{"id":41828,"date":"2023-08-10T10:15:53","date_gmt":"2023-08-10T09:15:53","guid":{"rendered":"https:\/\/www.gt-engineering.it\/?post_type=approfondimento&#038;p=41828"},"modified":"2025-05-31T09:38:31","modified_gmt":"2025-05-31T08:38:31","slug":"fault-considerations-and-fault-exclusion","status":"publish","type":"approfondimento","link":"https:\/\/www.gt-engineering.it\/en\/insights\/functional-safety-300321\/fault-considerations-and-fault-exclusion\/","title":{"rendered":"Fault Considerations and Fault exclusion."},"content":{"rendered":"\n\n    \n        \n    \n\n\n\n\n    \n        <section\n            data-name=\"Contenuto testuale con immagine\"\n            class=\"bow-gte-testo-media u-spacer-base\"\n            id=\"\"\n        >\n            \n<div class=\"o-text-media px-side-spacer sm:px-side-spacer-sm lg:px-side-spacer-tablet 2xl:px-side-spacer-desktop flex flex-wrap items-start md:block\">\n\n    \n                    <div class=\"mb-6 relative w-full md:mb-4 lg:mb-8 xl:mb-9\">\n                \n        <div                class=\"m-headings\"\n            >\n    \n    \n<h2 class=\"a-heading text-left text-primary font-heading text-2xl lg:text-3xl xl:text-4xl font-normal mt-2 first:mt-0\">\n                     How many faults should be considered?    <\/h2>\n        <\/div>\n                <\/div>\n        \n                    <div\n                class=\"h-auto mb-6 md:mb-4 lg:mb-8 xl:mb-9 float-left mr-6 md:mr-4 lg:mr-8 xl:mr-9  overflow-hidden shadow-content-image w-full md:w-1\/4\"\n            >\n                \n\n    \n        \n            \n                \n                    <picture\n                        class=\"\"\n                                            >\n                                                                                                        <source\n                                media=\"(max-width: 150px)\"\n                                width=\"150\"\n                                height=\"139\"\n                                srcset=\"https:\/\/www.gt-engineering.it\/wp-content\/uploads\/2023\/08\/1oo3-150x139.jpg.webp\"\n                                type=\"image\/webp\"\n                            \/>\n                                                                                <source\n                                media=\"(max-width: 203px)\"\n                                width=\"203\"\n                                height=\"139\"\n                                srcset=\"https:\/\/www.gt-engineering.it\/wp-content\/uploads\/2023\/08\/1oo3.jpg.webp\"\n                                type=\"image\/webp\"\n                            \/>\n                                                                                <source\n                                media=\"(max-width: 203px)\"\n                                width=\"203\"\n                                height=\"139\"\n                                srcset=\"https:\/\/www.gt-engineering.it\/wp-content\/uploads\/2023\/08\/1oo3.jpg.webp\"\n                                type=\"image\/webp\"\n                            \/>\n                                                                                <source\n                                media=\"(max-width: 203px)\"\n                                width=\"203\"\n                                height=\"139\"\n                                srcset=\"https:\/\/www.gt-engineering.it\/wp-content\/uploads\/2023\/08\/1oo3.jpg.webp\"\n                                type=\"image\/webp\"\n                            \/>\n                                                                            <img\n                            class=\"a-image transparent border-image h-auto  w-full\"\n                                                        srcset=\"https:\/\/www.gt-engineering.it\/wp-content\/uploads\/2023\/08\/1oo3.jpg.webp\"\n                                                        width=\"203\"\n                            height=\"139\"\n                                                                                    title=\"1oo3\"\n                                                        type=\"image\/webp\"\n                            loading=\"eager\" fetchpriority=\"high\" decoding=\"async\"                        \/>\n                    <\/picture>\n\n                \n\n                    \n    \n\n            <\/div>\n        \n                    <div class=\"relative w-full\">\n                \n<div class=\"a-text font-text text-base normal mt-8 first:mt-0 space-y-4\">\n    <p>A Safety system has to be reliable; but <strong>how many faults should be taken into consideration<\/strong>? A redundant system can be designed with two sensors and two redundant final elements but, in case of two faults, we are in trouble!<\/p>\n<p>In machinery safety, why is maximum architectural reliability typically achieved with redundant channel subsystems (1oo2D)? <strong>And why isn&#8217;t a 1oo3D architecture required to reach SIL 3 or PL e in this context<\/strong>?<\/p>\n<p>In general, the following fault criteria shall be taken into account:<\/p>\n<ul>\n<li>If, because of a fault, further components fail, the first fault together with all following faults <strong>shall be considered as a single fault<\/strong> (known as a dependent fault).<\/li>\n<li>Two or more separate faults, <strong>having a common cause,<\/strong> shall be considered as a single fault. This situation is analysed in detail in 3.6.<\/li>\n<li>The simultaneous occurrence of two or more faults having separate causes <strong>is considered highly unlikely and therefore needs not be considered <\/strong>(<em>[ISO 13849-1] 6.1.10.2 Fault consideration<\/em>).<\/li>\n<\/ul>\n<p>That means, in machinery, due to the advantage of having, most of the time, a high demand mode of operations, only one independent fault has to be considered. <strong>Two faults are considered very unlikely during the time between two demands upon the safety function<\/strong>. The assumption becomes less sustainable in case of demands of few times a year or in case of a safety system in low demand mode.<\/p>\n<\/div>            <\/div>\n        \n        \n                <div class=\"clear-both\"><\/div>\n        \n\n    <\/div>\n        <\/section>\n\n    \n","protected":false},"excerpt":{"rendered":"<p>A Safety system has to be reliable; but how many faults should be taken into consideration? A redundant system can be designed with two sensors and two redundant final elements but, in case of two faults, we are in trouble! In general, the following fault criteria shall be taken into account:<\/p>\n","protected":false},"author":182,"featured_media":41829,"parent":0,"menu_order":36,"template":"","meta":{"_acf_changed":false,"footnotes":""},"tipologia_approfondimento":[48],"class_list":["post-41828","approfondimento","type-approfondimento","status-publish","has-post-thumbnail","hentry","tipologia_approfondimento-functional-safety-300321"],"acf":{"sottotitolo":"","allegati":null},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.7 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Fault Considerations and Fault exclusion. - Gt-Engineering<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.gt-engineering.it\/en\/insights\/functional-safety-300321\/fault-considerations-and-fault-exclusion\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Fault Considerations and Fault exclusion. - Gt-Engineering\" \/>\n<meta property=\"og:description\" content=\"A Safety system has to be reliable; but how many faults should be taken into consideration? 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