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Tham khảo tài liệu 'assessing product reliability_13', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 8.4.2.I. Graphical estimation É mill IL lĩ í ÍỈÚĨỈ ar IHhlE IEmMJLLHIJLE CELLS Note that the lines are somewhat straight a check on the lognormal model and the slopes are approximately parallel a check on the acceleration assumption . The cell ln T5Q and sigma estimates are obtained from the FIT function as follows FIT Y1 X1 FIT Y2 X2 FIT Y3 X3 Each FIT will yield a cell Ao the ln T5Q estimate and A1 the cell sigma estimate. These are summarized in the table below. Summary of Least Squares Estimation of Cell Lognormal Parameters Cell Number ln T50 Sigma 1 T 85 8.168 .908 2 T 105 6.415 .663 3 T 125 5.319 .805 The three cells have 11605 T 273.16 values of 32.40 30.69 and 29.15 respectively in cell number order. The Dataplot commands to generate the Arrhenius plot are LET YARRH DATA 8.168 6.415 5.319 LET XARRH DATA 32.4 30.69 29.15 TITLE ARRHENIUS PLOT OF CELL T50 S http www.itl.nist.gov div898 handbook apr section4 apr421.htm 4 of 6 5 1 2006 10 42 28 AM 8.4.2.I. Graphical estimation With only three cells it is unlikely a straight line through the points will present obvious visual lack of fit. However in this case the points appear to line up very well. Finally the model coefficients are computed from LET SS DATA 5 35 24 WEIGHT SS FIT YARRH XARRH This will yield a lnA estimate of -18.312 A g 18.312 .1115x10-7 and a AH estimate of .808. With this value of A H the acceleration between the lowest stress cell of 85 C and the highest of 125 C is which is almost 14x acceleration. Acceleration from 125 to the use condition of 25 C is 3708X . The use T50 is e-18.312 x e.808x11605x1 298.16 e13.137 507383. A single sigma estimate for all stress conditions can be calculated as a weighted average of the 3 sigma estimates obtained from the experimental cells. The weighted average is 5 64 X .908 35 64 X .663 24 64 X .805 .74. Fitting More Complicated models http www.itl.nist.gov div898 handbook apr section4 apr421.htm 5 of 6 5 1 2006 10 42 28 AM 8.4.2.I. Graphical estimation .
