The autodiagnosis system of an intelligent measuring instrument

The methodological aspects and the design of the automatic self-diagnosis (auto-diagnosis) system of a high-performance measuring instrument for electrical quantities are described. The auto-diagnosis system can recognise not only severe failures which require out-of-service instrument setting, but also slight failures simply affecting accuracy or not basic features; in the latter case, the instrument is set working in degraded conditions. The auto-diagnosis process is performed making reference to the instrument architecture, based on independent and interconnected functional units, and using an analysis technique, called 'extending ring', to detect failing subsystems. The auto-diagnosis system is divided into two main parts, conceived for separate aims: one is named 'off-line full test auto-diagnosis system' and performs, at power up or on user request, a full comprehensive test; the other, named 'on-line auto-diagnosis system', continuously monitors the instrument behaviour while operating normally to reveal failures or error conditions that can derate the whole performance.