Answer :

Capacitive sensors are noncontact devices capable of high-resolution measurement of the position and/or change of position of any conductive target. The nanometer resolution of high-performance sensors makes them indispensible in today's nanotechnology world. Capacitive sensing can also be used to measure the position or other properties of nonconductive targets.

Capacitive sensors use the electrical property of "capacitance" to make measurements. Capacitance is a property that exists between any two conductive surfaces within some reasonable proximity. Changes in the distance between the surfaces changes the capacitance. It is this change of capacitance that capacitive sensors use to indicate changes in position of a target. High-performance displacement sensors use small sensing surfaces and as a result are positioned close to the targets (0.25-2mm).

Advantages and limitations

Compared to other noncontact sensing technologies such as optical, laser, eddy-current, and inductive, high-performance capacitive sensors have some distinct advantages.

• Higher resolutions including subnanometer resolutions
• Not sensitive to material changes: Capacitive sensors respond equally to all conductors
• Inexpensive compared to laser interferometers.

Capacitve sensors are not a good choice in these conditions:

• Dirty or wet environment (eddy-current sensors are ideal)

• Large gap between sensor and target is required (optical and laser are better)

   

Application:

• Position measurement
• Dynamic motion
• Thickness measurement
• Nonconductive thickness