Method for determining a physical parameter of a compressible medium with a measuring transducer of vibration-type and measuring transducer for performing such a method

A method for determining a physical parameter of a compressible medium using a measuring transducer of vibration-type, the method comprising:

• providing a measuring transducer of vibration-type having at least two oscillators, each oscillator including a pair of measuring tubes, wherein the pairs of measuring tubes are arranged for parallel flow, and wherein the at least two oscillators have mutually independent oscillator oscillations with mutually differing eigenfrequencies for corresponding oscillation modes;
• determining the values of the eigenfrequencies of at least two different oscillator oscillations;
• determining at least two preliminary density measured values based on the values of the eigenfrequencies;
• and
• determining a correction term for one of the preliminary density measured values, and/or for a preliminary measured value of flow, based on the preliminary density measured values and the values of the eigenfrequencies.

A measuring transducer of vibration-type for determining a physical parameter of a compressible medium, comprising:

• first, second, third and fourth measuring tubes, each having an inlet end and an outlet end, wherein all inlet ends and all outlet ends of the measuring tubes are combined with respective collectors at each end for parallel flow;
• a first actuator arrangement and a second actuator arrangement;
• a first sensor arrangement and a second sensor arrangement, each configured to register oscillations and generate signals based thereon;
• and
• an operating and processing circuit configured to drive the first and second actuator arrangements and to register the signals of the first and second sensor arrangements,
• wherein the first measuring tube and the second measuring tube are connected at or near their inlet ends with a first rigid node plate and at or near their outlet ends with a second rigid node plate, the first and second node plates arranged spaced from each respective collector at its respective end to form a first oscillator, wherein the first actuator arrangement is adapted to excite a wanted mode between the two measuring tubes of the first oscillator,
• wherein the third measuring tube and the fourth measuring tube are connected at or near their inlet ends with a third rigid node plate and at or near their outlet ends with a fourth rigid node plate, the third and fourth node plates arranged spaced from each respective collector at its respective end to form a second oscillator, wherein the second actuator arrangement is adapted to excite a wanted mode between the two measuring tubes of the second oscillator,
• wherein the first oscillator and the second oscillator each have at least one wanted mode with first and second wanted mode eigenfrequencies, respectively,
• wherein the magnitude of the difference between the wanted mode eigenfrequencies of the two oscillators is at least 0.1 times the lesser of the first and second wanted mode eigenfrequencies,
• wherein the first sensor arrangement is adapted to register oscillations of the first oscillator, and the second sensor arrangement is adapted to register oscillations of the second oscillator,
• wherein the operating circuit and evaluating circuit is configured to drive the first and second actuator arrangements such that bending oscillation modes of the first and second oscillators are excited at at least the eigenfrequencies of the wanted modes independently of one another, and
• wherein the operating and evaluating circuit is further configured to:
• determining the values of the eigenfrequencies of at least two different oscillator oscillations;
• determining at least two preliminary density measured values based on the values of the eigenfrequencies;
• and
• determining a correction term for one of the preliminary density measured values, and/or for a preliminary measured value of flow, based on the preliminary density measured values and the values of the eigenfrequencies.