7. Safety functions
System requirements
Database for failure rates
System type
Applied standard
Beta factor
7.1. Safe switch-off
Ambient temperature
MTBF [years] Mean time to failure
Switch-off time [ms]
λsd [FIT] safe, detectable
λsu [FIT] safe, undetectable
λdd [FIT] dangerous, detectable
λdu [FIT] dangerous, undetectable
SFF [%] Safe Failure Fraction
DCS [%] Diagnostic coverage safe
DC [%] Diagnostic coverage
PFD Probability of Failure on Demand
PFH Probability of a dangerous failure
per hour
Safety level
7.2. Motor Protection
Ambient temperature
Switch-off time [ms]
λsd [FIT] safe, detectable
λsu [FIT] safe, undetectable
λdd [FIT] dangerous, detectable
λdu [FIT] dangerous, undetectable
SFF [%] Safe Failure Fraction
DCS [%] Diagnostic coverage safe
DC [%] Diagnostic coverage
PFD Probability of Failure on Demand
Safety level
26
SN 29500
Type B, consisting of sub-systems
IEC 61508
1 %
ELR W3-24DC/500AC-...
40°C
45.6
40
666
947
215
2.5
99.86
50.56
98.86
2.48 x 10
according to
IEC 61508-1: SIL 3
ISO 13849-1: PL e
EN 954-1:
ELR W3-24DC/500AC-...
40°C
645
866
238
17
99
42.6
93.3
according to
IEC 61508-1: SIL 2
60°C
23,0
1561
1643
446
5.01
99.9
48.73
99
compare diagram 7.3.
-9
5.01 x 10
Category 3
60°C
according to Class 10 A, IEC 60947
1487
1408
488
37
98.9
51.36
93
compare diagram 7.4.
ELR W3-230AC/500AC-...
40°C
46.0
80
641
879
399
4.43
99.77
42.17
98.9
compare diagram 7.3.
-9
-9
4.43 x 10
ELR W3-230AC/500AC-...
40°C
647
812
413
17
99.1
44.4
96
compare diagram 7.4.
60°C
23.0
1217
1814
896
9.67
99.75
40.2
98.93
-9
9.67 x 10
60°C
1212
1622
915
37
99
42.8
96.1