The data acquisition system uses the "Flock of Birds" position tracker from Ascension Technology Corporation. The Flock of Birds outputs 6-degree of freedom, namely, x, y, z and three angular readings (azimuth, elevation and roll). This is an external device, connected to the computer by means of an RS 232 interface and is capable of collecting position and orientation information at a rate of up to 144 measurements per second. At the maximum possible positional resolution of 0.03 inches, this measurement speed translates to a horizontal speed of 4.32 inches per second.

The ultrasonic data acquisition and analysis system uses a personal computer (PC) to control the overall operation. Data from the UT transducer driven by a pulser-receiver is sampled and digitized by the computer. The transducer is also rigidly attached to the receiver of the position tracker by means of a plexi-glass strip. This allows the system to simultaneously collect both UT data and the position information required to create a C-scan map of the sample being inspected. A GUI-based software package has been developed for controlling the operation of the scanner, displaying the data, and interpreting the data in terms of classification into Crack, Counterbore and Rootweld.

The data analysis system employs a multilayer perceptron neural network classifier. The network is trained to identify the statistical variance of a group of A-scans in a neighborhood of the C-scan image. The data analysis algorithm exploits the fact that although individual A-scans from cracks and conterbores appear to be very similar, statistical properties of an ensemble of reflections from counterbores and cracks are significantly different. The analysis system also calculates the reliability of its classification decision and uses this information to improve its performance. The software is implemented in a user friendly windows -based environment and has been validated using blind test data.

The system can be used in conjunction with ultrasonic and eddy current transducers and can therefore be of potential interest to other industries such as aerospace and pipeline industries.