Siemens SITRANS LR250 Operating Instructions Manual page 33

FISCO Concept
Under the FISCO evaluation concept, SITRANS LR250 has the following characteristics:
(input voltage) U
(input current) I
i
(input power) P
i
(internal capacitance) Ci
(internal inductance) Li
Note: For complete details and instructions regarding the FISCO Concept The FM/CSA
connection drawing number A5E02358161 can be downloaded from the product page of
our website at: www.siemens.com/LR250. Go to More Info > Installation Drawings >
Level Measurement > SITRANS LR250.
The FISCO Concept allows interconnection of Intrinsically Safe apparatus to associated
apparatus not specifically examined in such combination. The criteria for interconnection
is that the voltage (Ui or Vmax), the current (Ii, or Imax) and the power (Pi, or Pmax) which
Intrinsically Safe apparatus can receive and remain Intrinsically Safe, considering faults,
must be equal to or greater than the voltage (Uo or Voc or Vi), the current (lo or Isc or li),
and the power (Po or Pmax) levels which can be delivered by the associated apparatus,
considering faults and applicable factors. In addition, the maximum unprotected
capacitance (Ci) and inductance (Li) of each apparatus (other than the termination)
connected to the fieldbus must be less than or equal to 5 nF and 10 µH respectively.
In each segment only one active device, normally the associated apparatus, is allowed to
provide the necessary energy for the fieldbus system. The allowed voltage Uo (or Voc or
Vt) of the associated apparatus is limited to the range of 14V dc to 24V dc. All other
equipment connected to the bus cable has to be passive, meaning that they are not
allowed to provide energy to the system, except for a leakage current of 50 µA for each
connected device. Separately powered equipment needs a galvanic isolation to assure
that the Intrinsically Safe fieldbus circuit remains passive.
7ML19985KL01
= 17.5 V
i
= 380 mA
= 5.32 W
= 0
= 0
SITRANS LR250 (FF) – OPERATING INSTRUCTIONS Page 27