MTBF is called Mean Time Between Failures which is the average value of the time when the new product starts to work under the specified working environment until the first failure. Specifically, it refers to the average working time in between two failures. Longer the MTBF means higher the reliability and better ability. The unit of MTBF is by hour, only used for repairable products.
Due to MTBF is an important reference value to be considered when designing products, engineers or designers will use various methods and standards to evaluate the MTBF value of products. There is an easy way to calculate the MTBF. We could estimate the MTBF according to a formula based on failure rate. The formula is MTBF=1/λ. λ: Failure rate (times/year). So, we need to collect data from the actual performance of the product first, and then, we could use this formula to get the MTBF.
As mentioned above, MTBF is a reliability estimation standard. However, the reliability refers to the ability of the product to complete the specified function under the specified conditions and within the specified time; and the failure of the product to complete the specified function means that it is faulty. For example, 100 pcs hard drivers in operation have 2 failures within a year, and its failure rate (λ) is 0.02 times/year.
且MTBF=1/λ。假設一個硬碟的MTBF為120萬小時。 120萬小時約為137年，但這並不代表每個硬碟都能無故障運作137年。代入MTBF=1/λ公式可知λ=1/MTBF=1/137年，可計算出年平均故障率約0.7%。這意味著一年內，平均每1000個硬碟中，會有7個發生故障。
