Rockwell Automation 1771-QC , D17716.5.25 SER/B SERVO POS - Manual (Page 20)

Positioning Concepts
Chapter 3
3Ć7
An incremental digital encoder provides feedback that indicates the
magnitude and direction of any change of axis position. As shown in
Figure 3.6, the encoder shaft is attached to a transparent disc marked with
uniformly spaced lines. Strategically located photodiodes detect light. As
the disc rotates, the lines break up the light reaching the photodiodes. As
a result, the output (channel A, channel B, and marker) from each
photodiode is a series of electrical pulses.
Figure 3.6
Incremental Encoder Ć Showing How Signals Are Generated
Photodetectors
Light
Source
Marker
Channel B
Channel A
Marker
Marker
11000
Disc
A
B
Encoder Feedback