In a coal fired power station, either hard coal or brown coal is burned as the main energy source. Most plants have a so-called ''wet deslagger'' for removing the bottom ash (slag) from the combustion chamber. Level control in the wet deslagger fulfils two important functions: First and foremost, it controls the water level, which cools and removes the hot slag. Secondly, it maintains a hermetic seal on the furnace chamber - a reliable level measurement avoids unwanted air that would otherwise get sucked into the combustion chamber.