FIELD: measurement technology.
SUBSTANCE: invention relates to a Coriolis mass flow meter. The flow meter contains a primary measuring transducer with at least one measuring tube (10), an excitation system and a sensor system as well as an electronic transducer (ME) electrically connected to the excitation system and the sensor system with measuring and control electronics (MCE) and an electronic excitation unit (Exc) connected to the measuring and control electronics and/or controlled by it. The measuring tube carries the fluid, which is at least temporarily measured, and executes vibrations. In addition, the excitation system converts the supplied electrical power into mechanical power causing forced mechanical vibrations of at least one measuring tube, and the sensor system detects mechanical vibrations of at least one measuring tube and transmits the first vibrational measuring signal (s1) representing at least partially oscillatory movements of at least one measuring tube as well as at least the second oscillatory measurement signal (s2) representing at least partially oscillatory movements of at least one measuring tube. The first and second oscillatory measurement signals monitor the change in the mass flow rate of the measured medium transferred inside the measuring tube on the basis of the change in the phase difference and namely on the basis of the change in the difference between the phase angles of the first and second oscillatory measuring signals. In addition, the sensor system is also electrically connected to the measuring and control electronics. The electronic excitation unit is electrically connected to the excitation system and generates an electrical start signal (e1) in the first operating mode (I) and feeds with it electrical power into the excitation system in such a way that at least one measuring tube performs forced mechanical vibrations for at least one usable frequency, namely the frequency specified by the electrical start signal, corresponding, in particular, to the resonant frequency of the oscillation of the primary measuring transducer. The electronic excitation unit stops the formation of the electrical start signal in the second operating mode (II). So, the electronic excitation unit does not feed electrical power into the excitation system in the second operating mode. The present Coriolis mass flowmeter has the electronic converter which is designed to cause the electronic excitation unit to switch from the first operating mode (I) to the second operating mode (II) in such a way that at least one measuring tube with the electronic excitation unit operating in the second operating mode (II) performs free damped oscillations at least during the measurement interval, and the measuring and control electronics receives the oscillatory measurement signals during the measurement interval and determines using their phase difference the measured values of the mass flow representing the mass flow.
EFFECT: elimination of phase error particularly if resonant or usable frequency changes rapidly or if there is a wide range of changing resonant or usable frequency.
11 cl, 4 dwg
