WIKA SC64 - Handbuch (Seite 14)

14 WIKA operating instructions models SC58, SC64
14054366.01 10/2012 GB/D
GB
General rules for installation
In the installation of processor-controlled control systems, the following
principles must be observed:
1. If possible, do not allow any interference sources, i.e. implement
interference suppression and minimise the level of interference
(noise suppression in accordance with VDE 0875, implementation in
accordance with VDE 0874). In principle, eliminate an interference at
its point of generation. Introduce the suppression devices as close as
possible to the interference source.
2. Place unavoidable interference sources far away from the control
systems.
3. All sensor and signal wires must be separated from the powered and
mains wiring, in order to avoid capacitive or inductive coupling.
4. Use screened measuring cable, and ground the screen. Only provide
a single common ground connection, in order eliminate ground loops
and fault currents.
5. It is advisable to provide a separate power cable for the control
system's power supply, so that noise levels introduced via the power
cable are less strong and voltage drops when switching heavy loads
are less noticeable.
6. When switching inductive loads, cut out the resulting induction
voltages with protective elements, which will be different for direct and
alternating current systems.
In direct current systems, in the simplest case, a flyback diode with a
high surge current resistance can limit the induction voltage.
With alternating current operation, an RC filter is often used, which
is placed directly on the inductance and must be matched to it. The
determination of the filter values can made by calculation, if the
inductance of the coil is known, or experimentally. Only use approved
capacitors in accordance with VDE 0565.
The installation of an RC filter at the controller‘s switch contact is very
problematic, as even when the switch is open, a reactive current flows
through the filter. This may be greater than the holding current of the
contactor, whereby a closed contact will no longer open.
6. Commissioning, operation