Mean Time Between Failures (MTBF) and Mean Time To Repair (MTTR) - two most-cited reliability metrics.
Formula
$$ \text{MTBF} = \frac{T_\text{op}}{N_\text{fail}}, \quad \text{MTTR} = \frac{T_\text{down}}{N_\text{fail}} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $T_\text{op}$ | Total operating hours | h | running-hours meter |
| $T_\text{down}$ | Total repair time | h | maintenance log |
| $N_\text{fail}$ | Number of failures | - | failure report |
Sources
- IEEE 493 - Reliability in Industrial Power Systems.