7
Figure 7-1
PFH values depending on switching frequency c
7.1.3
Determining MTTF
d
for single-channel operation
The value for MTTF
d
depends on the load for the contacts and the switching frequency.
In this section, the values are given for single-channel assignment, and these values only
refer to one internal safety relay.
If the contacts of a safety relay have different loads, use the least favorable load for the
calculation (see assignment of outputs to the safety relay in Section "Terminal point
assignment" on page 3-4).
If the calculated PFH value is < 1%, a value of 1% should be used.
Table 7-2
MTTF
d
depending on the load for the contacts and the switching fre-
quency
Load for the contacts
(according to DIN EN 60947-4-1/
DIN EN 60947-5-1)
Channel 1 or channel 2
MTTF
d
>
10 years
MTTF
d
>
30 years
MTTF
d
>
100 years
Switching frequency [1/h]
AC 15; 3 A
< 214
< 65
< 13
DC 13; 5 A
< 85
< 25
< 5
0
10
20
30
40
50
60
70
0
1
2
3
4
5
6
% SIL 2
c [1/h]
75561013
AC 15; 3 A
DC 13; 5 A
7-2
User manual IC220SDL840 -
May 2018
GFK-2734