3.6.2 Interference Supression Measures
Electrical and electronic devices are capable of influencing or disturbing each other
through their connection cables or other intended and unintended metallic connections.
Interference suppression measures (electromagnetic compatibility) consist of two elements:
raising interference resistance and suppressing interference emission.
Correct installation of the drive in conjunction with local interference suppression
measures has a crucial effect on minimizing or suppressing mutual interference.
The following guidelines assume a power source that is not already contaminated by high
frequency interference. Other measures may be necessary to reduce or suppress
interference if the power source is already contaminated. Please consult Benshaw's
Electrical Application Engineering Department if the following recommended interference
suppression measures do not produce the desired result. Refer to Appendix C for more
information.
•
When dealing with RFI (radio frequency interference), the surface area of the conductors
is a more critical consideration than its cross sectional area. Since high frequency
interference currents tend to stay towards the outer surface (skin effect), braided copper
tapes of equal cross section should be used.
•
A central grounding (or earthing) point should be used for interference suppression.
Route the ground cables radially from this point (star connection). Avoid making any
ground loops that may lead to increased interference. The drive and all components used
for interference suppression, particularly the shield of the motor cable, should be
connected over as large a surface area as possible when connecting it to ground.
Remove the paint from contact surfaces if necessary to ensure a good electrical
connection.
•
Take care not to damage the shield's cross section and verify the continuity of the shield
when splicing wires. Splices raise the RF resistance of the shield and can cause RF to
radiate rather than continue in the shield. Shields, particularly those on control cables,
must not be routed through pin contacts (pluggable connectors). When shielded cables
must pass through a plug connection, use the metallic hand guard of the plug for the
continuation of the shield. It is strongly recommended that the shield be uninterrupted
whenever possible.
•
Use a shielded motor cable that is grounded over a large surface area at both ends. The
shield on this cable should be uninterrupted. If a shielded motor cable can not be used,
the unshielded motor lines should be laid in a metal conduit or duct which is
uninterrupted and grounded at both ends.
29
3 - RECEIVING AND INSTALLATION
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