Endress+Hauser PROline promag 53 - 4.5 Degree of Protection

Proline Promag 53 FOUNDATION Fieldbus
28 Endress+Hauser
<
0
• Fieldbus device Cerabar S:
I
B
= 10.5 mA (basic current)
U
B
= 9...32 V (perm. operating voltage)
I
FDE
= 0 mA (fault current)
I
startup
=0 (< I
B
)
Step 2 – calculation of cable length and checking of network structure
An approved maximum length of 1000 meters has been set with the FISCO model for
EEx ia IIC applications in order that the inductance and capacitance of the fieldbus
cable can be ignored when used in hazardous area applications. This length comprises
the length of the main cable and the total length of the drop cables together. In addition,
it must be taken into account that the approved maximum length of a drop cable is
30 m.
Calculation of actual cable length L
SEG
:
L
SEG
=L
main.
+ Σ L
spurs
= 580 m + 80 m
=660 m
Checking the conditions:
If one of the conditions is not met then the network structure must be revised.
Step 3 – current calculation
The number of field devices that can be connected to the H1 segment depends on the
fieldbus power supply selected (supply voltage and supply current) and the current
consumption of the field devices. Thus, the number of devices that can be connected
is reduced if a field device consumes a basic current of more than 10 mA, e.g. 20 mA.
By adding up the basic currents I
B
of the field devices plus the response current in the
event of a fault I
FDE
for the FDE (Fault Disconnect Electronics) and the current for the
data modulation I
MOD
(+9 mA) you can determine the minimum supply current that the
fieldbus power supply must supply.
If, on switching on the device, the startup I
startup
current is greater than the basic cur-
rent, then the startup current must be taken into consideration in the calculation. The
response current for the FDE (I
FDE
) is calculated for each field device from the differ-
ence between the maximum current in the event of a fault and the basic current. The
field device with the greatest response current is taken into consideration in the current
balance sheet.
Provided that no more than one FDE responds, the following condition must be taken
into consideration in the calculation of the segment current I
SEG
:
I
SEG
≤ I
S
where
I
SEG
= Σ
IB
+ max I
FDE
+ I
MOD
+ I
startup
Consideration Condition met?
L
SEG
< 1000 m
660 m < 1000 m
✓ Yes
L
spurs
< 30 m ✓ Yes