GE FVP110 Maintenance Manual page 30

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Note 4. FISCO rules
The FISCO concept allows the interconnection of intrinsically 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) and the power
(Po) which can be provided by the associated apparatus (supply unit). 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.
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 of the associated apparatus used to supply the bus is limited to the range of 14 V dc.
to 24 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 to 24 V (I.S. maximum value)
Io according to spark test result or other assessment,
e.g. 133 mA for Uo = 15 V (Group IIC, rectangular characteristic)
No specification of Lo and Co in the certificate and on the label.
Cable
The cable used to interconnect the devices needs to comply with the following
parameters:
loop resistance R': 15 to 150 Ω/km
inductance per unit length L': 0.4 to 1 mH/km
capacitance per unit length C': 80 to 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. 30 m (Group IIC) or 120 m (Group IIB)
length of trunk cable: max. 1 km (Group IIC) or 1.9 km (Group IIB)
FVP 110 Fieldbus Valve Positioner Manual
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