BECKHOFF TwinSAFE - Manual (Page 80)

Circuit examples
78 Application Guide TwinSAFE
This produces for the calculation of the PFH value for block 1:
PFH
tot
=
β
* (PFH(S1)+PFH(S2))/2 + PFH(EL1904) + PFH(EL6900) + PFH(EL2904) +
β
*
(PFH(K1)+PFH(K2))/2 +PFH(EL1904)
to:
PFH PFH PFH PFH
tot tot tot tot
= == =
10%*
(1.26E-09+1.26E-09) / 2 +1.11E-09 + 1.03E-09 + 1.25E-09 + 10%*
(1.93E-08+1.93E-08) / 2 + 1.11E-09 = 6.56E 6.56E 6.56E 6.56E----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
ௗ
(ܵ1) +
1
ܯܶܶܨ
ௗ
(ܧܮ1904) +
1
ܯܶܶܨ
ௗ
(ܧܮ6900) +
1
ܯܶܶܨ
ௗ
(ܧܮ2904)
+
1
(ܯܶܶܨ
ௗ
(ܭ1)) +
1
ܯܶܶܨ
ௗ
(ܧܮ1904)
with:
ܯܶܶܨ
ௗ
(S1) =
ܤ10
ௗ
(ܵ1)
0.1 כ ݊
௢௣
ܯܶܶܨ
ௗ
(S2) =
ܤ10
ௗ
(ܵ2)
0.1 כ ݊
௢௣
ܯܶܶܨ
ௗ
(K1) =
ܤ10
ௗ
(ܭ1)
0.1 כ ݊
௢௣
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 െ 0.99)
1.11E െ 09 ଵ
୦
כ 8760 ୦
୷
=
0.01
9.72E െ 06 ଵ
୷
= 1028.8y
ܯܶܶܨ
ௗ
(EL6900) =
(1 െ ܦܥ(ܧܮ6900))
ܲܨܪ(ܧܮ6900) =
(1 െ 0.99)
1.03E െ 09 ଵ
୦
כ 8760 ୦
୷
=
0.01
9.02E െ 06 ଵ
୷
= 1108.6y