User`s manual

2 - 2 2 - 2
MELSEC
2 EMC COMMAND
2
2.1.2 Installation on the control panel
Installing devices on the control panel has a considerable effect not only in securing
safety but also in shutting down the noise generated from the PC by the control panel.
(1) Control panel
(a) Use an electrically conductive control panel.
(b) When fastening tightening the control panel's top or bottom panel with bolts,
mask the coating so that surface contact is feasible.
(c) To ensure the electrical contact between the inside panel of the control panel
and the main control panel, mask any coating around the installation bolts
connecting to the main unit to secure conductivity in the largest surface area
possible.
(d) Ground the control panel main unit using a thick ground cable so that a low
impedance can be secured even with a high frequency.
(e) Make the holes on the control panel less than 10 cm (3.94 in.) in diameter. A
hole larger than 10 cm (3.94 in.) may leak electric waves.
(2) Layout of power supply cable and ground cable
The layout of power supply cable and ground cable for a PC should be set as
described below.
(a) Specify a grounding point that enables grounding of the control panel close to
the power supply to the PC and ground the FG (frame ground) terminal of
the PC or the SLD (shield) terminal of the CC-Link board using the thickest,
shortest cable possible (about 30 cm (11.81 in.) or less in length). Since the
FG and SLD terminals play a role in grounding the noise generated in the
PC, it is necessary to ensure the lowest possible impedance. Because the
power line is used to allow the noise to escape, it actually contains a great
deal of noise. Therefore, shortening the wire length prevents the power line
from becoming an antenna.
Note : A long conductive material can become an antenna that emits noise more
efficiently.
(b) Twist the ground cable leading to the ground point with the power supply
cable. By twisting them with the ground cable, the noise leaking out of the
power supply cable may be grounded at a higher rate. However, when a
noise filter is installed to the power supply cable, twisting with the ground
cable may not be necessary.