Mass flow sensor and methods of determining mass flow of a fluid

Apparatus for determining mass flow rate of a fluid in a flow passage having a predetermined area, comprising

• a sensor including a waveguide disposed in the flow passage and having a section exposed to the fluid flowing in the passage;
• means in the flow path for shedding vortices;
• an exciter for propagating an ultrasonic wave along said waveguide including along said section and having a propagation velocity dependent upon the density of the fluid adjacent said section;
• first means coupled to said waveguide for detecting the propagated wave and providing a first output signal proportional to the transit time of the propagated wave along the density-responsive section of the waveguide for determining the density of the fluid;
• second means forming part of said sensor for detecting the shedding frequency of the vortices shed from said vortex shedding means and providing a second output signal proportional thereto for determining the velocity of the fluid;
• and
• a processor for generating an indication of the mass flow rate of the fluid through the passage based on the first and second signals and the predetermined area of the flow passage.