A position sensor utilizing a slender ferromagnetic element, a small permanent magnet, and interactive conductors is described. The element, first uniformly magnetized by passage of the magnet over its entire length, is divided by subsequent motion of the magnet into two regions having opposite polarizations on each side of the magnet position. The regions are differentiated by their unequal incremental permeabilities in small bias fields. The effective ac permeability of the element as a whole is shown to be a linear function of magnet position. Data from an experimental sensor in which permeability was sensed by the inductance of an encircling solenoid confirm this linear transfer function. Utility as a measurement and control element in machinery, instruments, and liquid level devices is apparent from the achievable performance. Expected applications will be in the range from a few centimeters to a few meters.
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