Patent ID: 8448509

Claim:
A measurement device for determination regarding the liquid level in a container with a wall, which measurement device comprises at least a first actuator arranged on a corresponding level on the wall, which actuator comprises an influence part which is arranged for influencing the wall on the outside of the container, a vibration sensor for each one of said at least one actuator, for measurement of the vibrations in the wall, and a control unit, which is connected to said at least one actuator and the vibration sensors, and which is arranged to apply to the actuators a predetermined drive signal which makes the influence part to influence the wall with an oscillating force, wherein the vibration sensors are arranged fixed in relation to the corresponding influence part so that the vibration sensors moves in the same way as the influence part, wherein the measurement device is arranged to receive at least one resulting measurement signal from each one of the vibration sensors, which measurement signals depends on the size of the vibrations, and to compare the measurement signals with earlier measured measurement signals in order to make a determination regarding the liquid level in the container, wherein the control unit is arranged to determine a system response for the container using the predetermined drive signal and the measured measurement signals and to make a determination regarding the liquid level in the container starting from the determined response and at least one earlier measured response with a known liquid level, wherein the system response is an amplitude response containing at least two natural resonance frequencies.