Eddy current lift-off: a study guide to signal context
Use two fictional cases to separate a lesson’s observations from the explanations they support.
Understand the spacing variable
For a surface probe, changing the separation between the coil and a conductive part changes electromagnetic coupling and can change the coil’s impedance. The IAEA’s Eddy Current Testing at Level 2 manual calls this proximity effect lift-off.
The same manual identifies material properties, frequency, geometry and probe handling among the variables that affect a response. A changed signal alone does not establish its cause.
Sources: IAEA TCS-48: variables and proximity effects, pages 112–114.
Compare two fictional study cases
Read these as supplied lesson descriptions, not instructions to operate equipment. Neither case includes a measured trace or a component acceptance decision.
| Study case | What is established | What remains unproved |
|---|---|---|
| A: The description says only probe separation changed. | A spacing change is part of this example. | A universal signal direction or numerical sensitivity loss. |
| B: The response changes, but the description omits what changed in the setup. | An observation is available; its context is incomplete. | The cause of the response or whether a discontinuity exists. |
Write and check your study notes
For each case, write two short sentences. Begin the first with “The description states…” and the second with “I can explain…”. Underline the words in the case that support each sentence. If a sentence has no supporting words, turn it into a question.
Case A supports an explanation about lift-off. Case B leaves the cause unresolved. Each answer must stay within its supplied description.
Now give your notes to a study partner without the case headings. Can they identify which facts were supplied and which questions remain open? Compare your reasoning, rather than trying to produce identical wording. This exercise develops a habit of making the evidence behind an explanation visible.
Connect the exercise with ET Level I and II training
The IAEA’s training guidelines include lift-off within coupling effects at both Level 1 and Level 2. It is a topic to revisit as your study progresses.
NDT Academy’s ET course includes Reading the Impedance Plane, Lab: Generating Liftoff Curves and Lab: Liftoff and Frequency Effects in Level I, followed by a Liftoff lesson in Level II. Review the syllabus to place this introductory exercise alongside those topics.
The online course provides formal training and completion records. Personnel certification and work authorization depend on the applicable certification program and employer requirements; completing this article or course does not by itself award them.
Sources: IAEA training guidelines: ET outlines, pages 154 and 162.
Sources and further reading
- IAEA TCS-48: variables and proximity effects, pages 112–114
- IAEA training guidelines: ET outlines, pages 154 and 162
Sources checked on September 18, 2026. Follow the current requirements from your employer or certification body when planning qualification or an examination.