| 摘要 |
A pricisely dimensioned gap between relatively movable surfaces (14,16) is maintained in a magnetic bearing by use of proximity sensors (22a, 22b, 23a, 23b). Each sensor includes a magnetic assembly (32) having a bar core (36) secured to a middle leg (42) of an F-shaped core (34). The bar core and the vertical leg (38) of the F-shaped core have approximately equal lengths. The magnetic assembly is fixed with respect to one of the surfaces (16) and is so positioned that the end (52,54) of the F-core vertical leg (38) and the bar core are spaced from the other surface (14) to provide the variable gap dimension. The end (48) of the suppermost leg (40) of the F-shaped core is spaced from the bar core and provides a reference dimension (44). Any differences in the variable gap and reference dimensions are furnished to a driver (27, 72-86) which moves one surface with respect to the other until the gap dimension corresponds to the reference dimension. By making the magnetic materials of the F-core and the bar core the same, the magnetic path lengths approximately the same and the permeability of the magnetic material high over the desired temperature range, by matching the sensor housing temperature coefficient with that of the core, the differential reluctance of the two parallel paths is mode inherently insensitive to temperature changes. Accordingly, the sensor null displacement becomes solely determined by the condition where the clearance between the moving and fixed parts is equal to the reference gap.
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