Ultrasound (US) refers to sound above the human hearing threshold, with frequencies between 20 kHz and 1 GHz. (Sounds with even higher frequencies are called hypersound, while sounds below the level audible to humans are called infrasound.) Ultrasound propagates as a longitudinal wave in gases, liquids, and solids. The transition from airborne sound to solids or liquids only occurs when the sound waves are emitted in close proximity or when a coupling medium with adapted acoustic properties and a certain thickness is present between them. Depending on the material of an obstacle, ultrasound is reflected or absorbed (insulated, swallowed). To determine the water level, the distance between the sensor on the top of the container and the level is determined non-contact using ultrasonic distance measurement. The propagation time of ultrasonic pulses is determined. With ultrasound, it must be taken into account that the speed of sound depends on the temperature and composition of the gas in the container.
Main features of the analog ultrasonic sensor are:
