It is important that a desalter unit runs efficiently to prevent corrosion to downstream equipment. When the crude oil mixes with the emulsifying chemicals and water, the resulting emulsion layer makes it difficult for standard level measurement technologies to reliably track the interface. Radiation-based measuring instruments are not affected by this and allow to track the interface even with thick emulsion layers present in the tank to make sure that the desalting process can be controlled efficiently at maximum throughput.