Dräger Safety Barrier Zone 2 Gebrauchsanweisung Seite 9

3.1 Example for calculation of the cable length
The example is applicable for bay units with L
Safety barrier for gas group IIC:
Max. connectable capacity C :
o
Max. connectable inductance L :
o
Internal resistance R :
i
Series diode voltage U :
D
Max. inductance resistance ratio
L
o
------ :
R
o
Maximum cable length l
max
L
o
------
R
l
o
= ------ -
max inductance resistance ratio
max Induktivitätswiderstandsverhältnis
L
K
------ -
R
K
Maximum cable length l
max
C – C
83 nF 0 F
–
l o i
----------------- - ---------------------------------- -
l = =
max capacity
max Kapazität
C 120 nF/km
K
Maximum cable length l
max
L – L
4 mH 50 H
l
o i
l --------------- - --------------------------------------
= =
max inductance
max Induktivität 
L 0 68 mH/km
K
Safety Barrier Zone 2
< 1% of the L
i
Cable parameters
83 nF Cross section Q: 1,5 mm
Resistance R : 12 Ω/km
4 mH
K
Capacity C :
400 Ω 120 nF/km
K
Inductance L :
0,5 V 0,68 mH/km
K
H
54 ------- -

as per inductance ratio
H
------- - km 
54

 
--------------------------- - 0 95 km
=

0 68 mH
----------------------- -
12
as per cable capacity
 
0 69 km
as per cable inductance
–
 
5 8 km
-value and C < 1% of the C -value.
o i o
Bay unit (Polytron 7000)
Min. operating voltage U
2
at bay unit current I :
F
Input capacity C :
i
Input inductance L :
i
Maximum cable length l
U U U
– –
B D
------------------------------------- - R
I
F
l
= -------------------------------------------------------------- -
max

2 R
24 V –
--------------------------------------------------------------- - 250  400 
l = --------------------------------------------------------------------------------------------------------------
max 3 mA
24 V –
--------------------------------------------------- - 250  400 
l = ------------------------------------------------------------------------------------------------- -
max 22 mA
The maximum possible cable length l
calculated cable length of l
l and I
max 22 mA max inductance resistance ratio
l = l
l = l
max max capacity
max max Kapazität
Central controller
16,5 V at 3 mA,
min
Operating voltage U
8 V at 22 mA
Load R
0 µF
50 µH
as per function
max
min
– – R
B i
K
 
0 5 V – 16 5 V
– –
3 mA
2 12 /km 

0 5 V – 8 V
– –
22 mA

2 27 km
2 12 /km 
corresponds to the shortest
max
, l
max capacity max inductance
.
 
0 69 km
Installation
: 24 V
B
:
250 Ω
B

70 km

, l ,
max 3 mA
9