A method is provided that involves a wall configured to circumscribe and be radially adjacent a rotor. During this method, a tri-axial capacitance probe is provided that includes a tri-axial conduit with an outer conductor member. The tri-axial capacitance probe is configured to output data indicative of a characteristic of the rotor. The tri-axial capacitance probe is configured within a wall aperture in the wall. The outer conductor member is electrically coupled with the wall. The wall is configured as a housing for the tri-axial capacitance probe.