BECKHOFF TwinSAFE - Manual (Page 10)

Circuit examples
8 Application Guide TwinSAFE
2.1.2 Block formation and safety loops
2.1.2.1 Block 1
2.1.3 Calculation
2.1.3.1 PFH / MTTF
d
/B10
d
– values
Component Value
EL1904 – PFH 1.11E-09
EL2904 – PFH 1.25E-09
EL6900 – PFH 1.03E-09
S1 – B10
d
100,000
S2 – B10
d
10,000,000
K1 – B10
d
1,300,000
K2 – B10
d
1,300,000
Days of operation (d
op
) 230
Hours of operation / day (h
op
) 16
Cycle time (minutes) (T
cycle
) 10080 (1x per week) (7 days, 24 hours)
Lifetime (T1) 20 years = 175200 hours
2.1.3.2 Diagnostic Coverage DC
Component Value
S1 with testing/plausibility DC
avg
=99%
K1/K2 with testing and EDM (actuation 1x per week) DC
avg
=60%
K1/K2 with testing and EDM (actuation 1x per shift) DC
avg
=90%
2.1.3.3 Calculation for block 1
Calculation of the PFH and MTTF
d
values from the B10
d
values:
From:
݊
௢௣
ൌ
݀
௢௣
כ ݄
௢௣
כ 60
ܶ
஼௬௖௟௘
and:
ܯܶܶܨ
ௗ
ൌ
ܤ10
ௗ
0.1 כ ݊
௢௣
S1 EL1904 EL6900 EL2904
K1
K2