Rockwell Automation 1771-DE Absolute Encoder Module User Manual - Manual (Page 54)

Appendix
B
BĆ1
Application Considerations
The absolute encoder module can control outputs within a one-count
resolution (turn an output on at position 065 and off at position 066) if
shaft speed does not exceed a certain limit. This speed limit depends on
the number of outputs and the number of counts on the encoder. It can be
found from:
S = K/N
where S = maximum shaft speed for one-count resolution; K = a constant;
and N = number of counts on the encoder. The value of K depends on
whether you want to express shaft speed in revolutions per second (rps) or
revolutions per minute (rpm).
If you control: Then K = (for rps) OR K=(for rpm)
8 outputs 5000 300,000
6 outputs 6493 389,610
4 outputs 9009 540,540
2 outputs 14,084 845,070
For example, if you control eight outputs with a 0 to 359-count encoder,
and the encoder shaft speed is given in revolutions per minute, the
equation is:
300,000
S = 360
= 833 rpm
The maximum encoder shaft speed at which you can control eight outputs
within a one-count resolution is 833 rpm.
Let’s consider two examples to show the importance of shaft speed,
number of outputs to be controlled, and number of encoder counts in
obtaining optimum module operation.
In both examples we use a 0 to 359-count encoder, all eight outputs are
under control, and the output is to turn on at position 000 and off at
position 001.
Application Considerations