Guided wave radar level gauge system with dual transmission line probes for dielectric constant compensation

A method of determining a filling level of a product in a tank using a radar level gauge system comprising a transceiver arrangement, a first transmission line probe configured to guide a given electromagnetic signal through a surrounding medium with a first propagation velocity exhibiting a first dependence on a dielectric constant of the surrounding medium, a second transmission line probe configured to guide said given electromagnetic signal through said surrounding medium with a second propagation velocity exhibiting a second dependence, different from said first dependence, on said dielectric constant of the surrounding medium, and processing circuitry for determining the filling level, said method comprising the steps of:

• propagating, by said first transmission line probe, an electromagnetic first transmit signal originating from said transceiver towards a surface of the product in the tank;
• propagating, by said first transmission line probe, an electromagnetic first surface echo signal resulting from reflection of said first transmit signal at said surface back towards said transceiver;
• receiving, by said transceiver, said first surface echo signal;
• propagating, by said second transmission line probe, an electromagnetic second transmit signal originating from said transceiver towards a surface of the product in the tank;
• propagating, by said second transmission line probe, an electromagnetic second surface echo signal resulting from reflection of said second transmit signal at said surface back towards said transceiver;
• receiving, by said transceiver, said second surface echo signal;
• determining, by said processing circuitry, said filling level based on said first surface echo signal, said second surface echo signal, and a known relation between said first dependence and said second dependence on said dielectric constant of the surrounding medium.