Specifications

Minimizing EMI: System Design Guidelines I/O Wiring: General Guidelines
VisiLogic: Getting Started 9
I/O Wiring: General Guidelines
1
. Route each I/O signal / signal-group along with a dedicated common wire
(e.g. 0V). This serves as a signal return path and increases interference
immunity.
Connect common wires at the respective common pins of the module
where the specified I/O port is located. Please refer to the module
installation guide for details.
2. For all types of analog and high-speed I/Os:
3. Use shielded twisted pair cable
4. Do not use the shield as a signal or as a return conductor
5. Ground the shield at the closest grounding point to the I/O port,
preferably a grounding plate or the cabinet body.
This connection method usually gives the best interference immunity.
However, in some cases, grounding the shield at both ends of the cable is
preferable. In this case, be sure that both points have the same potential
in order to eliminate ground currents through the shield.
6. Route those signals separately from high voltage / high current and AC
wiring, as explained in the section Wiring Separation.
Signal (Communication, I/O) Line Filtering
Some environments may induce greater EMI than the typical industrial
environment. Extra power and/or signal line filtering may improve the system’s
immunity to EMI.
If signal-line filtering is required, please use the following guidelines in addition
to the guidelines provided by the filter manufacturer:
1. Place the filter as close as possible to the target device(s); maximum wire
length is 10 cm.
2. Signal lines can be filtered using rounded ferrite cores. To maximize their
effect, wind the wire through the ferrite core multiple times to attentuate
high frequencies as shown below.
3. Always pass both the signal and signal return wires thru the ferrite core.
If multiple I/O lines share the same common return wire, pass all of these
I/O lines and their return wire through the same ferrite core.