Abstract: It's generally viewed that system operating time is measured deterministically. Unfortunately this viewpoint becomes unreasonable due to uncertainties attached to the system operating time; Randomness and fuzziness. In this paper we show the system reliability behavior in the presence of uncertainties attached to the system operating time. The concepts of fuzzy reliability and equivalent operating time are then proposed.

Key words: nacertainty, operating time, randomness, fuzziness, fuzzpreliability, equivalent operating time