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the following ratio: Σ(λ MPF(Per/Det) +λ S) /Σ(λ MPF +λ S).Īgain, this concept looks very similar to the concept of IEC 61508 diagnostic coverage, except that it also includes the possibility of driver “perception” of and response to faults.
Iso metric plus#
The latent fault metric is defined as the sum of the multiple-point faults that are perceived by the driver or detected by diagnostics plus the safe faults divided by the total multiple-point and safe faults, i.e. In other words, if the single-point fault metric is to low, additional fault tolerance will convert those faults to multiple point faults and improve the metric. The inclusion of multiple-point faults is a somewhat unusual approach, but it is probably why the latent-fault metric is also calculated.Ī quantitative target for the single-point fault metric is set by the standard based on the ASIL target:īy combining safe faults and multiple-point faults into the same metric, this metric has a similar impact to the SFF-based hardware fault tolerance requirements in IEC 61508. This ratio looks suspiciously like the IEC 61508 concept of Safe Failure Fraction (SFF), with the notable exception that multiple-point faults are also considered “safe”.
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Note: The name “single-point fault metric may initially be confusing, since the single point fault rate (λ SPF) does not appear in the formula! However, the formula can equivalently be written as: 1- Σ(λ SPF + λ RF) / Σ(λ) the following ratio: Σ(λ MPF + λ S) / Σ(λ) The single-point fault metric is defined as the sum of the multiple-point faults and the safe faults divided by the total failure rate, i.e. Λ S: Safe Faults Single-point Fault Metric a DU fault where there are no diagnostics) The total failure rate λ can be broken down into:
Iso metric iso#
B, C, or D).īefore discussing the metrics, it is useful to remember the taxonomy of faults/failures (from Part 1) used by ISO 26262, which is different from IEC. Higher is better.Īs with many of the ISO requirements, these metrics only apply to higher ASIL function (i.e.
Iso metric verification#
The later sections of Part 5 discuss the quantitative verification of the hardware via various metrics, which is where the rest of this article will focus. The ISO standard does not go into great detail on the hardware design process (neither does IEC 61508), so I will not either. Hardware Safety Requirements Verification Report.Hardware-software Interface Specification.Hardware Safety Requirements Specification.The hardware detailed design is captured in three main deliverables Consistency with the higher-level safety specifications.
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Iso metric software#
In this part, the technical safety requirements developed in Part 4 are allocated to specific hardware and software designs. Part 5 of the standard is dedicated to the development of the hardware required to achieve safety goals (software is covered in the next part).
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As we will see below, some of these differences are just terminology, while others are more fundamental. This part is where ISO 26262 differs the most from IEC 61508. In particular, we will take a close look at the Fault Metrics defined by the standard. In today’s post, we will take a deep dive into Part 5 of ISO 26262, which covers product development at the hardware level.