Radar level gauging with wait state

A radar level gauge for determining a process variable of product in a tank, said gauge comprising:

• transceiver circuitry configured to obtain a tank signal by combining an electromagnetic transmit signal and an electromagnetic return signal caused by a reflection of said transmit signal in the tank, said tank signal including a plurality of peaks representing echoes from the interior of said tank;
• and
• processing circuitry configured to:
• process said tank signal to identify a surface echo,
• when a surface echo can be identified, determine said process variable based on said surface echo, and
• when no surface echo can be identified in the tank signal, entering a wait state, said wait state including:
• a) storing the tank signal in memory,
• b) obtaining a wait state tank signal,
• c) comparing said wait state tank signal with the stored tank signal to determine a tank signal difference measure,
• d) repeating steps b) and c) until the tank signal difference measure is greater than a predefined threshold,
• e) processing said wait state tank signal to identify a surface echo, and
• f) when no surface echo can be identified in said wait state tank signal, setting an alarm.