BECKHOFF TwinSAFE - Manual (Page 26)

Circuit examples
24 Application Guide TwinSAFE
MTTF
d
Designation for each channel Range for each channel
low 3 years ≤ MTTF
d
< 10 years
medium 10 years ≤ MTTF
d
< 30 years
high 30 years ≤ MTTF
d
≤ 100 years
DC
avg
Designation Range
none DC < 60 %
low 60 % ≤ DC < 90 %
medium 90 % ≤ DC < 99 %
high 99 % ≤ DC
For practical usability, the number of the ranges was limited to four. An accuracy of 5% is assumed for the limit
values shown in this table.
Category B 1 2 2 3 3 4
DC
MTTF
d
none none low medium low medium high
low a -
a
b b c -
medium b - b c c d -
high - c c d d d e