Abstract: A device for gauging the level of a fluid in a container with a microwave signal is described. The device comprises a vertical tube (1) mounted in the container, and a transmitter and a receiver and an electronic unit for determining the level based on the reflex position of the microwave signal. The device is characterized particularly by a calibration device in the form of a polarization means (6, 7) for polarizing the microwave signal in two polarization planes separated from each other and at least one reflecting reactance (10) in the tube (1) arranged to give a substantially stronger reflex of the microwave signal in the first polarization plane than in the second.

Abstract: A device for gauging the level of a fluid in a container having a gas above the surface of the fluid. The device comprises a microwave transmitter transmitting a microwave radio signal through the gas to the surface and a receiver for receiving the microwave signal reflected by the surface. An electronic unit is arranged to calculate from the propagation time of the microwave signal a first distance from the transmitter to the surface of the fluid and thereby the level in the container. The microwave signal is preferably within the radar frequency range. A sound transmitter is also provided for transmitting a sound signal through the gas to the surface of the fluid and is capable of receiving a sound signal reflected from the surface of the fluid. A means is provided for correcting the first distance to a second corrected distance as a function of the microwave velocity and the known relation between the sound velocity and the microwave velocity.

Abstract: The invention concerns a method and an apparatus for measuring the level of a material with microwave signals. The apparatus consists of a signal processing unit (10) and a transmitter unit (1) of known type. The transmitter unit produces a measuring signal having a frequency (f.sub.m) corresponding to the distance (H) to be measured and a reference signal having a frequency (f.sub.r) corresponding to an accurately known length (L). In the signal processing unit (10) the reference signal is multiplied by a selectable number (AQ) which is proportional to the quotient of an assumed value for the distance divided by the known length (L), after which the frequency is divided by a fixed number (Z) so that the frequency of the signal after multiplication and division becomes equal to the expected frequency of the measuring signal.

Abstract: In a method of measuring the level of a flowing material kept in a container there is employed a microwave signal that is fed from a transmitter through a tubular waveguide (7) that extends vertically downwardly through the container and communicates therewith so that the surface (10) of the material in the waveguide follows the level of the surrounding material. The signal is reflected from the surface back up through the waveguide and is conducted to a receiver to be employed, after signal processing in an electronic unit, for determining the level of material in the container. The microwave signal is fed to the waveguide by way of a mode generator (11) that produces only one dominant propagation mode of the signal, the wavelength of which is smaller than the diameter of the waveguide (7).