Yokogawa digitalYEWFLO (DY-FF) - Manual (Page 57)

<10. EXPLOSION PROTECTED TYPE INSTRUMENT>
10-8
IM 01F06F00-01EN
• FISCO rules
The FISCO Concept allows the interconnection of intrinsically safe apparatus to Safety Barrier not
specifi cally examined in such combination. The criterion for such interconnection is that the voltage (Vmax),
the current (Imax) 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 (1o, Isc, It,)
and the power (Po) which can be provided by the Safety Barrier (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 5nF and 10
μH respectively.
In each I.S. Fieldbus segment only one active source, normally the Safety Barrier, is allowed to provide the
necessary power for the Fieldbus system. The allowed voltage (Uo, Voc, Vt) of the Safety Barrier used to
supply the bus must be limited to the range of 14V d.c. to 24V d.c. 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. Separately powered equipment needs a galvanic
isolation to insure that the intrinsically safe Fieldbus circuit remains passive.
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 ... 1mH/km
Capacitance per unit length C’: 80 ... 200 nF/km
C’ = C’ line/line + 0.5 C’ line/screen, if both lines are fl oating
or
C’= C’ line/line + C’ line/screen, if the screen is connected to one line
Length of spur Cable: max. 30m
Length of trunk cable: max. 1Km
Length of splice: max. 1m
Terminators
At each end of the trunk cable an approved line terminator with the following parameters is suitable:
R = 90 ... 100
Ω
C = 0 ... 2.2 μF.
System evaluation
The number of passive devices like transmitters, actuators, 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.
Installation Notes For FISCO and Entity Concepts:
1. The Intrinsic Safety Entity concept allows the interconnection of FM Approved Intrinsically safe devices
with entity parameters not specifi cally examined in combination as a system when:
Uo or Voc or Vt ≤ Vmax, Io or Isc or It ≤ Imax, Po ≤ Pi. Ca or Co ≥ ∑Ci + ∑Ccable, For inductance use
either La or Lo ≥ ∑Li + ∑Lcable or Lc/Rc ≤ (La/Ra or Lo/Ro) and Li/Ri ≤ (La/Ra or Lo/Ro)
2. The Intrinsic Safety FISCO concept allows the interconnection of FM Approved Intrinsically safe devices
with FISCO parameters not specifi cally examined in combination as a system when:
Uo or Voc or Vt ≤ Vmax, Io or Isc or It ≤ Imax, Po ≤ Pi.
3. The Safety Barrier shall be a linear supply for Entity installations and either a linear supply or a trapezoidal
supply for FISCO Installations.
4. Dust-tight conduit seals must be used when installed in Class II and Class III environments.
5. Control equipment connected to the Safety Barrier must not use or generate more than 250 Vrms or Vdc.
6. Installation should be in accordance with ANSI/ISA RP12.06.01 (except chapter 5 for FISCO Installations)
“Installation of Intrinsically Safe Systems for Hazardous (Classifi ed) Locations” and the National Electrical
Code® (ANSI/NFPA 70) Sections 504 and 505.
7. The confi guration of Safety Barrier must be FM Approved under the associated concept.
8. Safety Barrier manufacturer’s installation drawing must be followed when installing this equipment.
9. The (Product Name) Series are Approved for Class I, Zone 0, applications. If connecting AEx[ib] Safety
Barrier or AEx ib I.S. Apparatus to the (Product Name) Series the I.S. circuit is only suitable for Class
I, Zone 1, or Class I, Zone 2, and is not suitable for Class I, Zone 0 or Class I, Division 1, Hazardous
(Classifi ed) Locations.”
10. No revision to drawing without prior FM Approval.