Eddy currents are electrical currents induced in a conductor by a time-varyingmagnetic field. Eddy currents flow in a circular pattern, but their paths are oriented perpendicular to the direction of the magnetic field.
The Eddy current inspection method is a highly capable, reliable inspectionmethod. When used by a trained technician, it can be used to detect surface and somesubsurface cracks, determine materialproperties, and measure the thickness of thin materials, conductive coatings and non-conductive coatings on conductivesubstrates.
Eddy Current is based on these properties, which also proves crucial in all its application:
- Conductivity of material.
- Permeability of material.
- Frequency applied on the specimen.
- Geometry of specimen.
- Temperature.
In all above points mentioned, point no. 3,4 & 5 are controlled either by circuitry or by human intervention. (i.e frequency is fixed by electronic unit, geometry for all parts under testing is confirmed same by operator, temperature variation is nulled by using two coils method and for some application temperature is maintained same by operator.). SoEddy current is directly proportional to the conductivity and permeability of the material under test.
All eddy current application is based on this phenomenon.
Eddy Current Application
- Coating Thickness Measurement
- Material sorting based on Metallurgical properties
- Conductivity Measurements
- Defect detection
- Stationary Coil – 1. Encircling Type Segment Type 3. Bobbin Type
- Rotating Type (Probe) – 1. Part Rotating Probe rotating.
Eddy currents application frequency range:
- Lower Frequency range (10hz – 30khz)
- Metallurgical sorting
- Remote field Eddy currents
- Middle Frequency Range (5Khz – 800Khz)
- Crack detection (Stationary and Rotating)
- Coating Thickness measurement.
- Higher Frequency range (1Mhz-4Mhz)
- Crack detection (Aluminum and Titanium) in Aerospace.