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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

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Posted by: Wu Xiangping ( )
Date posted: Tue Aug 3 22:44:36 US/Eastern 1999
Subject: Reliability Prediction
We all know that the result of reliability prodiction is much higher than the true reliability level.Does anyone know the proportion between them? Another problem is,a new product,has no reliability requirement from customer,how to decide the reliability requirement that the product should achieve? Thanks very much.

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Subject: Reliability Prediction
Reply Posted by: Jon Ilseng ( )
Organization: Schlumberger Oilfield Services
Date Posted: Mon Aug 9 15:27:09 US/Eastern 1999
Regarding the Bellcore Reliability Prediction for Method 1, Case 3. I have done Bellcore Reliability Predictions using Method 1, Case 3 and compared these predictions vs. field data. One example is for a Wireline Interface Telemetry PCB. The Bellcore Reliability Prediction for this PCB using Method 1, Case 3 was: a) first-year MTBF prediction of 9,569 hours (based on a 48-hour burn-in at 50 Degrees C); b) steady-state MTBF prediction of 29,666 hours. The first year this PCB was fielded, the field MTBF was 20,023 hours (compared to the Bellcore MTBF prediction of 9,569 hours). We are only 5 months into the steady-state operating period for this PCB, therefore, it is premature to compare steady-state field MTBF vs. the Bellcore predicted steady-state MTBF. I did calculate a MIL-HDBK-217F,N2 MTBF prediction for this PCB and its calculated MTBF was 11,782 hours. The field MTBF for a 17-month period for this PCB was 17,804 hours. In my 20 years of working in the reliability field, the field MTBFs are usually higher than any calculated MTBFs. By how much, it varies.

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