Installation
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3.15.2
Wiring
Lay the signal lines such that they are separate from the power cables. Please note that AC
voltages and current spikes can induce stray voltages in neighboring lines. Shielded cables
should therefore be used for EMC-tested devices.
Grounding bars can be laid separately from the shielding (see IEC/EN 60079-14). The
shielding is grounded at one point (to PA in explosion-hazardous areas).
Field wiring
Depending on the application, the shielding of the wiring must be grounded at one point or at
both ends. If possible, avoid grounding at both ends to prevent ground loops and ensure no
current flows through the shielding in the case of a ground potential difference.
Sound results can be obtained with grounding at one end of the cable if the cable is laid on a
grounded metal cable support. The metal frame in the immediate vicinity of the conductor
ensures that only small areas are exposed to the field, so that interference is largely reduced.
Digital inputs are normally controlled by NAMUR proximity switches with a low-impedance
signal. In this case, noise has a far lower impact than in circuits containing open switches that
do not have an additional resistor circuit. For this reason, do not connect digital inputs to
exposed wiring.
The analog signals of resistive sensors or thermocouples are particularly susceptible to noise.
Signal converters have built-in filters to reduce this noise. The filters can be switched on if
fluctuations in the measuring signal cannot be reduced sufficiently by other means. For more
information, refer to the software manual for the com unit used.
Eliminating noise
The following measures can improve power.
1. Install power filters in power lines.
Please make sure that supply cables leading to power filters are laid separately from other
cables to ensure that any filtered noise is not picked up again.
2. Fit surge protection filters in signal lines.
3. Change to galvanically isolated circuits.
Danger!
Explosion hazard due to improper installation
Improperly installed wiring can cause explosive mixtures to ignite.
Observe the wiring specifications set out in IEC/EN 60079-14 for laying lines in an explosion-
hazardous area.
