Multi-Frequency Eddy Current
Multi-frequency eddy current testing uses two or more simultaneous frequencies whose responses are mixed in software to suppress unwanted variables (support-plate signals, tube-end effects) and isolate the defect signal of interest.
Definition
By mixing a frequency optimized for the support plate with a frequency optimized for defect detection, multi-frequency techniques produce a residual signal that contains the defect response without the geometric interference. Tube inspection at refineries and nuclear plants relies on multi-frequency mixing.
Related terms
- Frequency Response — Frequency response describes how an eddy current signal varies with the test frequency, governed by the standard depth of penetration (skin effect) and used to select frequencies that optimize defect detection at the target depth.
- Bobbin Coil — A bobbin coil is a differential or absolute eddy current probe that travels axially inside a tube, inspecting the entire tube circumference simultaneously for wall loss, pitting, and through-wall defects.
- Rotating Probe — A rotating probe (also called RPC or motorized rotating pancake coil) is an eddy current probe with one or more pancake coils mounted on a rotating head, used inside tubes to detect circumferentially-localized defects that bobbin probes cannot characterize.
More procedure terms
Contact Coupling · Immersion Testing · Source-to-Film Distance · Exposure Chart · Wet Particle Method · Dry Particle Method · Fluorescent Particles · Visible Particles · Demagnetization · Multi-Directional Magnetization
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.