Eddy current probe head for testing workpiece surfaces - has bias magnet surrounding two probe coils supplied by HF AC

摘要

The surface of a workpiece (1) is scanned by a probe having two h.f. coils (3, 4) which are connected to a measuring appts. via a cable (34). Surrounding the probe coils is a further coil (7) connected to a d.c. supply and providing a magnetic biassing field (arrows M). To improve handling, the coils are encapsulated in a plastics body (9). As an alternative to the electromagnet, a permanent magnet, e.g. of ceramic oxide, may be provided. Eddy current measurements using the probe coils give an indication of surface flaws in the workpiece.