I am looking to find what the mean time between failure, or mean time between repair or something quantitative about walk in coolers/freezers. I know that you can calculate MTBF by looking at each component and knowing its MTBF, however, I am not sure where to find this information and if it is even out there? Thanks for any info.
I am not looking for the formula, but for some actual usable numbers for what the MTBF of the devices are
Mean time between failures (MTBF) is the arithmetic mean (average) time between failures of a system. The MTBF is typically part of a model that assumes the failed system is immediately repaired (zero elapsed time), as a part of a renewal process. This is in contrast to the mean time to failure (MTTF), which measures average time between failure with the modeling assumption that the failed system is not repaired.
MTBF value prediction is an important element in the development of products. Reliability engineers / design engineers, often utilize Reliability Software to calculate products’ MTBF according to various methods/standards (MIL-HDBK-217F, Telcordia SR332, Siemens Norm, FIDES,UTE 80-810 (RDF2000), etc.). However, these “prediction” methods are not intended to reflect fielded MTBF as is commonly believed. The intent of these tools is to focus design efforts on the weak links in the design.
Mean Time Between Failures (MTBF)
MTBF is a basic measure of reliability for repairable 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.
MTBF can be calculated as the inverse of the failure rate for constant failure rate systems. For example: If a component has a failure rate of 2 failures per million hours, the MTBF would be the inverse of that failure rate.
MTBF = (1,000,000 hours) / (2 failures) = 500,000 hours
Mean Time To Failure (MTTF)
MTTF is a basic measure of reliability for non-repairable systems. It is the mean time expected until the first failure of a piece of equipment. MTTF is a statistical value and is meant to be the mean over a long period of time and large number of units. For constant failure rate systems, MTTF is the inverse of the failure rate. If failure rate is in failures/million hours, MTTF = 1,000,000 / Failure Rate for components with exponential distributions.
Technically MTBF should be used only in reference to repairable items, while MTTF should be used for non-repairable items. However, MTBF is commonly used for both repairable and non-repairable items.
The formula that is most commonly used is:
MTTF
A = —————–
MTTF + MTTR
Where “A” stands for the availability, presented as a percentage. “MTTF” is mean time to failure. That’s the time that the system is actually operational and “MTTR” is the time it takes to repair, restore, or recover the system. Normally you only consider the period of time when the system was required to be operational.
So, if your system is down 30 minutes during a full seven days, 168 hour week, you would divide 167.5 (the uptime) by 168 (the total available time) and get 99.7%.
