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Connecting the Control Signals
5-5-3
Screening
5-5-4
Single-ended or double-ended connection?
5-5-5
Current signals ((0)4-20 mA)
48
For all signal cables the best results are obtained if the screening is con-
nected to both ends: the VSD side and the at the source (e.g. PLC, or com-
puter). See Fig. 41.
It is strongly recommended that the signal cables be allowed to cross mains
and motor cables at a 90 angle. Do not let the signal cable go in parallel with
the mains and motor cable.
In principle, the same measures applied to motor cables must be applied to all
control signal cables, in accordance with the EMC-Directives.
For all signal cables as mentioned in section 5-5-2 the best results are
obtained if the screening is connected to both ends. See Fig. 41.
Note Each installation must be examined carefully before applying the proper EMC
measurements.
Fig. 41 Electro Magnetic (EM) screening of control signal cables.
A current signal like (0)4-20 mA is less sensitive to disturbances than a 0-10 V
signal, because it is connected to an input which has a lower impedance (250
) than a voltage signal (20 k). It is therefore strongly advised to use current
control signals if the cables are longer than a few metres.
Control board
External control
(e.g. in metal housing)
Section 5-5
Pressure
sensor
(example)
Control consol
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