Avery Dennison ALS 204, Service And Installation Manual

Page: 9 / 224

9
1 P
LEASE OBSERVE THE FOLLOWING
1.1 G
ENERAL INFORMATION
ALS
20X
256
Rules for electromagnetic compatibility
Connect all metallic parts to each other via large
surfaces, ensuring electric conductivity.
– Only polished metal surfaces are electrically con-
ductive. Painted or oxidised surfaces are unsuita-
ble. Aluminium which appears to be polished still
has an invisible oxidation layer on the surface.
– Coated or plated surfaces, though electrically con-
ductive, can reach very high resistance values at
high frequencies (skin effect).

Clean contact surfaces, polish the metal, use fan
disks (washers) or mounting plates.

Carry out EMC grounding, preferably as a neutral
(star) point. A neutral (star) point prevents loops.
When laying the signal lines and power cable,
space them apart.

Lay all control and signal lines at least 50 cm distant
from power cables (e.g. motor line). Minimum dis-
tance in the switch cabinet: 20 cm.

Spatially lay out all the lines in the switch cabinet as
close as possible to the reference potential.
Lead the signal lines into the unit or switch cabinet
from one side only.
– The more lines that are laid in front and in back be-
tween the switch cabinet and the machine, the larg-
er the radiation surface of the radiated
electromagnetic energy.

Lead the signal lines out of the machine (in one
bundle and from one location, if possible) and into
the switch cabinet.
Twist together unshielded lines from the same cir-
cuit.
– This reduces interference effects of various kinds.
Wire inductive components to suitable interference
suppressors.
– Possible inductive components: Relay, solenoid
valve
– Possible interference suppressors: Diodes, varis-
tors, RC combinations

House all components suspected of being sources
of RF interference fields in a closed metal casing
(Faraday screen).
Shield all signal and control lines.

Ground the shielding on both sides at its large sur-
faces.

For insufficient potential equalisation between the
shielding lines: Lay an additional equalisation lead
parallel to the shielding with a cross section at least
10 mm
2
.
Avoid equalisation currents in the shielding of the
signal lines
– Equalisation currents can arise between subassem-
blies with different grounding conditions.

When the grounding conditions are different, only
shield the side with the better grounding condition.

Only shield both sides when the grounding condi-
tions are the same (e.g. inside a machine).
Power filter

Mount the power filter direct at the power supply.

Connect the filter casing to the EMC grounding via
large metal surfaces.
Lay all lines as close as possible to metal parts,
even reserve cables
– Freely hanging lines act as transceiver antennas.

Ground all reserve cables and unused wires in the
cables at least at one end.
Keep the cables as short as possible
– Cable resistance and signal distortion increase with
the length of the cable.