1.4 Types of Equipment Available
Contemporary ultrasonic flaw detectors are small, portable, microprocessor-based instruments suitable for both shop and field use. They generate and display an ultrasonic waveform that enables a trained operator to locate and categorize flaws in test pieces, often with the aid of analysis software. They typically include an ultrasonic pulser/receiver, hardware and software for signal capture and analysis, a waveform display, and a data logging module. Most contemporary instruments use digital signal processing for optimum stability and precision.
Modern flaw detectors typically capture a waveform and then perform various measurement and analysis functions on it. An internal clock is used to synchronize transducer pulses and provide distance calibration. Signal processing may be as simple as generation of a waveform display that shows signal amplitude versus time on a calibrated scale, or as complex as sophisticated digital processing algorithms that incorporate distance/amplitude correction and trigonometric calculations for angled sound paths. Alarm gates are often employed to monitor signal levels at selected points in the wave train to flag echoes from flaws.
The display may be a liquid crystal, an electroluminescent display, or a CRT. The screen is normally calibrated in units of depth or distance. Multicolor displays can be used to provide interpretive assistance. Internal data loggers can be used to record full waveform and setup information associated with each test, if required for documentation purposes, or selected information like echo amplitude, depth or distance readings, or presence or absence of alarm conditions.
A special advanced category of portable ultrasonic flaw detectors is phased array instruments, which utilize more complex hardware with software similar to that used in medical diagnostic imaging to provide a higher level of both test and interpretive capability. Instead of a single element transducer, phased arrays use probes with a large number of elements, all individually pulsed and time-delayed. Ultrasonic beams are formed by constructive and destructive interference from these multiple sources. Unlike conventional instruments, phased array systems can electronically focus, steer and sweep the beam and then generate detailed cross-sectional images of the test piece. Phased array systems are explored in detail in the Olympus Phased Array Tutorial.
