Power repeater / power supply according to IEC 61158-2
instrumentFOUNDATION FieldbusIntroduction to intrinsic safety for
Subject to reasonable modifications due to technical advances.
Copyright Fuchs, Printed in Germany
Fuchs Group • Tel.: Germany (06 21) 7 76-0 • USA (330) 4 25 35 55 • Singapore 7 79 90 91 • Internet http://www.pepperl-fuchs.com
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instrumentFOUNDATION FieldbusIntroduction to intrinsic safety for
field bus systems
Fuchs GmbH offers power repeaters with an intrinsically safe interface. They
are used if an intrinsically safe bus segment is in operation. The following illustration
shows the topology of an intrinsically safe bus segment of this nature:
Figure 4.1: Topology of an intrinsically safe bus segment
A verification of intrinsic safety must be performed for the intrinsically safe bus seg-
ment.
To make this demonstration as simple as possible, two different models have been
developed, the FISCO model and the Entity model of the field bus foundation. The two
are distinguished in a number of ways, including the way the cable is considered.
While the FISCO model considers the transmission line as distributed inductance and
capacitance, the basis of this consideration for the Entity model is concentrated induc-
tance and capacitance. The result of this is that lower quantities of power can be
transmitted with the Entity model into the Ex area, and that the number of field device-
sinstrument that can be operated on a power repeater is therefore lower than with the
FISCO model.
These two models will be briefly explained in the following section.
The spur in the example above is determined for each station by the
distance between the T piece and the field device or, in the case where
a distributor is located in between in the circuit, by the distance between
the T piece and the distributor plus the distance between the distributor
and the field device
Note the national requirements for explosion protection by intrinsic
safety. Which of the two ways to view the matter is determined here.
Power repeater
intrinsically safe
Not intrinsically
safe
Bus segment
Bus segment
Fieldbus
terminator
safe
sp
ur
distributor
