ABSTRACT
J. Kamenicky Technical University of Liberec, Liberec, Czech Republic
ABSTRACT: There is often used simple measurement of physical quantity for controlling and/or safety systems in praxis. If there is higher level of safety (availability) needed, it can be used more reliable items. It means to use better materials or affect the environment, where sensor should work in. Next option is usage of so called Self Validating Sensors. However the reliability of items is limited and when it is needed more and more reliable system, one must back up, otherwise the solution would cost excessive price. Multiple measurements and its sequential processing by logical evaluating item is the gist of submitted paper. There is very often used “2 out of 3” system in praxis, but it is not the only one possible solution of described situation. This contribution deals with assessment of justification of using such systems in comparison with other options – simple analog combination of three signals and “advanced k out of n” system, which can reduce number of inputs depending on their validity. I supposed physical quantity measuring by three independent sensors. There are well-arranged advantages and disadvantages of each connection method and graphically compared reliability parameters of reflected options. These parameters depend on ratio between failure rate of revealed and unrevealed failures. There are shown graphs and tablets with results of computing reliability parameters for mentioned options of signals evaluation. This contribution deals only with hardware of measuring systems, not with human factor, common cause failures and other hardly defined states. On the other hand I varied revealed and unrevealed failures, dangerous states and “safe” false actions of safety systems, so every sensor (information line) has five possible states, including operating one.
