The cables led from the control cabinet contain a high frequency noise element and
outside the control panel these cables act as antennae and radiate noise. The
cables connected to input/output modules or special modules which leave the
control panel must always be shielded cables.
Mounting of a ferrite core on the cables is not required (excluding some models) but
if a ferrite core is mounted, the noise radiated through the cable can be suppressed
Use of a shielded cable is also effective for increasing the noise immunity level. The
PLC system's input/output and special function module provide a noise immunity
level of equivalent to that stated in IEC801-4 : 2 k V when a shielded cable is used.
If a shielded cable is not used or if the shield earthing treatment is not suitable even
when used (See Section 22.214.171.124), the noise immunity level is less than 2 kV.
prEN50082-2 specifies the noise resistance level based on the signal wire
Signals involved in process control :
Signals not involved in process control : 1kV
The meaning of "involved in process control" is not defined in prEN50082-2.
However, when the purposes of the EMC Directive are considered, the signals that
could cause personal injury or risks in the facility if a malfunction occurs should be
defined as "signals involved in process control". Thus, it is assumed that a high
noise immunity level is required.