{"id":3222,"date":"2023-01-04T16:22:35","date_gmt":"2023-01-04T15:22:35","guid":{"rendered":"https:\/\/www.gt-engineering.it\/normative-tecniche\/%tipologia_normativa%\/tr-24119-the-fault-masking-and-the-diagnostic-coverage\/"},"modified":"2024-09-22T10:31:21","modified_gmt":"2024-09-22T09:31:21","slug":"tr-24119-the-fault-masking-and-the-diagnostic-coverage","status":"publish","type":"normativa_tecnica","link":"https:\/\/www.gt-engineering.it\/en\/technical-standards\/en-iso-standards\/tr-24119-the-fault-masking-and-the-diagnostic-coverage\/","title":{"rendered":"ISO\/TR 24119: Fault Masking and Diagnostic Coverage"},"content":{"rendered":"\n\n \n \n \n
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ISO\/TR 24119 is a Technical Report published for the first time in November 2015 with the title “Safety of machinery \u2014 Evaluation of fault masking serial connection of interlocking devices associated with guards with potential free contacts”. Its content is now included in Annex J of ISO 14119: 2024<\/a>. The key concepts remain the same as in the ISO TR.<\/strong><\/p>\n

Before this document was issued, it wasn’t clear how many interlocks could be wired to one safety channel and how much was the Diagnostic Coverage of the Safety Subsystem (Input\u00a0+ Logic). When connecting several interlock to one safety channel a fault may be masked: the problem is therefore called Fault Masking<\/strong>.<\/p>\n

This Technical Report explains what the problem is and, depending upon the number of interlocks, how they are connected (Loop or Star) and how often they are activated, it gives a method how to calculate the DC of the Subsystem.<\/p>\n

The goals of this Technical Report are therefore the following:
\n\u2014 guidance for users for estimation of the maximum DC values;
\n\u2014 design guidance for SRP\/CS.
\nN.B. Interlocking devices with integrated self-monitoring are not included in the scope of this Technical\u00a0Report.<\/strong>
\nN.B.\u00a0Limitation is also given by the diagnostic means implemented in the logic unit.
\nN.B.\u00a0This Technical Report is not restricted to mechanical actuated position sensors.<\/p>\n

Hereafter are some useful\u00a0definitions contained in the standard:<\/p>\n

3.1 Fault Masking<\/strong>. unintended resetting of faults or preventing the detection of faults in the SRP\/CS by operation of parts\u00a0of the SRP\/CS which do not have faults.<\/p>\n

3.2 Series Connected devices.<\/strong> devices with potential free contacts (B1 to Bn) are connected in series to one logic unit (K) which does\u00a0the diagnostics<\/p>\n

3.6 Star Cabling.<\/strong> cabling structure where every interlocking device is wired with a single cable to the electric cabinet or\u00a0enclosure<\/p>\n

3.8 Loop Cabling.<\/strong> cabling structure where a single cable from the electric cabinet is wired to the first interlocking device\u00a0and from this interlocking devices to the next, and so on, until the last interlocking device while the\u00a0signals return to the electric cabinet in a separate cable<\/p><\/blockquote>\n

 <\/p>\n

In the picture above, there are two Interlocks in series. Two cases are considered:<\/strong><\/p>\n

Case\u00a01 (No fault Masking):<\/strong><\/p>\n