System for monitoring a predetermined level of a fluid in a container

摘要

The liquid level (11) monitoring device uses two identical ultrasonic transducers (13,15) positioned on the outside of the container (10) at the upper and lower limits (Hmax, Hmin) and wired to excitation and processing electronics (14,16). A pulse of ultrasound at the resonant frequency of the container wall in thickness mode is transmitted to it through a diaphragm. The ultrasonic vibrations transmitted from the wall to the transducer are converted into electrical signals. The processing circuit ascertains whether echo signals are present or absent, and hence whether or not there is liquid at the level of each transducer.