Endress+Hauser PROline promag 53 - Page 61

Proline Promag 53 FOUNDATION Fieldbus
Endress+Hauser 25
0
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Step 2 – technical safety considerations
This step uses the existing data to check whether connecting the equipment is permis-
sible from the point of view of technical safety. The conditions shown in Table 5
(Page 22) apply to these safety considerations. First the functional data of the equip-
ment used is compared. In this consideration it is crucial that the maximum output volt-
age and output current of the bus power supply does not exceed the permitted maxi-
mum input voltage and input current of the individual field devices. Here we consider
possible error behaviour by the bus power supply that could result in the stated maxi-
mum values on the intrinsically safe sides.
In addition to these values the limit values and the maximum permissible external
capacitance C
o
and inductance L
o
must be observed for the supply circuit. To do this
the sum of all effective inductance and capacitance in the hazardous area is formed (the
internal capacitance of the bus termination is assumed to be 0). The resulting value
must be less than the maximum permissible value specified by the fieldbus power
supply.
The equivalent concentrated capacitance and inductance in the hazardous area is
calculated as follows:
C
eff.
=(C
i/Promag 53
x 2) + (C
i/Cerabar S
x 2) + C’
eff./cable
+ C
i/bus termination
= (5 nF x 4) + 95.6 nF
= 115.6 nF
L
eff.
=(L
i/Promag 53
x 2) + (L
i/Cerabar S
x 2)+ L’
eff./cable
=(10 µH x 4) + 383.1 µH
=423.1 µH
Intrinsically safe equipment Condition Associated equipment
MTL 5053
Condition met?
Promag 53
U
i
= 30 V ≥ U
o
= 22 V ✓ Yes
I
i
= 500 mA ≥ I
o
= 216 mA ✓ Yes
P
i
= 5.5 W ≥ P
o
= 1.2 W ✓ Yes
As a further condition galvanic isolation must be provided due to the local
supply
✓ Yes
Cerabar S
U
i
= 24 V ≥ U
o
= 22 V ✓ Yes
I
i
= 250 mA ≥ I
o
= 216 mA ✓ Yes
P
i
= 1.2 W ≥ P
o
= 1.2 W ✓ Yes
FBT1
U
i
= 30 V ≥ U
o
= 22 V ✓ Yes
P
i
= 1.2 W ≥ P
o
= 1.2 W ✓ Yes