The FMEDA (Failure Modes Effects and Diagnostics Analysis) is a critical systematic analysis process to determine the Safety Integrity Level (SIL) of a hardware design and is required by IEC 61508, IEC 62061, ISO 13849-1, and ISO 26262 to limit the probability of dangerous undetectable failures in hardware.

Safety Parameters

Each component in our component database (located on a SQL server) has a set of parameters which include data sheets, 3D models, safety parameters, stock control, purchasing information etc.

For each part that we add to the database we start off by setting the lambda value (FIT – Failures per 10^9hrs of operation). Typically these values are available from the manufacturer (often under NDA) or from various calculation tools or military handbooks.

Next we enter in the failure modes. Failure modes are often derived from historical sources such as military handbooks. The failure mode distribution is important because it is used later on in the FMEDA process when we apply diagnostic tests to the hardware.

Finally we enter the component ratings. Ratings are parameters like limiting voltages or temperatures, currents and frequencies. The component ratings are used to determine sufficient design margin later on in the FMEDA process.

In the next entry we will discuss configuring components in Altium Designer for use with the SafeTool FMEDA process.

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To setup the FMEDA process in SafeTool a few elements must be manually entered:

• The Altium Designer PCB Project
• The type of hardware architecture:
  • Type A: Components with well known failure modes
  • Type B: Complex components / silicon
• The number of channels in the system
• A justification for each choice
• The Demand Mode

The information entered into SafeTool is used at the final step in determining the SIL level for the current design.

The next step in the FMEDA process is to apply any diagnostic coverage to each failure mode of each component.

The failure mode entry consists of:

• The implemented diagnostic
• The effect of the diagnostic (high, medium, low)
• The justification per IEC61508 tables.

For each component we have a series of minimum and maximum ratings as specified in the schematic capture phase.

SafeTool details each of the ratings and determines the upper and lower percentage for each rating item.

Items that are greater than 60% of their tolerance are highlighted in orange, and items that are around or greater than 100% of their tolerance is highlighted in red allowing further testing or component changes.