VEGA VEGASON 64 Profibus PA - Manual (Page 24)

In systems with potential equalisation, connect the cable screen
directly to ground potential at the power supply unit, in the connection
box and at the sensor. The screen in the sensor must be connected
directly to the internal ground terminal. The ground terminal outside on
the housing must be connected to the potential equalisation (low
impedance).
In systems without potential equalisation, connect the cable screen
directly to ground potential at the power supply unit and at the sensor.
In the connection box or T-distributor, the screen of the short stub to
the sensor must not be connected to ground potential or to another
cable screen. The cable screens to the power supply unit and to the
next distributor must be connected to each other and also connected
to ground potential via a ceramic capacitor (e.g. 1 nF, 1500 V). The low
frequency potential equalisation currents are thus suppressed, but the
protective effect against high frequency interference signals remains.
The total capacitance of the cable and of all capacitors must not exceed
10 nF in Ex applications.
Take note of the corresponding installation regulations for Ex
applications. In particular, make sure that no potential equalisation
currents flow over the cable screen. In case of grounding on both sides
this can be achieved by the use of a capacitor or a separate potential
equalisation.
With the Exd version, the minus side of the signal output is galvanically
connected to ground via protective diodes. When connecting the
instrument to a grounded PLC, equalising currents can flow in case of
potential differences which can cause malfunctions. Make sure that
there is sufficient potential equalisation from the system side or realise
the connection via switching amplifier.
5.2 Connection procedure
Warning:
Before connecting to voltage supply, the plug connection between
transducer and remote electronics must be provided in idle condition
(see illustration below). Non-observance will damage the electronics!
Cable screening and
grounding
Installation with
Ex applications
24 VEGASON 64 • Profibus PA
5 Connecting to power supply
28787
-EN
-081127