The functional principle of the DW-S Flowtransmitter is based on two ultrasonic sensors which are placed in opposing positions. The delay time of the sound depends on the velocity of the flow. Both sensors work alternately as transmitter and receiver. The difference of the delay time is proportional to the flow velocity. The HSW system works unlike other ultrasonic measuring systems parallel to the liquid stream. This system offers high accuracy, an excellent measuring dynamic and the possibility to measure very high flow speed without reduced cross-section in a very compact design.