For many safety-critical or safety-relevant medical devices as governed by IEC 60601-1, in order for some components to meet the single fault safe requirements i.e. remain free of unacceptable risk, components with high-integrity characteristics may be required as defined in section 4.9 of the standard.
How do you go about verifying that the component fulfils these high-integrity characteristics?
There are several techniques listed in Annex A of 60601-1, including calibration, lot testing and control of manufacturing defects. However, much of the assessment of suitable components and their implementation in a product can be achieved through inherent good design techniques. Also, listed in Annex A are techniques such as:
– use of relevant component standards;
– failure mode characteristics;
– environmental conditions.
There are many applicable standards cited in other industries that enable the assessment of failure mode characteristics and also based on the environmental conditions and the component usage.
Standards such as the Siemens SN 29500, IEC TR 62380 or the MIL-HDBK-217 enable estimation of Failure in Time (FIT) rates for components. These FIT rates, then being factored based on component stress e.g. voltage levels, temperature, current consumption or ripple current. Through these techniques, a designer can assess derating measures for the component stress, to reduce the likelihood of premature component failure.
Automotive components are also qualified through stress testing in accordance with the Automotive Electronics Council AEC-Q200 (passive components) or AEC-Q100 (integrated circuits). Choosing components that meet these qualification standards also gives increased confidence in the component robustness for an application within a product where a high-integrity component is required.
Hence for meeting the requirements of IEC 60601-1 High-Integrity Components, there are many industry sources around that enable the designer to identify and assess the components suitability for the given application. These techniques will not guarantee a component will not fail, but they do provide a quantitative means to assess the probability of failure.
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