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3.1.3 Cables
The cables extracted from the control panel contain a high frequency
noise component. On the outside of the control panel, therefore, they
serve as antennas to emit noise. To prevent noise emission, use
shielded cables for the cables which are connected to the I/O modules
and intelligent function modules and may be extracted to the outside of
the control panel.
The use of a shielded cable also increases noise resistance.
The signal lines (including common line) of the programmable
controller, which are connected to I/O modules, intelligent function
modules and/or extension cables, have noise durability in the condition
of grounding their shields by using the shielded cables. If a shielded
cable is not used or not grounded correctly, the noise resistance will not
meet the specified requirements.
(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.
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.
Shield section
Clamp fitting
Paint mask
Shielded cable
Screw
Crimp terminal
Wire
Shielded cable
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