Oil/water interface detection

An apparatus and method for use of a separator for an oil/water interface 26. Apparatus comprising a separation tank 12, having an inlet 16 for an oil/water mixture, an oil outlet 18 for separated oil and a water outlet for separated water. A radio transmitter 30 and receiver 32 are mounted within the separation tank. A controller 28 is configured to transmit a radio pulse, said pulse is reflected by an interface between an oil 22 and a water 24 layer in the separation tank and is received by the receiver after reflection. The radio pulse has a duration of less than 10ns or nanoseconds. The level of the interface may be based upon the reflected waveform received, including time-of-flight of the reflected radio waveform. The radio pulse may be one or more frequency components between 300 MHz and 30 GHz or an ultra-wideband radar pulse having a bandwidth of at least 500 MHz and. The sampling signal may comprise at least 100 samples at a sampling frequency of at least 500 MHz. The receiver may have a passive Vivaldi antenna, which may be further laminated in resin to reduce corrosion.