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Incremental Rotary Encoders
Encoders transform rotary movement into a sequence of electrical pulses. A number of bright/dark segments on a disc are photoelectrically scanned. The number of segments determine the resolution of the movement and hence the accuracy of the position. Because only increments of rotation are detected with a single channel, an additional signal, phase shifted by 90 degrees, is generated by inserting a grid diaphragm. This 90 degrees out of phase signal enables, together with the initial signal, the direction of rotation to be determined. Once per revolution a reference signal may also be generated.