An apparatus useful for detecting the speed and/or position of an object moving along a defined path and more particularly to such an apparatus configured to minimize the spacing between a sensing face of the apparatus and a target surface on the object. Embodiments of the invention are particularly suited for sensing the speed of a rotating member, e.g., a gear, by utilizing a sensor, such as a Hall-effect sensor, to detect the movement of each gear tooth past the sensor. An apparatus in accordance with the invention is configured to mount the sensor for adjustable positioning along a sensor path between an initial position and a final operational position. Movement of the sensor along the sensor path is restricted, e.g., by frictional engagement, but can be overcome by contact with the target surface so as to move the sensor to its final position with the spacing, i.e., airgap between the sensing face and the target surface, minimized.

A generator air-gap flux probe for determining rate of change of flux density includes a resilient support spanning the air gap between the stator and the rotor of a dynamoelectric machine to support radial and/or tangential flux coils stably within a short distance of the rotor. The resilient support permits the portion of the flux probe spanning the air gap to deflect substantially during assembly or disassembly of the machine thereby to permit permanent installation of the air-gap flux probe. In one embodiment adapted to longer air gaps, the flux probe is mounted on a pedestal block installed on a dovetail slot wedge in the stator. This reduces the cantilevered distance which the flux probe must span. A tangential flux coil axis stripe marking the axis of the tangential flux coil aids in alignment.

To provide a measuring method on an electric motor with a rotor and a stator for determining the fly height and/or axial play, the rotor being mounted, and in particular fluid-mounted, on the stator, with which method the axial position of the rotor in relation to the stator can be determined with high levels of accuracy and reproducibility, it is provided that the electric motor is operated at a defined measuring speed, at which the rotor is in a specific axial position in relation to the stator, with this relative axial position being determined in that the rotor is brought in a defined manner, with the motor at a standstill, into a first stop position in relation to the stator, in that the rotor is brought in a defined manner, with the motor at a standstill, into a second stop position in relation to the stator, lying opposite the first stop position, and in that the relative axial position between the rotor and the stator is respectively measured in the two stop positions.