter, comprising:

summing first and second diagnostic potentials received from corresponding first and second electrodes of a flowtube;

sampling the diagnostic potentials;

calculating an absolute value of the diagnostic potentials;

comparing the absolute value of diagnostic potentials to a stored reference;

indicating electrode leakage as a function of the comparing; and

correcting the transmitter output for the indicated leakage.

14. A magnetic flow meter, comprising:

a flowtube having an insulated tube adapted to carry a flowing liquid that is coupled to ground, the flowtube having an electromagnet, and first and second electrodes;

a processor system coupled to the electromagnet, and the first and second electrodes, the processor system generating a transmitter output representing a flow rate of the liquid as a function of a differential potential between the first and second electrodes, and the processor system sensing a first diagnostic potential between the first electrode and ground, and sensing a second diagnostic potential between the second electrode and ground, and generating a diagnostic output indicating a presence of electrode leakage as a function of a sum of the first and second diagnostic potentials.