8EMC 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
(1) | Control cabinet | |
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| (a) Use a conductive control cabinet. |
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| (b) When attaching the control cabinet's top plate or base plate, mask painting |
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| and weld so that good surface contact can be made between the cabinet |
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| and plate. |
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| (c) To ensure good electrical contact with the control cabinet, mask the paint on |
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| the installation bolts of the inner plate in the control cabinet so that contact |
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| between surfaces can be ensured over the widest possible area. |
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| (d) Earth the control cabinet with a thick wire so that a low impedance |
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| connection to ground can be ensured even at high frequencies. |
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| (e) Holes made in the control cabinet must be 10 cm (3.94 inch) diameter or |
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| less. If the holes are 10 cm (3.94 inch) or larger, radio frequency noise may |
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| be emitted. |
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| In addition, because radio waves leak through a clearance between the |
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| control panel door and the main unit, reduce the clearance as much as |
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| practicable. |
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| The leakage of radio waves can be suppressed by the direct application of |
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| an EMI gasket on the paint surface. |
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| Our tests have been carried out on a panel having the damping |
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| characteristics of 37 dB max. and 30 dB mean (measured by 3 m method |
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| with 30 to 300 MHz). |
| (2) Connection of power and earth wires | |
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| Earthing and power supply wires for the PLC system must be connected as |
| described below. | |
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| (a) Provide an earthing point near the power supply module. Earth the power |
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| |
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| supply's LG and FG terminals (LG : Line Ground, FG : Frame Ground) with |
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| the thickest and shortest wire possible. (The wire length must be 30 cm |
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| (11.81 inch) or shorter.) The LG and FG terminals function is to pass the |
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| noise generated in the PLC system to the ground, so an impedance that is |
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| as low as possible must be ensured. As the wires are used to relieve the |
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| noise, the wire itself carries a large noise content and thus short wiring |
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| means that the wire is prevented from acting as an antenna. |
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| (b) The earth wire led from the earthing point must be twisted with the power |
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| supply wires. By twisting with the earthing wire, noise flowing from the power |
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| supply wires can be relieved to the earthing. However, if a filter is installed |
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| on the power supply wires, the wires and the earthing wire may not need to |
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| be twisted. |
8 - 2 | 8 - 2 | |