User's Manual

Electrical installation
Page 14
Figure 7 Grounding cable shield with RS-485 and HART / analog output signal
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Figure 8 Selecting terminal resistor in RS-485 cabling
The shielding of the RS-485 and HART / analog output signals must be connected to ground at
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both sides of the cable. There can be a potential difference between tank ground and ground in the
control room. Therefore, capacitors should be applied in the shield grounding between tank and
control room, preferably in (one of) the junction box(es). Capacitance value: 10 to 100 nF. The
capacitor can be located in a terminal. Such devices are available from for instance Phoenix.
At the end of a RS-485 transmission
line a 120 Ω resistor must be placed
(figure 6).
On the ICU_RS-232C/485
communication board the terminal
resistance can be connected by
means of jumper 1 (figure 8).