E2S BExBG10D-P-SIL, Instruction Manual, Page: 7 / 18

_______________________________________________________________________________________________________________________________
European Safety Systems Ltd. Impress House, Mansell Road, Acton, London W3 7QH sales@e-2-s.com Tel: +44 (0)208 743 8880
www.e-2-s.com Fax: +44 (0)208 740 4200
Document No. D197-00-112-IS Issue B 16-06-17 Sheet 7 of 17 (7)
Multiple Unit Configuration
When multiple units are used in the system, the following considerations are to be made by the customer:
1. Customer panel capabilities -
The customer is required to identify the minimum change in current the panel can detect (Panel resolution). This will
therefore determine what resistors values to pick in section 3 below.
2. Topology -
The customer has a number of options on how to set up the system.
▪
A single unit topology is where only one unit is connected to the customer interface line, as shown in figure 6.
▪
A series topology is where each unit is connected to one another as shown in figure 14.
▪
A star topology is where each unit is connected to a central source as shown in figure 15.
3. Resistor
– TB1 Current Sense Resistor (default 3.3kΩ)
The customer is required to calculate the total resistance of the system, to determine the change in current when a
fault occurs
. The default customer sense resistor value is 3.3kΩ. Examples of calculations of resistance for steady
mode and fault mode are shown in table 1.
Panel
Resolution
Topology
Resistor:
TB1 CSR
No. of
Units
Steady Mode:
Active/Monitoring
Fault Mode
1 unit fault All units fault
2mA Series
3.3kΩ
3
3 x 3.3kΩ = 9.9kΩ
0mA
If one unit fails the
whole system fails
7mA Star
3.3kΩ
3
(3.3kΩ ~ 7.3mA)
3 x 7.3mA = 21.9mA
(Fault unit):
1 x 0mA = 0mA
(Normal):
2 x 7.3mA = 14.6mA
(Fault unit):
3 x 0mA = 0mA
1.5mA Series
3.3kΩ
4
4 x 3.3kΩ = 13.2kΩ
0mA
If one unit fails the
whole system fails
7mA Star
3.3kΩ
4
(3.3kΩ ~ 7.3mA)
4 x 7.3mA = 29.2mA
(Fault unit):
1 x 0mA = 0mA
(Normal):
3 x 7.3mA = 21.9mA
(Fault unit):
4 x 0mA = 0mA
Table 1
Note: - Cable fault
•
Between the panel and the first unit, a cable short, increases the current (presenting a short circuit to the panel), and a
cable cut/open reduces current (presenting an open circuit to the panel).
•
In series topology a cable short between units will short out one of the current sense resistors which results in an increase
in the current used by the unit, and a cable cut/open reduces current (presenting an open circuit to the panel).
•
In star topology a cable short between units will short circuit the SIL 2 monitoring line hence presenting a short circuit to the
panel, an open circuit fault on one of the units will effectively remove one of the current sense resistors reducing total
effective resistance hence decreasing the total current seen by the panel.