7
6
SM Surge Rev 2
SD range surge suppression devices
Failure mode
Failure rate (FIT)
SD07/16/
32/55
SDyyR/X (i)
SD07z3 (ii)
SD16/32/
55z3 (ii)
SDRTD
Connected signal not affected
23.9
14.9
22.0
22.0
21.1
Connected signal interrupted
14.5
14.5
20.1
17.8
20.1
Errors in connected signal
1.5
1.5
6.9
5.9
9.0
Correct operation (failures have no effect)
51.4
32.4
51.3
49.9
50.1
(i)
SDyy used to represent SD07, SD16, SD32 and SD55
(ii)
z3 used to represent R3, T3 and X3
SLP range surge suppression devices
Failure mode
Failure rate (FIT)
SLP07D
SLP16D
SLP32D
Connected signal not affected
70
70
70
Connected signal interrupted
76
76
76
Errors in connected signal
2
2
2
Correct operation (failures have no effect)
23
23
23
IOP range surge suppression devices
Failure mode
Failure rate (FIT)
IOP32
IOP32D
IOP HC32
Connected signal not affected
5.4
5.4
5.4
Connected signal interrupted
65
65
65
Errors in connected signal
0
0
0
Correct operation (failures have no effect)
4.6
4.6
4.6
•
FITs means failures per 10
9
hours or failures per thousand million hours.
•
Reliability data for this analysis is taken either from the Electrical and Mechanical Component Reliability
Handbook, 2006, by Exida L.L.C., or from IEC TR 62380:2004.
It is assumed that the device is installed, operated and maintained according to the product specification. The
product has been assumed to operate at an average ambient temperature of 40°C under normal conditions. For a
higher average temperature of 60°C, or if subject to frequent temperature fluctuation, the failure rates should be
multiplied with an experience based factor of 2.5.
The information given here is to help the designer of a Safety Instrumented Function assess the impact of
including surge protection devices on the operation and availability of the instrument loops.
The surge devices themselves are not ‘safety elements’.
