{"id":54366,"date":"2021-07-26T15:15:06","date_gmt":"2021-07-26T13:15:06","guid":{"rendered":"https:\/\/www.reersafety.cn\/safety-guide\/iso-13849-12safety-of-machinery\/choice-of-self-diagnosis-techniques-and-dcavg-computation\/"},"modified":"2022-05-06T15:00:11","modified_gmt":"2022-05-06T13:00:11","slug":"choice-of-self-diagnosis-techniques-and-dcavg-computation","status":"publish","type":"page","link":"https:\/\/www.reersafety.cn\/zh-hans\/academy\/safety-guide\/iso-13849-12safety-of-machinery\/choice-of-self-diagnosis-techniques-and-dcavg-computation\/","title":{"rendered":"Choice of self-diagnosis techniques and DC computation"},"content":{"rendered":"\n<div class=\"row\"  id=\"row-1034984099\">\n\n\n\t<div id=\"col-1851007427\" class=\"col small-12 large-12\"  >\n\t\t<div class=\"col-inner\"  >\n\t\t\t\n\t\t\t\n\n  <div id=\"page-header-1575339424\" class=\"page-header-wrapper\">\n  <div class=\"page-title light simple-title\">\n\n    \n    <div class=\"page-title-inner container align-center flex-row medium-flex-wrap row-reverse\" >\n            <div class=\"title-content flex-col flex-left text-left medium-text-center\">\n        <div class=\"title-breadcrumbs pb-half pt-half\"><nav class=\"woocommerce-breadcrumb breadcrumbs uppercase\">\u9996\u9875<\/nav><\/div>      <\/div>\n    <\/div>\n\n       <\/div>\n    <\/div>\n  \n\n\n\t\t<\/div>\n\t\t\t<\/div>\n\n\t\n\n<\/div>\n<div class=\"row\"  id=\"row-2029907919\">\n\n\n\t<div id=\"col-1496302528\" class=\"col small-12 large-12\"  >\n\t\t<div class=\"col-inner\"  >\n\t\t\t\n\t\t\t\n\n<div class=\"row\"  id=\"row-1975956803\">\n\n\n\t<div id=\"col-806119894\" class=\"col small-12 large-12\"  >\n\t\t<div class=\"col-inner text-left\"  >\n\t\t\t\n\t\t\t\n\n\t<div id=\"text-221628027\" class=\"text cutom-ul\">\n\t\t\n\n<h3>Choice of self-diagnosis techniques and DC\u00a0computation<\/h3>\n<p>If it is supposed:<\/p>\n<ul>\n<li>That a failure can always occur (otherwise there would be no reason to define the MTTF)<\/li>\n<li>That the mechanisms for faults detection are not all equally efficient and immediate (it depends on the type of fault, for some faults it may take longer time) and that it is not possible to be able to detect all faults<\/li>\n<li>However, by adopting suitable circuit arrangements, it is possible to detect most of the dangerous faults<\/li>\n<\/ul>\n<p>Then it&#8217;s possible to define a DC parameter that specifies how efficient the system is in detecting its own malfunctions &#8220;in time&#8221; (in time means before a second dangerous fault can occur).<\/p>\n<h3>DC computation &#8211; General rule<\/h3>\n<p>The DC parameter is expressed as the ratio between the failure rate of dangerous failures detected by the implemented self-diagnostic measures, \u03bbdd, and the failure rate of all possible dangerous failures \u03bbd (detected and undetected).<\/p>\n\t\t\t<\/div>\n\t\n\t<div class=\"img has-hover x md-x lg-x y md-y lg-y\" id=\"image_35341899\">\n\t\t\t\t\t\t\t\t<div class=\"img-inner dark\" >\n\t\t\t<img width=\"386\" height=\"129\" src=\"https:\/\/www.reersafety.cn\/wp-content\/uploads\/2021\/07\/Formula_DC.png\" class=\"attachment-large size-large\" alt=\"\" decoding=\"async\" loading=\"lazy\" srcset=\"https:\/\/www.reersafety.cn\/wp-content\/uploads\/2021\/07\/Formula_DC.png 386w, https:\/\/www.reersafety.cn\/wp-content\/uploads\/2021\/07\/Formula_DC-300x100.png 300w\" sizes=\"(max-width: 386px) 100vw, 386px\" \/>\t\t\t\t\t\t\n\t\t\t\t\t<\/div>\n\t\t\t\t\t\t\t\t\n<style>\n#image_35341899 {\n  width: 21%;\n}\n<\/style>\n\t<\/div>\n\t\n\n<p>Knowing \u03bbd and the percentage of fault coverage provided by the diagnostic measures implemented, it is possible to derive \u03bbdd (detectable) and \u03bbdu (not detectable) and then compute the value of DC for the entire subsystem.