DCS ADR24 Operations Instructions download pdf (Page 36)

36 VEGASON 51P … 53P

Electrical connection

The distributed resistance of the cable, in

conjunction with the output voltage of the

segment coupler and the current requirement

(VEGASON 10 mA) or the voltage require-

ment (VEGASON 9 V) of the sensor, deter-

mines the max. length of the cable.

In practical application of a PA bus branch,

the max. length of the cable is also deter-

mined (beside the required supply voltage

and max. current consumption of all partici-

pants on the PA bus branch) by the bus

structure and the type of segment coupler

used.

The cable length results from the sum of all

cable sections and the lengths of all stubs.

The length of the individual stubs must not

exceed the following lengths:

1 … 12 stubs 120 m (Ex: 30 m)

13 … 18 stubs 60 m (Ex: 30 m)

19 … 24 stubs 30 m (Ex: 30 m)

No more than 24 stubs are permitted,

whereby each branch longer than 1.2 m is

counted as a stub. The total length of the

cable must not exceed 1900 m (in Ex version

1000 m).

Ground terminal

The electronics housings of the sensors have

a protective insulation. The ground terminal in

the electronics is galvanically connected with

the metallic process connection. For sensors

with a plastic thread as process fitting, the

sensor grounding must be made by a

ground connection to the outer ground termi-

nal.

Screening

"Electromagnetic pollution“ caused by elec-

tronic actuators, energy cables and transmit-

ting systems has become so pervasive that

shielding for the two-wire bus cable is usually

a necessity. According to the Profibus speci-

fication the screening should be made on

both ends. To avoid potential equalisation

currents, a potential equalisation system

must be provided in addition to the screen-

ing.

According to specification, we recommend

the use of twisted and screened two-wire

cable, e.g.: SINEC 6XV1 830-5AH10 (Sie-

mens), SINEC L26XV1 830-35H10 (Siemens),

3079A (Belden).

Alternatively, when grounding at both ends in

non-Ex areas, the cable shielding can be

connected on one ground side (in the switch-

ing cabinet) via a capacitor (e.g. 0.1 µF;

250 V) to the ground potential. Make sure

that the ground connection has the lowest

possible resistance (foundation, plate or

mains earth).

Profibus PA in Ex environment

When used in Ex area, a PA bus with all con-

nected instruments must be carried out in

intrinsically safe protective class "i“. Four-wire

instruments requiring a separate supply

must at least have an intrinsically safe PA

connection. VEGA sensors for PA-Ex envi-

ronment are generally "ia” two-wire instru-

ments“.

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