Timed window ultrasonic gas meter with nose cone

A method of detecting the arrival at a transducer of an acoustic wave packet within a series of acoustic wave packets, where the transmission of any one wave packet in said series, excepting a first wave packet, is initiated upon detection of arrival at said transducer of an immediately preceding wave packet in said series, and the detection comprises identifying a particular part of a waveform received at said transducer after arming a receiving arrangement that detection is imminent, characterised in that said method includes, prior to transmission of said series, transmitting a single acoustic wave packet to said transducer and determining a nominal propagation time of said single wave packet by identifying a corresponding particular part of a corresponding waveform received without arming said receiving arrangement, whereby said nominal propagation time is used to arm said receiving arrangement for the detection of each said wave packet within said series.

A method of measuring a fluid flow parameter, said method comprising the steps of:

• transmitting an ultrasonic test pulse from a first location within a fluid flow path,
• receiving said ultrasonic test pulse at a second location within the fluid flow path to determine a time delay value between a start of transmission of said test pulse and a zero amplitude crossing of said received ultrasonic test pulse,
• thereafter transmitting from said first location, a plurality of successive ultrasonic measurement pulses for reception at said second location, said reception being detected by crossing said zero amplitude after expiration of said time delay value, said transmission being started simultaneously with reception of the preceding ultrasonic measurement pulses.