| 摘要 |
An incremental measuring system comprises a scale member provided in one track with a measuring scale, and an optoelectronic scanning unit for generating measured-valve signals in response to a scanning of the scale. The scale member is provided in an additional track with two or more reference marks and the scanning unit is operable to scan the reference marks and to generate reference signals in response to the scanning of the additional track at one or more selectable reference points provided with such reference marks. The scale member and the scanning unit are encapsulated in an enclosure, which is formed with a slot, which is covered by a seal. An actuating member for the scanning unit extends through the slot past the seal. Covers for covering at least part of the reference marks are provided and are adapted to be inserted and/or removed into and from the enclosure or shifted along the tracks by a positioning member, which extend through apertures formed in the enclosure. The covers are used to select the reference points which are entirely exposed for being scanned by the scanning unit. The apertures are closed and sealed or are adapted to be closed and sealed.
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