Справочник Пользователя для Mitsubishi Electronics Q25HCPU

 

 

 

8 - 2                                                                                                                                                       8 - 2 

MELSEC-Q

 

8   EMC AND LOW VOLTAGE DIRECTIVE 

 

8.1.2 Installation instructions for EMC Directive 

The PLC is open equipment and must be installed within a control cabinet for use. This 

not only ensures safety but also ensures effective shielding of PLC-generated 

electromagnetic noise. 

 

(1)   Control cabinet 

(a)   Use a conductive control cabinet. 

 

(b)   When attaching the control cabinet's top plate or base plate, mask painting 

and weld so that good surface contact can be made between the cabinet 

and plate. 

 

(c)   To ensure good electrical contact with the control cabinet, mask the paint on 

the installation bolts of the inner plate in the control cabinet so that contact 

between surfaces can be ensured over the widest possible area. 

 

(d)   Earth the control cabinet with a thick wire so that a low impedance 

connection to ground can be ensured even at high frequencies. 

 

(e)   Holes made in the control cabinet must be 10 cm (3.94 inch) diameter or 

less. If the holes are 10 cm (3.94 inch) or larger, radio frequency noise may 

be emitted. 

In addition, because radio waves leak through a clearance between the 

control panel door and the main unit, reduce the clearance as much as 

practicable. 

The leakage of radio waves can be suppressed by the direct application of 

an EMI gasket on the paint surface. 

Our tests have been carried out on a panel having the damping 

characteristics of 37 dB max. and 30 dB mean (measured by 3 m method 

with 30 to 300 MHz). 

 

(2)   Connection of power and earth wires 

Earthing and power supply wires for the PLC system must be connected as 

described below. 

(a)   Provide an earthing point near the power supply module. Earth the power 

supply's LG and FG terminals (LG : Line Ground, FG : Frame Ground) with 

the thickest and shortest wire possible. (The wire length must be 30 cm 

(11.81 inch) or shorter.) The LG and FG terminals function is to pass the 

noise generated in the PLC system to the ground, so an impedance that is 

as low as possible must be ensured. As the wires are used to relieve the 

noise, the wire itself carries a large noise content and thus short wiring 

means that the wire is prevented from acting as an antenna. 

 

(b)   The earth wire led from the earthing point must be twisted with the power 

supply wires. By twisting with the earthing wire, noise flowing from the power 

supply wires can be relieved to the earthing. However, if a filter is installed 

on the power supply wires, the wires and the earthing wire may not need to 

be twisted. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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