BECKHOFF TwinSAFE - Manual (Page 134)

Circuit examples
132 Application Guide TwinSAFE
2.22.3.2 Diagnostic Coverage DC
Component Value
EL1904/EL2904 DC
avg
=0%
2.22.3.3 Calculation for block 1
This produces for the calculation of the PFH value for block 1:
PFH
tot
= PFH(EL1904) + PFH(EL2904)
to:
PFH PFH PFH PFH
tot tot tot tot
= == = 1.11E-09 + 1.25E-09 = 2.36E 2.36E 2.36E 2.36E----09 09 09 09
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
ௗ
(ܧܮ1904) +
1
ܯܶܶܨ
ௗ
(ܧܮ2904)
If only PFH values are available for EL1904 and EL6900, the following estimation applies:
ܯܶܶܨ
ௗ
(ELxxxx) =
(1 െ ܦܥ(ܧܮݔݔݔ))
ܲܨܪ(ܧܮݔݔݔ)
Hence:
ܯܶܶܨ
ௗ
(EL1904) =
൫1 െ ܦܥ(ܧܮ1904)൯
ܲܨܪ(ܧܮ1904) =
(1 െ 0)
1.11E െ 09 ଵ
୦
כ 8760 ୦
୷
=
1
9.72E െ 06
ଵ
୷
= 102881y
ܯܶܶܨ
ௗ
(EL2904) =
(1 െ ܦܥ(ܧܮ2904))
ܲܨܪ(ܧܮ2904)
=
(1 െ 0)
1.25E െ 09
ଵ
୦
כ 8760
୦
୷
=
1
1.1E െ 05
ଵ
୷
= 90909.1y
MTTF
d tot
=
ଵ
భ
భబమఴఴభ೤
ା
భ
వబవబవ.భ೤
= 48262.6ݕ
DC
avg
=
బ%
భబమఴఴభ
ା
బ%
వబవబవ.భ
భ
భబమఴఴభ
ା
భ
వబవబవ.భ
= 0%