Misconceptions about MTBF

Misconceptions about MTBF

| 2/20/2011 12:05:15 PM

“Mean time between failures (MTBF) is an important element when considering the purchase of any product. This is particularly true with network equipment, as reliability is very important. Many companies have to quantify the performance and longevity of a product as part of the bid process,” says Susan Stanley, Senior Technical Support Engineer.
MTBF is a basic measure of reliability for reparable items. It can be described as the number of hours that pass before a component, assembly, or system fails. It is a commonly-used variable in reliability and maintainability analyses. It is typically represented in units of hours. The higher the MTBF number is, the higher the reliability of the product.

MTBF Defined
A common misconception about MTBF is that it is equivalent to the expected number of operating hours before a system fails, or the “service life”. It is not uncommon, however, to see an MTBF number on the order of 1 million hours, and it would be unrealistic to think the system could actually operate continuously for over 100 years without a failure. The reason these numbers are often so high is because they are based on the rate of failure of the product while still in their “useful life” or “normal life”, and it is assumed that they will continue to fail at this rate indefinitely. While in this phase of the product’s life, the product is experiencing its lowest (and constant) rate of failure. In reality, wear-out modes of the product could limit its life much earlier than its MTBF figure based on variables such as whether the product has been properly installed per the instructions. It is quite possible to have a product with an extremely high MTBF, but an average or more realistic expected service life.
A product is often assembled with many components, and each component has its own MTBF. An algorithm is used to calculate the MTBF by factoring in all of the components and determining the overall MTBF. A Bill of materials (BOM) provides the list of components and each one is identified along with its MTBF value based on the component manufacturer’s specification sheet.

B&B Electronics submits such data to an independent organization that reviews and compiles the MTBF value for each component in our products. Over time, as products are redesigned (for enhancements, cost reduction and to reduce environmental impact) the MTBF can change. As a result, B&B Electronics does not publish MTBF information on its website nor in other documentation. While the customer will need to contact B&B Electronics to request the MTBF, the customer can be sure that he will receive the most current and accurate information.

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