As the distance changes, the electronics sense the change in the field interaction and produce a voltage output which is proportional to the change in distance between the probe and target.Įddy Current Transducer The Eddy Current Transducer uses the effect of eddy (circular) currents to sense the proximity of non-magnetic but conductive materials.
The interaction of the magnetic fields is dependent on the distance between the probe and the target. The eddy currents create an opposing magnetic field which resists the field being generated by the probe coil. This creates an alternating magnetic field with induces small currents in the target material these currents are called eddy currents. The driver creates an alternating current in the sensing coil in the end of the probe. Linear Displacement Eddy-Current sensors operate with magnetic fields. If the target surface is smaller than 50% of the probe diameter, output signals decrease substantially. The targeted flat surface area should not be smaller that the probe tip diameter.For example, a 2.5 mm (0.1 in) range eddy current transducer is generally considered effective from 0.5 to 3 mm (0.2 to 1.2 in) from the target surface. In practice, the effective range of an eddy current transducer is given by the vendor suggested range offset from the target surface by 20%.This is because the transducer assumes that the eddy currents are localized near the surface of a semi-infinite solid, and the actual eddy current amplitude decreases quadratically with distance. The target material must be at least three times thicker than the effective depth of the eddy currents to make the transducer successful.The eddy currents are confined to shallow depths near the conductive target surface. This change in impedance can be detected by a carefully arranged bridge circuit. When the distance between the target and the probe changes, the impedance of the coil changes correspondingly.This local electric current in turn induces a magnetic field opposite in sense to the one from the active coil and reduces the inductance in the coil. An eddy current is a local electric current induced in a conductive material by the magnetic field produced by the active coil.
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