BECKHOFF TwinSAFE - Manual (Page 131)

Circuit examples
Application Guide TwinSAFE 129
The MTTF
d
value for block 1 (based on the same assumption) is calculated with:
1
ܯܶܶܨ
ௗ ௧௢௧
ൌ ෍
1
ܯܶܶܨ
ௗ ௡
௡
௜ୀଵ
as:
1
ܯܶܶܨ
ௗ ௧௢௧
ൌ
1
ܯܶܶܨ
ௗ
ሺܵ1ሻ ൅
1
ܯܶܶܨ
ௗ
ሺܧܮ1904ሻ ൅
1
ܯܶܶܨ
ௗ
ሺܧܮ6900ሻ ൅
1
ܯܶܶܨ
ௗ
ሺܣܺ5805ሻ
൅
1
ܯܶܶܨ
ௗ
ሺܣܺ5805ሻ ൅
1
ܯܶܶܨ
ௗ
ሺܣܺ5805ሻ ൅
1
ܯܶܶܨ
ௗ
ሺܣܺ5805ሻ
with:
ܯܶܶܨ
ௗ
ሺS1ሻ ൌ
ܤ10
ௗ
ሺܵ1ሻ
0.1 כ ݊
௢௣
ܯܶܶܨ
ௗ
ሺS2ሻ ൌ
ܤ10
ௗ
ሺܵ2ሻ
0.1 כ ݊
௢௣
If only PFH values are available for EL1904 and EL6900, the following estimation applies:
ܯܶܶܨ
ௗ
ሺELxxxxሻ ൌ
ሺ1 െ ܦܥሺܧܮݔݔݔሻሻ
ܲܨܪሺܧܮݔݔݔሻ
Hence:
ܯܶܶܨ
ௗ
ሺEL1904ሻ ൌ
൫1 െ ܦܥሺܧܮ1904ሻ൯
ܲܨܪሺܧܮ1904ሻ ൌ
ሺ1 െ 0.99ሻ
1.11E െ 09 ଵ
୦
כ 8760 ୦
୷
ൌ
0.01
9.72E െ 06 ଵ
୷
ൌ 1028.8y
ܯܶܶܨ
ௗ
ሺEL6900ሻ ൌ
ሺ1 െ ܦܥሺܧܮ6900ሻሻ
ܲܨܪሺܧܮ6900ሻ ൌ
ሺ1 െ 0.99ሻ
1.03E െ 09 ଵ
୦
כ 8760 ୦
୷
ൌ
0.01
9.02E െ 06 ଵ
୷
ൌ 1108.6y
ܯܶܶܨ
ௗ
ሺEL2904ሻ ൌ
ሺ1 െ ܦܥሺܧܮ2904ሻሻ
ܲܨܪሺܧܮ2904ሻ ൌ
ሺ1 െ 0.99ሻ
1.25E െ 09 ଵ
୦
כ 8760 ୦
୷
ൌ
0.01
1.1E െ 05 ଵ
୷
ൌ 913.2y
ܯܶܶܨ
ௗ
ሺAX5805ሻ ൌ
ሺ1 െ ܦܥሺAX5805ሻሻ
ܲܨܪሺAX5805ሻ ൌ
ሺ1 െ 0.99ሻ
5.15E െ 09 ଵ
୦
כ 8760 ୦
୷
ൌ
0.01
4.51E െ 05 ଵ
୷
ൌ 221.7y
MTTF
d tot =
ଵ
భ
ఱరయర.ఴ೤
ା
భ
భబమఴ.ఴ೤
ା
భ
భభబఴ.ల೤
ା
భ
మమభ.ళ೤
ା
భ
మమభ.ళ೤
ା
భ
మమభ.ళ೤
ା
భ
మమభ.ళ೤
ൌ 49.8ݕ