Rockwell Automation 1771-VHSC , D17716.5.74 Very High S - Manual (Page 23)

1–15 Overview of the Very High Speed Counter Module
Operation of Outputs
When the outputs for the VHSC module are enabled and assigned to
a counter they operate in an ON-OFF fashion. For example, assume
that the module were programmed to turn ON an output when a
count value of 2000 was reached. Further, assume that the user
desired to have the output remain energized for a period of 3000
counts and then turn OFF. The end result would be that the outputs
would turn ON at count of 2000, would remain energized for 3000
additional counts, and would turn OFF at 5000 counts. The ON and
OFF values are circular around zero. In the rate measurement mode,
the On and Off values associated with each output represent a
frequency value instead of a count value. The maximum frequency
value which may be entered in an On or Off value is 500,000Hz.
Refer to 1.11.
Figure 1.11
OnĆOff Operation of Output
Output turns on at count value of 2000
Output remains energized for 3000 additional counts
Output turns off at count value of 5000
10686ĆI
Refer to 1.12. Using output 0 as an example, when the value in
words 26 and 27 is less than the value in words 28 and 29, the output
turns on at 2000 and off at 5000. If the value in words 26 and 27 is
greater than the value in words 28 and 29, the output turns off at
2000 and on at 5000.
Figure 1.12
Effect of Values in Words 26 through 29
Output turns ON
at count of 2000.
Output remains energized
for 3000 additional counts.
Output turns OFF
at count of 5000.
Output turns OFF
at count of 2000.
Output turns ON
at count of 5000.
When values in words 26Ć27 are greater than
values in words 28Ć29.
When values in words 26Ć27 are less than
values in words 28Ć29.
10687ĆI
Refer to words 26-29, 31-34, 36-39, 41-44, 46-49, 51-54, 56-59,
61-64 of the block transfer write initialization file in chapter 5.
Isolation of Outputs
The module provides 1500V ac forced rms isolation between each of
the counters and the backplane of the I/O rack.