14.3.2.3
Ferrites
Ferrites operating via data lines work in a similar way to current-compensating
chokes. The wanted signals (see illustration) can pass unhindered and the
interference signals are damped. A fundamental difference from current-com-
pensating chokes is that in the case of ferrites the application range takes place
at higher frequencies and therefore the material losses are responsible for the
damping and the interference is not reflected, as in the case of inductance, but
is converted into heat.
Fig.14-10:
Current flow for ferrites
I
S
... Interference current
I
B
... Operating current
1
... Ferrite
2
... Data lines
14.3.2.4
Prevention of couplings
Coupling between interference sensitive signals (e.g. analogue signals) and
the lines that carry the interference signals (e.g. motor lines) can be reduced
by laying cables separately.
14.3.3
EMC measures on KeTop
The KeTop is designed for industrial applications. Considerable electromag-
netic and electrostatic interference can occur in this environment. For this
reason special emphasis was placed on interference immunity and data se-
curity in the design of the device. The EMC design implemented and described
below considers all the above named sources of interference and the possible
coupling paths.
●
All shielding and filter measures (filtered power supply) in the KeTop are
carried out directly on the printed circuit board.
●
The special design of the KeTop cable guarantees interference immunity
even for greater connection lengths, i.e. the data lines (communication sig-
nals) are shielded and so they are separated from the control lines (power
supply, enabling button, emergency off, key-operated switch etc.) inside
the KeTop cable.
●
Power supply lines in the control cabinet are usually unshielded. They are
therefore laid outside the KeTop cable shield in order to prevent a coupling
with the sensitive data lines.
●
The unshielded control and power supply lines are either filtered on entry
into the shielded housing of the KeTop or separated from the electronics
in such a way that any interference signals carried by these lines cannot
affect the internal electronics of the KeTop.
CE Conformity, Directives and Standards
© KEBA 2009
User's Manual V1.50
149