BECKHOFF TwinSAFE - Manual (Page 53)

Circuit examples
Application Guide TwinSAFE 51
Inserting the values, this produces:
S1:
݊
௢௣
ൌ
230 כ 16 כ 60
15
ൌ 14720
ܯܶܶܨ
ௗ
ൌ
1000000
0.1 כ 14720
ൌ 679.3y ൌ 5951087h
S2:
݊
௢௣
ൌ
230 כ 16 כ 60
15
ൌ 14720
ܯܶܶܨ
ௗ
ൌ
2000000
0.1 כ 14720
ൌ 1358.7y ൌ 11902174h
K1/K2:
݊
௢௣
ൌ
230 כ 16 כ 60
1
ൌ 14720
ܯܶܶܨ
ௗ
ൌ
1300000
0.1 כ 14720
ൌ 883.2y ൌ 7736413h
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
ୢ
S1:
ܲܨܪ ൌ
1 െ 0.99
679.3 כ 8760
ൌ 1.68E െ 9
S2:
ܲܨܪ ൌ
1 െ 0.99
1358.7 כ 8760
ൌ 8.4E െ 10
K1/K2:
ܲܨܪ ൌ
1 െ 0.90
883.2 כ 8760
ൌ 1.29E െ 8
The following assumptions have to be made now:
The door switches S1/S2 are always actuated in opposite directions. Since the switches have different
values, but the complete protective door switch consists of a combination of break and make contacts
and both switches must function, the poorer of the two values (S1) can be taken for the combination!