Magnetic-inductive flowmeter and method for measuring the flow velocity of low conductivity media with a narrowing measuring tube and a field guide-back device

A magneto-inductive flow measuring device for measuring flow velocity or volume flow of a medium, the flow measuring device comprising:

• a measuring tube having a first longitudinal axis;
• a magnet system including a first coil system including at least a first coil having a first coil core, wherein the first coil system is arranged on the measuring tube and adapted to generate a magnetic field extending substantially perpendicular to the first longitudinal axis of the measuring tube;
• two measuring electrodes arranged in the measuring tube and coupled with the medium, the measuring electrodes adapted to register a flow-dependent voltage induced in the medium by the magnetic field;
• an electronic measuring/operating circuit configured to evaluate the flow-dependent voltage registered by the measuring electrodes;
• and
• a field guide-back structured to at least partially lead the magnetic field away from the measuring tube between the first coil system and a side of the measuring tube opposite the first coil system, wherein the field guide-back includes two guide-back sheet metal pieces disposed on opposing sides of the measuring tube, each adjacent a lateral side of the first coil core, and separated from each other by an air gap, and wherein the first coil core is adapted to at least partially lead the magnetic field between the measuring tube and the field guide-back.

An arrangement for measuring flow velocity or volume flow of a medium in a measuring tube using a magneto-inductive flow measuring device, the arrangement comprising:

• a pipeline;
• and
• at least one magneto-inductive flow measuring device including:
• a measuring tube having a first longitudinal axis;
• a magnet system including a coil system adapted to produce a magnetic field extending substantially perpendicularly to the longitudinal axis of the measuring tube;
• arranged in the measuring tube, at least two measuring electrodes, which are coupled with the medium and adapted to register a flow dependent voltage induced in the medium by the magnetic field;
• and
• a field guide-back structured to at least partially lead the magnetic field away from the measuring tube between the first coil system and a side of the measuring tube opposite the first coil system, wherein the field guide-back includes two guide-back sheet metal pieces disposed on opposing sides of the measuring tube, each adjacent a lateral side of the first coil core and separated from each other by an air gap, and wherein the first coil core is adapted to at least partially lead the magnetic field between the measuring tube and the field guide-back;
• an electronic measuring/operating circuit configured to evaluate the voltage registered by the at least two measuring electrodes, wherein the medium is led via the pipeline to the measuring tube of the magneto inductive measuring device, and
• wherein the pipeline has a first narrowing and/or the measuring tube has a second narrowing, which are/is arranged on an upstream side of the flow measuring device, wherein the first narrowing and/or the second narrowing have/has a flow shedding edge on a downstream side thereof.

A filling plant, comprising:

• an arrangement for measuring flow velocity or volume flow of a medium in a measuring tube using a magneto-inductive flow measuring device, the arrangement comprising:
• a pipeline;
• and
• at least one magneto-inductive flow measuring device including:
• a measuring tube having a first longitudinal axis;
• a magnet system including a coil system adapted to produce a magnetic field extending substantially perpendicularly to the longitudinal axis of the measuring tube;
• arranged in the measuring tube, at least two measuring electrodes, which are coupled with the medium and adapted to register a flow dependent voltage induced in the medium by the magnetic field;
• and
• a field guide-back structured to at least partially lead the magnetic field away from the measuring tube between the first coil system and a side of the measuring tube opposite the first coil system, wherein the field guide-back includes two guide-back sheet metal pieces disposed on opposing sides of the measuring tube, each adjacent a lateral side of the first coil core and separated from each other by an air gap, and wherein the first coil core is adapted to at least partially lead the magnetic field between the measuring tube and the field guide-back;
• an electronic measuring/operating circuit configured to evaluate the voltage registered by the at least two measuring electrodes, wherein the medium is led via the pipeline to the measuring tube of the magneto inductive measuring device, and wherein the pipeline has a first narrowing and/or the measuring tube has a second narrowing, which are/is arranged on an upstream side of the flow measuring device, wherein the first narrowing and/or the second narrowing have/has a flow shedding edge on a downstream side thereof, and
• wherein the filling plant is configured to provide a filling volume having a volume of at least 10 ml.