Learning Objectives

4s-1: Define reliability and compute the reliability of a product system.

Reliability is the probability that a component, product, or system can perform its intended function over a period of time under a given set of normal operating conditions. The reliability of a product or component can also be expressed as the average length of time elapsed before the product or component fails, known as MTBF (mean time between failures). Because a product or system is made up of many components, the overall reliability of a product or system depends on the reliability of its individual components and the way in which they are arranged. By ascertaining the number of working or failed components, the reliability of the product or system can be established. For example, for a system to function properly, all of its individual components must also be working. The overall reliability of that system is a product of the reliabilities of its individual components. Thus, if there are n components in a system (S) with individual reliabilities of R (C1), R (C2), R (C3), etc., up to R (Cn), then the overall reliability of the system RS is given by: R (S) = R (C1) × R (C2) × R (C3) … × R (Cn)

4s-2: Distinguish among the concepts of reliability, maintainability, and availability.

Reliability is the probability that a component, product, or system can perform its intended function over a period of time under a given set of normal operating conditions of its use. Availability is the percentage of the time that the system or equipment is operating properly when it is needed for use. The definition of availability implies it is that fraction of the time that the equipment or system has not failed or undergoing repairs. Maintainability is the ease with which the equipment or system can be repaired or serviced. Note that reliability does not take into consideration the time it would take to complete the repairs and bring the equipment or system back to working condition, making it, hence, available for use. If the equipment or system has been properly maintained, then it would take less time to repair and the availability of the equipment or system for use would be high.

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