Mitsubishi Electric MELSEC-Q Series User Manual page 116

(1) Installation in a control panel
Programmable controller is an open-type device intended to be placed in a conductive control panel or similar
type of enclosure.
This ensures safety as well as effective shielding of programmable controller-emitted electromagnetic noise.
*1 Modules on the remote station in each network must be also installed inside the control panel. However, the waterproof
type remote station can be installed outside the control panel.
(a) Control panel
• Use a conductive control panel.
• Mask off the area used for grounding when securing the top or bottom plate to the control panel using
bolts.
• To ensure electrical contact between the inner plate and the control panel, mask off the bolt installation
areas of an inner plate so that conductivity can be ensured in the largest possible area.
• Ground the control panel with a thick ground cable so that low impedance can be ensured even at high
frequencies.
• Keep the diameter of the holes on the control panel to 10cm or less.
If the diameter is larger than 10cm, electromagnetic wave may be emitted. In addition, because
electromagnetic wave leaks through a clearance between the control panel and its door, reduce the
clearance as much as possible. Use of EMI gaskets (sealing the clearance) can suppress undesired
radiated emissions.
The tests by Mitsubishi were conducted using a control panel having the damping characteristics of 37dB
(maximum) and 30dB (average) (measured at 3m distance, 30 to 300MHz).
(b) Wiring power and ground cables
Run the ground cable and the power cable of this product as instructed below.
• Provide a ground point to the control panel near the power supply module. Ground the LG (line ground)
and FG (frame ground) terminals of the power supply module for the programmable controller and the LG
terminal of the transmission cable terminal block to the ground point with the thickest and shortest ground
cable possible (about 30cm or shorter). Because the LG and FG terminals serve to dissipate noise
generated within the programmable controller to the ground, the impedance of the ground cable must be
as low as possible.
In addition, the ground cable must be kept as short as possible. The ground cable serves to dissipate
noise. Because the ground cable itself bear noise, keeping the cable short means that the cable prevents
itself from being an antenna.
• The ground cable run from the contact point must be twisted with the power cable. By twisting the power
cable with the ground cable, more noise flowing through the power cable can be dissipated to the ground.
However, when a noise filter is attached to the power cable, twisting with the ground cable may be
unnecessary.
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