Automation Direct Do-more H2 PLC Series, Руководство пользователя по оборудованию

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Do-more H2 Series PLC User Manual, 1st Edition, Rev. F - H2-DM-M B-7
Appendix B: European Union Directives (CE)
1
B
3
D
5
H
7
10
I
10
11
12
13
14
A
B
C
D
Equipotential Grounding
Adequate site earth grounding must be provided for equipment containing modern electronic
circuitry. The use of isolated earth electrodes for electronic systems is forbidden in some
countries. Make sure you check any requirements for your particular destination. IEC
1000–5–2 covers equipotential bonding of earth grids adequately, but special attention
should be given to apparatus and control cubicles that contain I/O devices, remote I/O racks,
or have inter-system communications with the primary PLC system enclosure. An equipotential
bond wire must be provided alongside all serial communications cables, and to any separate items
of the plant which contain I/O devices connected to the PLC. The diagram shows an example of
four physical locations connected by a communications cable.
Communications and Shielded Cables
Good quality 24 AWG minimum twisted-pair shielded cables, with overall foil and braid
shields are recommended for analog cabling and communications cabling outside of the PLC
enclosure. To date it has been a common practice to only provide an earth ground for one end
of the cable shield in order to minimize the risk of noise caused by earth ground loop currents
between apparatus. The procedure of only grounding one end, which primarily originated as
a result of trying to reduce hum in audio systems, is no longer applicable to the complex industrial
environment. Shielded cables are also efficient emitters of RF noise from the PLC system, and
can interact in a parasitic manner in networks and between multiple sources of interference.
Serial Communication Cable
Equi-potential Bond
Key
Screened
Cable
Equi-potential
Bond
Control Cubicle
To Earth
Block
Conductive
Adapter
Serial
I/O