Ultrasonically operative device for determining physical quantities of a medium

摘要

The invention relates to an ultrasonically operative device operable with an ultrasonic signal having a predetermined wave length for measuring physical quantities such as the flow speed of a medium such as water. The device includes an ultrasonic transmitter and an ultrasonic receiver with a tube unit therebetween defining a transmission path for the medium. The tube unit has an internal diameter less than about fifteen times the wavelength of the signal. The tube unit includes an outer metal tube and an inner plastics liner of a plastic such as a polyamide.