industrial//reliability

Reliability is the probability that a component or a system keeps performing its function, under stated conditions, for a stated time, and it is the quantity that maintenance, warranties and spare parts are planned on. It is estimated from the times at which units fail, and it is described by the distribution of those lifetimes rather than by one number, because two products with the same average life can fail on very different schedules.

Reliability is the probability that a component or a system keeps performing its function, under stated conditions, for a stated time, and it is the quantity that maintenance, warranties and spare parts are planned on. It is estimated from the times at which units fail, and it is described by the distribution of those lifetimes rather than by one number, because two products with the same average life can fail on very different schedules.

The tool that turns lifetimes into decisions is the hazard rate, the chance that a unit still working fails in the next short interval. A hazard that falls with age points at defects of manufacture, a constant one at random causes, a rising one at wear, and the bathtub curve puts the three in sequence.

Mean time between failures is the figure most often quoted and the least informative on its own. It says nothing about how failures are spread, and it is the reciprocal of the hazard only when the hazard is constant.

Parts that must all work multiply their reliabilities. Ten components each 99% reliable over a year give a system about 90% reliable, so long chains are made reliable by removing parts or by adding redundancy, rarely by perfecting each one.

Reliability predicts how often a system will fail; finding which part failed once it has is fault diagnosis.