<\/p>\n<h3>DC computation &#8211; Simplified method<\/h3>\n<p>This simplified method is based on the diagnostic techniques listed in Table E.1 of the Standard. Table E: 1 provides a list of 34 different diagnostic techniques divided into three families (for input circuits, for processing logic, for output circuits). If the designer decides to use diagnostic techniques to increase fault coverage, he can choose the preferred techniques among those listed in Table E.1 that best suit its application. A variable fraction of DC coverage ranging from0% to 99% is assigned to each technique.<\/p>\n<ul>\n<li>0% = the selected technique does not detect dangerous faults<\/li>\n<li>60% = a low fraction of dangerous failures is detected<\/li>\n<li>90% = an average fraction of dangerous failures is detected<\/li>\n<li>99% = a very high fraction of dangerous failures is detected<\/li>\n<\/ul>\n<p>It is also possible to select diagnostic techniques with different DC values for the individual parts. The formula that allows the computation of the DC of the entire system (DC) is<\/p>\n<div class=\"row\"  id=\"row-1529027955\">\n\n\n\t<div id=\"col-551104582\" class=\"col medium-6 small-12 large-6\"  >\n\t\t<div class=\"col-inner\"  >\n\t\t\t\n\t\t\t\n\n\t<div class=\"img has-hover x md-x lg-x y md-y lg-y\" id=\"image_1261789856\">\n\t\t\t\t\t\t\t\t<div class=\"img-inner dark\" >\n\t\t\t<img width=\"613\" height=\"190\" src=\"https:\/\/www.reersafety.cn\/wp-content\/uploads\/2021\/07\/Formula_DC_AVG.png\" class=\"attachment-large size-large\" alt=\"\" decoding=\"async\" loading=\"lazy\" srcset=\"https:\/\/www.reersafety.cn\/wp-content\/uploads\/2021\/07\/Formula_DC_AVG.png 613w, https:\/\/www.reersafety.cn\/wp-content\/uploads\/2021\/07\/Formula_DC_AVG-300x93.png 300w, https:\/\/www.reersafety.cn\/wp-content\/uploads\/2021\/07\/Formula_DC_AVG-510x158.png 510w\" sizes=\"(max-width: 613px) 100vw, 613px\" \/>\t\t\t\t\t\t\n\t\t\t\t\t<\/div>\n\t\t\t\t\t\t\t\t\n<style>\n#image_1261789856 {\n  width: 100%;\n}\n<\/style>\n\t<\/div>\n\t\n\n\n\t\t<\/div>\n\t\t\t<\/div>\n\n\t\n\n\t<div id=\"col-1955585372\" class=\"col medium-6 small-12 large-6\"  >\n\t\t<div class=\"col-inner text-left\"  >\n\t\t\t\n\t\t\t\n\n<p>Where MTTF<sub>Di<\/sub> and DC<sub>N<\/sub> are the values of MTTF<sub>D<\/sub> and DC of the individual components of the subsystem<\/p>\n<p>A component with a low DC and a low MTTFD has great weight and leads to a low DC value. A part that is not tested gets a <br \/>DC = 0 and contribute only to the value of the denominator. Once the calculation is completed, a DC class is chosen by means of the following table:<\/p>\n\n\t\t<\/div>\n\t\t\t<\/div>\n\n\t\n\n<\/div>\n<div class=\"row\"  id=\"row-597476524\">\n\n\n\t<div id=\"col-1316104339\" class=\"col medium-6 small-12 large-6\"  >\n\t\t<div class=\"col-inner\"  >\n\t\t\t\n\t\t\t\n\n<p>As was done for the choice of the MTTFD, also for the DC the Standard does not require knowledge of the exact value for the computation of the PFHd, but that a choice is made among four ranges of values.