tailieunhanh - Assessing Product Reliability_14

Tham khảo tài liệu 'assessing product reliability_14', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | . Fitting models using degradation data instead of failures Plot of linear degradation trends for 5 units read out at four time points In many practical situations D starts at 0 at time zero and all the linear theoretical degradation lines start at the origin. This is the case when D is a change parameter or failure is defined as a change of a specified magnitude in a parameter regardless of its starting value. Lines all starting at the origin simplify the analysis since we don t have to characterize the population starting value for D and the distance any unit travels to reach failure is always the constant DF. For these situations the degradation lines would look as follows Often the degradation lines go through the origin - as when change is the measurable parameter increasing to a failure level http div898 handbook apr section4 2 of 7 5 1 2006 10 42 30 AM . Fitting models using degradation data instead of failures It is also common to assume the effect of measurement error when reading values of D has relatively little impact on the accuracy of model estimates. Advantages of Modeling Based on Degradation Data Modeling based on complete samples of measurement data even with low stress cells offers many advantages 1. Every degradation readout for every test unit contributes a data point. This leads to large amounts of useful data even if there are very few failures. 2. You don t have to run tests long enough to obtain significant numbers of failures. 3. You can run low stress cells that are much closer to use conditions and obtain meaningful degradation data. The same cells would be a waste of time to run if failures were needed for modeling. Since these cells are more typical of use conditions it makes sense to have them influence model parameters. 4. Simple plots of degradation vs time can be used to visually test the linear degradation assumption. Drawbacks to Modeling Based on Degradation Data http .