European Safety Systems Ltd.
Impress House, Mansell Road, Acton, London W3 7QH
www.e2s.com
Tel: +44 (0)208 743 8880
Document No. D157-00-651-IS
Issue 2
06-03-2023
Sheet 11 of 14
Figure 14 - Schematic of SIL 2 system wiring for fault detection in standby mode only
–
2 wire installation
To evaluate the total current drawn from the SIL 2 unit, use the equation below.
In standby mode, where there is no fault, RLY 1-1 is open. This means the voltage only passes through the customer EOL resistor
and the current drawn from the SIL 2 board is 25mA. Therefore, the equation for a No Fault scenario is then:
In standby mode, where there is a fault, the circuit is closed. This means the voltage passes through both the customer EOL resistor
and current sense resistor and the current drawn from the SIL 2 board is 20mA. The customer must first calculate the resistance of
the two resistors in parallel before applying the currents to the equation. The equation for a Fault scenario is then:
Table 4: Resistor combinations and the currents drawn when no faults and faults occur
If multiple SIL 2 alarm horn sounders are to be cabled in series the monitoring connections differ from that of a single alarm horn
sounder. For more information see manual D197-00-651-IS available from the E2S website.
I
(Total Current
drawn)
=
I
FR
(Current drawn from
Fault Resistor)
+
I
EOL
(Current drawn from
Customer EOL resistor)
+
I
SIL
(Current drawn
from SIL board)
I
NF
(Standby Mode, Total Current drawn - No Fault)
=
I
FR
(0mA)
+
I
EOL
(See table 4)
+
I
SIL
(25mA)
I
F
(Standby Mode, Total Current drawn - Fault)
=
I
TR
(Total Resistance when EOL & FR in parallel)
+
I
SIL
(20mA)
Standby
Mode
Power Supply Fault Resistor Customer EOL Resistor
(Fault Mode Only)
Current
drawn
from SIL
Board
Total
current
drawn
Resistor
Value
Current
drawn (
I
FR
)
Resistor
Value
Current
drawn (
I
EOL
)
Total
resistance
Current
drawn (
I
TR
)
No Fault
2.2 kΩ
0 mA
2.2 kΩ
10.9 mA
-
-
25 mA
35.9 mA
Fault
-
-
1.1 kΩ
21.8 mA
20 mA
41.8 mA
No Fault
1.0 kΩ
0 mA
1.0 kΩ
24.0 mA
-
-
25 mA
49.0 mA
Fault
-
-
500 Ω
48.0 mA
20 mA
68.0 mA
No Fault
2.2 kΩ
0 mA
3.3 kΩ
7.3 mA
-
-
25 mA
32.3 mA
Fault
-
-
1.3
kΩ
18.2 mA
20 mA
38.2 mA
No Fault
1.8 kΩ
0 mA
3.9 kΩ
6.2 mA
25 mA
31.2 mA
Fault
-
-
1.2 kΩ
19.5 mA
20 mA
39.5 mA
No Fault
1.8 kΩ
0 mA
4.7 kΩ
5.1 mA
-
-
25 mA
30.1 mA
Fault
-
-
1.3 kΩ
18.4 mA
20 mA
38.4 mA
No Fault
2.2 kΩ
0 mA
4.7 kΩ
5.1 mA
-
-
25 mA
30.1 mA
Fault
-
-
1.5 kΩ
16.0 mA
20 mA
36.0 mA
