Signal-Based AE Analysis

Approaches in recording and analyzing AE signals can be divided into two main groups: parameter-based (classical) and signal-based (quantitative) AE techniques. Both approaches are currently applied, with success for different applications, and it is useful to understand their differences, which should here be summarized in addition to the more detailed description of parameter-based techniques in Chap. 4. The reason that two approaches exist is related to the rapid developments in microelectronics over the last few decades. Previously, it was not possible to record and store a large number of waveforms (signals) over a sufficiently short period of time. Even though significant technical advances have been made in recent years, it is still not possible to use signal-based techniques to monitor large structures and buildings. In addition, the relatively high financial costs and the time required to apply modern signal-based techniques, are a reason why parameter-based techniques are still popular. Before the differences are described in detail, it should be emphasized that the discrepancies between the two approaches are becoming smaller. Some of the devices used for the classical AE technique are now able to store the waveforms of the detected AE signals, even though this is not the primary function of these devices. For applications using signal-based analysis techniques, equipment based on transient recorders is typically used. It is easy to apply custom software tools to extract AE parameters for statistical analyses of the data obtained with these instruments.