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An absolute encoder maintains position information when power is removed from the encoder. [5] The position of the encoder is available immediately on applying power. The relationship between the encoder value and the physical position of the controlled machinery is set at assembly; the system does not need to return to a calibration point to maintain position accuracy.
An encoder is a sensor which turns a position into an electronic signal. There are two forms: Absolute encoders give an absolute position value. Incremental encoders count movement rather than position. With detection of a datum position and the use of a counter, an absolute position may be derived.
Many incremental encoders have an additional output signal, typically designated index [2] or Z, [3] which indicates the encoder is located at a particular reference position. Also, some encoders provide a status output (typically designated alarm) [4] that indicates internal fault conditions such as a bearing failure or sensor malfunction.
A linear encoder is a sensor, transducer or readhead paired with a scale that encodes position. The sensor reads the scale in order to convert the encoded position into an analog or digital signal, which can then be decoded into position by a digital readout (DRO) or motion controller. The encoder can be either incremental or absolute.
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Some types of resolvers include both types, with the 2-pole windings used for absolute position and the multipole windings for accurate position. Two-pole resolvers can usually reach angular accuracy up to about ±5 ′, whereas a multipole resolver can provide better accuracy, up to 10″ for 16-pole resolvers, to even 1″ for 128-pole resolvers.
Audio encoder, converts digital audio to analog audio signals; Video encoder, converts digital video to analog video signals; Simple encoder, assigns a binary code to an active input line; Priority encoder, outputs a binary code representing the highest-priority active input; 8b/10b encoder, creates DC balance on a communication transmission line
Absolute encoders can determine their position at power-on but are more complicated and expensive. Incremental encoders are simpler, cheaper, and work at faster speeds. Incremental systems, like stepper motors, often combine their inherent ability to measure intervals of rotation with a simple zero-position sensor to set their position at start-up.