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3.1.3 Cables
The cables pulled out of the control panel contain a high frequency noise
component. On the outside of the control panel, therefore, they serve as
antennas to emit noise.
Ensure to use shielded cables for the cables, which are connected to the I/O
modules, special modules and those pulled out to outside of the control panel.
Mounting ferrite core is not required except some types of CPU however, noise
emanated via the cable can be restrained using it.
The use of a shielded cable also increases noise resistance. The signal lines
(including common line) connected to the programmable controller input/output
modules and intelligent modules use shielded cables to assure noise resistance,
as a condition, standardized on EN61131-2/A12 (2000).
If a shielded cable is not used or not earthed correctly, the noise resistance will
be less than the rated value
(1) Earthing of shielded of cables
(a) Earth the shield of the shielded cable as near the unit as possible taking
care so that the earthed cables are not induced electromagnetically by
the cable to be earthed.
(b) Take appropriate measures so that the shield section of the shielded
cable from which the outer cover was partly removed for exposure is
earthed to the control panel on an increased contact surface. A clamp
may also be used as shown in the figure below. In this case, however,
apply a cover to the painted inner wall surface of the control panel which
comes in contact with the clamp.
Shield sectio
Screw
Shielded cable
Paint mask
Clamp fitting
Note) The method of earthing by soldering a wire onto the shield section of
the shielded cable as shown below is not recommended. The high
frequency impedance will increase and the shield will be ineffective.
Shielded cable
Wire
Crimp terminal
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