Omron 3G3RX - Achievable Line Conducted Interference Limits Classes; Maximizing Immunity. Control and Signal Lines

2-26
2-2 Wiring
2
Design
Achievable line conducted interference limits classes:
Maximizing immunity. Control and signal lines
Using EMC compliant cables for control signals: To ensure reliable operation of the frequency
inverter, analog and digital control lines (encoder connection, all analog inputs, the serial interfaces,
etc.) should be laid shielded. You should allow the effective shielding surface to remain as large as
possible, i.e., do not move the shield further away than absolutely necessary. As a general rule, the
shield has to be applied on both sides on PE, unless differently stated in the device manufacturers
documentation. As a basic principle, the shielding of these lines should not be interrupted. Using
this shielding can reduce the interference coupled into and out of the cable. The effectiveness of the
shielding heavily depends on the construction and the material of the shielding. The screening
effectiveness can be characterized by the so called transfer impedance. This effectiveness or
performance can be improved by keeping the transfer impedance as low as possible. The transfer
impedance is mainly affected by the following variables:
•The cable covering, which is the cable area actually covered by the shielding. It is normally
indicated as a percentage value and should be at least 85%.
•The shielding’s design. Possible design alternatives are braided cables or shieldings made of
metal conduit. These two types should be preferred when shielding is to be implemented.
•The contact (or transition) resistance between the individual stranded conductors of the shielding.
The performance of the shielding improves if the resistance is kept as low as possible.
The following diagram shows the transfer impedance for various cable types. By comparing the
cables individual design, the shielding effectiveness can be estimated and a suitable cable be
chosen.
Test standard Test Comment
EN61800-3: 2004 Conducted emissions
Category C1/C2
25m motor cable
Pass
EN61800-3: 2004 Conducted emissions
Category C2
100m motor cable
Pass
EN61800-3: 2004 Radiated emissions
Category C1/C2
25m motor cable
Pass
EN61800-3: 2004 Radiated emissions
Category C2
100m motor cable
Pass