Endress+Hauser PROline prosonic flow 93 II2 GD Mode D'emploi page 55

PROline Prosonic Flow 93 FOUNDATION Fieldbus
!
Endress+Hauser
Proof of intrinsic safety
Proof of intrinsic safety for the intrinsically safe bus segment can be made by using one
of the following models:
• Entity model
• FISCO model
Both models differ from one another by their consideration of the cable. While the FISCO
model considers the transmission line as distributed inductance and capacitance, the
basis of this consideration for the Entity model is concentrated inductance and capac-
itance. The result of this is that lower quantities of power can be transmitted with the
Entity model into the Ex area, and that the number of field devices instrument that can
be operated on a power repeater is therefore lower than with the FISCO model.
In the case of failure, instruments from different manufacturers can be exchanged when
their safety-relevant data is taken into consideration. This data is: electrical parameters,
device group and category, and the temperature class.
Both these models are briefly described in the following.
The Entity model
The Entity model is based on the observation that the cable represents concentrated
inductance and capacitance. The result is that less electrical power can be transmitted
into the area subject to the risk of explosion when compared with the FISCO model.
The following conditions must be met in the safety according to the entity model consid-
erations:
Field device
Hazardous area
Maximum voltage
[U ]
i
Maximum current
[I ]
i
Maximum power
[P ]
i
Effective internal capacitance
[C ]
i
+ cable capacitance
Effective internal inductance
[L ]
i
+ cable inductance
Tab. 4: General dependencies
In addition, the following measures must be taken:
• determine permissible explosion group for the bus segment
• determine all effective energy stores (L
length)
• check locally supplied operating units for galvanic isolation
• harmonize temperature class and ambient temperature
Note:
Configuration example see Page 21
Mandatory
≥
≥
≥
≤
Maximum permitted external
≤
Maximum permitted external
, C , capacitance and inductance per unit
i i
<
Power supply
Safe area
Idle voltage of the
safety element [U ]
o
Short-circuit current
[I ]
o
[P ]
o
capacitance [C ]
o
inductance [L ]
o
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