The D-FL 220 measuring system operates according to the acoustic transit time differential method.

Two identical sensors transmit and receive ultra-sonic pulses reciprocally. The system calculates precisely the gas velocity and the gas temperature from the transit time difference dependent on the direction. The volume flow is calculated taking into consideration the cross-section, the sample gas temperature and the absolute pressure. The D-FL 220 performs internal self-monitoring routines and is very low maintenance.