Patent ID: 9335151
Filing Date: 2016-05-10
CPC Classification: G01B

Claim Text:
1. A method of measuring a test sample having a film of unknown thickness, comprising: sensing the test sample using an eddy current sensor at an unknown first distance from the test sample to generate eddy currents in the test sample to produce a sensor output signal of a single parameter at a first output level which is a function of the first unknown distance of the sensor from the test sample and the unknown thickness of the film of the test sample; incrementing the distance between the eddy current sensor and the test sample by a known incremental distance to a second unknown distance; sensing the test sample using the eddy current sensor at the second unknown distance from the test sample to generate eddy currents in the test sample to produce a sensor output signal of the single parameter at a second output level which is a function of the second unknown distance of the sensor from the test sample and the unknown thickness of the film of the sample; comparing the sensor first and second output levels and the known incremental distance to calibration data correlating a plurality of measured output levels of a sensor output signal of the single parameter to a plurality of known thicknesses of films of a plurality of calibration samples and to a plurality of known distances of the calibration samples from an eddy current sensor; and determining at least one of the unknown distances of the sensor from the test sample and the thickness of the film of the test sample as a function of the comparison of the first and second sensor output levels of the single parameter and the known incremental distance to the calibration data.