Process Grade Factors and Pi Factor Multipliers
The scores for process grade factors are used to calculate Pi factor multipliers. Pi factor multipliers affect the predicted failure rate for the system or assembly positively or negatively.
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If a custom Prediction Process Grade is not enabled for or trickled down to an assembly, PRISM uses the default Prediction Process Grade file.
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The following table lists the Pi factor multiplier associated with a process grade factor, provides a descriptions of the process grade factor, and indicates the method by which the process grade factor is scored. While both the 217Plus and PRISM models use the same process grade factors and question sets, the values these models use for the Pi factor multipliers differ.
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Process Grade Factor
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Pi Factor Multiplier
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Description
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Method for Scoring Process Grade Factor
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CND (Can Not Duplicate)
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Pi N
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Indicates whether the number of incidents that cannot be duplicated is minimized.
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Weighted Responses to Questions
Required Questions: 6
Total Questions: 25
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Design
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Pi D
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Indicates whether the design is reliable and robust.
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Weighted Responses to Questions
Required Questions: 43
Total Questions: 145
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Environmental Multiplier
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Pi E
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Even though environmental variables such as system temperature, dormant system temperature, and system vibration level are defined outside of the Process Grade file, they directly contribute to the process grade calculation. Therefore, the Environmental multiplier is included in this table and shown in the Calculation Results window for the assembly.
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Supplied System Information
The parameters supplied in the Calculation Data pane are used to calculate this Pi factor multiplier.
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Growth
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Pi G
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Indicates whether reliability growth is emphasized throughout the design and development phases.
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Weighted Responses to Questions
Required Questions: 7
Total Questions: 7
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Induced
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Pi I
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Indicates whether externally applied stresses, such as electrical overstress, induce failures.
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Weighted Responses to Questions
Required Questions: 3
Total Questions: 16
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Infant Mortality
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Pi IM
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Indicates whether infant mortality issues are understood and addressed.
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User-Entered Parameters
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Manufacturing
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Pi M
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Indicates whether manufacturing practices degrade reliability performance.
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Weighted Responses to Questions
Required Questions: 13
Total Questions: 92
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Part Quality
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Pi P
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Indicates whether parts are of an acceptable quality to perform their intended functions. n the PRISM model, the Part Quality process grade factor is used to assign a quality level. For more information, see PRISM Quality Levels.
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Weighted Responses to Questions
Required Questions: 18
Total Questions: 55
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System Management
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Pi S
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Indicates whether management processes soundly interpret system requirements and supply adequate resources for system design and construction.
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Weighted Responses to Questions
Required Questions: 23
Total Questions: 100
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Wearout
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Pi W
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Indicates whether wearout issues are understood and addressed.
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Weighted Responses to Questions
Required Questions: 4
Total Questions: 23
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The Pi factor multipliers for an assembly are shown in its Process Grade pane. For more information, see Process Grade Pane. The Induced (Pi I) and Cannot Duplicate/No Defect Found (Pi N) factors are shown when process grades are calculated using the Inherent model, even though this model does not take these two Pi factor multipliers into account. The values for Pi factor multipliers for the 217Plus and PRISM models differ.