1. A method for non-contact measurement of a displacement between a surface and a capacitive sensor comprised of at least two superimposed conductive plates electrically insulated one from the other and a sensor circuit coupled to the plates, said method comprising: (a) positioning said capacitive sensor proximate to the surface such that the displacement is a distance of a gap between the surface and one of the plates; (b) applying a high frequency signal to the plates; (c) applying the high frequency signal and a signal from a sensor plate of the conductive plates to control a voltage gain of an amplifier in the circuit, said signal from the sensor plate being indicative of the displacement between the sensor and the surface; (d) differentiating an output of the amplifier and the high frequency signal, and (e) determining a value of the displacement based on the difference between the output of the amplifier and the high frequency signal.