Output Voltage Characteristics of Eddy Current Displacement Sensor for Various Heat Treatments of Measuring Objects

The output voltage of an eddy current displacement sensor (EC displacement sensor) depends on the heat treatment of the measuring object. The EC displacement sensor must detect a displacement of several tens of μm to allow the examination of the change in output voltage due to the heat treatment of the measuring object. Thus, we measure the relative permeability and resistivity of four objects made of chromium molybdenum steel that have undergone different heat treatments (initial condition (INT), salt quenching (SAQ), annealing (ANL), and vacuum furnace cooling (VFC)). In addition, we examine the relationship between the heat treatment of the measuring objects and the output voltage characteristics of the sensor at a displacement between the measuring object and the sensor of 1 mm. The result shows that the relative permeability of measuring object varies between 35 and 80, and resistivity varies between 0.18 μΩm and 0.35 μΩm due to different heat treatment conditions. The sensitivities of the sensor after SAQ and VFC treatments of the measuring object are 82.0 V/m and 73.0 V/m, respectively; thus, the difference is -11%.