MTBF - Background and Calculation

MTBF stands for Mean Time Between Failure and gives an average interval in operating hours between delivery and first failure or between two failures of the product. This only includes failures due to technical or production issues or due to aging process of components. External sources like overvoltage, extending the temperature range or mechanical issues due to mishandling are not included in this statistical figure.

How is MTBF calculated at Spectrum Instrumentation?

At Spectrum calculation of MTBF is a statistical figure and based on the return rate of fielded Spectrum products. As Spectrum has a large number of different products, only differing in number of channels, speed, bandwidth and platform, single products sometimes have a very low number of shipments. Therefore, the MTBF is always calculated for a full series of products (like all M2p.59xx series products). That gives a good base for statistical calculation. As this calculation only works if enough products have been shipped and the first returns are seen, the MTBF is provided some time after releasing a product.

As Spectrum products do not track usage, we use an average working time model base for the calculation. Product can have any usage between laying in the shelf for weeks and only used occasionally to a runtime of 24/7. Spectrum decided to use a conservative estimation of only 40 operation hours per week for the calculation. That means if a product is returned one year after shipment, we calculate this products' operating hours to 52 weeks x 40 hours = 2080 hours. As many products are used in OEM systems and experiments all day long, the MTBF is probably far better than we specify.

The MTBF is regularly calculated by [sum of MTBF-counting failures / sum of operating hours of all products].

Although many Spectrum products are used for a very long time and even products that are more than 20 years old are still in use, we decided to limit the number of operating hours that count for a shipped product to 15 years.

What failures count for MTBF calculation?

As MTBF should show how long a board can normally operate before it has a damage, there are some board-returns that didn’t count as an error concerning the MTBF:

How long wll my product work until it fails?

Please keep in mind that the MTBF figure is a statistical figure, not a minimum figure. Single products may even fail after a week of operation while most products will never fail in their lifetime. The MTBF at Spectrum is calculated without knowing the operation environment. That means a good lab operation environment with temperature control, good power supply and without any high voltage, EMC or radiation pulses will increase the MTBF for your particular product. On the other hand, an environment at or over the limits of the specification with a bad power supply, always generating power variations will decrease the MTBF for your particular product.