Endress+Hauser PROline prosonic flow 93 II2 GD Mode D'emploi page 67

PROline Prosonic Flow 93 FOUNDATION Fieldbus
Endress+Hauser
• Fieldbus device Cerabar S:
I = 10.5 mA (basic current)
B
U = 9...32 V (perm. operating voltage)
B
I = 0 mA (fault current)
FDE
I = 0 (< I )
startup 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
+ Σ L
L = L
SEG main.
= 580 m + 80 m
= 660 m
Checking the conditions:
Consideration
L < 1000 m
SEG
660 m < 1000 m
L < 30 m
spurs
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
event of a fault I for the FDE (Fault Disconnect Electronics) and the current for the
FDE
data modulation I (+9 mA) you can determine the minimum supply current that the
MOD
fieldbus power supply must supply.
If, on switching on the device, the startup I
rent, then the startup current must be taken into consideration in the calculation. The
response current for the FDE (I
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
≤
I I
SEG S
where
Σ
I = + max I
SEG IB
:
SEG
spurs
Condition met?
✓
Yes
✓
Yes
of the field devices plus the response current in the
B
current is greater than the basic cur-
startup
) is calculated for each field device from the differ-
FDE
+ I + I
FDE MOD startup
<
:
SEG
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