Lift-Off
Lift-off is the change in eddy current signal caused by a variation in the distance between the probe coil and the test surface, used both as a calibration tool and as a nuisance variable to be minimized.
Definition
Lift-off produces a characteristic signal direction on the impedance plane, typically used to null the instrument and to set the phase angle for crack detection.
Related terms
- Impedance Plane — The impedance plane is a 2D display in eddy current testing showing the probe coil's resistive (X-axis) and inductive reactive (Y-axis) components, on which signals from lift-off, defects, and conductivity changes trace characteristic vectors.
- Edge Effect — The edge effect is the distortion of an eddy current signal as the probe approaches a part edge, hole, or geometric discontinuity, which can mask defect signals near edges.
- Fill Factor — Fill factor is the ratio of the cross-sectional area of an encircling or bobbin coil to that of the tube it inspects, governing inspection sensitivity and the strength of geometric (e.g., support-plate) signals.
More physics terms
Back-Wall Echo · Beam Spread · Near-Field · Far-Field · Dead Zone · Shear Wave · Longitudinal Wave · Surface Wave · Lamb Wave · Mode Conversion
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.