Rockwell Automation 1771-VHSC , D17716.5.74 Very High S User Manual
Page 68
Questions and Answers
D–2
Q. What does it mean when an output indicator is on?
A.
Since the output indicator is tied to the control side of the
module, it means that the module has commanded the output
on. It does not necessarily mean that the output is on. The
indicator illuminates even when no connection is made to the
outputs or to the output supply. For an output to actually turn
on, the output supply must be connected.
Q. What are the delay times for turning the outputs on and
off?
A.
The outputs turn on in < 10
µ
sec, and turn off in < 100
µ
sec.
Typical on time is 3
µ
sec and typical on-off time is 50-60
µ
sec.
Q. Can I parallel my outputs?
A.
Any or all of the 8 module outputs can go to the same output
device, as long as the output commons and Vcc are the same.
Q. Can I parallel my inputs?
A.
You can parallel inputs if the device can supply enough current
to drive multiple inputs.
Q. If I have different sources of power for my input devices,
will I have input common problems?
A.
You don’t need to tie commons together. The isolation between
channels is large enough to eliminate common mode voltage
problems.
Q. If I set both the preset and reset bits to one counter in one
BTW, what will happen?
A.
The preset has priority, so only the preset will occur. The
outputs will follow the preset.
Q. If I change the BTW configuration data, how long will it
take for the module to process the changes and execute
them?
A.
It depends on the length of the BTW. The module spends about
80
µ
sec decoding each word of new data in binary. It takes
twice as long to decode BCD. A worst case example of 64
words will take about 5.5msec in binary, and 11msec in BCD.
These times start after the module receives the BTW. Don’t
forget that it may take additional time based on changes in rate
measurement sample periods. If you changed the sample period
to 2 seconds, it will take an additional 2 seconds to receive a
new frequency value.
Q. In frequency mode, how are my samples taken?