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Absolute encoder

An absolute encoder is a measuring instrument which outputs position information of a detector in relation to a graduation on a coder with an absolute position signal inherently adapted to the relative position. Position sensors and precise measurement devices generally require a detector that converts relative motion or position of two elements into an electrical signal. The electrical signal is then processed to determine the position and/or displacement. Position encoders are used to accurately determine a position difference between elements of a device or system. Position encoders generally fit into one of two categories: relative or incremental and absolute. An incremental encoder measures the distance moved from a starting position, and hence relies entirely on stored information. An absolute encoder provides a readout of the position of an apparatus relative to some predetermined location. For example, an absolute shaft encoder provides a readout of the number of degrees the shaft would need to be rotated to return to a predetermined starting position. An absolute encoder uses an output which is unique for any particular position, and updates its position frequently. The absolute encoder is thus less dependent on the use of stored information and is therefore generally more reliable than the incremental encoder. In an absolute encoder, sensors located on a detector section of the encoder read special detected patterns formed on a code plate and thus generate a signal which indicates an absolute position of a detector section around a code plate. The detected patterns indicate each of different address information of various positional relationships between the code plate and the detector section. Typical absolute encoders are of the so-called discrete or digital type wherein position information is encoded on a rotary disk or a linear transducer element as binary ones and zeroes, or as on and off states. The binary information is typically encoded as a series of concentric rings or bands on a rotary disk, or as a series of adjacent bands or strips on a linear encoder. A number of absolute position encoders have developed. These position encoders include optical encoders wherein a decoder track is moved between a source of light and a photo detector so that the position of the track relative to the photodetector can be determined.

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