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Can I compare analysis results using different settings in
DOE++?
Beginning with version 1.0.2,
DOE++ offers the
Analysis History window, which allows you to view the results
for previous analyses of a selected response. To access the
history, select a response in the Analysis tab Control Panel in
a Standard Folio or Multiple Linear Regression Tool then choose
Data
> View History or click the Analysis History icon.
The Analysis History window is
shown next.
 
Each time you make a change to
the analysis settings and perform an analysis, DOE++
saves a copy of the contents of the Analysis tab, along with the
alias structure. The list of saved results is presented in a
hierarchical tree structure on the left side of the window. The
response name is displayed at the top of the tree structure and
the historical sets of results, from newest to oldest, are
displayed below. Click an item to display the results in the
spreadsheet area on the right.
You can apply the analysis
settings from the currently selected historical results to the
Analysis tab by clicking the Apply Settings button in the
toolbar then clicking the Calculate icon the Main page of
the Analysis tab Control Panel.
This will include the alpha value,
distribution, transformation, type of sum of squares, test terms
and selected effects.
What are the Severity Class and Failure Probability ratings
scales for in Xfmea/RCM++?
A typical FMEA incorporates some
method to identify and evaluate the risk associated with the
potential problems identified through the analysis.
Xfmea and
RCM++ support both
Risk Priority Numbers (RPNs) and Criticality Analysis.
RPNs: To use the Risk
Priority Number (RPN) method to assess risk, the analysis team
must:
- Rate the severity of each
effect of failure.
- Rate the likelihood of
occurrence for each cause of failure.
- Rate the likelihood of
detection for each cause of failure.
- Calculate the RPN by
obtaining the product of the three ratings:
RPN = Severity x
Occurrence x Detection
Criticality Analysis: To
use the quantitative Criticality Analysis method, the
analysis team must:
- Define the
reliability/unreliability for each item and use this to
estimate the expected number of failures at a given
operating time.
- Identify the portion of
the items unreliability that can be attributed to each
potential failure mode.
- Rate the probability of
loss (or severity) that will result from each failure mode
that may occur.
- Calculate the criticality
for each potential failure mode by obtaining the product of
the three factors:
Mode Criticality
= Expected Failures x Mode Ratio of Unreliability x Probability
of Loss
- Calculate the criticality
for each item by obtaining the sum of the criticalities for
each failure mode that has been identified for the item.
Item Criticality
= SUM of Mode Criticalities
To use the qualitative
Criticality Analysis method, the analysis team must:
- Rate the severity of the
potential effects of failure.
- Rate the likelihood of
occurrence for each potential failure mode.
- Compare failure modes via
a Criticality Matrix, which identifies severity on the
horizontal axis and occurrence on the vertical axis.
You can see that the processes
for RPNs and for qualitative Criticality Analysis both involve
rating the severity of the effect and rating the likelihood of
occurrence.
Although most practitioners tend to use one risk assessment
method or the other, some organizations may choose to employ
both analysis approaches in order to satisfy customer
requirements or for other reasons. Therefore, beginning with
Xfmea/RCM++
version 4.0.1, you can assign separate rating scales in the same
project for the "Severity" rating used to calculate an RPN and
the "Severity Class" used for Criticality Analysis; likewise for
the "Occurrence" rating used to calculate an RPN and the
"Failure Probability" used for Criticality Analysis. These
scales are managed via the Severity, Occurrence, Severity Class
and Failure Probability pages of the Project Properties window
and via the Severity and Occurrence pages of the
Profiles/Libraries Manager. |
