Measure of reliability - Mean Time between failure (MTBF) - Software Specification & Measurement

Discussion

• Nirja Shah   -Posted on 05 Oct 15
  Mean time between failures (MTBF)
  - It is the predicted elapsed time between inherent failures of a system during operation.
  
  - It can be calculated as the arithmetic mean (average) time between failures of a system.
  
  - It is typically a part of the model that assumes the failed system that is immediately repaired (mean time to repair, or MTTR), as a part of the renewal process.
  
  - This is in contrast to the mean time to failure (MTTF), which measures the average time to failures with the modeling assumption that the failed system is not repaired (infinite repair time).
  
  - The definition of MTBF depends on the definition of what is considered a system failure.
  
  - For complex, repairable systems, failures are considered to be those out of design conditions which place the system out of service and into a state for repair.
  
  - Failures which occur that can be left or maintained in an unrepaired condition, and do not place the system out of service, are not considered failures under this definition.
  
  - In addition, units that are taken down for routine scheduled maintenance or inventory control are not considered within the definition of failure.
  
  Mean Time To Repair (MTTR)
  - It is a basic measure of maintainability of repairable items.
  
  - It represents the average time required to repair a failed component or device.
  
  - Expressed mathematically, it is the total corrective maintenance time for failures divided by the total number of corrective maintenance actions for failures during a given period of time.
  
  - It generally does not include lead time for parts not readily available or other Administrative or Logistic Downtime (ALDT).
  
  - In fault-tolerant design, MTTR is usually considered to also include the time the fault is latent (the time from when the failure occurs until it is detected).
  
  - If a latent fault goes undetected until an independent failure occurs, the system may not be able to recover.
  
  - MTTR is often part of a maintenance contract, where a system whose MTTR is 24 hours is generally more valuable than for one of 7 days if mean time between failures is equal, because its Operational Availability is higher.

➨ Post your comment / Share knowledge