Since the interference signals must not enter into the shielded area, the poten‐
tial of the shielded housing must also be the reference potential for the filter
circuits.
Filter circuits or filter components must therefore be placed precisely where the
lines enter the shielded area. If the filters are placed inside or outside the shield
wall, this can lead to a field coupling between the filtered and unfiltered lines.
The connection to the reference potential must be as low impedance as pos‐
sible and therefore it is necessary for there to be contact over a large surface
area between the filter housing, which is usually metallic, and the shield wall of
the device. Pig tails may not be used to make such a contact.
Line filters
Typical line filters have a metal housing that has to be connected to the earth
wire (PE) for safety reasons and consist of a current-compensated choke (see
following figure) consisting of Y-capacitors, which are connected to the metal
housing on one side, and X-capacitors (connected between the phases or be‐
tween phase and neutral conductor).
Fig.4-33:
Line filters
The desired filter effect is basically governed by the correct contact between
the filter housing and the shielded housing of the device. The line filters must
therefore be placed directly at the inlet to the shielded housing of the device
and a very good connection must be made between the metal housing of the
filter and the shielded housing of the device. If placement at the inlet is not
possible for reasons of space, partly shielded connection lines must be used.
In doing so the following procedure is to be followed:
If the filter is placed inside the shielded housing of the device, the line cable
must be shielded from the inlet through to the line filter and the cable shield
contacted on both ends. This prevents the propagation of interference on the
line cable inside the device. It also prevents any electromagnetic fields that may
be present inside the device from penetrating the line cable.
Device
Clips for screen contacting
Line filter
Line cable outside
the housing
(shielded or unshielded)
Shield is required in this section!
L, N and PE - as short as possible!
Line filter well-
connected to the
housing.
Fig.4-34:
Correct connection of a compact line filter within the device
If the line filter is placed outside the shielded housing, the device connection
line must be shielded from the line filter through to the shielded housing of the
DOK-SUPPL*-VCH*08.1***-PR02-EN-P
Rexroth IndraControl VCH 08.1 Hand-held Terminal
Bosch Rexroth AG
47/117
Technical Data