The PCU has a roll of 50 mm in diameter, with an accurately machined slot parallel to the roll axis; this simulated spall/crack is 0.020 mm wide and 1 mm deep. A motor turns the roll at a preset speed, resulting in a calibration speed of 127 cm/sec on the roll surface. This surface, or tip speed, is the normal ET Tester inspection roll surface speed.

The PCU motor is powered by a battery pack, making the unit completely portable and self-contained. The low voltage power supply ensures a safe calibration procedure on the work floor. The batterypack will have to be recharged occasionally.

The PCU slides over the sensor head of the ET Tester and is held in place by two screws. The gap distance (the distance between the roll surface and eddy current sensor) can be adjusted by turning the screws.