What is MTBF (Mean Time Between Failure)?
Mean Time Between Failure measures the time that passes between one previous failure of a mechanical/electrical system to the next failure during normal operation. In simpler terms, MTBF helps you predict how long an asset can run before the next breakdown happens. In simpler terms, Mean Time Between Failure is a measure of how reliable or durable something is. It’s especially useful for predicting the lifetime of mechanical assets such as machinery, vehicles and equipment. The MTBF of a system is only an estimate of the mean time between failure. It doesn’t factor in unscheduled downtimes for preventive maintenance, or routine replacements of parts. It only estimates the mean time between failures due to design conditions that force the equipment out of service before it can be repaired.
Why Mean Time Between Failure is Helpful
MTBF Time Between Failure is helpful because it tells you how long it takes for a machine or device that has failed its quality control tests to fall into failure again. In other words, it gives you an idea of how reliable the item is. We use the mean time between failure as a quantifiable reliability metric for all of our products. 
This test was conducted to verify and document the reliability of the
MaxSonar product lines. Test parameters were selected that, if met, would establish and verify a mean time between failure of at least 20 years. Additionally, industry practice states that product performance at temperature extremes (-40°C, +70°C), during and after a significant number of temperature cycles, is required to validate the mean time before failure.
Operational Life Test Conditions for an MTBF of 232,896 hours with a 90% Confidence Level
Our product lifetime test was set up in an industry standard way. To facilitate reasonable test duration, the test temperature of 85°C allowed an acceleration factor. For the purposes of this test, the Arrhenius model was used. The equations used in the calculation of the acceleration factor can be found in the
full report. The test was conducted on 25 of the WR products (both the LV and the XL in the WR product lines) and 25 of the XL products. The product lifetime (MTBF) test started on January 18, 2010, and the test was stopped March 15, 2010, for an actual test duration of 67,025 cumulative test hours. During the course of the product life test, there were no failures. As a result, the MTBF value was calculated using an acceleration factor and a standard Chi-squared distribution. The MTBF of the MaxSonar product line is 232,896 hours, with a 90% confidence, for products operated at 45°C or less. Because no failures were observed during our testing, we believe that the values in this report can be taken as a conservative estimate of product lifetime.
Temperature Cycling Test Conditions for 229,139 hours with a 90% Confidence Level
The goal for this temperature test was to demonstrate product performance with the sensors subjected to a large number of temperature cycles. The test was completed on twenty of the MaxBotix MaxSonar™ products consisting of ten WR products (both the LV and the XL in the WR product lines) and ten indoor XL products. These products were subjected to 177 temperature cycles from –40°C to +70°C. For each cycle, the product soaked at the temperature extreme for 30 minutes. Product operation was daily verified during the first 101 temperature cycles. At 101 cycles the products received a full test. Then an additional 76 temperature cycles were run and the product was again tested and verified to operate properly. The cumulative total of 3540 temperature cycles was completed. No products failed during this temperature cycling test. The mathematical relationship of temperature cycling to product lifetime showed a product lifetime MTBF value of 229,139 hours. The equations used in the calculation can be found in the
full report.
Extending the Test Results to the LV-MaxSonar-EZ Products
The LV-MaxSonar-EZ (LV-EZ) line of sensors was not subjected to this test, but MaxBotix Inc., believes that these test results can be extended to the LV-EZ products because the LVEZ products use very similar circuits (except with fewer components) and the LV-EZ product lines actually subject the transducer and circuitry to less stress than the products that were tested during this evaluation.
