Patent ID: 8575931

Claim:
A length measurement apparatus ( 10 ), comprising: a bistable magnetic element ( 102 ), an elongated physical scale ( 200 ) having a plurality of measurement graduation elements ( 202 ) spaced apart from one another, a reading head ( 100 ) which is movable relative to the elongated physical scale ( 200 ) in a longitudinal extent, and at least one first reading head magnet ( 114 a ) and at least one second reading head magnet ( 114 b ) which are arranged transverse to the longitudinal extent and with opposite polarity to one another, wherein: the bistable magnetic element ( 102 ) is part of the reading head ( 100 ); the measurement graduation elements each have a magnetic short-circuit element ( 202 ) and an arrangement of one of the first and second reading head magnets ( 114 a - b ) at respective measurement graduation elements is configured such that a magnetic field ( 116 a - b ) of the reading head magnets ( 114 a - b ) is predominantly suppressed by the magnetic short-circuit element ( 202 ), wherein the magnetic field ( 116 a b) does not penetrate through the bistable magnetic element ( 102 ); the first and second reading head magnets ( 114 a - b ) are spaced apart from one another so that the short-circuit element ( 202 ) substantially suppresses only the magnetic field ( 116 a ) of the first reading head magnet ( 114 a ) in a first relative position of the reading head ( 100 ) and substantially suppresses only the magnetic field ( 116 b ) of the second reading head magnet ( 114 b ) in a second relative position of the reading head ( 100 ); and the reading head ( 100 ) has a plurality of magnetic sensors ( 112 a - c ) arranged next to one another and an evaluation unit ( 106 ) is provided which is configured to determine an intermediate position of the reader head ( 102 ) with respect to adjacent measurement graduation elements ( 202 ) by comparing the strength of the magnetic field at the respective positions of the magnetic sensors ( 112 a - e ).