Large diameter pipes of prestressed concrete with a length of 10–20 ft. used for water transport are made in rotating moulds. To control the thickness of these concrete pipes during production, an ultrasonic pulse-echo system mounted at the end of the feeder is used. Basically, the air gap between feeder and inner pipe wall is continuously measured, whereby deviations due to misalignment of the feeder are electronically compensated. A prototype version of the system has proved its usefulness. An accuracy of ±5% of the nominal wall thickness was obtained.
