Method and apparatus for ascertaining volume- or mass-flow

An apparatus for measuring volume- or mass-flow of a magnetically conductive medium flowing through a measuring tube in direction of a measuring tube axis, comprising:

• a magnet system, which produces a periodically reversing, magnetic field passing through the measuring tube essentially transversely to the measuring tube;
• at least one measuring electrode coupled with the medium and arranged in a region of the measuring tube;
• and
• a control/evaluation unit, which, based on measurement voltage induced in said at least one measuring electrode, ascertains information concerning volume- or mass-flow of the medium according to the following:
• causing a periodically alternating magnetic field to pass through the flow-measuring device;
• ascertaining an actual rise time until reaching a constant magnitude of the magnetic field;
• comparing the actual rise time with a desired rise time ascertained for the case of flow of a reference medium through the flow-measuring device;
• interpreting a difference between the actual rise time and the desired rise time to mean flow of a magnetically conductive medium;
• and
• ascertaining a measurement error based on a difference between actual rise time and desired rise time as a function of the difference, and the actually measured volume- or mass-flow of the magnetically conductive medium is so corrected, that the measurement error is canceled.