Power repeater / power supply according to IEC 61158-2
FOUNDATION FieldbusGeneral
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
D
a
te
of
is
su
e1
2.
02
.2
00
2
14
missioning Manual.
Current calculation
Power is fed to the field bus instrumentsfield bus instruments from the bus. They act
as current sinks. The current consumption of each station from the bus line must be
at least 10 mA for Ex applications. There are no restrictions for non-Ex applications.
Power repeaters always have a current limit. The amount of the current value de-
pends on whether the power repeater is a non Ex power repeater, a power repeater
in accordance with the FISCO model or a power repeater according to theEntity mod-
el. You must ensure that the current consumption of all stations is less than the cur-
rent the segment coupler is capable of providing. The following applies:
I
out_Power_Repeater
>
Σ
I
in_field devices
The current consumption of the field devices determines the maximum number of sta-
tions per field bus segment. For example, field devices with a current consumption of
22.8 mA are used, 4 field devices can be connected to one segment for Ex applica-
tions according to the FISCO model.
If the current consumption per field device falls to 10 mA, 10 field devices can be con-
nected.
Dimensioning may be especially critical in the case of 10 field devices, since in the
event of an error (a fault in one of the field bus instrumentsfield bus instruments) it
may happen that this field device receives a higher current that the specified basic
current from the bus line. Under worst case conditions, it may happen that the entire
field bus segment is destroyed by a defective slave.
To avoid this, some field bus devices offer the Fault Disconnect Electronic (FDE). This
is an electronic current limitation that limits additional current consumption of a defec-
tive slave in a failure case. This I
FDE
can also vary between field bus instrumentsfield
bus instruments. For details, see the relevant data sheet. If an error case is included
in the current calculation, the situation described above changes as follows:
I
out_Power_Repeater
> I
FDE
+
Σ
I
in_field devices
This means that when taking into account an error and a current consumption of
10 mA per slave, 9 stations can still be operated on a segment.
