Patent ID: 8547083

Claim:
An apparatus for determination of an axial position of an armature of a linear motor, the apparatus comprising: at least one pair of magnetically permeable, annular elements, disposed substantially coaxially and at a short distance from one another, such that an air gap is defined between the magnetically permeable annular elements, wherein each of the annular elements is magnetically permeable so as to represent a magnetic short circuit such that a magnetic potential of each annular element is always constant along a circumference of the respective annular element; and a magnetic field sensor disposed in the air gap for measurement of the magnetic field in the air gap; wherein the magnetically permeable annular elements surround the armature of the linear motor, in the installed state; and wherein: (a) the annular elements comprise different radii from one another and are concentric, such that the distance consists of a radial distance; or (b) the annular elements comprise identical radii and are axially spaced from one another, such that the distance consists of an axial distance; or (c) the annular elements comprise different radii and are axially spaced from one another, such that the distance comprises a radial component and an axial component; wherein the magnetically permeable annular elements comprise at least one common annular element and at least two individual annular elements, wherein the common annular element is associated with both of the individual annular elements to thereby define at least two pairs of annular elements.