tailieunhanh - Assessing Product Reliability_12

Tham khảo tài liệu 'assessing product reliability_12', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Graphical estimation ENGINEERING STATISTICS HANDBOOK hW tools raids lỉEÂtCH BACK Nixf 8. Assessing Product Reliability . Reliability Data Analysis . How do you estimate life distribution parameters from censored data . Graphical estimation Every line on probability paper uniquely identifies distribution parameters Once you have calculated plotting positions from your failure data and put the points on the appropriate graph paper for your chosen model parameter estimation follows easily. But along with the mechanics of graphical estimation be aware of both the advantages and the disadvantages of graphical estimation methods. Most probability papers have simple procedures that go from a line to the underlying distribution parameter estimates Graphical Estimation Mechanics If you draw a line through the points and the paper is commercially designed probability paper there are usually simple rules to find estimates of the slope or shape parameter and the scale parameter. On lognormal paper with time on the x-axis and cum percent on the y-axis draw horizontal lines from the 34th and the 50th percentiles across to the line and drop vertical lines to the time axis from these intersection points. The time corresponding to the 50th percentile is the T50 estimate. Divide T50 by the time corresponding to the 34th percentile this is called T34 . The natural logarithm of that ratio is the estimate of sigma or the slope of the line fT ln T50 T34 . On commercial Weibull probability paper there is often a horizontal line through the percentile point. That estimation line intersects the line through the points at a time that is the estimate of the characteristic life parameter . In order to estimate the line slope or the shape parameter some papers have a special point on them called an estimation point. You drop a line from the estimation point perpendicular to the fitted line and look at where it passes through a special estimation scale. The estimate