II - DCE FEL ČVUT v Praze

Mechanical Configuration of an Automation System with SIMATIC S7 Ex Modules
1.8 Shielding and Measures to Counteract Interference Voltage
Shielding Shielding is a method of attenuating magnetic, electric or electromagnetic
interference fields. Shielding can be subdivided into
Equipment shielding
Line shielding
1.8.1 Equipment Shielding
I/O Modules with Intrinsically-Safe Signals
C79000-G7076-C152-04
Particularly observe the following when cabinets and housings are
incorporated in control system shielding:
Cabinet covers such as side panels, rear panels, top and bottom panels,
must make contact in an overlapping arrangement at adequate distances
(e.g. 50 mm).
Doors must be given additional contact with the cabinet ground. Use
several grounding strips.
Lines exiting the shielded housing should either be shielded or routed via
filters.
Where the cabinet contains sources of sever interference (transformers,
lines to motors, etc.), they must be partitioned from sensitive electronic
areas with metal plates. The metal plates must have several
low-impedance bolted joints to the cabinet ground.
Interference voltages picked up in the programmable controller via non-Ex
signal and supply lines are diverted to the central ground point (standard
sectional rail).
The central ground point should have a low-impedance connection to the PE
conductor via a copper conductor
(> = 10 mm2 ) which is a short as possible.
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