![]() ![]() ![]() If oil changes were properly scheduled as a maintenance activity, then availability would be 100%. With an unscheduled half-hour oil change every 50 hours – when a dashboard indicator alerts the driver – availability would increase to 50/50.5 = 99%. The automobile in the earlier example is available for 150/156 = 96.2% of the time. The "availability" of a device is, mathematically, MTBF / (MTBF + MTTR) for scheduled working time. Even if noticed, these failures may not trigger immediate corrective measures because the "protected" machine is still running and it may be more important to keep it running than to repair or replace the UPS. Failures for functions 2, 3 or 5 may not be obvious, because the "protected" machine is still running on main power or on the battery supply. ![]() There is no question that the UPS has failed if it prevents main power from flowing to the machine being protected (function 1). Emit a signal to indicate that the main power is off.Supply continuous power to the machine being protected.Store power in a battery, up to the battery's full charge.Condition the power by limiting surges or brownouts.Allow power to flow from the main source to the machine being protected.Let us briefly examine one device's "failures":Īn Uninterruptible Power Source (UPS) may have five functions under two conditions: Like automobiles, most manufacturing equipment will be repaired, rather than replaced after a failure, so Mean Time Between Failures is the more appropriate measurement. Assuming 6 hours to remove and replace the engine (MTTR), Mean Time Between Failures is 150 hours. On the other hand, without oil changes, an automobile's engine may fail after 150 hours of highway driving – that is the MTTF. A light bulb in a chandelier is not repairable, so MTTF is most appropriate. This distinction is important if the repair time is a significant fraction of MTTF. Some would define MTBF – for repair-able devices – as the sum of MTTF plus MTTR. .In other words, the mean time between failures is the time from one failure to another. "Mean Time To Repair" is the average time that it takes to repair something after a failure.įor something that cannot be repaired, the correct term is "Mean Time To Failure" (MTTF). As reliable production processes are crucial in a Lean Manufacturing environment, MTBF is vital for all lean initiatives Usually people think of it as the average time that something works until it fails and needs to be repaired (again). "Mean Time Between Failures" is literally the average time elapsed from one failure to the next. "Mean Time" means, statistically, the average time. Mean Time To Repair = (Total down time) / (number of breakdowns) Mean Time Between Failures = (Total up time) / (number of breakdowns) Mean Time Between Failures and Mean Time To Repair are two important KPI's in plant maintenance management and lean manufacturing. ![]()
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