Bosch REXROTH IndraControl VEH 30.2, Руководство по планированию проекта

Страница: 46 / 112

Multi-stage filters are often necessary for filtering. Nearly all filter combina‐
tions contain Y-capacitors. Y-capacitors are capacitors that are connected to
the filter housing for the dissipation of interference currents. In order for these
filters to function correctly, the housing must be connected to a stable refer‐
ence potential.
Since the interference signals must not enter into the shielded area, the po‐
tential of the shielded housing must also be the reference potential for the fil‐
ter 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-impedant as possi‐
ble. Therefore a contacting over a large surface area is necessary 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 pro‐
tective conductor (earth wire; PE) for safety reasons. Typical line filters (see
fig. 4-6 "Line filters" on page 44 ) consist of a current-compensated choke,
of Y-capacitors, which are connected to the metal housing on one side, and
of X-capacitors.
Fig.4-6: 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 the metal housing of the filter must be well-contacted to 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 follow‐
ing 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
must be contacted on both ends. This prevents the propagation of interfer‐
ence 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.
Bosch Rexroth AG DOK-SUPPL*-VEH*30.2***-PR03-EN-P
Rexroth IndraControl VEH 30.2 Hand-Held Terminal
44/109
Technical Data