Non-contact measuring method and apparatus for producing a signal representative of a distance between facing surfaces

A non-contact measuring apparatus for producing a signal representative of a distance between facing surfaces of first and second parts which are closely spaced apart, the second part being grounded, comprising:

• a sensor adapted to be mounted on the surface of the first part, the sensor including first and second parallel, superimposed conductive plates electrically insulated from one another, the plates being parallel to the surface of the first part and electrically insulated therefrom, the second plate being located in between the first plate and the surface of the first part;
• a high frequency signal generator having an output for generating a high frequency signal;
• a resistance connected in series with the output of the high frequency signal generator;
• and
• a high impedance, low input capacity, unitary gain voltage amplifier having an input connected to both the resistance and to the first plate of the sensor, and an output connected to the second plate of the sensor, the output of the amplifier providing an output signal representative of the distance between the two surfaces.