SRC Forum - Message Replies
Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and Answers
Topic Posted by: Reliability & Maintainability Forum
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Posted by: SPM
Date posted: Thu Nov 30 9:48:11 US/Eastern 2000
Subject: Reliability Prediction Calculations
Being new to the field of reliability, I would be grateful for some advice.
I have used MIL-HDBK-217 to calculate predictions i.e. 500 fpmh. However I have been asked to provide a prediction for a stipulated operational life i.e. a failure rate is to be less than 500 fpmh over an operational life of 20 years. At the same time I have been asked to predict the failure rate after 1 year and 10 years.
I have managed to calculate the generic failure rate but donít know how to proceed in proving that it is within the operational life or what the failure rate will be after 1 yr and 10 yrs.
I believe this is typical of Bellcore standards (1209, 1221 and 332) to provide this sort of information.
Can anybody provide me with some guidelines as to how I would go about this calculation?
I hope I have made the question clear and I look forward to any help that can be provided.
Subject: Reliability Prediction - First Year Multiplier
Reply Posted by: bruce Dudley
Organization: Reliability Analysis Center
Date Posted: Thu Nov 30 13:54:29 US/Eastern 2000
Both the Bellcore (Telcordia)reliability models and the RAC PRISM program have the capability of projecting the component and item failure rate for the early operation periods of up to a year. The Bellcore models have worksheets that expand the pretest hours by acceleration factors and then compute the impact which is a factor of 1 to 4 depending the length of test time. The RAC PRISM model has adjustment factors that accounts for the infant mortality process grade which is based on options averaged over one year. The degree of impact of the infant mortality failure rates on the assembly and system predicted reliability is a function of the temperature and vibration screening tests that are performed prior to the delivery of the product to the customer. The process of calculating either method requires the use of worksheets for Bellcore or the software for PRISM. Follow-on calculations for out years should be base on the steaty state failure rates that would be determine without the early period estimation.