{"id":41840,"date":"2023-08-10T10:40:11","date_gmt":"2023-08-10T09:40:11","guid":{"rendered":"https:\/\/www.gt-engineering.it\/?post_type=approfondimento&p=41840"},"modified":"2024-02-29T09:30:06","modified_gmt":"2024-02-29T08:30:06","slug":"other-examples-of-fault-exclusions","status":"publish","type":"approfondimento","link":"https:\/\/www.gt-engineering.it\/en\/insights\/functional-safety-300321\/fault-considerations-and-fault-exclusion\/other-examples-of-fault-exclusions\/","title":{"rendered":"Other examples of Fault Exclusions"},"content":{"rendered":"\n\n \n \n \n
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\n Short circuit between any two conductors <\/h2>\n <\/div>\n \n
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Figure 4.16 {4.11.3.1.1} shows an output subsystem in Architecture D or Category 4. Provided both contactors and the Safety Module are inside the same control panel, it is possible to use the scheme shown in Figure 4.17 {4.11.3.1.2} and do a fault exclusion for the probability of a short circuit of the cable connecting the output of the Safety Module with the contactors KP1<\/sub> and KP2<\/sub>.<\/p>\n<\/div> <\/div>\n <\/div>\n \n \n \r\n\r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n <\/picture>\r\n\r\n \r\n\r\n \r\n \r\n <\/div>\n \n <\/div>\n <\/section>\n\n \n\n\n\n\n \n \n \n

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That possibility is stated in ISO 13849-2, Table D-4.<\/p>\n<\/div> <\/div>\n <\/div>\n \n \n \r\n\r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n <\/picture>\r\n\r\n \r\n\r\n \r\n \r\n <\/div>\n \n <\/div>\n <\/section>\n\n \n\n\n\n\n \n \n \n

\n\n \n
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\n Welding of contact elements in contactors <\/h2>\n <\/div>\n <\/div>\n \n \n \r\n\r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n <\/picture>\r\n\r\n \r\n\r\n \r\n \r\n <\/div>\n \n
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Manufacturers may consider to adopt the architecture shown in Figure 4.18 {4.11.3.2.1} and claim that a PL = d or a SIL 2 level of reliability can be reached. In order to make that possible, a fault exclusion on the contactor KP1<\/sub> is needed. However that is not allowed by neither IEC 62061 nor ISO 13849-1. That is clearly stated in ISO 13849-2, Table D.9.<\/span><\/p>\n<\/div> <\/div>\n \n \n

<\/div>\n \n\n <\/div>\n <\/section>\n\n \n\n\n\n\n \n \n \n
\n\n \n \n \n \r\n\r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n <\/picture>\r\n\r\n \r\n\r\n \r\n \r\n <\/div>\n \n
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 <\/p>\n

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<\/div>\n \n\n <\/div>\n <\/section>\n\n \n\n\n\n\n \n \n \n
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In other words, it is not possible to claim compliance with neither of the two standards for high demand mode Safety systems when a fault exclusion is applied on the Non-opening of contact elements due to permanent welding. <\/em>That is valid even in case the value of the nominal current of the contactor overcurrent protective device has a safety factor of 0,6 or lower<\/strong>.<\/p>\n

The reason is that a contactor has to be protected from overloads and short circuits with a proper overcurrent protective device<\/strong> (Branch Circuit Protective Device, in North American language): the reason is to avoid systematic failures<\/strong>. Once that is done, the contactor random failure rates can be considered \u201creal\u201d. The fact of \u201cover protecting\u201d the contactor may increase its B10D<\/sub> value but it is not correct to claim an infinite value of B10D<\/sub><\/strong>. ISO 13849-1, table C.1, states a value of B10D<\/sub> of 400.000 in case the contactor is subject to a current equal to its \u201cnominal load\u201d. It also indicates a B10D<\/sub> of 20.000.000 in case the contactor is subject to a \u201csmall load\u201d (meaning 20% of its nominal load). Please also refer to \u00a74.12.3.2.<\/p>\n

Those considerations are also valid for auxiliary contactors used as inputs of a safety logic. Figure 4.19 {4.11.3.2.3} shows two examples of input subsystems (Pressure Transmitter, a safety module with an internal threshold and auxiliary contactors) that can reach PL d or SIL 2.<\/p>\n<\/div> <\/div>\n <\/div>\n \n \n \r\n\r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n <\/picture>\r\n\r\n \r\n\r\n \r\n \r\n <\/div>\n \n <\/div>\n <\/section>\n\n \n\n\n\n\n \n \n \n

\n\n \n\n
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However, using the architecture shown in Figure 4.20 {4.11.3.2.4}, a maximum of PL c or SIL 1 can be reached.<\/p>\n<\/div> <\/div>\n <\/div>\n \n \n \r\n\r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n \r\n <\/picture>\r\n\r\n \r\n\r\n \r\n \r\n <\/div>\n \n <\/div>\n <\/section>\n\n \n","protected":false},"excerpt":{"rendered":"

it is not possible to claim compliance with neither of the two standards for high demand mode Safety systems when a fault exclusion is applied on the Non-opening of contact elements due to permanent welding. That is valid even in case the value of the nominal current of the contactor overcurrent protective device has a safety factor of 0,6 or lower.<\/p>\n","protected":false},"author":182,"featured_media":41847,"parent":41828,"menu_order":1,"template":"","meta":{"_acf_changed":false,"footnotes":""},"tipologia_approfondimento":[48],"class_list":["post-41840","approfondimento","type-approfondimento","status-publish","has-post-thumbnail","hentry","tipologia_approfondimento-functional-safety-300321"],"acf":{"sottotitolo":"","allegati":null},"yoast_head":"\nOther examples of Fault Exclusions - 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\/other-examples-of-fault-exclusions\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Other examples of Fault Exclusions - Gt-Engineering\" \/>\n<meta property=\"og:description\" content=\"it is not possible to claim compliance with neither of the two standards for high demand mode Safety systems when a fault exclusion is applied on the Non-opening of contact elements due to permanent welding. 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