What tools do Xfmea and RCM++ provide to assess risk
other than Risk Priority Numbers?
Traditionally, the RPN is defined by
obtaining the product of the three ratings: Severity x
Occurrence x Detection. The FMEA team then uses the RPN
values to rank the issues, assess the relative risk and determine which
corrective actions to take.
However, it is important to remember that the RPN
is the product of three subjective ratings and different
circumstances may produce similar or identical RPNs. For
example, an RPN of 100 could mean:
- Severity =
10, Occurrence = 10, Detection = 1
- Severity = 2,
Occurrence = 5, Detection = 10
- Severity = 1,
Occurrence = 10, Detection = 10
accordance with some common industry practices,
Xfmea/RCM++ support multiple additional ways that FMEA
practitioners may wish to use the severity, occurrence
and detection ratings for evaluating risk and
prioritizing corrective actions. This includes:
- SxO: This metric is calculated based on the product of
the severity and occurrence ratings only.
- SOD: This
metric displays the severity, occurrence and detection
ratings together, but it is not a calculated value. For
example, if the severity is 8, the occurrence is 4 and
the detection is 7, then the resulting SOD metric will
be 847. When the issues are sorted in descending order,
they will be prioritized first by severity, then by
occurrence and then by detection.
- SD: This metric
displays the severity and detection ratings together and
is similar to the SOD value except that it is based on
the severity and detection ratings only.
Within the software, you can
display the initial and revised values of any metric or
rating in the FMEA Hierarchy. And you can use the
Priority Highlights feature to use red, yellow and green
highlight colors to identify high, medium and low
priority issues within the analysis.
For even more control over how the software
prioritizes and highlights failure causes, you can use the
Risk Ranking feature to customize the number of priority
levels, as well as their associated names and colors.
For information on how to do so, refer to the
Tool Tip in
Issue 128 of the Reliability HotWire.
also base your decision on which actions to take by
ranking the issues by a single rating. For example, you
can use the FMEA filtered view to see a list of causes and
then sort by the desired rating; you can run a query on
the causes with the highest occurrence ratings; you
can generate an "Effects Ranked by Initial Severity" plot,
To see a graphical
chart that displays the issues based on their severity
and occurrence ratings you can use the Plot Viewer to
create an Occurrence / Severity Matrix chart. The matrix
includes thresholds for high, medium and low priority
Is there a fast way to calculate multiple metrics for any analyzed data sheet?
you analyze a data sheet in
is easy to use the Quick Calculation Pad (QCP) to
calculate any particular metric of interest whenever you
need it. But did you know that you can also access these
calculations (and many others) by using the Function
Wizard in conjunction with a spreadsheet-based report?
spreadsheets can save time and increase your analysis
capabilities. For example, you can use them to:
- Calculate and display multiple different metrics
- Compare metrics from different data
- Integrate a metric into another
calculation (e.g., multiply the BX% life by the
population size in order to estimate the number of
- Generate a standard report
template with the typical results that are of interest
for any analyzed data set.
- And much more.
add a report to a project in Weibull++ 7, ALTA
7 or RGA 7, choose Project > Add Report
or right-click the Reports node in the Project Explorer.
The Report Wizard will allow you to select the
default data source for any function that is based on
an analyzed data sheet (e.g., reliability, BX% life,
mean life, failure rate, etc.). This is not required to
create the report and you can change it at any time from
within the report window’s control panel.
you use the Function Wizard to define a metric, you can
choose to base the calculation on whatever data sheet is
currently defined as the default data source for the
report (e.g., if you want the report to function as a
template) or specify a particular data sheet for each
individual function (e.g., if
you want to compare results from two different
In the simple Weibull++
report shown next, all of the functions are based on a
default data source that could be changed at any time if
you want to obtain the same results for a different
analysis. In this example, the user can enter any time into cell
C15, and any 1-sided confidence levels into cells C16
and C17. The functions in row 21 have been configured to
automatically calculate the reliability based on the
current inputs (shown in blue text) and whatever data
sheet is currently associated with the report.
information is available in the user documentation for
Weibull++, ALTA and RGA. Each user’s guide includes a
detailed appendix of the available functions with
information about any inputs that are required.