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Chapter 4
Accessory and Cable Connections
NI 951x User Manual
4-8
ni.com
•
Add clamp-on ferrites to cables to further reduce emissions.
•
Add a balun to the power cable to attenuate conducted and radiated
emissions.
Caution
Do
not
exceed the maximum specifications on any input or output. Refer to
Appendix A,
Specifications
, for more information.
Limit and Digital Input Connection Recommendations
Use the following additional recommendations when connecting limits and
other digital inputs:
•
For the end of travel limits to function correctly, the forward limit must
be located at the forward or positive end of travel, and the reverse limit
at the reverse or negative end of travel.
•
Limit, home, and digital input signals are digitally filtered. Software
configurable filters are provided to filter or debounce the input signals.
Use shorter filter periods for noise filtering and longer filter periods to
debounce the input.
Caution
Failure to follow these guidelines may result in motion that stops at, but then
travels through, a limit, potentially damaging the motion system. Limits that are wired
incorrectly may prevent motion from occurring at all.
Encoder Connection Recommendations
The encoder inputs are connected to incremental decoder/counter circuits.
It is very important to minimize noise at this interface. Excessive noise
on these encoder input signals may result in loss of counts or extra
counts and reduced motion system accuracy. The following additional
recommendations apply to encoder signal connections:
•
National Instruments strongly recommends you use encoders with
differential line driver outputs for all applications. You
must
use
differential encoders if the encoder cable length is longer than 3.05 m
(10 ft). Shielded, 24 AWG (0.25 mm
2
cross section) wire is the
minimum recommended size for the encoder cable.
•
Wire encoder signals and their ground connections separately from all
other connections. Wiring these signals near the motor drive or other
signals can cause positioning errors and faulty operation.