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DOK-SUPPL*-VEH*30.2***-PR03-EN-P
Rexroth IndraControl VEH 30.2 Hand-Held Terminal
Coupling paths
4.13.3
EMC Measures
Shield system
Interference suppressors, filter
components
The transfer of interference from an interference source to an interference
sink can take place via various coupling paths. Coupling paths very often ex‐
ist of two or more parallel lines running closely together. The coupling is a
field coupling that takes place at low frequencies either via the electrical field
(capacitive coupling) or via the magnetic field (inductive coupling). At high fre‐
quencies and with corresponding expansion of the parallel running lines one
speaks about an "electromagnetic coupling" due to close linking of both field
types. Direct coupling can occur when electrical circuits from the interference
source and electrical circuits from the interference sink have common line
components If there is a large distance between an interference source and
an interference sink then one speaks of "radiation coupling".
In principle, all devices should be designed in such a way as to function relia‐
bly in the planned environment and in doing so should not interfere with other
systems. The IndraControl VEH 30.2 devices meet these requirements. It is
not necessary to use any of the EMC measures described below if the speci‐
fied additional units, cables and wiring are used. However, additional EMC
measures may be necessary for various reasons. The following text is de‐
signed to help the user to correctly implement additional EMC measures, if
required.
Electromagnetic emission problems and immunity problems often occur in
products at the same time. Likewise, EMC measures are mostly effective in
the case of both emission problems and immunity problems.
Shielding fulfils two main tasks. On the one hand, the penetration of electro‐
magnetic fields into sensitive electronic parts is prevented. On the other
hand, the radiation of electromagnetic fields is also to be prevented. A com‐
plete EMC shield consists of a shielded housing, which protects the sensitive
electronics and prevents it from transmitting interference, and cable shields
that shield the sensitive interface signals and prevent the device from trans‐
mitting interference via its interfaces.
The cable shield connects two shielded houses. Therefore the cable shield
must be connected directly to the shielded housings of the sensitive electron‐
ics (connection points). Particular attention should be paid to the connection
between the cable shield and the shielded housings of the devices. In order
that the shield effect is maintained even at higher frequencies, ensure that
the cable shield connects to the largest possible surface area and thereby
acts as a continuation of the device's shielded housing. Pig tail connections
are not suitable.
It may be necessary to earth cable shields and shielded housings for safety
reasons but this is not an effective EMC measure.
Filtering is always necessary when unshielded signal and power supply lines
are brought into shielded areas. Alongside the wanted signals, these lines of‐
ten also carry interference signals that must not enter into shielded areas. Fil‐
ters should therefore guarantee the interference immunity of the device but
should also prevent the emission of interference from the device via unshiel‐
ded lines.
Unshielded lines are usually used when the wanted signals that are carried
are of a very low frequency. The normally high frequency interference signals
are separated from the wanted signals by means of frequency selective filter‐
ing with the aid of low-pass filtering. Low-pass filters must be sized in such a
way that the lower frequency wanted signals can pass through and the higher
frequency interference signals are filtered.
Bosch Rexroth AG
43/109
Technical Data
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