Siemens SITRANS LR250 Operating Instructions Manual page 50

Radar transmitters profibus pa
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Connecting
5.3 Wiring setups for hazardous area installations
FISCO Concept
Note
For complete details and instructions regarding the FISCO Concept The FM/CSA connection
drawing number A5E02358161 can be downloaded from our website at:
Product page (http://www.siemens.com/LR250)
Go to Support > 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.
Under the FISCO evaluation concept, SITRANS LR250 has the following characteristics:
(input voltage) U
(input current) I
(input power) P
(internal capacitance) Ci
(internal inductance) Li
48
i
i
i
= 17.5 V
= 380 mA
= 5.32 W
= 0
= 0
SITRANS LR250 (PROFIBUS PA)
Operating Instructions, 08/2014, A5E32221386-AC

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