Proof test of radar level gauge system

A method of operating a radar level gauge system arranged to determine a filling level of a product in a tank, the radar level gauge system being controllable between a filling level measuring state and a proof test state, wherein the method comprises the steps of:

• receiving a state signal indicating a desired state of the radar level gauge system;
• when the state signal indicates the filling level measuring state:
• transmitting an electromagnetic transmit signal towards a surface of the product in the tank;
• receiving an electromagnetic reflection signal resulting from reflection of the transmit signal at the surface of the product;
• forming a measurement representation based on the transmit signal and the reflection signal, the measurement representation comprising surface echo information indicative of the filling level of the product;
• and
• determining the filling level based on the measurement representation;
• and
• when the state signal indicates the proof test state,
• transmitting an electromagnetic transmit signal towards a surface of the product in the tank;
• receiving an electromagnetic reflection signal resulting from reflection of the transmit signal at the surface of the product;
• forming a measurement representation based on the transmit signal and the reflection signal, the measurement representation comprising surface echo information indicative of the filling level of the product;
• adding, to the measurement representation, proof test echo information indicative of a predefined proof test level, resulting in a modified measurement representation;
• processing the modified measurement representation to determine a proof test level based on the modified measurement representation;
• and
• providing a signal indicative of a result of the processing.

The method according to wherein:

• the step of forming the measurement representation comprises the step of:
• combining the reflection signal and a reference signal being timing related to the transmit signal to form the measurement representation as an analog measurement signal;
• and
• the step of adding comprises the step of:
• adding a proof test level signal to the analog measurement signal to form the modified measurement representation as a modified analog measurement signal.

A radar level gauge system for determining a filling level of a product in a tank, the radar level gauge system comprising:

• a transceiver for generating, transmitting and receiving electromagnetic signals;
• a signal propagation arrangement connected to the transceiver and arranged to propagate an electromagnetic transmit signal from the transceiver towards the product in the tank, and to return to the transceiver an electromagnetic reflection signal resulting from reflection of the electromagnetic transmit signal at a surface of the product;
• and
• measurement representation forming circuitry for forming a measurement representation based on the transmit signal and the reflection signal, the measurement representation comprising surface echo information indicative of the filling level of the product;
• proof test echo information adding circuitry, for adding to the measurement representation, proof test echo information indicative of a predefined proof test level, resulting in a modified measurement representation;
• and
• level determining circuitry coupled to the transceiver and configured to determine a proof test level based on the modified measurement representation.