Four concepts come up repeatedly throughout this menu. Understanding them will help you avoid most mistakes.<\/p>\n\n\n\n
A piece of data is censored<\/strong> when the product has not yet failed<\/strong> at the end of the observation. All we know is that it lasted at least until then.<\/p>\n\n\n\n \u26a0\ufe0f Ignoring censoring is a classic mistake\u2014and a serious one at that: keeping only the defective products is like looking only at the students who are struggling. The estimated reliability becomes dramatically pessimistic. Censorship conveys information and must be taken into account.<\/strong><\/p>\n<\/blockquote>\n\n\n\n That is why all of Ellistat's data entry formats include a censoring column.<\/p>\n\n\n\n It is the benchmark law in reliability because its form adapts to the three stages of a product's life cycle. Its parameter \u03b2 (beta), the form<\/strong>, is interpreted directly:<\/p>\n\n\n\n \ud83d\udca1 \u03b2<\/strong> is the first number to look at, even before the service life.<\/strong> It identifies the nature of the problem and, therefore, the area for action: a \u03b2 less than 1 is addressed during production, while a \u03b2 greater than 1 is addressed during design or preventive maintenance. Choosing the wrong regime means choosing the wrong action plan.<\/p>\n<\/blockquote>\n\n\n\n The second parameter,\u00a0\u03b7 (eta), the scale<\/strong>, is the time at which 63 % of the population failed. Ellistat proposes\u00a0Two-parameter Weibull<\/strong>\u00a0and\u00a03-Parameter Weibull<\/strong>, the third being the\u00a0estimated position \u03b4<\/strong>, an initial delay, which is useful when no failure is possible before a certain amount of time has elapsed.<\/p>\n<\/blockquote>\n\n\n\n \u26a0\ufe0f MTTF is a convenient but misleading figure. An MTTF of ten years does not mean that the product will last ten years: with an exponential failure rate, More than one-third of the fleet has already failed<\/strong> after an MTTF. For a contractual commitment, think in terms of R(t) at the maturity date of the guarantee<\/strong>, not in MTTF.<\/p>\n<\/blockquote>\n\n\n\n This is the natural format for after-sales service data: a triangle<\/strong> values. Each row represents a sales period; the columns show the returns observed over the subsequent periods. Products sold more recently have a shorter track record, which explains the triangular shape.<\/p>\n\n\n\n \ud83d\udca1 Nevada contains two distinct pieces of information, which Ellistat can distinguish between: diagonally<\/strong> We look at the shelf life (of products of the same age), in columns<\/strong> We can see the seasonal patterns (what happens at the same time of year, regardless of age).<\/p>\n<\/blockquote>","protected":false},"featured_media":0,"menu_order":20,"template":"","meta":{"_acf_changed":true},"menu-guide-dutilisateur":[36],"class_list":["post-4601","guide-dutilisateur","type-guide-dutilisateur","status-publish","hentry","menu-guide-dutilisateur-9-fiabilite"],"acf":[],"yoast_head":"\n\n
The Weibull Distribution<\/h2>\n\n\n\n
\u03b2<\/strong><\/td> Diet<\/strong><\/td> Interpretation<\/strong><\/td><\/tr><\/thead> \u03b2 < 1<\/td> Early Failures<\/td> Infant mortality: manufacturing and assembly defects. The failure rate decreases<\/strong>.<\/td><\/tr> \u03b2 = 1<\/td> Random Failures<\/td> Default Rate constant<\/strong> : The law follows an exponential pattern; the failure is accidental.<\/td><\/tr> \u03b2 > 1<\/td> Wear and Tear<\/td> The default rate grows<\/strong> : aging, wear and tear, abrasion.<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n \n
\n
R(t), MTTF, and failure rate<\/h2>\n\n\n\n
\n
\n
Nevada<\/h2>\n\n\n\n
\n