Yokogawa EJA115 - Manual (Page 10)

IM 01C22T03-00E 2-3
2. HANDLING CAUTION
᭹ 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 intrinsi-
cally safe apparatus can receive and remain intrinsi-
cally 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).
P o
Ϲ P
i , U o
Ϲ U
i , I o
Ϲ I
i
In addition, the maximum unprotected residual capaci-
tance (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
␮H respectively.
C i
Ϲ 5nF, L
i
Ϲ 10␮H
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
␮A 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 assess-
ment. 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 Rc: 15...150 /km
Inductance per unit length Lc: 0.4...1 mH/km
Capacitance per unit length Cc: 80...200 nF/km
Length of spur cable: max. 30 m (Group IIC and
IIB)
Length of trunk cable: max. 1 km (Group IIC) or 5
km (Group IIB)
Terminators
At each end of the trunk cable an approved line
terminator with the following parameters is suitable:
R = 90...102
C = 0...2.2
␮F (0.8...1.2 ␮F is required in operation)
The resistor must be infallible according to IEC 60079-
11.
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. Further-
more, 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 installa-
tion.
SAFE AREA HAZARDOUS AREA
F0205.EPS
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