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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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Original Message:

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: Sumandra Ghosh Chowdhury ( )Lucent Technology
Date Posted: Tue Aug 24 1:04:35 US/Eastern 1999
My experience always says Predicted MTBF always less than field MTBF. For example for UPS, predicted MTBF as per MIL 217F, was 37000 hours but field MTBF was 50000 hours after 2 years. Initially, field MTBF was in the order of 20000 hours in the first year. Similarly, for a sevocontroller, predicted MTBF was 12000 hours. but field MTBF was 25000 hours. Predicted Field Similarly, Inverter 33000 19000 (Ist year) AC Servo 15000 40000 Converter 18000 21000 CNC 12000 40000 DRO 34000 22000 (Ist year) Volatge Regulator 33000 45000 It is very difficult to assign a factor for same. However, the proportion depends on action based on effective FRACAS, continuous improvement, customer service driven action, more population of products & management focus/attention on than particular product. Reliability Growth occurs as per Duane plot. Thanks Sumandra

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