Capacitive sensor and method for non-contacting gap and dielectric medium measurement

A method for measurement of a characteristic of a medium proximate a capacitive sensor comprised of at least three superimposed conductive plates electrically insulated from each other and a sensor circuit coupled to the plates, wherein said plates include a sensor plate, an active shield plate sandwiched between a sensor plate and a passive shield plate, said method comprising:

• (a) positioning the capacitive sensor proximate to the medium, such that the medium is capacitively coupled to the sensor plate;
• (b) applying a high frequency signal to the active shield plate, wherein the medium affects a response of the sensor plate to the high frequency signal;
• (c) applying a signal induced on the sensor plate by the high frequency signal and the high frequency signal to control a voltage gain of an amplifier in the circuit, said applied signal induced by the high frequency signal being indicative of the medium;
• (d) differentiating the output of the amplifier and the high frequency signal, and
• (e) determining a magnitude value indicative of a width of the medium based on the difference between the applied signal induced by the high frequency signal and the high frequency signal.

A method for non-contact measurement of a dielectric related characteristic of a medium 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 medium is between the surface and a sensor plate of the plates;
• (b) applying a high frequency signal to at least one of the plates and a dielectric of the medium affects a response signal of the sensor plate to the high frequency signal;
• (c) applying the high frequency signal and the response signal from the sensor plate to control a voltage gain of an amplifier in the circuit, said response signal being indicative of the medium between the sensor and surface;
• (d) differentiating an output of the amplifier and the high frequency signal, and
• (e) determining a magnitude of the displacement based on the difference between the output of the amplifier and the high frequency signal.

A method for non-contact measurement of a medium proximate to 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 medium;
• (b) applying a high frequency signal to at least one of 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 a property of the medium;
• (d) differentiating an output of the amplifier and the high frequency signal, and
• (e) determining a magnitude of the property of the medium based on the difference between the output of the amplifier and the high frequency signal.