The displacement transducers operate according to the principle of the differential choke, i.e. an inductive half bridge. They consist of two coils which are encapsulated in a stainless steel cylinder ensuring positive protection against vibration, shock, humidity, oil and corrosive matter. A mu-metal plunger core causes opposing changes of inductance when it is displaced through the centre of the coils. The displacement transducers are designed for a carrier frequency of 10 kHz. Other frequencies can be used but may involve changes of output values.