What is an ‘axial displacement’? How is it measured?

Axial displacement is the movement of the rotary shaft in the axial direction to and fro. Every centrifugal shaft is permitted to have a fixed axial movement designed by the manufacturer, this is to allow the compressor to take the load on the thrust collar.

Axial displacement is measured using an eddy probe system. It is measured using the proportional change in the DC voltage (gap voltage) caused by the movement of the shaft from its center position to either side (+or-).