<\/p>\n\n\t\t<\/div>\n\t\t\t<\/div>\n\n\t\n\n\t<div id=\"col-1053418206\" class=\"col medium-6 small-12 large-6\"  >\n\t\t<div class=\"col-inner text-left\"  >\n\t\t\t\n\t\t\t\n\n<table style=\"border-collapse: collapse; width: 100%; height: 121px;\">\n<tbody>\n<tr style=\"height: 41px;\">\n<td style=\"width: 50%; height: 41px;\"><strong>Denomination DC<\/strong><\/td>\n<td style=\"width: 50%; height: 41px;\"><strong>Range of values DC<\/strong><\/td>\n<\/tr>\n<tr style=\"height: 20px;\">\n<td style=\"width: 50%; height: 20px;\">\n<p>None<\/p>\n<\/td>\n<td style=\"width: 50%; height: 20px;\">DC &lt; 60%<\/td>\n<\/tr>\n<tr style=\"height: 20px;\">\n<td style=\"width: 50%; height: 20px;\">\n<p>Low<\/p>\n<\/td>\n<td style=\"width: 50%; height: 20px;\">60% \u2264 DC &lt; 90%<\/td>\n<\/tr>\n<tr style=\"height: 20px;\">\n<td style=\"width: 50%; height: 20px;\">\n<p>Mediun<\/p>\n<\/td>\n<td style=\"width: 50%; height: 20px;\">90% \u2264 DC &lt; 99%<\/td>\n<\/tr>\n<tr style=\"height: 20px;\">\n<td style=\"width: 50%; height: 20px;\">\n<p>High<\/p>\n<\/td>\n<td style=\"width: 50%; height: 20px;\">99% \u2264 DC<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n\n\t\t<\/div>\n\t\t\t<\/div>\n\n\t\n\n<\/div>\n\t<div id=\"gap-752760697\" class=\"gap-element clearfix\" style=\"display:block; height:auto;\">\n\t\t\n<style>\n#gap-752760697 {\n  padding-top: 30px;\n}\n<\/style>\n\t<\/div>\n\t\n\n<div class=\"is-divider divider clearfix\" style=\"max-width:100px;\"><\/div>\n\n<div class=\"row\"  id=\"row-1241925333\">\n\n\n\t<div id=\"col-262524655\" class=\"col medium-4 small-12 large-4\"  >\n\t\t<div class=\"col-inner\"  >\n\t\t\t\n\t\t\t\n\n\t<div class=\"ux-menu stack stack-col justify-start ux-menu--divider-solid\">\n\t\t\n\n\t<div class=\"ux-menu-link flex menu-item\">\n\t\t<a class=\"ux-menu-link__link flex\" href=\"https:\/\/www.reersafety.cn\/en\/academy\/industrial-safety-guide\/iso-13849-12safety-of-machinery\/fault-exclusion\/\"  >\n\t\t\t<i class=\"ux-menu-link__icon text-center icon-angle-left\" ><\/i>\t\t\t<span class=\"ux-menu-link__text\">\n\t\t\t\tFault exclusion\t\t\t<\/span>\n\t\t<\/a>\n\t<\/div>\n\t\n\n\n\t<\/div>\n\t\n\n\t\t<\/div>\n\t\t\t<\/div>\n\n\t\n\n\t<div id=\"col-1110250840\" class=\"col medium-4 small-12 large-4\"  >\n\t\t<div class=\"col-inner\"  >\n\t\t\t\n\t\t\t\n\n\n\t\t<\/div>\n\t\t\t<\/div>\n\n\t\n\n\t<div id=\"col-1798077410\" class=\"col medium-4 small-12 large-4\"  >\n\t\t<div class=\"col-inner text-right\"  >\n\t\t\t\n\t\t\t\n\n\t<div class=\"ux-menu stack stack-col justify-start ux-menu--divider-solid\">\n\t\t\n\n\t<div class=\"ux-menu-link flex menu-item\">\n\t\t<a class=\"ux-menu-link__link flex\" href=\"https:\/\/www.reersafety.cn\/en\/academy\/industrial-safety-guide\/iso-13849-12safety-of-machinery\/ccf-evaluation-for-redundant-architectures\/\"  >\n\t\t\t<i class=\"ux-menu-link__icon text-center icon-angle-right\" ><\/i>\t\t\t<span class=\"ux-menu-link__text\">\n\t\t\t\tCCF evaluation for redundant architectures\t\t\t<\/span>\n\t\t<\/a>\n\t<\/div>\n\t\n\n\n\t<\/div>\n\t\n\n\t\t<\/div>\n\t\t\t<\/div>\n\n\t\n\n<\/div>\n\n\t\t<\/div>\n\t\t\t<\/div>\n\n\t\n\n<\/div>\n\n\t\t<\/div>\n\t\t\t<\/div>\n\n\t\n\n<\/div>\n\n","protected":false},"excerpt":{"rendered":"","protected":false},"author":7,"featured_media":0,"parent":54342,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"om_disable_all_campaigns":false,"inline_featured_image":false,"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"_uf_show_specific_survey":0,"_uf_disable_surveys":false},"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v20.1 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Choice of self-diagnosis techniques and DC computation | ReeR<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, 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