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Eddy Current Sensor

Eddy-Current sensors are noncontact devices capable of high-resolution measurement of the position and / or change of position of any conductive target. Eddy-Current sensors are also called inductive sensors, but generally, “eddy current” refers to precision displacement instruments( or non-destructive testing probes) and “ inductive” refers to inexpensive proximity switches. High resolution and tolerance of dirty environments make eddy-current sensors indispensable in today’s modern industrial operations. Eddy current sensors are used to detect non-magnetic but conductive materials. They comprise of a coil, an oscillator, a detector and a triggering circuit. Figure shows the construction of eddy current sensor. When an alternating current is passed through this coil, an alternative magnetic field is generated. If a metal object comes in the close with the coil, then eddy currents are induced in the object due to the magnetic field. These eddy currents create their own magnetic field which directs the magnetic field responsible for their generation. As a result, impedance of the coil changes and so the amplitude of alternating current. This can be used to trigger a switch at some pre-determined level of change in current. Eddy current sensors are relatively inexpensive available in small in size, highly reliable and have high sensitivity for small displacements. Advantages of Eddy Current Sensor Tolerance of dirty environments. Not sensitive to material in the gap between the probe and target. Less expensive and much smaller than laser instrumentation. Less expensive than capacitive sensor. Eddy current sensors are not good choice in these conditions: Extremely high resolution ( capacitive sensors are ideal) Large gap between sensor and target is required ( optical and laser are better) applications of Eddy Current Sensors Automation requiring precise location. Machine tool monitoring Final assembly of precision equipment such as disk drives Drive shaft monitoring Vibration measurements