I used to do eddy current inspection in machined parts, mostly aluminum. It should work well in brass tubing, as long as the tubing is homogenous. But if the material has been brazed or otherwise had its properties modified, that could mask defects.
Ben is correct; it measures the inductive coupling of eddy currents. A coil with a high frequency signal is held close to the part under tests, and it induces "eddy currents" to flow in the part. The eddy currents create magnetic fields that in turn, affect the impedence of the coil. When the eddy currents encounter a discontinuity in the material, the current path length changes and the inductive coupling changes. The tester detects that change in impedence.
We had a Magnaflux instrument when I did this kind of work (15+ years ago), but when I look at their website I don't see any mention of eddy current instruments.
What I recall about eddy current testing is that the fixturing and the calibration standard were very important. In theory (and in the sales literature) you could operate the test probe free hand, but in my experience, it was almost always necessary to build a fixture to maintain the relative alignment between the probe and the part under test. Likewise, it was usually necessary to manufacture a calibration standard which was nearly identical in all respects to the part to be tested, except for the addition of manufactured defects (usually notches cut by EDM) to calibrate the eddy current machine.
Ed
Edward Motts
Certified LabVIEW Associate Developer
