Rockwell Automation 1769-HSC Compact High Speed Counter Module - Manual (Page 33)

Rockwell Automation Publication 1769-UM006E-EN-P - July 2013 33
Module Operation Chapter 2
The generalized rate calculation is Rate =  count/  time.
The cyclic method is better suited to high pulse rates.
Hysteresis Detection and Configuration
Because physical vibration can cause an encoder to generate pulses that you do
not wish to consider as valid motion, a hysteresis value is used to eliminate a
certain number of pulses in either direction as vibration-generated. These pulses
are not used to calculate the Ctr[
n].CurrentRate value. You program the
minimum number of counts that are considered to be valid motion, using the
Ctr
nHysteresis configuration word/menu. If the change in counts over the
update time cycle is equal to or less than the minimum number of programmed
counts, the Ctr[
n].CurrentRate is reported as zero.
This concept is not used to alter actual count values.
IMPORTANT The rate calculation is based on net counts. If a counter goes up 500
counts and down 300 counts, the net count is 200. Therefore, changes in
direction and speed affect the Ctr[n].CurrentRate value.
IMPORTANT Hysteresis does not depend on the direction of the change in count.
Therefore, creeping, a slow change in count in one direction only, can
also be reported as zero frequency when it falls below the hysteresis
threshold.