Rockwell Automation 1771-QC , D17716.5.25 SER/B SERVO POS - Manual (Page 23)

Positioning Concepts
Chapter 3
3Ć10
Therefore, if we cause the leadscrew to move the slide 2 inches, we will
get 2,000 feedback pulses.
Now, consider replacing the 250-line encoder with a 500-line encoder. By
doubling the number of feedback pulses per revolution of the leadscrew,
we improve the feedback resolution from 0.001 inch to 0.0005 inch.
Another way to improve feedback resolution is to use a higher feedback
multiplier. You can select a multiplier of x1, x2, or x4. For example, with
the 4-pitch (per inch) leadscrew and the 250-line encoder, if you select an
x2 multiplier you get the same feedback resolution improvement of from
0.001 inch to 0.0005 inch. With an x4 multiplier, you improve the
feedback resolution to 0.00025 inch.
Marker
Besides the channel A and B output, an incremental encoder has a marker
output (Figure 3.6 and Figure 3.7). The marker pulse occurs once every
revolution. With a 4-pitch leadscrew, the marker pulse occurs at each 1/4
inch interval of slide travel.
We can use a market pulse to establish a home position somewhere along
the slide travel. For example, we can place a limit switch near the end of
the slide travel. The first market pulse after the limit switch is activated
could then designate the home position (Figure 3.8).