LEC4-Maintainability Measures and Functions

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LEC4-Maintainability Measures and Functions
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Maintainability Measures and Functions   ã Various measures are used in maintainability analysis: 1.Mean time to repair (MTTR) 2.Mean preventive maintenance time 3.Mean maintenance downtime In addition to these measures, maintainability functions are used to predict the probability that a repair, starting at time t =0, will be completed in a time t.  Mean Time to Repair (MTTR) ã It measures the elapsed time required to perform a given maintenance activity. ã MTTR is expressed by: MTTR = ( ∑   λi CMTi ) / ∑   λi  Where: k = number of units or parts λi  = failure rate of unit/part i , for i= 1, 2, 3, ....., k, CMTi= corrective maintenance or repair time required to repair unit or part i, for i= 1, 2, 3, ....., k,  Mean Time to Repair (MTTR)   ã Usually, times to repair follow exponential, lognormal, and normal probability distributions.  Mean Preventive Maintenance Time ã The mean preventive maintenance time is defined  by: MPMT = ( ∑  FPMi x ETPMTi) / ∑  FPMi Where: MPMT = mean preventive maintenance time M = total number of preventive maintenance tasks FPMi = frequency of preventive maintenance task i, for I = 1, 2, 3, ....., m, ETPMTi = elapsed time for preventive maintenance task i, for i= 1, 2, 3, ....., m,

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