Electromagnetic flow sensor

1. An electromagnetic flow sensor for an electromagnetic flow meter, the electromagnetic flow sensor comprising:

a body or frame;

a passage through the body or frame;

at least part of a magnetic circuit supported by the body or frame for directing a magnetic field across the passage; and

at least first and second electrodes supported by the body or frame, the at least first and second electrodes arranged to sense a voltage in response to a conductive fluid flowing through the passage;

wherein the at least part of the magnetic circuit comprises:

a central pole piece; and

outer pole piece(s) extending around the central pole piece and the passage so as to serve as a magnetic screen from an external magnetic field;

wherein the passage has a central protrusion extending into and along the passage so as to present a profile to the flow of the conductive fluid which turns back on itself, wherein the central protrusion is electrically insulated and includes the central pole piece.

2. An electromagnetic flow sensor according to claim 1 , wherein at least a portion of the body or frame supporting the part of the magnetic circuit and the at least first and second electrodes are configured to be insertable into a flow tube through a single aperture in the flow tube.

3. An electromagnetic flow sensor according to claim 1 , comprising

electrically-conductive parts which are not the at least first and second electrodes;

wherein the body or frame is, in use, in direct contact with the conductive fluid and the electrically-conductive parts are electrically insulated from the conductive fluid.

4. A sub-assembly comprising:

an electromagnetic flow sensor according to claim 1 ; and

a meter register;

wherein the electromagnetic flow sensor and the meter register form a single unit.

5. A sub-assembly according to claim 4 , wherein the part of the magnetic circuit and the at least first and second electrodes are integrally formed in the meter register.

6. A sensor according to claim 1 , wherein the at least part of the magnetic circuit is electrically insulated from the conductive fluid.

7. An electromagnetic flow meter comprising:

a sensor according to claim 1 .

8. An electromagnetic flow meter comprising:

a tubular fluid housing having a fluid housing wall and a fluid housing aperture in the fluid housing wall; and

an electromagnetic flow sensor having a body or frame; a passage through the body or frame; a part of a magnetic circuit supported by the body or frame for directing a magnetic field across the passage; and at least first and second electrodes supported by the body or frame, the at least first and second electrodes arranged to sense a voltage in response to an conductive fluid flowing through the passage; wherein at least a portion of the body or frame supporting the magnetic circuit part and the at least first and second electrodes are configured to be insertable into a flow tube through a single aperture in the flow tube

wherein the electromagnetic flow meter is a whole flow meter.

9. An electromagnetic flow meter according to claim 8 , wherein the electromagnetic flow sensor is removably inserted in the tubular fluid housing.

10. An electromagnetic flow meter according to claim 8 , wherein the tubular fluid housing is a T-piece pipe.

11. An electromagnetic flow meter according to claim 8 , wherein the electromagnetic flow meter has a meter body configured to provide electrical safety ground continuity across the electromagnetic flow meter.

12. An electromagnetic flow meter according to claim 11 , wherein the meter body is configured to provide an electrical reference point for an electronic module.

13. An electromagnetic flow meter comprising:

a tubular fluid housing having a fluid housing wall and a fluid housing aperture in the fluid housing wall;

a conditioning tube disposed within the tubular fluid housing and having a fluid conditioning tube wall and a conditioning tube aperture in the fluid conditioning tube wall; and

an electromagnetic flow sensor having a body or frame; a passage through the body or frame; a part of a magnetic circuit supported by the body or frame for directing a magnetic field across the passage; and at least first and second electrodes supported by the body or frame, the at least first and second electrodes arranged to sense a voltage in response to an conductive fluid flowing through the passage; wherein at least a portion of the body or frame supporting the magnetic circuit part and the at least first and second electrodes are configured to be insertable into a flow tube through a single aperture in the flow tube.

14. An electromagnetic flow meter comprising:

a tubular fluid housing having a fluid housing wall and a fluid housing aperture in the fluid housing wall;

a conditioning tube disposed within the tubular fluid housing and having a fluid conditioning tube wall and a conditioning tube aperture in the fluid conditioning tube wall; and

a sub-assembly having an electromagnetic flow sensor and a meter register, wherein the electromagnetic flow sensor and the meter register form a single unit, the electromagnetic flow sensor inserted in the tubular fluid housing so as to at least partially pass through the fluid housing aperture and to at least partially pass through the conditioning tube aperture.