Ultrasonic flow meter including a single transmitting transducer and a pair of receiving transducers

A method for determining the flow parameters of a streaming gas in a conduit for medical applications, the method comprising the steps of:

• generating longitudinal waves inside the conduit with a transducer,
• transmitting said longitudinal waves in two different cross directions relative to the streaming direction (upstream and downstream direction) through the conduit,
• receiving said waves with transducers,
• determining transit time values of the waves between the transducer used as a transmitter and the transducers used as receivers,
• generating a difference value on the basis of the determined transit time values, and
• determining the flow parameters of the streaming gas on the basis of said difference value,
• wherein the method further includes the steps of:
• determining a first pair of transit time values of the waves between the transducer used as a transmitter and the transducers used as receivers,
• determining an approximate flow rate of the streaming gas on the basis of a difference between the first pair of transit time values and the transit times corresponding to a zero flow rate,
• determining a time shift value necessary for the streaming gas to propagate from a first wave transmission path to a second wave transmission path,
• determining a second pair of transit time values of the waves between the transducer used as a transmitter and the transducers used as receivers with a delay between the upstream and downstream transmission path transit time measurements, the delay being determined by said time shift value, and
• determining a more accurate flow rate of the streaming gas on the basis of a difference between the second pair of transit time values.