Level detector for liquid in reservoir - uses transmit-receive pulsed acoustic probe in contact with outside wall to monitor level of reflection of acoustic pulses

摘要

The device described can detect the presence of a liquid at a certain level through the wall of a reservoir. It comprises a transmit-receive pulsed acoustic probe (1) which is placed in contact with the external surface of the reservoir wall at the level at which the presence (or absence) of liquid is to be determined. Acoustic pulses are emitted and these propagate into the wall. Echoes are received due to successive reflections at the internal surface of the wall and at the probe's transmit-receive surface. The echoes received are selected from a predetermined burst and a signalling system (6) is triggered when the selected echoes reach a predetermined threshold amplitude. The echo selection unit comprises two monostable circuits (4, 8) and an AND gate (5).