Displacement sensing device utilizing adjustable tuned circuit

Abstract

Disclosed are two embodiments of displacement sensing devices utilizing adjustable tuned circuits. In a first embodiment, a sensor comprising a capacitor and an adjustable coil connected together is attached to two relatively movable objects; the relative displacement of which is to be measured. An electrical circuit is provided which includes an oscillator which may be swept through a predetermined range of frequencies so as to variably excite a source coil. As the oscillator is swept through these frequencies, a comparator compares the voltage output of the oscillator with the voltage output of the source coil. When the frequency of the oscillator is equal to the resonant frequency of the sensor circuit at its particular coil displacement, a voltage drop across the source coil will be sensed by the electrical circuitry and from this information, the circuitry may calculate the actual displacement of the two objects with respect to one another. In a second embodiment of the present invention, the same sensor is used and the electrical circuitry includes an oscillator which places a voltage across a source coil while the oscillator frequency is swept between two predetermined extremes. A separate detector coil is provided in the electrical circuitry and this detector coil senses phase changes caused by the effect of the source coil frquency upon the sensor circuitry. A phase-to-voltage converter converts the phase of the detector coil to a voltage which is indicative of the displacement of the objects with respect to one another.