Magnetics Business & Technology - Summer 2012 - (Page 11)

FEATURE ARTICLE with made up coils of the magnetic material. It is to treat the magnetic coil as an electrical coil. That is, measure the inductance of the coil since the ends of the wire coil are available. Stripping the surface insulation off the ends and end to end inductance can be measured. Current, voltage and wattage can be measured with a power analyzer. The sine wave excitation can be at line frequency or at other frequencies (even up to resonant points). Sensitive to shorted turns just as a shorted secondary of a transformer, a set of readings from a made-up coil can give measurements of the soft magnetics as well as surface insulation resistance integrity. Small Sample Testing for Wire Magnetic Material the “Three Coil Test” This is a test that we and our industrial partner made use of both in static and on-the-fly testing. In our lab manifestation three air core coils of 0.6 millihenries are placed end to end and Figure 2. Three Coil Test Fixture mounted permanently of a wooden base. The center coil is connected to the test equipment (scope and sensitive voltmeter) as pickup or sense coil. The coils on each end of the pickup coil are connected series aiding and are connected to a sine wave source. A nylon push stick is arranged so as to easily push samples back out of the chamber formed by the three coils. The 87 millimeter length of sample wires gave a reliable measure as that length allowed the sample to be placed in a centered position with each end protruding about two millimeters. With this arrangement we could achieve reliable results. With a uniformity of driving force on both end coil sections of the sample chamber the sense coil picks up on flux changes from sample to sample. Further, we could drive this arrangement variously either with line voltage sine waves or by a function generator/power amplifier, using even higher frequencies operating near resonance of the test unit. But simple line frequencies offer more than sufficient sensitivity. The test is so sensitive that if a single wire in the sample chamber is tested, removed, bent once to a 45° angle, straightened and then re-inserted into the chamber, the reading will be lowered significantly. Also, multiple wires can be placed in the sample chamber. This approach can be used on line for continuous monitoring of a wire during production. The Drop Test Remember the physics demo where a copper or aluminum disc is dropped down a tube with and without magnets affecting the trajectory? The same can be applied small lengths of wire. By measuring the time or a voltage referenced to time remanence can be measured comparatively. Remanence, co- www.MagneticsMagazine.com Summer 2012 • Magnetics Business & Technology 11 http://www.meda.com http://www.meda.com http://www.MagneticsMagazine.com

Table of Contents for the Digital Edition of Magnetics Business & Technology - Summer 2012

Magnetics Business & Technology - Summer 2012
Editor's Choice
Injection Molded Magnets for Electrical Machines
The Process of Developing and Testing a New Transformer
Rare Earths & Corporate Social Responsibility
Research & Development
RE-use, RE-duce, RE-cycle, RE-place
Magnets • Materials • Measurement
Application • Component Developments
Industry News
Rare Earth Crisis Dissected: Securing the Future
Marketplace
Advertising Index
Spontaneous Thoughts: The End of Axial Pressing?

Magnetics Business & Technology - Summer 2012