Non-destructive testing of spot welds - via eddy current search coil and electronic circuit to measure length and thickness of welds

摘要

A converter generating a prim. electromagnetic field (I) is moved over a spot weld and thus generates eddy currents creating a second magnetic field (II), which interacts with field (I) to produce a third field (III); and the intensity and phase of field (III) depend on the quality of the weld. The max. phase value (epsilon max) occurs where no weld is present, and the min. phase value (epsilon min) occurs at the spot weld. The difference between the two phase values is used to indicate the thickness (t1) of the wled; whereas the path length over which epsilon min has a constant value is used to indicate the dia. of the spot weld. The pref. appts. includes a sine-wave generator feeding an electronic bridge circuit contg. a phase shifter and phase measuring appts.