Vega VEGAPULS 43 Profibus PA Bedienungsanleitung PDF herunterladen (Seite 29)

VEGAPULS 43 – Profibus PA 29

Electrical connection

The distributed resistance of the cable, in

conjunction with the output voltage of the

segment coupler and the current requirement

(VEGAPULS 10 mA) or the voltage require-

ment (VEGAPULS 9 V) of the sensors, deter-

mines the max. cable length.

In a 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 structure

and the type of segment coupler used.

The cable length results from the sum of all

cable sections and the length 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)

More than 24 stubs are not 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 housing is galvanically con-

nected with the metallic process connection.

For sensors with a plastic thread as process

fitting, the sensor must be grounded through

a ground connection to the exterior ground

terminal.

Screening

„Electromagnetic pollution“ caused by elec-

tronic actuators, energy cables and transmit-

ting systems has become so pervasive that

shielding for normal two-wire bus cable is

usually a necessity. According to the Profibus

specification, the screening should be

grounded on both ends. To avoid potential

equalisation currents, a potential equalisation

system must be provided in addition to the

screening.

According to the specification, we recom-

mend the use of twisted and screened two-

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

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

mens), 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 an Y capacitor

1)

to ground

potential. Make sure that the ground connec-

tion has the lowest possible resistance (foun-

dation, plate or mains earth).

Profibus PA in Ex environment

When used in Ex area, the PA bus (including

all connected instruments) must be

configured as intrinsically safe protection

class „i“. Four-wire instruments requiring

separate supply must at least have an intrin-

sically safe PA connection. VEGA sensors for

PA Ex environment are generally „ia two-wire

instruments“.

1)

max. 10 nF, e.g. voltage resistance 1500 V,

ceramic

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