FIELD: metallurgical, chemical and petroleum refining industries. SUBSTANCE: one acoustic radiator is used to excite normal antisymmetrical wave of zeroth order (Lamb wave) and longitudinal wave which spreads in parallel to surface plane of liquid to be checked, over reservoir perimeter (Lamb wave) and through walls and medium being checked, over chord in plane of reservoir horizontal cross-section (longitudinal wave). Ultrasonic are received by one acoustic receiver. Acoustic signals of two types of waves arrive at receiver input with delay relative to excitation pulse for time determined by speed of spreading of these waves in definite medium and by distance to acoustic receiver. Values of information signals of every wave changing as much as possible depending on presence of liquid at level being checked are separated in received signal. These values are then compared with sensitivity threshold of receiving device and normalized by comparison results. Signals thus separated and normalized are supplied to input of intermediate storage which forms necessary states on storage elements for developing the indication signal. EFFECT: accuracy and reliability of level indication. 2 dwg
