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        How is fan life defined?


        The air moving industry typically rates fan life using two terms: L10 life of the bearing and MTBF of the electronic components.
        L10 life is defined as the number of hours after which 10% of the fans in operation would be expected to experience bearing failure. This number is obtained using fan life test data and Weibull function statistical analysis to obtain a failure distribution prediction. Bearings usually fail because of lubricant degradation over time, which is greatly affected by the ambient temperature in which the fan is operating. This is why bearing L10 life numbers are always provided at a specific ambient temperature. 
        MTBF (mean time between failures) predications are based on assumed constant failure rates over the useful lifetime of electronic components like resistors, capacitors and semi-conductors. These predictions are usually based on MIL-HDBK-217 or Bellcore TR-332. Sometimes requests are made for the MTBF of the complete air mover assembly. However, because mechanical or electromechanical components like bearing and motors do not have constant failure rates over time, this would not be a valid calculation


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