COMPARATOR TECHNOLOGY IN NDT

A frequent challenge in manufacturing and industry is how to separate different parts that have been intentionally—or accidentally—mixed. Electromagnetic comparators can be used to accomplish this quickly and economically.Non Destructive Testing for Production Comparator

  • This type of instrument “compares” variations in a test part to conditions in a known sample.
  • When a metal part is placed inside or near a test coil that is excited by an alternating current, the voltage output from the coil will be affected. This is the basic principle employed by all electromagnetic comparators.
  • The kinds of mixes that comparators will separate typically involve variations in alloy, heat treatment, hardness, structure, dimensions (including length) and certain other conditions.
  • The effect that the part has on the output of the coil is directly related to the permeability, conductivity and physical dimensions of the part.
  • If the test is for variations in just one property, those differences must be greater than those that may occur in other properties so that they can be separated using the instrument’s selective circuits.
  • Variations in hardness or heat treatment, for example, create a change in permeability; changes in alloy affect conductivity; and significant dimensional changes affect both conductivity and permeability.  These changes in the coil result in screen signals that can be selected based on differences in amplitudes, phase angles or harmonic distortions.

The best way to determine whether a comparator will make the particular separation that you need is to conduct a trial of the equipment with actual samples of your test material.

As a special service to our customers, a material sample can be sent to our trained staff of experts for a no-charge trial and report. For complete details, call or email MAC®.

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