BECKHOFF TwinSAFE - Manual (Page 105)

Circuit examples
Application Guide TwinSAFE 103
2.17.3.2 Diagnostic Coverage DC
Component Value
S1/S2 with testing/plausibility DC
avg
=99%
K1/K2 with testing and EDM DC
avg
=99%
2.17.3.3 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 ݊
௢௣
Inserting the values, this produces:
S1:
݊
௢௣
ൌ
230 כ 8 כ 60
15
ൌ 7360
ܯܶܶܨ
ௗ
ൌ
1000000
0.1 כ 7360 ൌ 1358.7y ൌ 11902212h
S2:
݊
௢௣
ൌ
230 כ 8 כ 60
15
ൌ 7360
ܯܶܶܨ
ௗ
ൌ
2000000
0.1 כ 7360 ൌ 2717.4y ൌ 23804424h
K1/K2:
݊
௢௣
ൌ
230 כ 8 כ 60
15
ൌ 7360
ܯܶܶܨ
ௗ
ൌ
1300000
0.1 כ 7360 ൌ 1766.3y ൌ 15472788h
and the assumption that S1, S2, K1 and K2 are in each case single-channel:
ܯܶܶܨ
ௗ
ൌ
1
ߣ
ௗ
results in a
ܲܨܪ ൌ
0.1 כ ݊
௢௣
כ ሺ1 െ ܦܥሻ
ܤ10
ௗ
ൌ
1 െ DC
MTTF
ୢ