DSP 104-plus, Справочное руководство

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164004.C03 H1
APPENDIX H: RELIABILITY
This Appendix provides reliability information on the TP400. Rather than just quote a
single MTBF figure, with no context and no reference to the assumptions made, DSP
Designed commissioned an analysis by the reliability consultancy, Landar Bonthron
Associates Ltd. Their report forms the basis of this Appendix.
Users interested in the reliability of the TP400 should read this Appendix carefully. In
particular, note the assumptions that have been made. In many cases these
assumptions are rather conservative. For example, the assumption has been made
that all components will be at the same temperature as the Geode processor, but since
the Geode generates most of the heat, the processor will often be much hotter than
many of the other components. Note also that reliability deteriorates as temperature
rises (as with any electronic device), so pay attention to cooling of the TP400.
H.1 ASSUMPTIONS AND METHODOLOGY
H.1.1 Reliability Standard
Many commercial electronic product companies are now choosing to use the Bellcore
handbook for their reliability predictions. Bellcore is Bell Communications Research (a
spin-off of AT&T Bell Labs), and was the research arm of the Bell Operating
Companies. The organisation has recently been renamed Telcordia.
Bellcore previously used MIL-HDBK-217 for their reliability predictions, but found that
217 gave pessimistic numbers for its commercial quality products. A few years ago
(1985), Bellcore used 217 as a starting point, modified (and simplified) the models to
better reflect their field experience, and developed the Bellcore reliability prediction
procedure, which is applicable to commercial electronic products.
"Reliability Prediction Procedure for Electronic Equipment" is Bellcore document
number TR-332, Issue 6. It has been used to calculate the reliability of the TP400.
H.1.2 Methodology
The reliability assessment has been carried out taking the following assumptions and
calculation methods:
Limited Stress – Method 1, Case 3: This method is one you would typically use for your
reliability predictions: it calculates device failure rates based on parameters such as
environment, temperature, stress, quality etc., then calculates the unit failure rate as
the sum of it’s device failure rates.
Component Quality -- Quality Level 1: This level shall be assigned to the commercial-
grade components that are procured and used without thorough, Military Standard
style, device qualification or lot-to-lot controls by the equipment manufacturer.