Ups Reliability Measures
Like most things, these can be massaged into looking more relaxed than they actually are. The important question to ask is: what was the basis for their calculation? There are two primary approaches: 1) A record of the total number of failures for a particular UPS size over a given time period. Commonly adopted by UPS manufacturers, this is a valuable approach if the field population is large and the time period long enough (more than the typical life expectancy of a UPS, which is five to ten years). 2) A system value calculated from the known MTBF values of components and assemblies. Obviously, this approach is more complex and relies on following standardised calculation formats.
Mean Time to Repair Mean Time to Repair (Mean Time to Restore) is the time taken to return an uninterruptible power supply to normal operation from shutdown. Online UPS are designed to fail safely to mains; therefore, the MTBF calculation of the mains power supply is also an important consideration along with mean time to repair (or average repair time). As it is highly unlikely for a service engineer to be onsite at the very moment a UPS fails, MTTR needs also to include a travel time element. This also assumes the service engineer is carrying the required parts needed to fix the problem in a single visit, which is sometimes not the case. Uninterruptible power supply manufacturers may only provide a figure based on the actual repair time.
Although this may be a satisfactory comparison tool, it is not a true representation of reliability.
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Pisac monitoring site
20.06.2010
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