A Magnetic Position Sensor

A simple magnetic device for determining the position of a movable member along a preestablished path is described. In operation, the local field from a small permanent magnet carried by the movable member divides a slender, semihard ferromagnetic element, coextensive with the path, into two remanently magnetized regions having distinct intensities and/or polarities. The instantaneous position of the magnet is defined by the relative length of each region. A characteristic or physical property that is distinguishable between the two regions by virtue of their differing remanent states is used to recover this positional information. An especially suitable property is the reversible permeability of the element as a whole which is shown to be a linear function of magnet position. Determining this permeability from the inductance of a solenoid wound on the element allows correction of non-linearities due to end effects by the local adjustment of winding pitch. Non-linear transfer functions required by specific applications are also obtainable in this manner. Performance of practical sensors is limited chiefly by the characteristics of the element and the extent to which these are affected by the ambient conditions associated with the application. Present status of development allows application in relatively non-rigorous environments for position sensors having a range from a few centimeters to a few meters.