Design of Algorithms to Extract Data from Capacitance Sensors to Measure Fastener Hole Profiles

This paper discusses algorithms used to process data from a multisegmented capacitance probe as the basis for a system for nondestructive testing of aircraft fastener holes. Measurement accuracies on the order of tenths of mils are achieved through a combination of accurate electronic measurement of capacity and use of the computer-implemented algorithms for estimating hole profiles. The estimation algorithms make possible the novel feature of allowing accurate determination of hole profiles for arbitrary positioning of the probe in the hole. The paper gives a brief description of the measurement system and the capacitance probe. The algorithms are discussed in detail and examples of measured profiles for known hole shapes are given.