II - DCE FEL ČVUT v Praze

1.8.3 Measures to Counteract Interference Voltages
Physical
arrangement of
equipment and
lines
Grounding of
inactive metal
elements
Protection against
electrostatic
discharge
Mechanical Configuration of an Automation System with SIMATIC S7 Ex Modules
I/O Modules with Intrinsically-Safe Signals
C79000-G7076-C152-04
Measures to suppress interference voltages are often only implemented when
the control system is already in operation and proper reception of a useful
signal is impaired. The overhead for such measures, such as special
contactors, can frequently be reduced considerably by observing the
following points during configuration of your control system:
Favorable arrangement of equipment and lines
Grounding of all inactive metal elements
Filtering of power cables and signal lines
Shielding of equipment and lines
Special interference-suppression measures
Magnetic DC or AC fields of low frequency, such as 50 Hz, can only be
sufficiently attenuated at great expense. In such a case, however, you can
often solve the problem by providing the greatest possible distance between
the interference source and sink.
Note
The analog Ex modules operate based on a method which suppresses faults
caused by AC system ripple.
Well implemented grounding is an important factor for interference-free
assembly. Grounding is understood to mean a good electrical connection of
all inactive metal elements (VDE 0160). The principle of surface grounding
should be followed. All conductive, inactive metal elements should be
grounded.
Observe the following when grounding:
All ground connections must have a low impedance.
All metal elements should have a large-area connection. Use particularly
wide grounding strips for the connection. The surface of the ground
connection and not its cross section is decisive.
Screw-type connections should always have spring washers or lock
washers.
To protect equipment and modules from electrostatic discharge, metal
housings or cabinets enclosed on all sides should be used; these should be
given good electrical connection to the grounding point on site, and also
connected to the main equipotential bonding conductor.
1-31