PRISM Forum - Message Replies
Topic: PRISM Questions and Answers
Topic Posted by: SRC
Date Posted: Wed Jan 12 8:33:33 US/Eastern 2000
Topic Description: Welcome to the PRISM forum! Please feel free to post your questions and comments about the PRISM assessment software here.
Posted by: Ralph Listl
Date posted: Mon Feb 27 5:27:44 US/Eastern 2006
Subject: Prism Reliability Model
The Prism Reliability Model uses an initial failure rate multiplied by a process grade factor. The calculation of the inital failure rate for all via RACrates model supported items (Capacitors, Resistors...) makes use of a temperature dependent factor in their models. Therefor all base failure rates are temperature dependent. The process grade factor does also include an environment factor that is temperature dependent. If a complete system has been set up and the temperature is changed it influences the base failure rates as well as the process grade factor.
From my point of view a temperature dependency should either be applied on the base failure rate or for the process grade factor but not on both, because this is double influence. A temperatue dependence on item level is understandable, but a temperature dependence on a process grade is for my understanding not correct. Could you please explain why the Prism model is set up like this?
Subject: Temperature dependency
Reply Posted by: David Dylis
Organization: System Reliability Center (SRC)
Date Posted: Mon Feb 27 15:19:02 US/Eastern 2006
As you identified, a component has a certain inherent failure rate that is affected by application and temperature. Processes that are used in the design, development and manufacturing of a system are also affected by temperature. Poor processes will result in more early life failures than good processes. Temperature is one factor that will precipitate these events. When PRISM was developed data was analyzed and the affect of temperature on failure rate was distributed between the component and process grade portions of the model.
If you have additional questions, feel free to contact me.