Yokogawa FVX110 - Manual (Page 15)

<2. Handling Cautions>
2-5
IM 01S01C01-01EN
Note: In the rating 1, the output current of the barrier must
be limited by a resistor “Ra” such that Io=Uo/Ra. In the
rating 2 or 3, the output characteristics of the barrier
must be the type of trapezoid which are certified as
the FISCO model (See “FISCO Rules”). The safety
barrier may include a terminator. More than one field
instruments may be connected to the power supply
line.
● FISCO Rules
The FISCO Concept allows the interconnection
of intrinsincally safe apparatus to associated
apparatus not specifically examined in such
combination. The criterion for such interconnection
is that the voltage (Ui), the current (Ii) and the power
(Pi) which intrinsically safe apparatus can receive
and remain intrinsically safe, considering faults,
must be equal or greater than the voltage (Uo,
Voc, Vt), the current (Io, Isc, It) and the power (Po)
which can be provided by the associated apparatus
(supply unit).
Po ≤ Pi, Uo ≤ Ui, Io ≤ Ii
In addition, the maximum unprotected residual
capacitance (Ci) and inductance (Li) of each
apparatus (other than the terminators) connected to
the fieldbus must be less than or equal to 5 nF and
10 µH respectively.
Ci ≤ 5nF, Li ≤ 10µH
In each I.S. fieldbus segment only one active
source, normally the associated apparatus, is
allowed to provide the necessary power for the
fieldbus system. The allowed voltage(Uo, Voc,Vt)
of the associated apparatus used to supply the
bus cable must be limited to the range of 14 V dc
to 17.5 V dc. All other equipment connected to
the bus cable has to be passive, meaning that the
apparatus is not allowed to provide energy to the
system, except to a leakage current of 50 µA for
each connected device.
Supply unit
Trapezoidal or rectangular output characteristic only
Uo = 14...17.5 V (I.S. maximum value)
Io according to spark test result or other
assessment. No specification of Lo and Co is
required on the certificate or label.
Cable
The cable used to interconnect the devices needs
to comply with the following parameters:
Loop resistance R': 15...150 Ω/km
Inductance per unit length L': 0.4...1 mH/km
Capacitance per unit length C': 45...200 nF/km.
C'=C' line/line + 0.5 C' line/screen, if both lines
are floating or C'=C' line/line + C' line/screen, if
the screen is connected to one line.
Length of spur cable: max. 60 m
Length of trunk cable: max. 1 km (Group IIC) or
5 km (Group IIB)
Length of splice: max.1m
Terminators
At each end of the trunk cable an FM approved line
terminator with the following parameters is suitable:
R = 90...100 Ω
C = 0...2.2 mF
System evaluations
The number of passive device like transmitters,
actuators, hand held terminals connected to
a single bus segment is not limited due to I.S.
reasons. Furthermore, if the above rules are
respected, the inductance and capacitance of the
cable need not to be considered and will not impair
the intrinsic safety of the installation.
SAFE AREA HAZARDOUS AREA
F0204.ai
Terminator
(FISCO Model)
Ex i
Field Instruments
(Passive)
Hand-
held-
Terminal
Supply Unit and
Safety Barrier
(FISCO Model)
Terminator
Data
U
U
I
I.S. fieldbus system complying with FISCO model