Length measurement apparatus

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 (114a) and at least one second reading head magnet (114b) 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 (114a-b) at respective measurement graduation elements is configured such that a magnetic field (116a-b) of the reading head magnets (114a-b) is predominantly suppressed by the magnetic short-circuit element (202), wherein the magnetic field (116a b) does not penetrate through the bistable magnetic element (102);
• the first and second reading head magnets (114a-b) are spaced apart from one another so that the short-circuit element (202) substantially suppresses only the magnetic field (116a) of the first reading head magnet (114a) in a first relative position of the reading head (100) and substantially suppresses only the magnetic field (116b) of the second reading head magnet (114b) in a second relative position of the reading head (100);
• and
• the reading head (100) has a plurality of magnetic sensors (112a-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 (112a-e).