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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.
The encoder can be either incremental or absolute. In an incremental system, position is determined by motion over time; in contrast, in an absolute system, motion is determined by position over time. Linear encoder technologies include optical, magnetic, inductive, capacitive and eddy current.
This page was last edited on 17 January 2020, at 23:10 (UTC).; Text is available under the Creative Commons Attribution-ShareAlike 4.0 License; additional terms may apply.
An incremental encoder interface is an electronic circuit that receives signals from an incremental encoder, processes the signals to produce absolute position and other information, and makes the resulting information available to external circuitry.
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.
Two optical sensors (phototransistors or photodiodes) are placed very close to each other to make a linear incremental encoder. When the machine axis moves, the dark marks move under the optical encoders triggering them in succession. If movement is from, for example, left to right, encoder A is triggered first and encoder B afterwards.
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.