{"id":4634,"date":"2023-01-09T15:39:39","date_gmt":"2023-01-09T14:39:39","guid":{"rendered":"https:\/\/www.gt-engineering.it\/?post_type=normativa_tecnica&#038;p=4634"},"modified":"2023-06-27T08:31:26","modified_gmt":"2023-06-27T07:31:26","slug":"annex-b-iec-62061-scs-design-methodology","status":"publish","type":"normativa_tecnica","link":"https:\/\/www.gt-engineering.it\/en\/technical-standards\/en-iec-standards\/iec-62061-functional-safety-of-machineries469677178\/annex-b-iec-62061-scs-design-methodology\/","title":{"rendered":"Annex B: Example of SCS design methodology"},"content":{"rendered":"\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        \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\/3\"\n            >\n                \r\n\r\n    \r\n        \r\n            \r\n                \r\n                    <picture\r\n                        class=\"\"\r\n                                            >\r\n                                                                                                        <source\r\n                                media=\"(max-width: 150px)\"\r\n                                width=\"150\"\r\n                                height=\"150\"\r\n                                srcset=\"https:\/\/www.gt-engineering.it\/wp-content\/uploads\/2023\/01\/Annex-B-150x150.jpg.webp\"\r\n                                type=\"image\/webp\"\r\n                            \/>\r\n                                                                                <source\r\n                                media=\"(max-width: 300px)\"\r\n                                width=\"300\"\r\n                                height=\"175\"\r\n                                srcset=\"https:\/\/www.gt-engineering.it\/wp-content\/uploads\/2023\/01\/Annex-B-300x175.jpg.webp\"\r\n                                type=\"image\/webp\"\r\n                            \/>\r\n                                                                                <source\r\n                                media=\"(max-width: 600px)\"\r\n                                width=\"600\"\r\n                                height=\"350\"\r\n                                srcset=\"https:\/\/www.gt-engineering.it\/wp-content\/uploads\/2023\/01\/Annex-B.jpg.webp\"\r\n                                type=\"image\/webp\"\r\n                            \/>\r\n                                                                                <source\r\n                                media=\"(max-width: 600px)\"\r\n                                width=\"600\"\r\n                                height=\"350\"\r\n                                srcset=\"https:\/\/www.gt-engineering.it\/wp-content\/uploads\/2023\/01\/Annex-B.jpg.webp\"\r\n                                type=\"image\/webp\"\r\n                            \/>\r\n                                                                            <img\r\n                            class=\"a-image transparent border-image h-auto  w-full\"\r\n                                                        srcset=\"https:\/\/www.gt-engineering.it\/wp-content\/uploads\/2023\/01\/Annex-B.jpg.webp\"\r\n                                                        title=\"Annex B\"\r\n                                                        type=\"image\/webp\"\r\n                        \/>\r\n                    <\/picture>\r\n\r\n                \r\n\r\n                    \r\n    \r\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 style=\"margin: 0cm 0cm 8pt; text-align: justify;\"><span style=\"text-align: justify;\"><strong>Annex B <\/strong>contain the methodology to be followed for the design of a <strong>Safety Related Control System (SCS)<\/strong>. The annex contains the following examples:<\/span><\/p>\n<ul style=\"list-style-type: square;\">\n<li style=\"margin: 0cm 0cm 0cm 36pt; text-align: justify;\"><span style=\"text-align: justify;\"><strong>B.4.2<\/strong> Subsystem 1 design \u2013 <strong>\u201cguard door monitoring\u201d<\/strong><\/span><\/li>\n<li style=\"margin: 0cm 0cm 0cm 36pt; text-align: justify;\"><span style=\"text-align: justify;\"><strong>B.4.3<\/strong> Subsystem 2 design \u2013 <strong>\u201cevaluation logic\u201d<\/strong><\/span><\/li>\n<li style=\"margin: 0cm 0cm 8pt 36pt; text-align: justify;\"><span style=\"text-align: justify;\"><strong>B.4.4<\/strong> Subsystem 3 design \u2013 <strong>\u201cmotor control\u201d<\/strong><\/span><\/li>\n<\/ul>\n<p style=\"text-align: justify;\"><span style=\"text-align: justify;\">In the first example there is an important consideration the standard does for the <strong>SFF<\/strong> calculation in case of <strong>single channel electromechanical devices<\/strong>.<\/span><\/p>\n<p style=\"text-align: justify;\"><span style=\"text-align: justify;\">Hereafter the important language:<\/span><\/p>\n<blockquote>\n<p style=\"margin: 0cm 0cm 8pt; text-align: justify;\"><strong><span style=\"text-align: justify;\">[IEC 62061: 2021] &#8211; B.4.2.2 Evaluation of SFF<\/span><\/strong><\/p>\n<p style=\"text-align: justify;\"><span style=\"text-align: justify;\">The theoretical failure effects of the position switch are:<\/span><\/p>\n<ul>\n<li style=\"margin: 0cm 0cm 0cm 36pt; text-align: justify;\"><span style=\"text-align: justify;\"><strong>the contact will not (anymore) open<\/strong>: dangerous failure (unintended closed); <\/span><\/li>\n<li style=\"margin: 0cm 0cm 0cm 36pt; text-align: justify;\"><span style=\"text-align: justify;\"><strong>the contact will open &#8220;by itself&#8221;<\/strong>: safe failure (unintended opened, can be considered as very unlikely for an electromechanical device);<\/span><\/li>\n<li style=\"margin: 0cm 0cm 0cm 36pt; text-align: justify;\"><span style=\"text-align: justify;\"><strong>the contact will not (anymore) close<\/strong>: safe failure which do not have any influence of the safety function (unintended opened);<\/span><\/li>\n<li style=\"margin: 0cm 0cm 8pt 36pt; text-align: justify;\"><span style=\"text-align: justify;\"><strong>the contact will close &#8220;by itself&#8221;<\/strong>: dangerous failure (unintended closed).