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System reliability
When installing a system, it is important that the system is reliable for users (system user departments). System reliability is improved by ensuring
the system remains operational with no functions coming to a halt during
operation.
Reference
MTBF
Abbreviation for “Mean Time Between
Failures.”
Reference
(1)Index for system reliability
“Availability” is used as an index for measuring system reliability. The
system availability is a percentage that indicates the level of uninterrupted
availability. The higher the availability value, the better the reliability of
the system.
Availability can be indicated by “MTBF (Mean Time Between Failures)” or “MTTR (Mean Time To Repair).” A higher MTBF or shorter
MTTR indicates better system availability.
The following formulas are used to calculate availability using MTBF and
MTTR.
MTTR
Availability =
Abbreviation for “Mean Time To Repair.”
MTBF
MTBF + MTTR
OR
Availability =
Total operational time − Failure time
Total operational time
MTBF
Time between failures.
Average time of continuous system operation.
MTTR
Average time to repair the system in the event of a failure.
Start of operation
End of operation
Failure
Operation
100
6
Failure
Operation
350
2
Failure
Operation
120
MTBF: (100 + 356 + 120 hours) ÷ (3 times) = 190 hours
MTTR: (6 + 2 + 4 hours) ÷ (3 times) = 4 hours
Availability :
MTBF
MTBF + MTTR
=
190
190+4
=0.9793814 … Approx. 0.979
OR
Total operational time − Failure time =
570
Total operational time
570+12
=0.9793814 … Approx. 0.979
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Time