04/13 Rev. 5.08-02 SERVICE MANUAL General information
ALX 73x
5
Rules for electromag-
netic compatibility Connect all metallic parts to each other via large surfaces, ensuring electric
conductivity.
Only polished metal surfaces are electrically conductive. Painted or oxidised sur-
faces are unsuitable. Aluminium which appears to be polished still has an invisible
oxidation layer on the surface.
Coated or plated surfaces, though electrically conductive, can reach very high re-
sistance 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. mo-
tor line). Minimum distance in the switch cabinet: 20 cm.
Spatially lay out all the lines in the switch cabinet as close as possible to the refe-
rence 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 between the switch cabinet and the
machine, the larger 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 circuit.
This reduces interference effects of various kinds.
Wire inductive components to suitable interference suppressors.
Possible inductive components: Relay, solenoid valve
Possible interference suppressors: Diodes, varistors, 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 surfaces.
For insufficient potential equalisation between the shielding lines: Lay an additio-
nal equalisation lead parallel to the shielding with a cross section at least 10 mm2.
Avoid equalisation currents in the shielding of the signal lines
Equalisation currents can arise between subassemblies 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 conditions 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.
