Frequently Asked Question
As per IEC 61508 part 2 (ed. 2) clause 7.4.9.4-J, diagnostics is considered in the realization of the SFF. As per IEC 61508 part 2 (ed.2) clause 7.4.5.4, diagnostic test interval shall be such that the sum of diagnostic test interval and the time to to pe
Last Updated 5 years ago
Does exSILentia conform to the SSF credit requirement of 7.4.4.1.5 for IEC 61508 1H Architectural Constraints? Yes.
There is a common misconception on the statement in the 61508 standard regarding the taking of credit for diagnostics; “credit shall only be taken for the diagnostics if the sum of the diagnostic test interval and the time to perform the repair of a detected failure is less than the MTTR used in the calculation”. The Mean Time To Restore, is by definition the sum of the detection time + time to prepare the repair + actual time to perform the repair + time to put component back into service. So, by definition, the MTTR is always greater than the sum of diagnostic test interval + time to perform the repair. Based on this, the standard states that we can always take credit for diagnostics.
There is a common misconception on the statement in the 61508 standard regarding the taking of credit for diagnostics; “credit shall only be taken for the diagnostics if the sum of the diagnostic test interval and the time to perform the repair of a detected failure is less than the MTTR used in the calculation”. The Mean Time To Restore, is by definition the sum of the detection time + time to prepare the repair + actual time to perform the repair + time to put component back into service. So, by definition, the MTTR is always greater than the sum of diagnostic test interval + time to perform the repair. Based on this, the standard states that we can always take credit for diagnostics.