| 摘要 |
An opto-electronic scale reading apparatus includes a scale (10) and a readhead (14) movable one relative to another. The readhead produces a pair of quadrature pulses which enable the generation of an incremental count corresponding to the displacement of the readhead (14) relative to a reference mark (80). The reference mark (80) is a permanent magnet mounted on the scale substrate inside a non-ferromagnetic casing (90). A pair of differential Hall sensors (62A, B) within the readhead, and associated processing circuitry generate a step-change ZERO pulse when the readhead (14) and scale (10) are in a particular relative position. This relative position can be adjusted to enable corresponding adjustment of the relative phase of the quadrature pulses emitted from the readhead and the ZERO pulse, by means of a ferromagnetic adjusting screw (92). Movement in the position of the screw (92) relative to the permanent magnet (80) changes the position of highest magnetic flux density in the region of the magnet, thereby altering the position of which the ZERO pulse will be emitted.
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