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PM-related reliability and safety

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PM-related reliability and safety

A device’s PM-related reliability is defined as how frequently the device fails from a PM-preventable cause, such as either the premature failure of a component identified by the manufacturer as not intended to last for the designed lifetime of the device without some kind of periodic restoration, or the deterioration of the device to an unacceptable level with respect to a critical performance or safety test – whichever is the most frequent. If the device failures can have adverse outcomes then the observed PM-related reliability also provides a measure of the level of safety of each device in the program. The different combinations have been divided into five levels of what the TF calls the device’s priority for PM. (See Table 12.)

Because they are usually quite rare, the rate at which these failures occur is best expressed as a mean time between failures (MTBF). The MTBF is simply the inverse of the failure rate. For example, a device that failed twice in 9 years has an MTBF of 4.5 years. It can also be expressed as the number of device-years of device experience divided by the total number of device failures occurring during the observation period.

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