Electromagnetic flow meter

Patent metadata

Field	Value
Publication number	US-10274358-B2
Application number	US-201615386016-A
Country	US
Kind code	B2
Filing date	Dec 21, 2016
Priority date	Dec 25, 2015
Publication date	Apr 30, 2019
Grant date	Apr 30, 2019

Abstract

A first detection electrode that outputs a first flow rate signal and a second detection electrode that outputs a second flow rate signal, a differential circuit that outputs a differential flow rate signal obtained by obtaining a difference between the first flow rate signal and the second flow rate signal, an AC signal generation circuit that causes a first AC current to flow between the first detection electrode and the ground electrode and causes a second AC current with a reverse phase at the same frequency as that of the first AC current to flow between the second detection electrode and the ground electrode, and a diagnosis unit that diagnoses an abnormality of at least either of the first detection electrode or the second detection electrode based on a differential flow rate signal.

First claim

What is claimed is:

1. An electromagnetic flow meter that measures velocity of fluid that is a measurement target flowing in a magnetic field formed inside a measurement pipe, the electromagnetic flow meter comprising:
a first detection electrode that detects electromotive force generated by the fluid to output a first flow rate signal having a magnitude of the detected electromotive force, and a second detection electrode that detects electromotive force generated by the fluid to output a second flow rate signal having a magnitude of the detected electromotive force;
a differential circuit that outputs a differential flow rate signal obtained by obtaining a difference between the first flow rate signal and the second flow rate signal;
an AC signal generation circuit that causes a first AC current to flow between the first detection electrode and a ground electrode and causes a second AC current with a reverse phase at the same frequency as that of the first AC current to flow between the second detection electrode and the ground electrode; and
a diagnosis unit that calculates a first resistance value between the first detection electrode and the second detection electrode based on the differential flow rate signal from the first flow rate signal and the second flow rate signal output in a state in which the first AC current and the second AC current are caused to flow, and diagnoses an abnormality of at least either of the first detection electrode or the second detection electrode based on the calculated first resistance value.

2. The electromagnetic flow meter according to claim 1 ,
wherein the diagnosis unit includes a timing signal generation unit that outputs an excitation current timing signal indicating a frequency of an excitation current output by an excitation circuit that forms the magnetic field in the measurement pipe, a first AC current timing signal indicating a frequency of the first AC current, and a second AC current timing signal indicating a frequency of the second AC current, and
the frequency of the first AC current timing signal and the second AC current timing signal is an integer multiple of the frequency of the excitation current timing signal.

3. The electromagnetic flow meter according to claim 1 ,
wherein the diagnosis unit includes a timing signal generation unit that outputs an excitation current timing signal indicating a frequency of an excitation current output by an excitation circuit that forms the magnetic field in the measurement pipe, and a first AC current timing signal indicating a frequency of the first AC current,
the AC signal generation circuit causes the first AC current at a frequency expressed by the first AC current timing signal to flow between the first detection electrode and the ground electrode, and causes the second AC current with a reverse phase at the same frequency as a frequency expressed by the first AC current timing signal to flow between the second detection electrode and the ground electrode, and
a frequency of the first AC current timing signal is an integer multiple of the frequency of the excitation current timing signal.

4. The electromagnetic flow meter according to claim 1 ,
wherein the diagnosis unit diagnoses an abnormality of at least one of the first detection electrode and the second detection electrode based on a first resistance value difference that is a difference between the first resistance value calculated in an installation step of the electromagnetic flow meter and the first resistance value calculated in an operation step of the electromagnetic flow meter.

5. The electromagnetic flow meter according to claim 4 ,
wherein the diagnosis unit determines that at least either of the first detection electrode or the second detection electrode is abnormal when the first resistance value difference is smaller than a predetermined threshold.

6. The electromagnetic flow meter according to claim 1 ,
wherein the diagnosis unit
calculates a second resistance value corresponding to the first detection electrode based on the differential flow rate signal from the first flow rate signal and the second flow rate signal output in a state in which only the first AC current is caused to flow,
calculates a third resistance value corresponding to the second detection electrode based on the differential flow rate signal from the first flow rate signal and the second flow rate signal output in a state in which only the second AC current is caused to flow, and
performs at least one of diagnosis of an abnormality of the first detection electrode based on the second resistance value and diagnosis of an abnormality of the second detection electrode based on the third resistance value.

7. The electromagnetic flow meter according to claim 6 ,
wherein the diagnosis unit performs at least one of diagnosis of an abnormality of the first detection electrode based on a second resistance value difference that is a difference between the second resistance value calculated in an installation step of the electromagnetic flow meter and the second resistance value calculated in an operation step of the electromagnetic flow meter and diagnosis of an abnormality of the second detection electrode based on a third resistance value difference that is a difference between the third resistance value calculated in the installation step and the third resistance value calculated in the operation step.

8. The electromagnetic flow meter according to claim 7 ,
wherein the diagnosis unit determines that the second detection electrode is abnormal when the second resistance value difference is within a predetermined range and the third resistance value difference is smaller than a predetermined threshold value.

9. The electromagnetic flow meter according to claim 7 ,
wherein the diagnosis unit determines that the first detection electrode is abnormal when the second resistance value difference is smaller than a predetermined threshold value and the third resistance value difference is within a predetermined range.

10. The electromagnetic flow meter according to claim 6 ,
wherein the diagnosis unit diagnoses an abnormality of the first detection electrode or the second detection electrode using a combination of a first operation resistance value that is the first resistance value calculated in the operation step of the electromagnetic flow meter, a second operation resistance value that is the second resistance value calculated in the operation step, and a third operation resistance value that is the third resistance value calculated in the operation step.

11. The electromagnetic flow meter according to claim 10 ,
wherein the diagnosis unit determines that the first detection electrode is abnormal in any one of
a case in which half the first operation resistance value is greater than the second operation resistance value,
a case in which a difference between the first operation resistance value and the third operation resistance value is within a predetermined range, and
a case in which a difference between the second operation resistance value and the third operation resistance value is smaller than a predetermined threshold value.

12. The electromagnetic flow meter according to claim 10 ,
wherein the diagnosis unit determines that the second detection electrode is abnormal in any one of
a case in which half the first operation resistance value is greater than the third operation resistance value,
a case in which a difference between the first operation resistance value and the second operation resistance value is within a predetermined range, and
a case in which a difference between the second operation resistance v

Assignees

• Yokogawa Electric Corp

Inventors

• Shimura Toru

Classifications

• G01F1/60 Primary

  Circuits therefor · CPC title

• G01F25/0007 Primary

  Physics · mapped topic

• G01F25/10 Primary

  of flowmeters · CPC title