Last edit: 26/06/2023
The Failure Modes, Effects, and Diagnostic Analysis (FMEDA) is used to calculate the product random failures: it is an extension of the classic FMEA procedure. The technique was first developed for electronic devices but it is now used for mechanical and electro-mechanical devices as well.
A FMEDA is done by examining each component in a product and, for each one, the effect of a random failure on the product is analysed. Questions asked are: will a failure in a specific resistor cause the product to fail safe, fail dangerous or lose calibration? If the serial communication line from the A/D to the microprocessor gets shorted, how does the product respond? If this spring fractures, does that cause a dangerous or a safe failure? In this way, the failure rate of each component is analysed and the various groups are added. The end result is a product specific set of failure data that includes failure rates for each failure mode: failure rates that are detected and undetected by diagnostics, Safe Failure Fraction calculations and, often, an explanation on how to use the numbers for safety verification calculations.
A FMEDA is sometimes done by the product manufacturer but, typically, it is done by third parties.
It should be emphasized that a FMEDA provides failure rates, failure modes and diagnostic coverage effectiveness for random hardware failures. It does not include failure rates due to “systematic” causes, including incorrect installation, inadvertent damage, incorrect calibration or any other human error.
Please also consider that, in order to estimate the component failure rates, it is also possible to use field data. That is what IEC 61508-2 refers to as Route 2H. Please look at § 7.4.4.3.3 of the mentioned standard.