What is the purpose of A-scan and Peak Modes in TDScan and how do you use them?
A-Scan and Peak Modes are methods of defining data acquisition and storage criteria. These modes are selected by the user from the Gates page in TDScan.
A-scan modes are instructions to the software defining how to store A-scan information in data files. All A-scans, or only A-scans that cross a user-defined amplitude threshold, may be saved in their entirety, enabling replay when analysing data. Alternatively, simple depth values derived from the A-scans may be saved making data files relatively small in comparison.
Defining a Peak Mode is, as with the A-scan modes, simply a menu choice. Peak Modes may, for example, allow depth measurements to be taken from the calibrated zero point, or only signals from the thinnest material in each encoder step recorded. In contrast, zero may be measured from the first signal that crosses a gate, and the first subsequent signal in the gate is measured as depth. In NDT jargon, this mode is often referred to as Echo-to-echo mode.
A different Peak Mode might determine that the highest amplitude signal in the gate be used to measure the depth or, the absence of a signal in the gate causes a particular colour to be displayed in the data imaging, signifying loss of signal. A special mode that has gained more use in recent years is the Interface Trigger mode which is used for immersion testing.
Peak Modes are usually used for applications where the thickness or the depth of reflectors are displayed as distance or time-related colour-graphic images. Examples of applications that employ this approach are Corrosion Mapping, Hydrogen Damage Surveys, and Composite Inspections. Peak Modes provide flexibility in data presentation and used in the appropriate context, may improve measurement accuracy.
Written by Mark Nel, Technical Sales and Application Specialist