Table 1 Hit-based AE waveform parameters
AE Waveform Parameters | Code | Definition | Unit | ||
|---|---|---|---|---|---|
Direct | 1 | Threshold | – | The predefined value such that signals with amplitude higher than which will be recorded | dB |
2 | Hits | H | The AE signal exceeds threshold | – | |
3 | Counts | N | The number of AE signal excursions over the threshold during an AE hit | – | |
4 | Amplitude | A | The maximum (positive or negative) AE signal excursion during an AE hit, which indicates the magnitude of the waveform | dB | |
5 | Duration | D | The time between the first and last threshold crossing of an AE hit | µs | |
6 | Rise Time | R | The time between the first threshold crossing and the peak amplitude | µs | |
7 | Counts to Peak | NP | The number of AE signal excursions over the threshold between the first threshold crossing and the peak amplitude | – | |
8 | Absolute Energy | ABE | The integral of the squared voltage signal divided by the reference resistance (10 k-ohm) over the duration of the AE waveform packet, which is a true energy measure of the AE hit | Joules | |
9 | Energy | E | The integral of the rectified signal over the duration of the AE waveform packet | µVolt-sec/count | |
10 | Signal Strength | S | picovolt-sec | ||
11 | Root Mean Square | RMS | An electrical engineering power term defined as the rectified time averaged AE signal, which is a measure of the continuously varying AE signal “voltage” | Volt | |
12 | Average Signal Level | ASL | An electrical engineering power term defined as the rectified time averaged AE signal, which is a measure of the continuously varying AE signal “amplitude” | dB | |
Indirect | 13 | Average Frequency | AF | Counts divided by Duration | kHz |
14 | Reverberation Frequency | RF | The “ring down” average frequency, which is determined after the peak of the AE waveform (Counts—Counts to peak) divided by (Duration—Rise-time) | kHz | |
15 | Initiation Frequency | IF | The “Rise-time” average frequency, determined before the peak of the AE waveform Counts to peak divided by the rise-time | kHz | |
16 | Frequency Centroid | CF | The value derived from the fast Fourier transformation of the waveform associated with the AE hit, and then calculated by SUM(magnitude*frequency)/SUM(magnitude) | kHz | |
17 | Peak Frequency | PF | The frequency contains the largest magnitude derived from the fast Fourier transformation on the waveform associated with the AE hit | kHz | |
18 | RA | RA | Rise time divided by peak amplitude Useful to classify AE signals | µs/dB | |