Most general-purpose industrial accelerometers tend to come with lifetime warranties so that if anything should happen within the boundaries of normal usage, you can receive a replacement quickly enough and get your vibration monitoring program back on track.  It is still important, however, to be aware of a sensor’s average lifetime for various reasons including inventory planning, maintenance scheduling and data viability.

Industrial accelerometers do not contain any moving parts and therefore are generally not repairable – when they fail, the unit is unusable and needs to be replaced.  Because of this, the aging process is only noticeable through physical changes such as rust, scratches or blemishes.  While the defective rate can be determined through the simple ratio of parts returned as failures versus total number of parts shipped, the MTBF (Mean Time Before Failure) can give a trustworthy estimation of the expected lifetime for each model.

The MTBF can be calculated in many different ways, depending on the standard you choose to reference.  Two common options are Bellcore TR-332, a “Reliability Prediction Procedure for Electronic Equipment,” and MIL-HDBK-217F, a similar document.  From a high level, both these standards take into account the number of possible failure points in a sensor’s Bill of Materials; resistors, capacitors, diodes and the crystal, to name a few, and sum the individual failure rates at a given temperature.  Perform a bit more calculation and you have the expected lifetime of a given electronic assembly, or its Mean Time Before Failure.

Knowing the MTBF is valuable not only for the reasons mentioned previously, but to gauge the expected lifetime of one company’s product versus its competitor.  If the company is willing to perform the calculation and stands behind the data, allowing customers to freely request it, that is just another reason to trust their people, processes and product.