Abstract
This paper presents a new method for planar inductive sensor to measure the gap between the sensor and a non-ferrite metallic target. The eddy current on the target plate is modeled as a virtual coil; the inductance change of the planar sensing coil is a result of the mutual inductance of the sensing coils and the virtual coil. We introduce a method to calculate the gap from measured coil inductance by studying the mutual inductance between the sensing coil and the virtual coil. From our analysis, we found that with this method only one calibration curve is needed for measuring the gap between the sensing coil and a metallic target plate made of different materials. When the target material is changed, the new calibration curve can be obtained by adding a constant to the base calibration curve. In comparison, traditional planar inductive sensors require a family of calibration curves for measuring gaps from targets made of different materials. To verify the validity of the method, three planar proximity sensors with different dimensions were manufactured and used to measure the gap from four different non-ferrite targets, titanium, copper, zinc and aluminum. Results showed that in a large measurement range (500 μm–5000 μm), the calibration was simplified; the calculated gaps using the method and the actual gaps were in good agreement, with a maximum error of 3.2%. The method is valid regardless of the dimensions of planar coils. It can be used for facilitating measuring gap and detecting metallic objects in machines and automation equipment made of various materials.
Published Version
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