Method for determining the temporal position of a wave packet and flow measuring device

Flow measuring apparatus (1, 11), comprising:

• a first sonic transducer (4, 14);
• a second sonic transducer (5, 15), wherein the two sonic transducers are aligned with respect to each other so that the second sonic transducer (5, 15) absorbs a part of the sound generated by the first sonic transducer (4, 14) and vice versa, wherein the two sonic transducers convert an electric signal to sound and vice versa;
• a driver circuit (7) which is connected to the first sonic transducer (4, 5, 14, 15) and temporarily supplies the first sonic transducer with an alternating voltage to generate sound;
• characterized by:
• an analog-digital converter (94, 95) for sampling and digitalizing the electric signal emitted by the second sonic transducer at a plurality of points in time, wherein a measured value is created at each point in time, wherein the input of the analog-digital converter (94, 95) is connected to the second sonic transducer (4, 5, 14, 15),
• a microprocessor (9) connected to the output of the analog-digital converter (94, 95) and to which the measured values are supplied, said microprocessor (9) performing the following steps:
• calculating a sum of products (43, 54, 55, 63, 64), wherein each product is calculated for a determined point in time from the plurality of points in time and each product is the product of a value of a compare function (44, 53, 56, 61, 62) at said determined point in time and the measured value at said determined point in time;
• and
• calculating (46, 47, 57, 58, 65-81) the temporal position of the wave packet from the sum of products.