Coriolis mass flowmeter with magnetic field detector

A Coriolis mass flowmeter for measuring mass flow of a fluid measured substance, the Coriolis mass flowmeter comprising:

• a measuring transducer having at least one vibration element, an exciter arrangement, and a sensor arrangement and which is adapted to be flowed through by the measured substance;
• and
• an electronic transmitter circuit electrically coupled with the exciter arrangement and the sensor arrangement, wherein the electronic transmitter includes at least one microprocessor;
• wherein the at least one vibration element is adapted to be contacted by the flowing measured substance and during that to be caused to vibrate,
• wherein the exciter arrangement is adapted to convert electrical power supplied to it into mechanical power effecting forced mechanical oscillations of the at least one vibration element, wherein the transmitter circuit is adapted to generate an electrical driver signal and therewith to supply electrical power to the exciter arrangement such that the vibration element executes wanted oscillations, namely forced mechanical oscillations having at least one wanted frequency, namely an oscillation frequency predetermined by the electrical driver signal corresponding to a resonant frequency of the measuring transducer and suitable to bring about in the flowing measured substance Coriolis forces dependent on mass flow,
• wherein, for registering mechanical oscillations of the at least one vibration element, the sensor arrangement includes an electrodynamic, first oscillation sensor and at least an electrodynamic, second oscillation sensor embodied equally to the first oscillation sensor,
• wherein the first oscillation sensor is adapted to convert oscillatory movements of the at least one vibration element at a first measuring point into an electrical, first oscillation measurement signal of the sensor arrangement such that the first oscillation measurement signal has at least a first wanted component, namely an alternating voltage component having a frequency corresponding to the wanted frequency and having an amplitude dependent on the wanted frequency and a first magnetic flux, namely a magnetic flux of the first oscillation sensor,
• wherein the second oscillation sensor is adapted to convert oscillatory movements of the at least one vibration element at a second measuring point removed from the first measuring point into an electrical, second oscillation measurement signal of the sensor arrangement such that the second oscillation measurement signal has at least a second wanted component, namely an alternating voltage component having a frequency corresponding to the wanted frequency and having an amplitude dependent on the wanted frequency and a second magnetic flux, namely a magnetic flux of the second oscillation sensor,
• wherein, for registering a magnetic field established outside of the first and second oscillation sensors, the sensor arrangement includes a first magnetic field detector adapted to convert changes of the magnetic field at a third measuring point removed both from the first measuring point and from the second measuring point into a first magnetic field signal of the sensor arrangement evaluating and/or quantifying the changes and/or an electrical, first magnetic field signal, which has an amplitude dependent on a third magnetic flux, namely a magnetic flux through the first magnetic field detector and/or on an areal density of the magnetic flux, in such a manner that the first magnetic field signal follows at least a change of the third magnetic flux and/or its areal density with a change of its amplitude, and
• wherein the transmitter circuit is adapted to receive and to evaluate both the first and second oscillation measurement signals and the first magnetic field signal, namely:
• based on the first and second oscillation measurement signals, to ascertain mass flow measured values representing the mass flow, wherein each of the first and second wanted components includes a phase angle dependent on the mass flow, and wherein the mass flow measured values are calculated from a phase difference between the phase angle of the first wanted component and the phase angle of the second wanted component;
• and
• based on the first magnetic field signal, to ascertain whether within the measuring transducer an external magnetic field is present, including an external magnetic field produced by an electrical field outside of the Coriolis mass flowmeter and/or caused by a magnet positioned outside of the Coriolis mass flowmeter, and to ascertain whether a disturbance of the measuring transducer due to the external magnetic field is present, including a disturbance lessening an ability of the sensor arrangement to function and/or effecting a malfunction of the sensor arrangement and/or reducing an integrity of at least one of the first and second oscillation measurement signals, or the mass flow measured values, and
• wherein the phase difference includes a phase difference error caused by the disturbance, which phase error affects an accuracy with which the transmitter circuit ascertains the mass flow measured values such that the accuracy is outside a predetermined tolerance range of the Coriolis mass flowmeter.