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Principle of Eddy Current Testing

Principle of ECT

Testing method using electro-magnetic induction is generally referred to as "Electro-magnetic Testing Method", and for the purpose of detecting surface and subsurface flaws it is called Eddy Current Testing Method (ECT).

Eddy Current Testing

Since the eddy current testing is a fast and purely electrical method, it is easy to be automated and widely used for detecting flaws of parts in production line.

Principle of ECT

Eddy currents are produced on the surface of any electrical conducting material where an alternating magnetic field is generated by AC coil.
In case that there is a crack on the surface of the material, circulation of the eddy currents is disturbed by the crack.
The Eddy Current Testing method is used to find surface and subsurface flaws and to determine characteristics of electrical conducting materials measuring impedance of coil generated by variation of eddy currents.

ECT Equipment

Standard ECT model is composed of oscillator for feeding AC, bridge circuit for measuring impedance of coil, AC amplifier, phase detector etc.
A model with PC for setting test conditions is also available.

Magnetic Coil

Ring coil is used for inspecting surface of pipe and bar, inserting coil is used for inspection of inside surface of pipe, and probe coil is for various inspections.

Typical application

  • Widely used in on-line inspection of steel pipe, copper pipe and aluminum pipe
  • Indispensable for maintenance of chemical plant, power generation plant and heat exchanger
  • Inspection of aircraft engine