Справочник Пользователя для Mitsubishi Electronics Q25HCPU

 

 

 

8 - 3                                                                                                                                                       8 - 3 

MELSEC-Q

 

8   EMC AND LOW VOLTAGE DIRECTIVE 

 

8.1.3 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 cable 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 

connected to the PLC I/O modules and intelligent function modules use shielded 

cables to assure noise resistance under the conditions where the shield is earthed. If a 

shielded cable is not used or not earthed correctly, the noise resistance will not meet 

the specified requirements. 

 

When the shield of a shielded cable is earthed to the cabinet body, please ensure that 

the shield contact with the body is over a large surface area. If the cabinet body is 

painted it will be necessary to remove paint from the contact area. All fastenings must 

be metallic and the shield and earthing contact must be made over the largest 

available surface area. If the contact surfaces are too uneven for optimal contact to be 

made either use washers to correct for surface inconsistencies or use an abrasive to 

level the surfaces. The following diagrams show examples of how to provide good 

surface contact of shield earthing by use of a cable clamp. 

 

(1)   Earthing of shielded of shield cable 

(a)   Earth the shield of the shielded cable as near the module as possible taking 

care so that the earthed cables are not induced electromagnetically by the 

cable to be earthed. 

 
(b)   Take an 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 section

 

Screw

Clamp fitting

Shielded cable

Paint mask

 

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