For ultrasonic immersion testing, it is especially
critical that the ultrasonic transducer is normally oriented with respect
to the surface of the test part. This orientation can be maintained by computer
control if enough axes are available for full contour following. A cheaper
way to follow a fairly regular but wavy surface is to use a skid plate such
as the one shown below. This plate houses an ultrasonic probe and keeps
it oriented properly as the plate moves across the surface of the test piece.