A radar level gauge (RLG) is suitably used for making measurements of a process variable, e.g. a filling level, of a product such as process fluids, granular compounds and other materials contained in a tank.
An example of such a radar level gauge can include transceiver circuitry for transmitting and receiving microwaves, a signal propagating device arranged to direct microwaves towards the surface and to return microwaves reflected by the surface to the transceiver, and processing circuitry adapted to determine the filling level based on a relation between microwaves transmitted and received by the transceiver.
There are different principles for performing radar level gauges, including frequency modulated continuous wave (FMCW) and time domain reflectometry (TDR). An FMCW based RLG will emit a radar sweep with gradually varying frequency, and mix the received signal with the original signal (homodyne mixing) to form a frequency domain tank signal. A TDR based RLG will emit a pulse train of very short pulses (order of ns), and sample the received signal with the original signal in a sample and hold circuit, thereby forming a time domain tank signal.
In both cases, the tank signal will include a set of peaks indicating echoes from the tank, and one of these peaks corresponds to the echo from the surface.
The processing is configured to identify, and typically also track, the relevant echoes, in order to distinguish the surface echo from other echoes, such as reflections from structures in the tank, double bounces, etc. The surface echo can then be used to determine the distance to the surface, and consequently the filling level.
However, each echo will typically also result in a series of smaller “ghost” echoes, flanking the “actual” echo. Such ghost echoes may be caused by imperfections in the RLG electronics, and may interfere with the echo identification. For example, a the processing circuitry may confuse the ghost echoes with actual echoes, and spend computation resources on tracking these ghost echoes. Further, the ghost echoes may reduce performance when the surface passes a structure in the tank, i.e. when the surface echo for a period of time is very close to, or completely coincides with, a stronger echo from the reflecting structure.