Section 1 Introduction FISCO (Fieldbus Intrinsically Safe Concept)
3BDS009029R5001 B 23
FISCO (Fieldbus Intrinsically Safe Concept)
To render the proof of Intrinsic Safety as simple as possible, the so-called FISCO
model was developed. FISCO stands for Fieldbus Intrinsically Safe COncept. The
German Federal Physical Technical Institute (PTB) developed the FISCO model
and has published it in Report PTB-W-53 "Examination of intrinsic safety for
fieldbus systems“.
This model is based on the following prerequisites:
To transmit power and data, the bus system uses the physical configuration defined
by IEC 61158-2. This is the case for PROFIBUS PA.
• Only one active source is permitted on a bus segment (in this case the Linking
Device). All other components work as passive current sinks.
• The basic current consumption of a bus station is at least 10 mA.
• It must be ensured for each bus station that
– Ui> Uo of the Linking Device/Power Link
– Ii> Io of the Linking Device/Power Link
– Pi> Po of the Linking Device/Power Link.
• Each bus station must fulfill the following requirement:
– Ci < 5 nF
– Li < 10 µH
• Total length of the PA segment, incl. spurs, to be kept
– when using passive T-junctions in EEx ia IIC applications <
1000 m
– when using Multibarries or in non intrinsically safe areas <
1900 m
• The permissible spur line length for Ex applications is 30 m per spur line. The
definition of the spur line must be observed in this connection.
• The transmission line that is used must conform to the following cable
parameters:
– resistor coating: 15 Ohm/km < R’ < 150 Ohm/km
– inductance coating: 0.4 mH/km < L’ < 1 mH/km
To Next Page
Loading...
