Rockwell Automation System Design for the Control of Electrical Noise - Manual (Page 42)

Publication GMC-RM001A-EN-P — July 2001
4-2 Shielding Wires, Cables, and Components
In the shielding example below the grey plastic wireway (front) is
shielded by 0.7 mm (0.03 in.) thick perforated and plated sheet steel.
The perforated steel is easy to cut and bend. You can safely route
very-dirty wires in the other (black) wireway behind the shield.
Note: By using grey colored wireway for clean zones and black for
dirty and very-dirty zones you will see more clearly when
shielding is necessary.
Figure 4.2
Shielding example
Ferrite Sleeves Shielded data cables grounded at both ends (important at high
frequencies) may carry noise current due to voltage differences
between the two ends. Because the shields have a low impedance,
currents may be quite high even though voltage is low. These currents
can cause spurious data reception.
By installing ferrite sleeves, the common-mode impedance of the
cable is greatly increased at HF thus blocking the noise currents
without affecting the signal currents.
In Figure 4.3 the capacitor grounding is very effective and avoids
no-grounding rules, but it’s awkward to implement.
’