The Eddy Current Transducer uses the effect of eddy (circular) currents to sense the proximity of non-magnetic but conductive materials. A typical eddy current transducer contains two coils: an active coil (main coil) and a balance coil. The active coil senses the presence of a nearby conductive object, and balance coil is used to balance the output bridge circuit and for temperature compensation.

	Size:	about 2 to 75 mm (0.079 to 3 in) in diameter, 20 to 40 mm (0.79 to 1.58 in) long
	Range:	0.25 to 30 mm (0.0098 to 1.2 in)
	Resolution:	Up to 0.1 µm (3.9 µin)
	Nonlinearity:	0.5%
	Bridge Circuit Frequency	50 kHz to 10 MHz

•	Pros:
	-	Non-contacting measurement.
	-	High resolution.
	-	High frequency response.
•	Cons:
	-	Effective distance is limited to close range.
	-	The relationship between the distance and the impedance of the coil is nonlinear and temperature dependent. Fortunately, a balance coil can compensate for the temperature effect. As for the nonlinearity, careful calibrations can ease its drawback.
	-	Only works on conductive materials with sufficient thickness. It can not be used for detecting the displacement of non-conductive materials or thin metalized films. However, a piece of conductive material with sufficient thickness can be mounted on non-conductive targets to overcome this drawback. A self-adhesive aluminum-foil tape is commercially available for this purpose. However, this practice is not always possible.
	-	Calibration is generally required, since the shape and conductivity of the target material can affect the sensor response.