TECO F33 Series, Инструкция по эксплуатации, Страница: 29 / 192

26 Control Connections
4.5.5 Current signals ((0)4-20 mA)
A current signal like (0)4-20 mA is less sensitive to dis-
turbances than a 0-10 V signal, because it is connected
to an input which has a lower impedance (250
Ω
) than
a voltage signal (20 k
Ω
). It is therefore strongly advised
to use current control signals if the cables are longer
than a few metres.
4.5.6 Twisted cables
Analogue and digital signals are less sensitive to inter-
ference if the cables carrying them are “twisted”. This is
certainly to be recommended if screening cannot be
used. By twisting the wires the exposed areas are mini-
mised. This means that in the current circuit for any
possible High Frequency (HF) interference fields, no
voltage can be induced. For a PLC it is therefore impor-
tant that the return wire remains in proximity to the sig-
nal wire. It is important that the pair of wires is fully
twisted over 360°.
4.6 Connecting options
The option cards are connected by the optional connec-
tors X4 or X5 on the control board see Fig. 28, page 21
and mounted above the control board. The inputs and
outputs of the option cards are connected in the same
way as other control signals.