Inductive position sensor with minimum output signal level capacitively coupled to indicate failure of device

Claim 1

Apparatus for indicating the angular position of one object with respect to another comprising: a source of power; an inductive position sensor having a primary coil connected to the source of power and a secondary coil, said secondary coil magnetically coupled to the primary coil and mounted for movement relative thereto in a manner which varies the magnetic coupling as relative movement occurs thereby producing an output signal on the secondary coil proportional to said relative movement, said inductive position sensor having a point of zero output in the middle of its range of positions; a coupling capacitor connected from the primary coil to the secondary coil to impress a minimum signal level at the output of the secondary coil; a phase detector connected to receive the output signal of the inductive position sensor and to generate a D.C. signal proportional to the output signal of the position sensor, but independent of the minimum signal level; and a level detector connected to the output of the position sensor to receive the minimum signal level, to compare said minimum signal level to a predetermined reference level, and to generate an alarm signal in response to changes in the minimum signal level.