BECKHOFF TwinSAFE - Manual (Page 124)

Circuit examples
122 Application Guide TwinSAFE
2.20.3.2 Diagnostic Coverage DC
Component Value
S1 with testing/plausibility DC
avg
=99%
AX5801 DC
avg
=99%
2.20.3.3 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
60
ൌ 1840
ܯܶܶܨ
ௗ
ൌ
100000
0.1 כ 1840 ൌ 543.5y ൌ 4761060h
AX5801:
݊
௢௣
ൌ
230 כ 8 כ 60
60
ൌ 1840
ܯܶܶܨ
ௗ
ൌ
780000
0.1 כ 1840 ൌ 4239.1y ൌ 37134516h
and the assumption that S1 is single-channel:
ܯܶܶܨ
ௗ
ൌ
1
ߣ
ௗ
results in a
ܲܨܪ ൌ
0.1 כ ݊
௢௣
כ ሺ1 െ ܦܥሻ
ܤ10
ௗ
ൌ
1 െ DC
MTTF
ୢ
S1:
ܲܨܪ ൌ
1 െ 0.99
543.5 כ 8760
ൌ 2.10E െ 9
AX5801:
ܲܨܪ ൌ
1 െ 0.99
4239.1 כ 8760
ൌ 2.70E െ 10