Time-Corrected Gain (TCG)
TCG is an ultrasonic instrument feature that automatically increases system gain as a function of time-of-flight, flattening the DAC curve so all reference reflectors display at the same amplitude regardless of depth.
Definition
Time-Corrected Gain (TCG) ramps the receiver gain with time so that the response from identical reflectors at different depths is normalized to the same amplitude. The DAC curve becomes a flat horizontal line, simplifying sizing.
Technical Context
TCG is essential for phased-array inspections, where many beams must produce consistent amplitude response, and is the basis for ASME Section V phased-array calibration.
What it represents
Electronic gain that increases with time of flight, compensating for beam spread and attenuation so that an identical reflector produces the same screen amplitude regardless of depth.
How it is derived
It flattens the response curve, which makes amplitude directly comparable across the thickness and makes automated evaluation practical. It is built from the same reference reflectors that would otherwise define a DAC curve.
Where it is defined
ASME Section V Article 4 permits TCG as an alternative to DAC; ISO 16811 covers the setting procedure.
How it is misread
Applying gain compensation beyond the depth range over which it was established. Extrapolated TCG amplifies noise as readily as signal, and the resulting apparent indications are an artefact of the setup.
Where Time-Corrected Gain fits in an inspection programme
A term is only useful when it connects to a decision. Time-Corrected Gain 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
- 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.
- Phased Array Ultrasonic Testing (PAUT) — PAUT is an advanced ultrasonic technique using a multi-element transducer (16–256 elements) with electronic beam steering and focusing, producing sectorial, linear, and compound scans for superior weld inspection and defect characterization.
More data terms
A-Scan · B-Scan · C-Scan · D-Scan · S-Scan · L-Scan · Distance-Gain-Size · Gating · Decibel · 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.