Without A-Scan the instrument gives a number and nothing more. With A-Scan it shows where that number comes from, and it becomes possible to distinguish a valid reading from one that merely seems so.
- ✓ Representation of signal amplitude over time
- ✓ Distinction between back-wall echo, flaw echo and noise
- ✓ Validation of the measurement on difficult materials
- ✓ Storage of the waveform for later review
The A-Scan is the graph of the signal received by the transducer: on the horizontal axis time, which corresponds to depth in the material, on the vertical axis signal amplitude. Every reflecting surface produces a peak, and the position of the peak tells how far away what generated it lies.
In a thickness measurement on sound material the trace is readable: the initial pulse, then the back-wall echo, possibly the subsequent echoes. On an attenuating material or a corroded wall the picture changes: the back-wall echo drops, intermediate peaks appear, noise rises. That is where the figure alone on the display becomes insufficient.
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In flaw detection the A-Scan is not an aid but the working tool: the operator assesses the amplitude and position of the peaks, compares them with a reference curve and decides. Without the waveform there is nothing to assess.
What can be read on the trace
| Element | What it indicates |
|---|---|
| Peak position | The depth at which the reflecting surface lies |
| Peak amplitude | How much energy has been sent back |
| Back-wall echo | The opposite surface of the part |
| Intermediate peaks | Possible internal discontinuities, to be assessed |
| High background noise | Attenuating material or insufficient coupling |
Peak detection modes
On Dakota NDT flaw detectors of the FX family the manufacturer’s documentation indicates three echo detection criteria: Z-Cross, Flank and Peak. They are different ways of establishing which point of the waveform is taken as the reference for the measurement.
The same instruments have a PRF adjustable from 8 Hz to 2 kHz and a 60 Hz screen refresh: a trace that updates quickly keeps the signal readable even while the probe moves over the part.
Instruments with A-Scan
| Instrument | Display type |
|---|---|
| Dakota FX70-DL | Portable A-Scan and B-Scan for field inspections |
| Dakota FX81-DL | Benchtop version with large display |
| Dakota CMX10-DL | Colour A-Scan on the flagship thickness gauge |
| Dakota MX2-DL | A-Scan with waveform storage |
Frequently asked questions
It is not indispensable on sound materials and regular surfaces. It becomes decisive on attenuating materials, on corroded walls and whenever one needs to understand why a reading is unstable.
The horizontal axis represents time, which corresponds to depth in the material; the vertical axis represents the amplitude of the received signal.
Yes, on models that provide waveform storage: the trace is saved together with the reading and remains available to review a doubtful measurement later.
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Further information and contacts
Systems division and sensor integration partner : www.roder.it
More information about RODER SRL : about us
Contact for general information : info@roder.it
Contact for information about these products : info@roder.it
The information contained on this web page is provided for information purposes only. Although it has been compiled with the utmost care, it does not constitute a contractual offer or a binding commitment to supply. It may contain transcription, translation or typographical errors. For precise and up-to-date information, please contact our company directly.
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