FIELD: instrument industry.
SUBSTANCE: device comprises oscillating unit (10), receiving-driving unit (11) that excites and receives the oscillations of the oscillating unit (10), and unit (12) for control of oscillating unit (1). Unit (12) generates an alarm signal when frequency of oscillations of oscillating unit (10) is lower that a given limit value. The limit lever is determined from the formula presented.
EFFECT: enhanced reliability.
6 cl, 2 dwg
