Eddy Current Type Displacement Sensor for Metal Position

An eddy current displacement sensor operates based on the eddy current effect and belongs to a non-contact inductive measurement principle. An alternating current is applied to the coil inside the sensor probe, generating an alternating magnetic field around the probe. When a conductive material enters this magnetic field, eddy currents are induced in the target according to Faraday’s law of electromagnetic induction. In accordance with Lenz’s law, the magnetic field generated by the eddy currents opposes the original magnetic field of the coil, resulting in a change in the coil’s impedance. This impedance variation is directly related to the distance between the probe and the target. The controller detects the corresponding voltage change and calculates the displacement or position value.

When installing an eddy current displacement sensor probe, both the sensor’s linear measurement range and the total variation of the measured gap must be considered. It is recommended that the selected sensor’s linear range be at least 15% greater than the maximum expected gap variation to ensure stable and accurate measurement. For vibration measurement applications, the probe gap is typically set at the midpoint of the linear range. For displacement measurement applications, the probe gap should be determined based on the direction of displacement: if the displacement mainly moves away from the probe, the gap should be set near the lower end of the linear range; if the displacement mainly moves toward the probe, the gap should be set near the upper end of the linear range.

The measurement characteristics of an eddy current displacement sensor are closely related to the electrical conductivity and magnetic permeability of the target material. For ferromagnetic materials such as carbon steel or structural steel, both eddy current effects and magnetic effects are present, and the magnetic effect counteracts the eddy current effect, resulting in reduced sensor sensitivity. In contrast, for weakly magnetic or non-magnetic conductive materials such as copper, aluminum, and alloy steels, the magnetic effect is relatively weak and the eddy current effect is stronger, leading to higher sensor sensitivity. Therefore, material properties should be carefully considered during sensor selection and calibration, especially in high-precision measurement applications.