Patent ID: 8875569

Claim:
A sensor for determining level of liquid in a reservoir, the reservoir defining a volume within an outer envelope surface, the sensor comprising: a liquid-proof housing having an inner side defining an interior space and an outer side, the outer side configured for location radially inside the reservoir outer envelope surface; at least one actuator operatively connected to the inner side of the liquid-proof housing, positioned within the interior space and configured to generate vibrations, the at least one actuator comprising an electromagnet having a longitudinal center axis, the electromagnet directly or indirectly fixedly connected to the inner side of the liquid-proof housing and positioned within the interior space, and a permanent magnet movably suspended in the interior space of said liquid-proof housing, the electro magnet and the permanent magnet configured such that an oscillating mutual displacement in parallel with the longitudinal center axis takes place upon activation of the actuator; and at least one vibration sensor operatively connected to an inner side of the liquid-proof housing, positioned within the interior space and configured to measure vibrations.