Biomedical Engineering Reference
In-Depth Information
It is therefore apparent that we need to determine how critical this failure mode is. To do this
we determine a Rating Priority Number (RPN) using
(7.5)
RPN everity OccurrenceDetection
We could use a simple number range, for example
0-25 No intervention required
26-50 Intervention required, sign off locally
50+ Intervention required, sign off by senior designer
However this simple rule can hide potential failures. It is therefore better to use a table similar
to that illustrated by
Table 7.12
.
There are three tables, one for each of the three levels of detection. One uses the
corresponding table and cross-correlates with the corresponding RPN. Note that the same
value of RPN can lead to vastly different outcomes. The numbers in the boxes are not carved
in stone; you will need to determine your own tables and only you can do this. There are no
guidelines apart from a severity of 5 being bad!
Table 7.12: Example Qualitative Criticality Matrix
(a)
Occurrence
Detect
=
1
1
2
3
4
5
1
1
2
3
4
5
2
2
4
6
8
10
3
3
6
9
12
15
4
4
8
12
16
20
5
5
10
15
20
25
(b)
Occurrence
Detect
=
3
1
2
3
4
5
1
3
6
9
12
15
2
6
12
18
24
30
3
9
18
27
36
45
4
12
24
36
48
60
5
15
30
45
60
75
(c)
Occurrence
Detect
=
5
1
2
3
4
5
1
5
10
15
20
25
2
10
20
30
40
50
3
15
30
45
60
75
4
20
40
60
80
100
5
25
50
75
100
125
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