<\/span><\/li>\n<\/ul>\n<\/blockquote>\n<p style=\"text-align: justify;\"><span style=\"text-align: justify;\">And the considerations continue with the following conclusion:<\/span><\/p>\n<blockquote>\n<p style=\"text-align: justify;\"><strong><span style=\"text-align: justify;\">[IEC 62061: 2021] &#8211; B.4.2.2 Evaluation of SFF<\/span><\/strong><\/p>\n<p style=\"text-align: justify;\"><span style=\"text-align: justify;\">Practical considerations: <\/span><\/p>\n<p style=\"text-align: justify;\"><span style=\"text-align: justify;\">The opening of the guard door defines the failure modes of the position switch\u00a0 to be considered. That means that practically no safe failures of the position switch related to this safety function exist: <\/span><\/p>\n<ul>\n<li style=\"margin: 0cm 0cm 0cm 36pt; text-align: justify;\"><span style=\"text-align: justify;\">the failure mode <strong>\u201cunintended closed\u201d<\/strong> contact is always dangerous (typical dangerous failure of the position switch); <\/span><\/li>\n<li style=\"margin: 0cm 0cm 8pt 36pt; text-align: justify;\"><span style=\"text-align: justify;\">the failure mode <strong>\u201cunintended opened\u201c<\/strong> contact is not relevant for the opening of the guard door and only has an influence on the availability of the machine. It is a no effect failure (IEC 615084:2010, 3.6.14) for the defined function. Therefore, it is not a safe failure and \u03bb<sub>S<\/sub>\u00a0 = 0.<\/span><\/li>\n<\/ul>\n<\/blockquote>\n<p style=\"text-align: justify;\"><span style=\"text-align: justify;\">The reasoning means, when evaluating the <strong>SFF<\/strong> of electromechanical Input Subsystems, that normally <strong>\u03bb<sub>S<\/sub>\u22480<\/strong> and therefore:<\/span><\/p>\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: 107%;\"><span style=\"font-family: Calibri,sans-serif;\"><span style=\"font-size: 11.0pt;\"><span style=\"line-height: 107%;\"><span style=\"font-family: 'Calibri',sans-serif;\"><img decoding=\"async\" style=\"width: 182px; height: 38px;\" src=\"data:image\/png;base64,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\" \/><\/span><\/span><\/span><\/span><\/span><\/span><\/p>\n<p style=\"margin: 0cm 0cm 8pt; text-align: justify;\"><span style=\"text-align: justify;\">That reasoning is valid for the majority of <strong>electromechanical components<\/strong>. Those components would be defined as <strong>Type A<\/strong>, according to <em><a href=\"https:\/\/www.gt-engineering.it\/en\/technical-standards\/en-iec-standards\/iec-61508\/\"><strong>IEC 61508-2<\/strong><\/a><\/em> (\u00a73.4.7.1). The reasoning is not applicable to <strong>Type B<\/strong> components.<\/span><\/p>\n<p style=\"text-align: justify;\"><span style=\"text-align: justify;\">You can find on the market electromechanical components, like pressure switches, certified for <strong><em><a href=\"https:\/\/www.gt-engineering.it\/en\/insights\/process-safety-processi-gt-engineering\/high-vs-low-demand-eng\/\">high demand<\/a><\/em> safety applications<\/strong> with a SIL 2 reliability level according to <strong>IEC 62061<\/strong>. That was made possible by assuming a certain number of Safe Failures that bring the <strong>SFF &gt; 90%<\/strong>. Using the Table 6, shown hereafter, with <strong>HFT = 0<\/strong>, the component has a SIL CLAIM (old language) or an architectural constraints = SIL 2.<\/span><\/p>\n<table class=\"MsoTableGrid\" style=\"margin-left: 56.45pt; border-collapse: collapse; border: solid windowtext 1.0pt;\">\n<tbody>\n<tr style=\"height: 22.1pt;\">\n<td style=\"border: solid windowtext 1.0pt; background: #f2f2f2; width: 4.0cm; padding: 0cm 5.4pt 0cm 5.4pt; height: 22.1pt;\" rowspan=\"2\" width=\"151\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><b><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\"><span style=\"color: black;\">Safe Failure Fraction (SFF)<\/span><\/span><\/b><\/span><\/span><\/p>\n<\/td>\n<td style=\"border: solid windowtext 1.0pt; background: #f2f2f2; width: 248.1pt; border-left: none; padding: 0cm 5.4pt 0cm 5.4pt; height: 22.1pt;\" colspan=\"3\" width=\"331\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><b><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\"><span style=\"color: black;\">Hardware fault tolerance (HFT)<\/span><\/span><\/b><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<tr style=\"height: 13.2pt;\">\n<td style=\"border-bottom: solid windowtext 1.0pt; background: #f2f2f2; width: 78.0pt; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 13.2pt;\" width=\"104\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><b><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\"><span style=\"color: black;\">0<\/span><\/span><\/b><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; background: #f2f2f2; width: 3.0cm; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 13.2pt;\" width=\"113\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><b><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\"><span style=\"color: black;\">1<\/span><\/span><\/b><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; background: #f2f2f2; width: 3.0cm; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 13.2pt;\" width=\"113\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><b><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\"><span style=\"color: black;\">2<\/span><\/span><\/b><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<tr style=\"height: 21.2pt;\">\n<td style=\"border: solid windowtext 1.0pt; width: 4.0cm; border-top: none; padding: 0cm 5.4pt 0cm 5.4pt; height: 21.2pt;\" width=\"151\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 9.0pt;\">SFF &lt; 60 %<\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 78.0pt; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 21.2pt;\" valign=\"top\" width=\"104\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">Not Allowed <\/span><\/span><\/span><\/span><\/p>\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 7.0pt;\">(NOTE 1)<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 3.0cm; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 21.2pt;\" valign=\"top\" width=\"113\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 1<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 3.0cm; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 21.2pt;\" valign=\"top\" width=\"113\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 2<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<tr style=\"height: 20.8pt;\">\n<td style=\"border: solid windowtext 1.0pt; width: 4.0cm; border-top: none; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.8pt;\" width=\"151\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: 150%;\"><span lang=\"EN-GB\" style=\"font-size: 9.0pt;\"><span style=\"line-height: 150%;\">60 % \u2264 SFF &lt; 90 %<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 78.0pt; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.8pt;\" valign=\"top\" width=\"104\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 1<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 3.0cm; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.8pt;\" valign=\"top\" width=\"113\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 2<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 3.0cm; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.8pt;\" valign=\"top\" width=\"113\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 3<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<tr style=\"height: 20.35pt;\">\n<td style=\"border: solid windowtext 1.0pt; width: 4.0cm; border-top: none; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.35pt;\" width=\"151\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 9.0pt;\">90 % \u2264 SFF &lt; 99 %<\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 78.0pt; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.35pt;\" valign=\"top\" width=\"104\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 2<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 3.0cm; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.35pt;\" valign=\"top\" width=\"113\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 3<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 3.0cm; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.35pt;\" valign=\"top\" width=\"113\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 3<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<tr style=\"height: 20.7pt;\">\n<td style=\"border: solid windowtext 1.0pt; width: 4.0cm; border-top: none; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.7pt;\" width=\"151\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 9.0pt;\">SFF \u2265 99 %<\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 78.0pt; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.7pt;\" valign=\"top\" width=\"104\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 3<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 3.0cm; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.7pt;\" valign=\"top\" width=\"113\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 3<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<td style=\"border-bottom: solid windowtext 1.0pt; width: 3.0cm; border-top: none; border-left: none; border-right: solid windowtext 1.0pt; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.7pt;\" valign=\"top\" width=\"113\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-family: Arial,Helvetica,sans-serif;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 10.0pt;\">SIL 3<\/span><\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<tr style=\"height: 20.7pt;\">\n<td style=\"border: solid windowtext 1.0pt; width: 361.5pt; border-top: none; padding: 0cm 5.4pt 0cm 5.4pt; height: 20.7pt;\" colspan=\"4\" width=\"482\">\n<p style=\"margin: 0cm 0cm 8pt; text-align: center;\"><span style=\"font-size: 11pt;\"><span style=\"line-height: normal;\"><span lang=\"EN-GB\" style=\"font-size: 8.0pt;\">NOTE 1: For subsystems which have a SFF &lt; 60 %, HFT = 0 and that use well-tried components, SIL 1 can be achieved.<\/span><\/span><\/span><\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p style=\"text-align: justify; margin: 0cm 0cm 8pt;\"><span style=\"text-align: justify;\">With the new edition of <strong>IEC 62061<\/strong>, that will be more difficult to demonstrate, since the standard recommends, in case of <strong>electromechanical components<\/strong>, that <strong>there are no safe failures<\/strong> and therefore, once again, <em><strong>SFF = DC<\/strong><\/em>.<\/span><\/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>Annex B contain the methodology to be followed for the design of a Safety Related Control System (SCS). 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