The are some items to quantify fan life:

- MTTF- Mean Time to Failure
- MTBF- Mean Time between Failure
- L10- Failed to 10% Times

Testing a batch of fan, untill some of them fail, and then caculate the fan life time. The failure criteria include:

- Fan not function.
- Current over 15% of original.
- Speed under 15% of original.
- Noise over 3dB(A) of original.

# MTTF Test Procedure and Calculation Method

- Random sampling 50 units.
- Perform function test in advance and set up temperature.
- Function test once a week.
- Test time for at least 3000 hrs.
- Based on Total Test Hours( T ) and Failure Quantity ( r ) and refer Chi-Square table with Confidential Level (CL) to get MTTF.

t : Total test time

χ : Chi- Square table

α : Producer ’s risk ; α=10% (CL:90%;CL=1- α )

: Failure Q ’ty

υ: Degrees of freedom, υ=2γ+2;

Chi-square-table:

http://sites.stat.psu.edu/~mga/401/tables/Chi-square-table.pdf

Example:

MTTF | 28020 |

test sample | 50 |

Test Time | 3000 |

Fail quantity | 2 |

Failure first time | 2400 |

Failure second time | 2736 |

Total test hour | 149136 |

coefficient | 10.645 |