Process and apparatus for measuring density and mass flow

A device for measuring density and mass flow of a disperse system with a gas as fluid phase, flowing through a pipe which has a cross-section and a diameter, said device comprising:

• a signal generator for generating an electrical signal;
• a sonic transducer for converting the electrical signal into a sound wave which is propagated simultaneously in both the direction of flow and against the direction of flow;
• said sound wave including sound in the frequency range of 20-2,000 Hz in the middle of the cross-section of the pipe, said sound wave having a wavelength which is at least half the magnitude of the diameter of the pipe, said sound wave being a pulsed sound which is the product of an envelope curve and a sinusoidal carrier oscillation having the formula I(t)=H(t)*sin(2πf*t);
• two sonic receivers, one located upstream of said sonic transducer and one located downstream of said sonic transducer, said two receivers being at different distances from said sonic transducer;
• first means for measuring the speed propagation of sound waves in the flowing disperse system in the axial direction of flow;
• second means for measuring the speed propagation of sound waves in the flowing disperse system in a direction against the axial direction of flow;
• said first and second means for measuring the speed propagation producing a cross-correlation function of two signals to provide transit times and at the same time being totally insensitive to disturbing influences;
• means for calculating a fill level based on the measured mass flow rate over a time period.