A-Scan

An A-scan is the basic ultrasonic display showing signal amplitude (vertical axis) versus time-of-flight (horizontal axis) from a single transducer position, used to identify, size, and locate reflectors.

Definition

The A-scan is the fundamental display format of an ultrasonic flaw detector: a single-line waveform with amplitude on the vertical axis and time (or equivalent path-length) on the horizontal axis. Each peak represents an echo from an interface or discontinuity.

Technical Context

Inspectors interpret A-scans by comparing peak amplitudes against the calibrated DAC or DGS curves and by measuring time-of-flight to compute depth and through-wall position.

When It Is Used

  • Every conventional ultrasonic test
  • Calibration verification
  • Thickness measurement

What it represents

The fundamental ultrasonic display: signal amplitude against time. Every other presentation — B, C, D, S-scans — is built from A-scans; every sizing and evaluation decision ultimately resolves to features of this trace.

How it is derived

Reading an A-scan is the core UT skill: identifying the back wall, recognising mode-converted ghosts, separating a near-surface flaw from the dead zone, watching echo dynamics as the probe moves — the echo-dynamic pattern often tells more about a reflector than its peak amplitude does.

Where it is defined

ASME Section V Article 4 evaluation is defined in A-scan terms (DAC/TCG amplitude comparison); encoded systems must retain A-scan data precisely so evaluations can be re-derived.

How it is misread

Flying on the C-scan and never opening the underlying A-scans. Colour maps compress away the evidence — the analyst who cannot say what the A-scan under a coloured pixel looks like is reporting the software's opinion, not an examination.

Where A-Scan fits in an inspection programme

A term is only useful when it connects to a decision. A-Scan appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.

Related terms

  • Ultrasonic Testing (UT) — Ultrasonic Testing (UT) is an NDT method that uses high-frequency sound waves (typically 0.5–25 MHz) to detect internal flaws and measure thickness in metals, plastics, and composites by analyzing reflected echoes from a transducer.
  • B-Scan — A B-scan is a cross-sectional ultrasonic display showing depth (vertical) versus probe position along the scan axis (horizontal), with signal amplitude encoded as brightness or color, used for thickness profiling and corrosion mapping.
  • C-Scan — A C-scan is a plan-view ultrasonic display showing peak signal amplitude (color-coded) at every (X, Y) probe position across the inspected surface, producing a top-down map of internal flaws or wall loss.
  • Distance-Amplitude Correction (DAC) — DAC is an ultrasonic calibration curve plotted on the A-scan display that shows expected echo amplitude from a reference reflector at varying depths, used to evaluate flaw size while compensating for beam spread and attenuation.

More data terms

D-Scan · S-Scan · L-Scan · Distance-Gain-Size · Time-Corrected Gain · Gating · Decibel · Indication · False Indication · Relevant Indication

Where this comes up in practice

Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.

Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.