Whenever mechanical rotary motions have to be
monitored, the encoder is the most important interface between the
mechanics and the control unit. 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.
